Predictive Gate-to-Gate Life Cycle Assessment of an Early-Stage Plasma-Based Ammonia Synthesis Technology

Abstract

A predictive gate-to-gate life cycle assessment (LCA) of plasma-assisted ammonia synthesis at TRL 4 is presented according to ISO 14040/44 standards. General plasma-assisted synthesis was evaluated through a mini-review‚ sensitivity analysis‚ and predictive LCA. The specific DBD needle-to-plate configuration LCA is performed using previously published experimental data. Two distinct scenarios were investigated. In the literature-based baseline scenario derived from sensitivity analysis, electricity consumption was 533 kWh/kg NH₃, giving a carbon footprint of 26.65–639.60 kg CO₂-eq/kg NH₃; electricity contributed 98.5% of total emissions, and impacts remained about 2.05 times higher than conventional Haber–Bosch. In contrast, the experimental DBD case study required 63,450 kWh/kg NH₃, showing reactor efficiency as the dominant driver of environmental performance. The BCS (≈1.39 kWh/kg NH₃) suggests that optimized plasma systems could potentially surpass conventional ammonia synthesis in energy efficiency. The environmental performance of plasma-assisted ammonia synthesis is affected by NH₃, NO_x, N₂O, and hydrogen emissions due to impacts on climate, air quality, water systems, and biodiversity. Future improvements may come from reactor and electrode optimization, catalyst integration, alternative plasma sources, and better process and heat integration, although deployment will likely depend on major efficiency gains and may be limited to niche decentralized applications.

1. Introduction

Conventional ammonia synthesis largely depends on the energy-intensive Haber–Bosch process using fossil-derived hydrogen, resulting in substantial greenhouse gas emissions [1,2,3]. Consequently, alternative pathways have attracted growing interest [4,5]. Among these, plasma-based synthesis allows nitrogen fixation under milder conditions [6,7,8,9,10]. However, despite validation at laboratory scale (TRL 4), efficiencies and yields remain highly variable [11], leaving environmental implications uncertain at this development stage.

Environmental assessments of plasma-assisted ammonia synthesis are relatively sparse. Knowledge on the environmental impacts from a life cycle point of view is particularly lacking. Life cycle assessment (LCA) is a commonly used tool for assessing the environmental impact. Nevertheless, studies involving LCA are primarily related to technology advancements that are fully mature in industry standards and full life cycle boundaries [12]. A complete cradle-to-grave life cycle assessment is generally unsuitable for technologies at an early stage of development.

Predictive (ex ante) LCA helps address these challenges by enabling early environmental screening to guide R&D decisions [13]. In this context, gate-to-gate LCA is particularly suitable for low technology readiness level systems, as it focuses on the transformation process within clearly defined system boundaries [14]. Focusing exclusively on the synthesis step allows these assessments to identify major environmental drivers without implying full life-cycle sustainability or commercial viability.

Given the gate-to-gate system boundary applied in this study, upstream and downstream processes are excluded. Therefore, comparisons with conventional Haber–Bosch studies are not directly equivalent and may underestimate their overall environmental impact. These comparisons should therefore be interpreted as conservative reference points rather than complete system-level evaluations. The gate-to-gate approach is intentionally applied to isolate reactor-level performance at this early stage of technology development. A more comprehensive life cycle assessment will be necessary as the technology matures and system integration becomes clearer.

Emerging technologies do not automatically outperform incumbent systems; low-yield, electricity-intensive processes may merely shift environmental burdens [15]. The four-stage framework to address comparability, data limitations, and uncertainty includes: (1) mini-review of plasma-ammonia synthesis; (2) sensitivity analysis; (3) predictive LCA; and (4) illustrative case studies derived from experimental data [16].

This work creatively combines several of these different approaches to make multiple novel contributions in the life cycle assessment of emerging ammonia synthesis processes. Unlike the majority of prior studies that focus on commercially available systems (TRL 7–9), it offers a predictive ex ante gate-to-gate LCA at Technology Readiness Level (TRL) 4. This early evaluation of technologies can provide timely evidence to help direct research in a way that will lead to design decisions before they are made. Integrating literature review with sensitivity analysis, forecasting, and experimental means provides better insight than what single methods could muster. It also specifies quantitative performance thresholds for commercialisation against conventional ammonia production, thus providing little room for discretion in future development. Lastly, the climate impact assessment is further enhanced by having outcomes from both Environmental Footprint (EF) and ReCiPe 2016 methods. These advances combine to set this work apart from the other studies and offer a framework for evaluating any type of next-generation energy technology.

Following the life cycle assessment (LCA) framework outlined in ISO 14040 [17] and ISO 14044 [18], this study performs a charge characterization of plasma-based ammonia synthesis at TRL4 that is gate-to-gate. We assess from feedstocks and electricity to ammonia at the reactor outlet, omitting upstream extraction and downstream stages. The study approaches the challenges of comparability, data scarcity, and uncertainty through (1) a mini-review deriving key sensitivity parameters; (2) sensitivity analysis computing CO₂-equivalent emissions over electricity grid mixes and efficiency scenarios; (3) predictive gate-to-gate life cycle assessment to identify break-even conditions; and (4) an experimental case study quantifying genuine environmental benefits vs. problem shifting.

2. Plasma Technologies for Ammonia Synthesis

A critical evaluation criterion at TRL 4 is production chain assessment. Given this, plasma system selection becomes a crucial parameter within a gate-to-gate study as it inherently affects energy consumption, conversion efficiency and waste generation. The rest of this paper summarizes the recent progress in plasma-assisted ammonia synthesis, covering the technological improvement and reported performance as well.

2.1. State of the Art of Plasma-Based Ammonia Synthesis

Plasma, often referred to as the fourth state of matter, consists of a mixture of free electrons, ions, molecules, radicals, and excited species that collectively maintain an overall quasi-neutral charge. Thermal plasmas exhibit uniform temperatures across species, while non-thermal plasmas feature hot electrons and cold heavy particles. Non-thermal plasmas generate excited species (e.g., N₂(v)), potentially overcoming the N₂ dissociation bottleneck in ammonia synthesis via plasma-enabled pathways.

A comparison of reported energy consumption values for ammonia synthesis using different plasma reactor types is provided in Figure 1. Since the 2000s, research on plasma-assisted ammonia synthesis has predominantly focused on dielectric barrier discharge (DBD) reactors [8,10,19]. Research on microwave (MW) and radiofrequency (RF) plasmas was particularly active in the 1980s–1990s, with a limited number of recent studies also exploring these systems [10]. Research on glow discharge plasmas dates back to the 1920s and continued until the 1990s, influenced by the Birkeland–Eyde process developed for industrial NO_x production in the early 20th century [10,19]. Alternative plasma systems, including arc discharges and plasma jets, appear in relatively few studies and are generally investigated in a preliminary or exploratory manner [10]. Several authors have provided extensive discussions of plasma reactor configurations [19,20,21].

2.2. Comparative Analysis of Small-Scale Haber–Bosch and Plasma-Assisted Technologies

A comparison of reported energy consumption values for electrolysis-based Haber–Bosch processes at 10 kW and 10 MW scales and plasma-assisted ammonia synthesis is illustrated in Figure 2. For both Haber–Bosch and plasma-assisted ammonia synthesis, hydrogen must be supplied via electrolysis, corresponding to an energy consumption of roughly 31.4 GJ per tonne of NH₃ [48,49]. Across all alternatives, nitrogen is separated and purified by pressure swing adsorption, corresponding to an energy requirement of around 1.0 GJ per tonne of NH₃ [49]. At a scale of 10 MW, the high-pressure synthesis loop used in the Haber–Bosch process operates with limited energy losses, resulting in an energy demand of roughly 3.6 GJ per tonne of NH₃ produced [4]. By comparison, operation at the 10 kW scale results in a markedly higher energy demand for the high-pressure ammonia synthesis loop, estimated at roughly 45–50 GJ per tonne of NH₃ (see Figure 2). The high energy demand mainly results from substantial heat losses in the synthesis reactor at high operating temperatures.

Figure 2 indicates that the energy demand of present plasma-catalytic ammonia synthesis systems is significantly greater than that of electrolysis-driven Haber–Bosch processes at both 10 kW and 10 MW scales. Nevertheless, plasma catalysis can operate under milder conditions than traditional catalytic synthesis using industrial iron catalysts. Plasma catalysis becomes favorable only if the energy demand of the process approaches that of the electrolysis-based Haber–Bosch system at the 10 kW scale (about 80 GJ t⁻¹ NH₃). The lowest reported energy requirement for plasma catalysis is approximately 95 GJ t⁻¹ NH₃ at 0.2 mol% NH₃ [29], whereas most reported values lie between 10³ and 10⁶ GJ t⁻¹ NH₃ across different conversion levels (see Figure 2) [10].

Recycling unconverted N₂ and H₂ also adds significantly to the overall energy demand of plasma-catalytic systems, mainly because of their low ammonia conversion levels (Figure 2). Although this recycling energy is often not reported in plasma catalysis studies, it becomes an important contribution when ammonia conversion remains below roughly 1.0 mol% NH₃ [4].

2.3. Pathways Toward Energy-Efficient Plasma-Assisted Ammonia Synthesis

For plasma catalysis to be competitive with the Haber–Bosch process, the total energy consumption would need to decrease to around 80 GJ t⁻¹ NH₃. This target is derived from comparisons with electrolysis-based Haber–Bosch systems operating at about 10 kW, corresponding to a production rate of roughly 10 kg NH₃ per day.

Hydrogen generation and nitrogen purification contribute comparable energy demands in both processes, totaling approximately 32 GJ t⁻¹ NH₃. In conventional Haber–Bosch systems, ammonia is recovered by condensation. This method becomes ineffective at mild pressures below about 70 bar because ammonia exhibits a relatively high vapor pressure under ambient conditions (about 7 bar) [4,49]. Sorbent-based systems are therefore being explored for ammonia separation and storage, as described in Section 2.3.2. The energy demand for ammonia separation using sorbents is typically around 10 GJ t⁻¹ NH₃ and is relatively insensitive to the ammonia concentration.

In conventional industrial ammonia synthesis, recycling costs are generally minor because the associated energy requirement remains below 1 GJ t⁻¹ NH₃ when the ammonia concentration in the reactor outlet exceeds 1.0 mol% NH₃ [4]. In contrast, the best reported plasma-catalytic systems currently achieve ammonia concentrations of only about 0.2% (see Figure 2). At such low concentrations, the energy required for recycling unconverted gases can reach values as high as 100 GJ t⁻¹ NH₃.

Consequently, increasing the ammonia concentration at the outlet of the plasma reactor to values above 1.0%, while maintaining reasonable energy consumption, is highly desirable. Higher conversion levels would also lower capital costs for gas recycling by reducing the required compressor capacity.

2.3.1. Best-Case Scenario (BCS) for Plasma Assisted Ammonia Synthesis

As illustrated in Figure 2, the combined energy demand of current plasma-catalytic systems and gas recycling remains very high, reaching approximately 197 GJ t⁻¹ NH₃. In addition, the energy required for recycling is inversely related to the single-pass conversion. Consequently, improvements in catalyst performance and plasma reactor design that increase conversion will naturally reduce the energy penalty associated with gas recycling. An outlet ammonia concentration of roughly 1.0 mol% is considered necessary to utilize the reactor volume efficiently for downstream separation.

To address this challenge, a target energy consumption of 40 GJ t⁻¹ NH₃ at an outlet concentration of 1.0 mol% NH₃ was proposed for the plasma reactor (see Section 2.2). To date, the lowest reported value corresponds to a pulsed dielectric barrier discharge (DBD) reactor, which achieved an energy consumption of 95 GJ t⁻¹ NH₃ at 0.16 mol% NH₃ over a Mg-Ru/Al₂O₃ catalyst [29]. However, the plasma-induced activation of ammonia imposes an intrinsic limitation on energy efficiency at higher conversions, since increasing ammonia concentrations lead to greater plasma activation of NH₃.

To estimate the BCS for plasma-assisted ammonia synthesis, it is assumed that the reduction in the activation barrier for N₂ dissociation corresponds to the effective energy input for the plasma-assisted process. For Ru-based catalysts, the decrease in the N₂ dissociation barrier is approximately 0.7 eV [22], which corresponds to about 4.0 GJ t⁻¹ NH₃ or 1.1 kWh kg⁻¹. Based on the analysis shown in Figure 3, an outlet ammonia concentration of approximately 0.35 mol% would be required to achieve an energy consumption of 40 GJ t⁻¹ NH₃. If the reactor outlet concentration reaches 1.0 mol% NH₃, the combined energy demand of the plasma reactor under BCS conditions and the associated recycling process would decrease to roughly 5.0 GJ t⁻¹ NH₃ (see Figure 3).

2.3.2. Conceptual Process Design and Ammonia Separation–Separation and Storage

Ammonia separation alternatives for plasma-assisted synthesis are evaluated against small-scale Haber–Bosch. Upstream hydrogen and nitrogen production are excluded.

Condensation is the standard method used to separate ammonia in conventional systems, but this is inefficient at low pressures due to its significant vapor pressure (~7 bar at ambient conditions). Alternative separation methods are therefore required for mild-pressure synthesis [4]. Various solid sorbent materials have been evaluated for this application [3].

Metal halides are preferred over zeolites for plasma-assisted ammonia synthesis due to higher ammonia density and elevated-temperature separation (150–250 °C vs. 20–100 °C), reducing heat integration costs with the plasma reactor (200–300 °C) (see

Table 1. Overview and comparison of technologies for ammonia separation. Based on references [49,51,52]. * At 20 bar, the required energy increases to about 20–25 GJ t⁻¹ NH₃ [4].

	Condensation	Metal Halide	Zeolite
Separation temperature (°C)	−20–30	150–250	20–100
Desorption temperature (°C)	-	350–400	200–250
Pressure (bar)	100–450	10–30	10–30
Energy consumption (GJ t−1 NH3)	3–5 *	6–11	8
Ammonia at outlet (mol%)	2–5	0.1–0.3	0.1–0.3
Ammonia capacity (wt%)	100	5–30	5–15
Ammonia density (kg m−3)	680	100–600	30–90
Chemical stability	-	Low/Medium	High
Technology readiness level (TRL)	9	4–5	4–5

). This is critical as the compressor and heat exchanger for gas recycling costs dominate in low-conversion systems [3]. Zeolites may suit room-temperature plasma systems using activated N₂.

Ammonia storage in metal halides occurs through diffusion into the lattice, resulting in the formation of ammine complexes (e.g., Ca(NH₃)_XCl₂ and Mg(NH₃)_XCl₂). This reduces potential leakage relative to liquid-phase ammonia due to lower equilibrium vapor pressure [53], enhancing safety. Ammonia is released on demand for combustion (e.g., fuel cells, engines) [49]. Figure 4 illustrates a simplified configuration of a plasma-catalytic ammonia synthesis loop. Cyclic adsorption and desorption can be realized either by periodically switching between multiple beds or through the use of moving-bed reactor designs.

2.3.3. Synergy Between Plasma Reactor and Ammonia Separation and Storage

Matching the operating temperatures of the plasma reactor and the ammonia separation unit can improve overall process integration. The plasma reactor can operate at temperatures above the light-off temperature (typically > 150 °C), where a higher temperature implies a higher ammonia synthesis rate. On the other hand, upon increasing the temperature too much (i.e., above 300 °C), the benefits of plasma catalysis over heterogeneous catalysis without a plasma are negligible. Some catalysts show substantial thermal activity above 300 °C [54,55,56,57].

Among metal halides, MgCl₂ offers suitable absorption-desorption cycles, absorbing 2 moles NH₃ at 200 °C (10 kPa) and releasing at 300 °C [58,59]. Supporting MgCl₂ on inert oxides (e.g., SiO₂) increases surface area and mechanical stability [59]. MgCl₂/SiO₂ (40 wt%) achieves ~5 wt% NH₃ capacity at 200 °C (theoretical maximum: 11 wt%).

The operating parameters and energy requirements for the state-of-the-art and BCS plasma reactors are presented in

Table 2. Process integration of plasma reactors with ammonia separation and storage systems. Recycling energy demand is estimated from outlet NH₃ concentration using interpolated values from [4,49]. The best reported plasma-catalysis performance is based on data from Kim et al. [29].

	State-of-the-Art Plasma Reactor	BCS Plasma Reactor	Separation
Type	DBD reactor (pulse)	DBD reactor (pulse)	Solid absorbent
Material	Promoted Ru/Al2O3 catalyst	More active catalyst	MgCl2/SiO2
Reaction temperature (°C)	300	200	200
Desorption temperature (°C)	-	-	300
Operating pressure (bar)	1.5	1.5	1.0
Outlet NH3 concentration (mol%)	0.16	1.0	0.1
Outlet ammonia pressure (kPa)	1.6	10	0.3
Energy consumption (GJ t−1 NH3) *	197 (PC:95, Rec:102)	5 (PC:4, Rec:1)	10
Syngas ratio (H2:N2)	1:4	1:4	1:4

* This accounts for the energy consumption of both plasma-catalytic ammonia synthesis (PC) and the recycling process (Rec).

, along with the conditions used for ammonia separation with a MgCl₂/SiO₂ sorbent. Similar reactor and absorption temperatures minimize heat integration, simplifying intermittent operation. As shown in Table 2, reducing the energy demand of the plasma reactor represents the most critical improvement.

2.4. Investment Cost Comparison

While energy cost dominates electricity-driven ammonia synthesis [60], investment costs become significant at a small scale. This section estimates investment costs associated with plasma-assisted ammonia synthesis versus decentralized Haber–Bosch, excluding hydrogen and nitrogen production costs common to both.

The ammonia synthesis loop exhibits a scaling exponent of 0.6 [61], whereas electrolyzer systems are typically scaled through modular expansion, increasing the loop’s cost contribution upon scale-down. Figure 5 presents a comparison of the capital investment required for the Haber–Bosch process, state-of-the-art plasma-assisted systems, and BCS plasma-assisted loops, with absorbent-enhanced Haber–Bosch included as a reference. The cost of the plasma generator is assumed to be 0.9 € W⁻¹ [62]. The capital costs of the remaining equipment are calculated using scaling relations reported in [4].

Current plasma-assisted synthesis loops have capital costs nearly an order of magnitude higher than those of small-scale Haber–Bosch systems due to large recycle compressors and inefficient ammonia separation at low concentrations. Even the BCS matches Haber–Bosch costs. Haber–Bosch requires substantial feed compression and heat integration (400–500 °C synthesis to ambient separation), but benefits from high ammonia partial pressures and about 15% single-pass conversion, reducing separation and recycle costs. The best-case plasma-assisted loop eliminates feed compression via low-pressure operation, yet low single-pass conversion (~1%) and ammonia partial pressure increase recycle and separation costs.

2.5. Outlook for Plasma-Assisted Ammonia Synthesis

Overall, the analysis indicates that plasma-assisted ammonia synthesis does not offer substantial capital cost advantages compared with the Haber–Bosch synthesis loop at small scales (about 10 kW), even in the BCS (see Section 2.3.1). Under BCS assumptions, the energy consumption of plasma-assisted ammonia synthesis is lower than that of the Haber–Bosch process operating at 10 kW (see Figure 6). However, at larger production scales, the Haber–Bosch process remains significantly more energy efficient. This suggests that plasma-catalytic ammonia synthesis is unlikely to serve as a competitive alternative for large-scale ammonia production.

Various technologies are being researched as small-scale Haber–Bosch alternatives, including electrochemical, photochemical, homogeneous catalysis, and chemical looping. The estimated energy consumption of these technologies at the current state of the art is illustrated in Figure 7. A comprehensive review of these approaches is provided by Rouwenhorst et al. [3]. While electrochemical ammonia synthesis is frequently proposed as a mild-condition alternative, attaining high ammonia production rates with low energy input remains difficult [63,64]. Even with viable energy costs, low conversion and electrolyte separation remain critical issues [65]. The currently reported energy consumption and low ammonia yields prevent these technologies from being practical for near-term deployment [3].

Gradual Haber–Bosch improvements remain active research. Industrial iron catalysts have evolved minimally over a century [66], while Ru-based catalysts (Ru/AC) have also seen limited industrial application [67] because of their higher catalyst cost and shorter operational lifetime. For traditional iron catalysts and early Ru-based systems (Ru/AC, Ru/Oxide), the dissociation of N₂ represents the rate-controlling step, and its activity can be enhanced by incorporating alkali or alkaline earth promoters [68]. In some ammonia converters, Ru catalysts have been replaced with Wüstite-derived iron catalysts, which demonstrate comparable catalytic activity [66]. Lower-temperature catalysts are essential to reduce heat loss and energy demand in small-scale operations.

Recent Ru-based catalysts using novel supports like electrides (e.g., C12A7:e⁻) show substantially improved activity [54,56,57,69,70,71,72,73,74,75,76,77]. The C₁₂A₇:e⁻, a stable ambient-temperature electride with [Ca₂₄Al₂₈O₆₄]⁴⁺ framework and cage electrons [78], enhances N₂ dissociation via a small band gap with Ru [72] and suppresses hydrogen poisoning [71]. Hydrogenation becomes rate-limiting [73], enabling 200–250 °C activity comparable to Fe catalysts at 350–400 °C [54]. These outperform plasma reactors, which are energy-efficient only at low conversions (<1.0 mol% NH₃) to avoid product activation. Pairing Ru–electride catalysts with metal halide sorbents enables absorbent-enhanced Haber–Bosch synthesis under relatively mild pressures (~7 bar) [49].

The capital investment required for a plasma-catalytic ammonia synthesis process is likely to exceed that of the absorbent-enhanced Haber–Bosch process. This is mainly due to the need for larger heat exchangers and recycle compressors, which result from the lower single-pass conversion achieved in plasma systems [4]. For comparison, an electrolysis-based Haber–Bosch plant operating at 10 MW reaches a power-to-ammonia efficiency of approximately 52% (LHV). In contrast, the best-case scenario (BCS) for plasma catalysis corresponds to an efficiency of about 39% (LHV). Under current reported conditions, plasma-catalytic ammonia synthesis requires around 240 GJ t⁻¹ NH₃, which corresponds to a power-to-ammonia efficiency of only ~8% (LHV).

Figure 6. Estimated energy consumption of state-of-the-art small-scale and large-scale electrolysis-based Haber–Bosch, plasma catalysis (also BCS), low-temperature absorbent-enhanced Haber–Bosch, single-pass absorbent-enhanced process, and electrochemical ammonia synthesis. Estimates based on [4,49,79,80]. Reproduced from [7] under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0). * For electrochemical ammonia synthesis, energy consumption refers only to ammonia generation, excluding separation and recycling steps.

Figure 6. Estimated energy consumption of state-of-the-art small-scale and large-scale electrolysis-based Haber–Bosch, plasma catalysis (also BCS), low-temperature absorbent-enhanced Haber–Bosch, single-pass absorbent-enhanced process, and electrochemical ammonia synthesis. Estimates based on [4,49,79,80]. Reproduced from [7] under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0). * For electrochemical ammonia synthesis, energy consumption refers only to ammonia generation, excluding separation and recycling steps.

Figure 7. General gate-to-gate LCA inventory on early-stage plasma-based ammonia synthesis.

Figure 7. General gate-to-gate LCA inventory on early-stage plasma-based ammonia synthesis.

3. Sensitivity Analysis Results

Based on the literature review in Section 2, this sensitivity analysis focuses on the three parameters identified as critical for TRL 4 systems: plasma reactor energy consumption, ammonia conversion efficiency, and electricity sourcing assumptions. The analysis draws from reported performance data across DBD, MW, and RF plasma systems to analyze the influence of changes in these parameters on overall environmental impacts.

Plasma-assisted ammonia synthesis is sensitive to the energy consumption of the plasma reactor, ammonia conversion efficiency, and assumptions on the source of electricity. Current-generation systems show energy consumptions ranging from 95 to 240 GJ t⁻¹ NH₃ for the best-performing configurations, whereas most reported systems remain in the range of 10³–10⁶ GJ t⁻¹ NH₃, generally at ammonia concentrations below 1.0 mol% [10,29]. An inverse relationship exists between energy consumption and ammonia concentration; a DBD reactor with 0.16 mol% outlet concentration requires 202 GJ t⁻¹ NH₃ [29,81] of energy to operate, of which 52% is consumed by recycling (102 GJ t⁻¹ NH₃ recycling and 95 GJ t⁻¹ NH₃ plasma catalysis). This shows that conversion efficiency is the most dominant sensitivity parameter, as can be seen by a BCS with an assumption of enhanced catalyst activity (1.0 mol% conversion at 200 °C), which saves a total amount of energy of 5 t⁻¹ NH₃ [29].

Secondary sensitivity parameters are the ammonia separation technology and thermal integration efficiency. Metal halide sorbents (and especially MgCl₂/SiO₂) can operate at 150–250 °C and require less heat transfer with plasma reactors, which run at 200–300 °C [49,55]. The matching temperature reduces the energy loss in comparison to zeolite-based separation (20–100 °C) and can be performed with energy consumptions of 6–11 GJ t⁻¹ NH₃ and 8 GJ t⁻¹ NH₃, respectively [4]. Low thermal coupling between the reactor and separation units (which may mean that 15–25% of total energy consumption is due to additional heating/cooling) suggests system integration is key to realizing environmental gains.

The system is highly sensitive to the carbon intensity of the electricity grid, which supersedes all the technological parameters regarding the impacts of climate change. The potential contribution of energy-related emissions to global warming is dominated by the baseline assessment with conventional grid electricity (97% contribution). Replacement of 100% renewable electricity lessens the effects of climate change by as much as 97%, to around 0.26 kg CO₂-eq per functional unit. However, other impact categories, including acidification, particulate matter formation, and terrestrial ecotoxicity, show lower sensitivity to the electricity source. These impacts are primarily driven by direct emissions (NH₃, NO_x, and N₂O) and material inputs such as catalysts and sorbents. As a result, renewable electricity replacement is not enough to get rid of every environmental hotspot.

In this analysis, the key parameters and their range of sensitivity used are summarized in

Table 3. Sensitivity analysis parameters for life cycle inventory and impact assessment of plasma-assisted ammonia synthesis.

Parameter Category	Variable	Baseline Value	Sensitivity Range	Unit	LCI Application	Impact Assessment Relevance
Plasma Reactor Performance	Energy consumption	1919	103–106	GJ t−1 NH3	Direct energy input to system	Climate change, resource use
	Energy consumption (BCS)	5	4–6	GJ t−1 NH3	Optimized energy input	Climate change, resource use
	Ammonia conversion efficiency	0.16	0.1–1.0	mol% NH3	Determines recycling flow rates	All impact categories via system scaling
	Outlet NH3 concentration	1.6	0.5–10	kPa (partial pressure)	Separation energy calculation	Climate change, acidification
	Operating temperature	300	200–400	°C	Heat integration requirements	Climate change (auxiliary energy)
	Operating pressure	1.5	1.0–5.0	Bar	Compression energy	Climate change, resource use
Ammonia Separation	Separation technology	Metal halide (MgCl2/SiO2)	Metal halide/Zeolite/Condensation	—	Material and energy inputs	All categories via energy/material flows
	Separation energy consumption	10	6–11	GJ t−1 NH3	Direct energy input	Climate change, resource use
	Absorption temperature	200	150–250	°C	Heat exchange requirements	Climate change (thermal integration)
	Desorption temperature	300	250–400	°C	Regeneration energy	Climate change
	Ammonia capacity (sorbent)	5	5–30	wt% NH3	Sorbent mass flow	Resource use, ecotoxicity
Gas Recycling	Recycling energy (state-of-the-art)	102	50–150	GJ t−1 NH3	Compression energy	Climate change, resource use
	Recycling energy (BCS)	1	0.5–2	GJ t−1 NH3	Compression energy	Climate change, resource use
	Syngas ratio (H2:N2)	01:04	1:3 to 1:5	Molar	Feedstock input flows	Resource use
Electricity Supply	Global grid electricity mix	0.96	0.8–1.1	kg CO2-eq kWh−1	Emission factors	Climate change (dominant)
	Renewable electricity EF factor	0.05	0.01–0.05	kg CO2-eq kWh−1	Climate change characterization	Climate change
	Coal-heavy grid EF factor	1.2	0.8–1.2	kg CO2-eq kWh−1	Climate change characterization	Climate change
Direct Emissions	N2O emission factor	Variable	0.001–0.1	kg N2O kg-NH3−1	Uncontrolled emission	Climate change, ozone depletion
	NOx emission factor	Variable	0.01–0.5	kg NOx kg-NH3−1	Uncontrolled emission	Acidification, PM formation, ozone
	NH3 slip/emission	Variable	0.001–0.05	kg NH3 kg-NH3−1	Uncontrolled emission	Acidification, eutrophication, PM
	Hydrogen leakage rate	2	0.2–10	% of H2 throughput	Indirect GHG emission	Climate change (indirect)
Material Inputs	Catalyst type	Ru/Al2O3	Ru/MgO/Al2O3, electride-supported Ru	—	Catalyst production and use	Resource use, ecotoxicity
	Catalyst lifetime	1	0.5–5	years	Replacement frequency	Resource use, ecotoxicity
	Sorbent (MgCl2) requirement	20	10–50	kg t−1 NH3	Sorbent production	Resource use, ecotoxicity

, which will give the quantitative input in the further process of life cycle inventory modeling and impact assessment. The sensitivity analysis results indicate both the importance of certain parameters and the uncertainty inherent in the inventory data. Laboratory-scale studies often overlook the formation of plasma-induced side products, such as ozone, nitrous acid, and nitrogen radicals. In addition, reported energy consumption frequently excludes auxiliary processes, including gas recycling, compression, and product separation [4,10]. The sensitivity ratios shown are thus to be viewed as suggestive as opposed to determinate, until full experimental characterization of complete process chains at pilot scales is conducted.

4. Methodology

4.1. Goal and Scope

This study aims to evaluate the potential environmental impacts of plasma-based ammonia synthesis during the early stages of technology development. This assessment is intended to support research and development by identifying key environmental contributors and influential process parameters. The results are not intended to support comparative assertions regarding full life-cycle environmental performance.

The study follows ISO 14040 [17] and ISO 14044 [18] and applies a predictive (ex-ante), gate-to-gate LCA framework, focusing exclusively on the ammonia synthesis step.

4.2. Functional Unit

Calculations are based on a functional unit of 1 kg of ammonia (NH₃) produced at the plasma reactor outlet.

4.3. System Boundary

The system boundary is limited to the production stage (gate-to-gate), covering feedstock input, electricity supply, plasma generation, and ammonia production up to the reactor outlet. Upstream raw material extraction beyond the process gate, infrastructure, and downstream stages, including storage, distribution, use phase, and end-of-life stage, are excluded. These exclusions are justified by the early stage of technological development and the focus on isolating the plasma synthesis process.

4.4. Life Cycle Inventory

Background inventory data were derived from the ecoinvent database (version 3.9.1), while foreground process modeling with impact evaluation was implemented through the Devera life cycle assessment tool (accessed on 7 March 2026).

4.5. Life Cycle Impact Assessment (LCIA) and Sensitivity Analysis

Life cycle impact assessment was conducted according to ISO 14040 and ISO 14044, applying the Environmental Footprint (EF) method within the Devera life cycle assessment tool. Characterization factors from the EF method were applied to life cycle inventory data derived from laboratory-scale experiments, literature sources, and background datasets based on data available in the ecoinvent database (version 3.9.1). The assessment focused on midpoint impact categories relevant to electricity and energy-intensive chemical processes, while normalization and weighting were not applied to avoid value-based interpretation.

4.6. Limitations

The use of generic background datasets from the ecoinvent database introduces additional uncertainty, particularly for laboratory-scale and emerging technologies. The model used in the Devera life cycle assessment tool may not fully encompass the specific parameters of plasma-ammonia synthesis systems or regional variations in energy grids. The results represent potential environmental impacts and should not be interpreted as indicators of commercial-scale or full life-cycle environmental performance.

5. Results

5.1. Life Cycle Inventory Results and Discussion

The baseline electricity consumption of 533 kWh/kg NH₃ adopted in this predictive LCA represents a conservative and literature-derived estimate obtained from a sensitivity analysis of reported plasma-assisted ammonia synthesis systems. As shown in Table 3, the analyzed literature data span a broad energy-consumption range of approximately 10³–10⁶ GJ/ton NH₃, reflecting the substantial variability among plasma technologies and operational conditions. The selected baseline value of 1919 GJ/ton NH₃ (≈533 kWh/kg NH₃) lies near the midpoint of the distribution presented in Figure 1, and was therefore considered a representative reference case for evaluating current plasma-assisted ammonia synthesis performance. It should be noted that this value is distinct from the experimental case study presented in Section 6, which reports measured performance from a specific dielectric barrier discharge (DBD) system.

The plasma synthesis process represents the largest contribution within the gate-to-gate system boundary, largely driven by electricity consumption for plasma generation, as shown in

Table 4. Result of CO₂eq calculated in Devera.

Datapoint	Value	EF	EF Source	Kg CO2eq	Assumption/Note
Nitrogen gas (N2) feedstock	0.824 kg N2 per 1 kg NH3 (stoichiometric: MW N2 = 28, NH3 = 17; 0.5 mol N2 per mol NH3 → 14/17 = 0.824 kg/kg)	-	Ecoinvent 3.9.1	0.32	Nitrogen gas is listed as a feedstock for plasma-assisted NH3 synthesis. Stoichiometric requirement: 0.824 kg N2 per kg NH3. The Ecoinvent activity “market for venting of nitrogen, liquid” represents cryogenic air separation production of nitrogen. EF of 0.39 kg CO2eq/kg includes upstream transport and cryogenic energy.
Water (H2O)—feedstock for hydrogen production via electrolysis	1.588 kg H2O per 1 kg NH3	-	Ecoinvent 3.9.1	0.00	Stoichiometric derivation: Ammonia synthesis requires 1.5 mol H2 per mol NH3 (from N2 + 3H2 → 2NH3). Water electrolysis (H2O → H2 + ½O2) requires 1 mol H2O per mol H2. Therefore, 1.5 mol H2O per mol NH3 × 18 g/mol H2O ÷ 17 g/mol NH3 = 1.588 kg H2O per kg NH3 (theoretical minimum). With practical purification losses (~15% for RO/ion exchange treatment), real systems require approximately 1.8 kg H2O per kg NH3. The conservative stoichiometric value of 1.588 kg/kg is used in this LCA. Water is delivered via municipal pipeline; EF includes delivery.
Anhydrous ammonia (NH3)–output reference (benchmark comparison)	1.0 kg NH3 output—conventional Haber–Bosch benchmark EF for comparison only	-	Ecoinvent 3.9.1	0.00	This value is not included in the total; rather, it serves as a benchmark. The ecoinvent dataset “market for ammonia, anhydrous, liquid” (RER) has a GWP of 2.833 kg CO2eq/kg NH3 and represents conventional fossil-based Haber–Bosch ammonia production, including steam methane reforming. The sensitivity analysis uses 2.5 kg CO2eq/kg NH3 as the conventional benchmark for break-even analysis. The ecoinvent value of 2.833 kg CO2eq/kg NH3 is slightly higher because it includes the European market mix and upstream transportation processes.
Plasma reactor electricity consumption (Base line—Ecoinvent GLO grid)	533 kWh/kg NH3 × 1 kg = 533 kWh	-	Ecoinvent 3.9.1	21.36	Plasma reactor electricity consumption = 533 kWh/kg NH3. Baseline uses Ecoinvent GLO medium voltage grid EF (0.040073 kg CO2eq/kWh).
SCENARIO A: Global average grid (0.96 kg CO2eq/kWh—IEA)	533 kWh × 0.96 kg CO2eq/kWh = 511.68 kg CO2eq/kg NH3	0.96	Ecoinvent 3.9.1	0.00	Scenario A = 533 kWh/kg × 0.96 kg CO2eq/kWh (IEA global average grid carbon intensity) = 511.68 kg CO2eq/kg NH3. This is ~205× the conventional Haber–Bosch benchmark (2.5 kg CO2eq/kg). NOT included in baseline total—scenario comparison only.
SCENARIO B: Renewable—dominated grid (0.05 kg CO2eq/kWh—IEA)	533 kWh × 0.05 kg CO2e/kWh = 26.65 kg CO2eq/kg NH3	0.05	Ecoinvent 3.9.1	0.00	Scenario B = 533 kWh/kg × 0.05 kg CO2eq/kWh = 26.65 kg CO2eq/kg NH3. This is ~10.7× the conventional benchmark. NOT included in baseline total.
SCENARIO C: Coal heavy grid (1.20 kg CO2eq/kWh—IEA)	533 kWh × 1.20 kg CO2eq/kWh = 639.60 kg CO2eq/kg NH3	1.20	Ecoinvent 3.9.1	0.00	Scenario C = 533 kWh/kg × 1.20 kg CO2eq/kWh = 639.60 kg CO2eq/kg NH3. Worst-case scenario. NOT included in baseline total.
SENSITIVITY: 10× efficiency improvement (53.3 kWh/kg)—Scenario A grid	53.3 kWh × 0.96 kg CO2eq/kWh = 51.16 kg CO2eq/kg NH3	0.96	Ecoinvent 3.9.1	0.00	The 10× efficiency improvement reduces consumption to 53.3 kWh/kg. Scenario A: 53.3 × 0.96 = 51.16 kg CO2eq. Still ~20.48× conventional benchmark. NOT included in baseline total.
SENSITIVITY: 100× efficiency improvement (5.33 kWh/kg)—Scenario A grid	5.33 kWh × 0.96 kg CO2eq/kWh = 5.12 kg CO2eq/kg NH3	0.96	Ecoinvent 3.9.1	0.00	The 100× efficiency improvement reduces consumption to 5.33 kWh/kg. Scenario A: 5.33 × 0.96 = 5.12 kg CO2eq. Still ~2.05× conventional benchmark. NOT included in baseline total.
BREAK-EVEN: kWh/kg required to match fossil ammonia (2.5 kg CO2eq)—all scenarios	ScenarioA: ≤2.60 kWh/kg|ScenarioB: ≤50.0 kWh/kg|ScenarioC: ≤2.08 kWh/kg	-	Ecoinvent 3.9.1	0.00	Break-even vs. conventional fossil ammonia (2.5 kg CO2eq/kg NH3): Scenario A (0.96): 2.5/0.96 = 2.60 kWh/kg (current = 533 → need 205× improvement). Scenario B (0.05): 2.5/0.05 = 50.0 kWh/kg (current → need 10.7× improvement). Scenario C (1.20): 2.5/1.20 = 2.08 kWh/kg (current → need 256× improvement).
BREAK-EVEN: kWh/kg required to match renewable H2 ammonia (0.6 kg CO2eq)—all scenarios	ScenarioA: ≤0.625 kWh/kg|ScenarioB: ≤12.0 kWh/kg|ScenarioC: ≤0.50 kWh/kg	-	Ecoinvent 3.9.1	0.00	Break-even vs. renewable hydrogen-based ammonia (0.6 kg CO2eq/kg NH3): Scenario A (0.96): 0.6/0.96 = 0.625 kWh/kg. Scenario B(0.05): 0.6/0.05 = 12.0 kWh/kg. Scenario C (1.20): 0.6/1.20 = 0.50 kWh/kg. These are even more stringent thresholds. For reference, conventional Haber–Bosch uses ~8–12 kWh/kg (including all energy).

.

Overall Carbon Footprint: The gate-to-gate life cycle assessment reveals a total carbon footprint of 21.36 kg CO₂eq per kg NH₃ for the plasma-assisted ammonia synthesis system at TRL 4. Manufacturing dominates at 98.5% (21.36 kg CO₂eq), while raw materials contribute negligibly (~1.5%). This result highlights plasma reactor electricity consumption as the primary environmental driver at this stage of development.

Electricity Consumption and Scenario Analysis: The baseline electricity consumption of general plasma ammonia synthesis systems, 533 kWh per kg NH₃, highlights the early developmental stage of plasma-based ammonia synthesis.

Table 5. LCIA Results for alternative grid scenarios.

Scenario	Grid Carbon Intensity (kg CO2eq/kg NH3)	Result (kg CO2eq/kg NH3)	Relative to Conventional NH3 Production 1
A: Global average	0.96	511.68	~205×
B: Renewable-dominated	0.05	26.65	~10.7×
C: Coal-heavy	1.2	639.60	~256×

¹ Conventional fossil-based benchmark: 2.5 kg CO₂eq/kg NH₃.

presents the scenario results for different electricity grid mixes. Even when assuming a 100× efficiency improvement and a fully renewable electricity grid, the carbon footprint remains ~2.05 times higher than the conventional Haber–Bosch process.

Sensitivity Analysis and Break-Even Conditions: Efficiency improvements of 10× and 100× reduce electricity consumption to 53.3 and 5.33 kWh/kg NH₃, respectively. The strict efficiency thresholds needed for carbon competitiveness are revealed by break-even analysis, which is described in

Table 6. Break-even analysis for carbon competitiveness.

Benchmark	Scenario A: Current Grid Mix	Scenario B: Renewable Dominated	Scenario C: Coal Heavy
Conventional (2.5 kg CO2eq/kg NH3)	≤2.60	≤50.0	≤2.08
Renewable H2-based (0.6 kg CO2eq/kg)	≤0.625	≤12.0	≤0.50

. Break-even analysis further shows that the environmental viability of plasma-assisted ammonia synthesis is highly dependent on the electricity source. To achieve carbon parity with conventional Haber–Bosch ammonia (2.5 kg CO₂eq/kg NH₃), plasma systems must reduce electricity consumption to ≤2.60 kWh/kg NH₃ under the global average grid and ≤2.08 kWh/kg NH₃ under coal-intensive electricity, corresponding to efficiency improvements of approximately 205–256× from current performance. In contrast, when powered by renewable electricity, the required threshold increases to ≤50.0 kWh/kg NH₃, reducing the improvement target to about 10.7×. More stringent performance is necessary to compete with renewable H₂-based Haber–Bosch ammonia (0.6 kg CO₂eq/kg NH₃), requiring electricity demands below ≤0.625 kWh/kg NH₃ for the global average grid, ≤0.50 kWh/kg NH₃ for coal-heavy grids, and ≤12.0 kWh/kg NH₃ under renewable electricity scenarios. These results highlight that decarbonized electricity substantially relaxes the energy efficiency requirements for plasma ammonia synthesis, while fossil-based grids impose extremely demanding performance targets.

Contribution Analysis: Raw material inputs contribute only 0.32 kg CO₂eq per kg NH₃, representing around 1.5% of the total carbon footprint. These inputs include N₂ produced via cryogenic air separation and H₂ supplied through water electrolysis. This result indicates that research and development efforts should primarily focus on improving the energy efficiency of the plasma reactor, while optimization of feedstock supply is unlikely to significantly influence environmental performance at the current TRL.

Critical Assessment: The analysis indicates that plasma-assisted ammonia synthesis at TRL 4 is not limited primarily by the carbon intensity of electricity, which could be mitigated by using renewable energy. Rather, there is an inherent inefficiency in terms of energy use. With energy requirements that are two to three orders of magnitude higher compared to competing benchmarks, the benefits of the technology, such as modularity and the use of readily available raw materials like air and water, cannot offset its weaknesses.

To reduce these existing atom economy losses, various major improvement pathways have been proposed to improve the plasma-assisted ammonia synthesis. These are enhancing the coupling efficiency of plasma energy to minimize power losses in the non-productive discharge modes, creating catalysts that can reduce the activation barrier for N₂ thus reducing the specific energy input, high conversion efficiency reactor designs able to yield beyond 1% per pass yields typical single-pass ammonia production, and adoption of heat recovery systems capable of harnessing exothermic reaction enthalpy (~46 kJ mol⁻¹ NH₃).

In the absence of significant progress on these fronts, the issue will only shift rather than be resolved. In such a scenario, our dependence on fossil fuels may be replaced by an excessive demand for electricity.

5.2. LCIA Results and Discussion

LCIA results obtained using the Environmental Footprint (EF) method show that electricity-related processes are the main contributors to environmental impacts across all categories. Within the system boundary considered in this study, most impacts are driven by energy use, while material inputs and auxiliary processes contribute only marginally. These results indicate that the environmental performance of the system largely depends on electricity consumption, the efficiency of the plasma system, and the carbon intensity of the electricity supply. This is mainly due to the substantial power demand of plasma generation, the efficiency of ammonia formation in the plasma reactor, and the characteristics of the electricity mix assumed in the analysis.

A scenario analysis was conducted to evaluate the potential benefits of electricity decarbonization. By replacing the baseline electricity supply with a fully renewable electricity mix using Environmental Footprint factors implemented in Devera, emissions associated with the synthesis process were significantly reduced. Under this scenario, climate change impacts decreased by up to 97%, reaching approximately 0.26 kg CO₂-eq per functional unit.

Based on the Environmental Footprint (EF) assessment, the system may contribute to several midpoint impact categories, including climate change (CO₂ equivalents), acidification, ozone depletion, ionizing radiation, land use, water use, and resource depletion. However, many laboratory-scale studies do not directly measure or report plasma-related by-products such as ozone, nitric acid, or other reactive species. As a result, these emissions are likely underrepresented in the currently available life cycle inventory data.

Based on insights from the current scientific literature, this study examines five key environmental impact pathways: (1) ozone depletion and atmospheric chemistry interactions, (2) acidification and potential water quality degradation, (3) particulate matter (PM_2.5) formation and oxidative potential, (4) biodiversity impacts in terrestrial and aquatic ecosystems, and (5) climate change effects related to reactive nitrogen compounds and greenhouse gas emissions.

5.2.1. Atmospheric Chemistry Interactions

In plasma-based ammonia synthesis, ammonia (NH₃) and ammonium ions (NH₄⁺) are the primary products. However, the process can also generate several short-lived reactive species, including nitrogen oxides (NO, NO₂, and N₂O) and unreacted reactive nitrogen intermediates such as NH, NH₂, and atomic nitrogen (N) [82,83]. These species may participate in various atmospheric and environmental processes. The relationships between these chemical species and their potential environmental effects are illustrated in Figure 8.

Hydrogen leakage: Hydrogen used as a feedstock may also raise indirect atmospheric chemistry concerns due to potential leakage during its production, storage, and use. Hydrogen in the atmosphere may be an indirect greenhouse gas through its reaction with hydroxyl radicals (OH), which are the most important oxidizing agents in the atmosphere. The reduction in the number of OH radicals may increase the life span of methane in the atmosphere and affect tropospheric ozone formation [81]. According to modeling studies, hydrogen leakage could constitute approximately 0.2 to 10% of total system throughput with significant effects on atmospheric composition [84]. The hydroxyl radicals influenced by hydrogen leakage are also associated with methane oxidation. Increased hydrogen concentrations can interfere with the oxidation of methane by the hydroxyl radicals and reduce the atmosphere’s oxidation potential. This process could prolong the lifetime of methane in the atmosphere, leading to radiative forcing. Also, the oxidation of hydrogen will increase the formation of water vapor in the stratosphere. Modeling studies show that the use of hydrogen, especially with leakage rates of above 1–2%, could lead to increases in methane lifetime and lower stratospheric ozone concentrations [84]. Thus, leakages of hydrogen should be reduced through better reactor design and gas recovery systems to minimize these indirect effects in the atmosphere.

Nitrogen oxides (NO_x): NO_x emissions have complicated effects on tropospheric ozone chemistry. Higher levels of NO_x, like those found in industrial or urban areas, can react to increase ozone concentrations via photochemical reactions with volatile organic compounds (VOCs). This relationship is, however, non-linear and reliant on the surrounding chemical regime. Under NO_x-limited conditions, more emissions generally mean higher ozone production, but in VOC-limited environments, increased NO_x can lead to lower ozone concentrations [85]. Finally, NO oxidizes to NO₂ and photolyzes to form ozone in sunlit environments with active hydrocarbons. More importantly, NO_x can also participate in reactions removing ozone via the formation of nitric acid, HNO₃, and other nitrogen reservoir species. Consequently, the net effect is determined by local photochemical conditions and meteorology as well as the co-emitted compounds. A key consideration for plasma-based ammonia facilities is effective NO_x control to minimize ozone-related impacts, which can be of concern in locations where ambient ozone levels are high.

Nitrous oxide (N₂O). N₂O emissions pose a direct risk to stratospheric ozone. Although relatively inert in the troposphere, N₂O is broken down in the stratosphere through photolysis and reactions with excited oxygen atoms, producing nitric oxide (NO) radicals that catalytically destroy ozone. With an atmospheric lifetime of around 120 years, N₂O is currently considered the most significant ozone-depleting substance emitted by human activities [85]. Plasma processes may generate N₂O as a byproduct through incomplete nitrogen oxidation or recombination reactions involving nitrogen radicals. Even small amounts formed relative to NH₃ production can lead to notable cumulative emissions because of the long atmospheric lifetime and high global warming potential of N₂O [86]. Therefore, minimizing N₂O formation through optimized plasma operating conditions and implementing post-treatment abatement technologies is important for reducing potential impacts on stratospheric ozone.

5.2.2. Acidification and Water Quality Degradation

Emissions of ammonia and nitrogen oxides during plasma-based ammonia production can contribute to atmospheric nitrogen deposition, which may lead to the acidification of soils and surface waters. In the atmosphere, ammonia can undergo gas-to-particle conversion, forming ammonium salts such as ammonium sulfate and ammonium nitrate. These particles are deposited through both wet and dry deposition processes. In addition, the oxidation of NO_x emissions can produce nitric acid, which deposits as a strong acid and further contributes to ecosystem acidification [87].

Nitrogen deposition can alter soil chemistry by increasing hydrogen ion concentrations, mobilizing toxic aluminum, and depleting base cations such as calcium and magnesium. Lower soil pH can alter important feedback cycles, plant communities, and soil microbial populations. Nitrogen deposition can lead to acidification of surface waters (especially in low-buffering systems), including aquatic ecosystems. Methods that could decrease biodiversity, disrupt fish spawning, and change food web dynamics [88]. Ecosystems that have inherently acidic soil or waters with low alkaline content are particularly sensitive to these impacts. Emission controls such as NO_x scrubbers and ammonia capture will help alleviate acidification impacts by reducing nitrogen deposition [87].

Nitrogen deposition may also regulate eutrophication in freshwater and coastal marine environments. Excess nitrogen that enters these systems can trigger rapid algae growth, typically resulting in blooms. When these blooms die, they use dissolved oxygen while breaking down, producing hypoxic or sometimes anoxic conditions that are detrimental to aquatic life. In aqueous systems, ammonia exists in equilibrium between ionized ammonium (NH₄⁺) and the more toxic un-ionized ammonia (NH₃), with higher pH and temperature favoring the formation of NH₃. Chronic levels of ammonia are toxic to fish and can damage gill function, osmoregulation, growth, and reproductive capacity [89]. Similarly, in marine habitats, higher nitrogen levels could lead to the proliferation of toxic algae species like cyanobacteria and dinoflagellates that pose serious threats to human well-being. Consequently, lowering ammonia and NO_x discharges is essential for sustaining healthy water systems and ecological balance [90].

5.2.3. Particulate Matter Formation

Ammonia emissions are a key precursor to the formation of secondary inorganic aerosols (SIA), and contribute to high concentrations of ammonium nitrate (NH₄NO₃) and ammonium sulfate that dominate fine particulate matter (PM_2.5). In the air, ammonia undergoes gas-to-particle conversion processes to form ammonium sulphate and ammonium nitrate by reacting with sulphuric and nitric acids. These reactions are highly dependent on environmental conditions, temperature, relative humidity, and/or presence of acidic species [91].

A number of studies have shown a high correlation between atmospheric ammonia concentrations and PM_2.5 levels. Ammonia plays a pivotal role in secondary aerosol formation, especially in high-NO_x environments. For example, a study conducted in the Seoul Metropolitan Area found that ammonia showed the strongest correlation with PM_2.5 concentrations compared to other pollutants such as NO₂ and SO₂, with a correlation coefficient of R = 0.51. These findings suggest that reducing ammonia emissions could be an important strategy for mitigating PM_2.5 pollution [92]. Similar studies done in North America and Europe have proven that there is a relationship between the reduction in ammonia emissions and low concentrations of PM_2.5, particularly in places where ammonia is plentiful in comparison to acidic compounds [91].

Aerosol pH is important in the formation of ammonium salts because it modulates the partitioning of ammonia between gas and particle phases. In ammonia-rich environments, higher pH conditions tend to favor the formation of ammonium nitrate, which is semi-volatile and sensitive to temperature. Conversely, ammonium sulfate forms more readily when sulfuric acid is abundant. Recent reductions in dust emissions have also changed aerosol pH by decreasing the abundance of alkaline species in the atmosphere, which may subsequently enhance ammonia gas-to-particle conversion efficiencies [93].

5.3. Implications of Cradle-to-Gate Boundary Expansion

The extension of the scope to the cradle-to-gate will include further contributions from hydrogen generation, its infrastructural requirements, and upstream processes. The resulting cradle-to-gate impacts may also vary substantially depending on the plasma configuration, ammonia production pathway, and feed source, as numerous plasma-assisted synthesis technologies with differing operational characteristics and material requirements have been reported, as discussed in Section 2.2.

For general plasma-based ammonia synthesis, hydrogen produced via renewable electrolysis (assuming 50 kWh/kg H₂ and wind electricity at 11 g CO₂-eq/kWh) would add approximately 0.10 kg CO₂-eq per kg NH₃, representing a negligible increase (≈0.3% for the experimental DBD case and 0.04% for the predictive baseline) due to the dominance of reactor electricity consumption. Under grid-based electrolysis (EU-27 mix: 475 g CO₂-eq/kWh), the additional burden (~4.2 kg CO₂-eq per kg NH₃) remains relatively small, corresponding to ~14% and ~1.7% increases for the experimental and predictive cases, respectively. Infrastructure and equipment contributions are estimated to add a further 5–10% based on comparable electrolysis studies. In contrast, for the Haber–Bosch process, inclusion of upstream hydrogen production via steam methane reforming would increase total emissions from 2.35 to approximately 2.8–3.2 kg CO₂-eq per kg NH₃, reflecting a 20–35% increase.

These additions would not affect the overall conclusions of the study. Electricity consumption within the reactor already dominates total impacts, and thus the relative ranking of scenarios remains unchanged. While absolute GWP values would increase, the conclusion regarding the current inefficiency of the technology would remain valid and may even be reinforced. In addition, the break-even thresholds would become slightly more stringent, further highlighting the scale of efficiency improvements required. In essence, deepening the system boundary would offer a more complete evaluation but not fundamentally change the findings of this study.

6. Case Study: Experimental System Characterization and Inventory Data

The selected case study involves the dielectric barrier discharge (DBD) needle-to-plate configuration due to various reasons. First, the design is relatively simple and requires minimal auxiliary equipment. Second, it operates at ambient temperature and pressure, which simplifies system requirements. Third, its modular structure makes it suitable for distributed ammonia production. In addition, comprehensive experimental validation data for this configuration are available from our laboratory [16]. Finally, the needle-to-plate setup is widely used as a common starting point in plasma ammonia research. Although this configuration may not represent the fully optimized system, it provides a practical baseline for demonstrating the proposed gate-to-gate LCA framework. Detailed experimental methods, parametric studies, and performance characterization are described in our previous publication [16]. The system boundary and major process flows considered in the gate-to-gate assessment are illustrated in Figure 9.

6.1. Experimental System and Performance

The DBD needle-to-plate reactor consists of a 30 mL borosilicate glass vessel, a steel needle electrode covered with quartz, and an aluminum plate that serves as the grounded electrode, with an optimized gap distance of 1.0 cm. Under the operating conditions used in this study (75 W input power, 1.4 L min⁻¹ N₂ flow rate, and 30 min of reaction time), the system produced an ammonia concentration of 19.7 ppm. Based on direct experimental measurements, the corresponding specific energy consumption was calculated to be 63,450 kWh kg⁻¹ NH₃ [16]. This value represents the actual measured performance of the investigated experimental configuration and should not be confused with the literature-derived baseline value of 533 kWh kg⁻¹ NH₃ adopted in the predictive LCA presented in Section 5.

The performance demonstrated above is typical for the initial stage (TRL 4) of plasma-based ammonia production, when the yield and energy efficiency of ammonia generation are low. During the experiments, the neon transformer was operated without frequency tuning capability, such that the output frequency could not be matched to the resonant frequency of the DBD reactor. This non-resonant operation contributed to high energy consumption and considerable waste heat generation. It is expected that the use of a frequency-adjustable neon transformer would enable resonant tuning and significantly improve the overall energy efficiency of the system.

These findings highlight the need for substantial improvements before the technology can become environmentally viable. Integrating catalysts into the plasma system is considered one of the most promising approaches to increase conversion efficiency and reduce energy demand. In this study, key operating parameters, including nitrogen flow rate, input power, electrode gap, and solution pH, were systematically investigated [16].

6.2. LCI and Impact Assessment

As shown in

Table 7. LCI of the case study.

Input Parameter	Value per kg NH3	Unit
Electricity	63,450	kWh
DI water	50,841	L
Nitrogen Gas	68,702	m3

, the Life Cycle Inventory for the 1 kg NH₃ functional unit includes electricity (63,450 kWh), nitrogen gas (68,702 m³), and deionized water (50,841 L), while the contribution from reactor infrastructure is negligible (<0.01%). Background processes use ecoinvent v3.8 [94] with fossil-heavy grid electricity (500 g CO₂-eq/kWh) as baseline [95].

For the experimental DBD case study, the ReCiPe 2016 method was primarily selected to allow direct comparison with previous LCA studies on plasma-assisted ammonia synthesis, as most reported studies have applied ReCiPe or other midpoint-based approaches [96,97]. This method provides a more detailed and transparent view of environmental trade-offs across different impact dimensions. In addition to that, since no normalization and weighting are used, the data becomes easier to interpret without aggregation. To further evaluate methodological consistency, the case study GWP was additionally compared with results obtained using the EF 3.0 method.

According to the life cycle impact assessment (ReCiPe 2016), it is clear that the electricity utilization component drives environmental impact in greater magnitude than other categories. This is due largely to an exorbitantly high SEC. With respect to Global Warming Potential (GWP), electricity contributes approximately 69% (31,725 kg CO₂-eq) of the total process emissions (45,719.61 kg CO₂-eq). Nitrogen gas is the second-largest contributor at approximately 30% (13,740.40 kg CO₂-eq), while deionized water contributes less than 1% (254.21 kg CO₂-eq).

From

Table 8. LCIA of the case study.

Impact Category	Unit	Electricity	DI Water	Nitrogen Gas	Total Impact
Global Warming Potential (GWP)	kg CO2-eq	31,725.00	254.21	13,740.40	45,719.61
Acidification (AP)	kg SO2-eq	95.17	1.02	34.35	130.54
Eutrophication (EP)	kg P-eq	6.35	0.25	0.69	7.29
Fossil Depletion (FDP)	kg oil-eq	9517.50	50.84	4122.12	13,690.46

, electricity is the dominant contributor across all impact categories, accounting for approximately 73% of acidification, 87% of eutrophication, and 70% of fossil depletion impacts. Nitrogen gas contributes a smaller share, whereas water contributes negligibly. Although switching to renewable energy could reduce impacts, the main limitation remains the process inefficiency due to the very low ammonia concentration of 19.65 ppm.

6.3. Sensitivity Analysis and Performance Targets

The current system shows an extremely high Global Warming Potential of about 45,720 kg CO₂-eq per kg NH₃, which is more than 18,000 times higher than the conventional Haber–Bosch process (around 2.5 kg CO₂ per kg NH₃). The main contributor is electricity use, with a very high energy demand of 63,450 kWh per kg, accounting for roughly 70% of the total carbon footprint. Even if the system were powered entirely by renewable energy, such as solar or wind (0.05 kg CO₂/kWh), the emissions would remain around 16,000 kg CO₂ per kg without improving energy efficiency. Nitrogen gas is the second major contributor, making up about 30% of the impact due to its extremely high consumption of 68,702 m³ per kg, which is nearly 100,000 times higher than the theoretical requirement. The major weakness in the process is the extremely low concentration of ammonia (19.7 ppm), which makes it necessary for high amounts of nitrogen and deionized water to be used per unit of product, causing considerable dilution effects on the environment.

For commercial viability and to be called “green ammonia,” the system would need a massive improvement in overall efficiency, over 9000 times its current effective performance. Currently, the electricity required is unreasonably high at 63,450 kWh per kg NH₃ as compared to what would be realistic, around 7 kWh per kg or about a nine thousand-fold reduction. And there are similar gaps for nitrogen use, which at 68,702 m³ per kg is currently acceptable but would need to fall to about 7.5 m³ per kg. The ammonia concentration is also a critical concern, having a level of only 19.7 ppm when some processes would need concentrations nearer 18% (180,000 ppm). These gaps together underscore the need for advances in energy efficiency, reactant utilization, and product concentration before this system can be regarded both environmentally and commercially viable.

A practical pathway to scale would start with gas recycling, since a closed-loop nitrogen cycle could cut the nitrogen footprint by more than 99%. A sensitivity scenario incorporating closed-loop nitrogen recycling was evaluated to reduce the demand for continuous air separation. In this configuration, unreacted nitrogen is recirculated back into the reactor, and only makeup nitrogen is supplied to compensate for system losses and ammonia formation, reducing fresh nitrogen demand by approximately 90%. The results indicate that nitrogen recycling decreases the global warming potential by 3.2% (from 30.1 to 29.1 kg CO₂-eq/kg NH₃) and reduces cumulative energy demand by 2.8%. The relatively modest improvement is attributed to the dominance of plasma reactor electricity consumption (63,450 kWh/kg NH₃), which far exceeds the contribution associated with nitrogen separation (~2000 kWh/kg NH₃ equivalent). Nevertheless, closed-loop nitrogen operation remains a promising strategy for future pilot-scale systems, particularly as improvements in plasma reactor efficiency reduce the relative contribution of auxiliary processes.

The next priority is improving the plasma-catalyst system so the single-pass conversion rate rises well above 19.7 ppm, which would lower the energy cost per unit of ammonia produced. Heat recovery is also important because operating at 75 W for 30 min likely wastes a large amount of thermal energy; capturing some of that heat for water preheating or pre-activation could improve overall efficiency.

6.4. Case Study GWP Assessment: EF 3.0 vs. ReCiPe 2016

The global warming potential (GWP) was additionally calculated using the Environmental Footprint (EF) 3.0 method to enable comparison with the ReCiPe methodology. The EF 3.0 method applies GWP-100 characterization factors based on IPCC AR5, following the EU PEF/OEF methodology. The comparative GWP results obtained using both LCIA methods are summarized in

Table 9. GWP results of the case study under EF 3.0 and ReCiPe 2016 methods.

Input	EF 3.0 (kg CO2-eq/kg NH3)	EF 3.0 (%)	ReCiPe 2016 (kg CO2-eq/kg NH3)	ReCiPe 2016 (%)
Electricity	32,041.2	64.8	31,725.0	~69.0
Nitrogen Gas (N2)	17,363.2	35.1	13,740.4	~30.0
DI Water	15.7	0.03	254.2	~0.6
Total	49,420.1	100	45,719.6	100

. Both the Environmental Footprint (EF) 3.0 and ReCiPe 2016 LCIA methods identified electricity consumption as the dominant contributor to the Global Warming Potential (GWP) of the ammonia production process, although differences were observed in the absolute impact values and proportional contributions. Using the EF 3.0 method, the total GWP was calculated as 49,420.1 kg CO₂-eq/kg NH₃, with electricity contributing 32,041.2 kg CO₂-eq/kg NH₃ (64.8%), followed by nitrogen gas production at 17,363.2 kg CO₂-eq/kg NH₃ (35.1%), while deionized (DI) water contributed only 15.7 kg CO₂-eq/kg NH₃ (0.03%). In comparison, the ReCiPe 2016 method yielded a lower total GWP of 45,719.61 kg CO₂-eq/kg NH₃, with electricity contributing approximately 31,725 kg CO₂-eq/kg NH₃ (~69%), nitrogen gas production contributing 13,740.40 kg CO₂-eq/kg NH₃ (~30%), and DI water remaining a negligible contributor at 254.21 kg CO₂-eq/kg NH₃ (<1%). Although both methods produced consistent rankings of impact contributors, EF 3.0 resulted in an approximately 8.1% higher total GWP than ReCiPe 2016, primarily due to differences in characterization factors and background emission models associated with electricity generation and industrial nitrogen production. Nevertheless, both methods consistently demonstrate that the extremely high Specific Energy Consumption (SEC) is the primary driver of environmental impact, emphasizing the importance of improving reactor efficiency and transitioning to low-carbon electricity sources to reduce the GWP of plasma-assisted ammonia synthesis.

6.5. Implications

At the moment, ammonia synthesis using DBD plasma is still in an early stage and not yet environmentally competitive, but the results clearly highlight where improvements can make the biggest difference. For example, the present system provides a Global Warming Potential of approximately 45,720 kg CO₂-eq/kg NH₃, which is significantly larger than that of the conventional Haber–Bosch process.

Fortunately, some obvious improvement opportunities already exist. This promotes the integration of embedded catalysts in plasma systems, making it a feasible method to enhance nitrogen activation, suppress undesired reactions such as NO_x formation, and enable operation at lower power. This opens new opportunities for future research for improving plasma–catalyst interactions, specific energy consumption, and coupling the system with renewables in order to enable an efficient final use of this process that could benefit from more intermittent energy sources such as solar or wind.

However, the technology still offers potential for small-scale or distributed ammonia production and renewable energy storage, although it is limited in its current performance. Continued advances in catalyst design, gas recycling, and heat recovery are expected to further improve process efficiency. Notably, the best-case scenario (≈1.39 kWh/kg NH₃) suggests that optimized plasma systems could potentially surpass conventional ammonia synthesis in terms of energy efficiency, highlighting the long-term promise of this technology.

7. Discussion

7.1. Current Performance Assessment

The large discrepancy between the baseline prediction of 533 kWh/kg NH₃ and the experimentally determined DBD case study of 63,450 kWh/kg NH₃ underscores the high degree of variation in the efficiency of plasma-enhanced ammonia production processes. The predictive baseline, derived from a sensitivity analysis of multiple plasma systems reported in the literature, represents a conservative but representative estimate for early-stage technology assessment. In contrast, the experimental DBD configuration investigated in this study reflects a low-yield TRL 4 system with substantially higher energy demand. This discrepancy demonstrates that plasma reactor performance can vary considerably depending on plasma type, reactor geometry, feed conditions, and process optimization. Nevertheless, both values remain substantially higher than conventional Haber–Bosch energy requirements, emphasizing the need for continued advances in plasma reactor engineering, catalyst integration, and energy efficiency optimization before plasma-assisted ammonia synthesis can become environmentally competitive.

Here, a fundamental predictive gate-to-gate LCA of an early-stage DBD plasma-based ammonia synthesis indicates significant environmental hurdles that must be overcome before the pathway can compete with traditional Haber–Bosch processes. The system is still in favor of TRL 4, reflecting its early development stage, and operates with a large energy consumption of 63,450 kWh per kg NH₃, resulting in global warming based on electricity use alone to be about 31,725 kg CO₂-eq/kg, or when taking nitrogen gas and deionized water into account, would be around 45,720 kg CO₂-eq/kg. This is much better compared to the incumbent Haber–Bosch production, but it shows quite clearly where improvements really move the needle. Under a completely renewable electricity scenario, even then emissions would still be about 3200 kg CO₂-eq per kg, reinforcing that increasing efficiency is the key priority moving forward.

The break-even analysis shows that moderate efficiency improvements combined with renewable electricity are still insufficient to make plasma-assisted ammonia synthesis environmentally competitive. For example, reducing electricity consumption from the predictive baseline of 533 to 100 kWh/kg NH₃ represents a substantial 5.3× improvement. However, even when powered entirely by renewable electricity with an emission factor of 0.05 kg CO₂-eq/kWh, the resulting carbon footprint would still be 5.0 kg CO₂-eq/kg NH₃.

This value remains approximately twice the gate-to-gate fossil Haber–Bosch benchmark of 2.5 kg CO₂-eq/kg NH₃. The analysis therefore indicates that environmental competitiveness would require electricity consumption to decrease to ≤50 kWh/kg NH₃, corresponding to approximately a 10.7× improvement from the predictive baseline and a 1269× improvement from the current experimental DBD case study. These results demonstrate that renewable electricity alone is insufficient to offset moderate process inefficiency and that substantial improvements in reactor energy efficiency remain the primary requirement for reducing environmental impacts.

At the current TRL 4 stage, plasma-assisted ammonia synthesis remains highly energy-intensive and environmentally unfavorable. Nevertheless, the sensitivity and break-even analyses help identify the technological improvements required for potential future competitiveness. Potential improvements may arise from advances in plasma–catalyst coupling, more efficient vibrational excitation of nitrogen, and overall process intensification to reduce energy demand. However, whether such advances can be achieved at industrially relevant scales remains uncertain and requires further investigation. This study therefore does not claim that environmental competitiveness is currently achievable or imminent, but rather identifies the performance improvements that would be required for future competitiveness and the key areas where further technological development is needed.

Simultaneously, this study underscores an empowering and pragmatic benefit of the process: it requires limited knowledge and equipment investment to realize localized ammonia fertilizer production. Such decentralized systems could offer a robust alternative in contexts of extreme supply deficits or disrupted distribution channels, enabling communities to sustain agro activity without substantial reliance on larger industrial infrastructure.

Integration of catalysts becomes the key technology to reach these goals. The interaction between plasmas and catalysts may revolutionize the nitrogen activation mechanism by increasing the vibration of N₂ molecules, reducing the energy barrier of N₂ dissociation, and blocking NO_x formation paths [19]. The most favorable plasma-assisted NH₃ synthesis result reported recently reached a very low specific energy consumption of 5 GJ/ton NH₃ (≈1.39 kWh/kg NH₃), approximately the same as in conventional Haber–Bosch processes, which require an additional amount of energy for their operation (~7–13 kWh/kg NH₃). This suggests that, in ideal conditions, highly engineered plasma-assisted systems might theoretically provide more efficient ammonia production than conventional pathways to the hydrogen sector; a performance which remains unexplored at industrially relevant scales.

In addition to energy efficiency considerations, plasma-based ammonia production systems present a complex environmental profile involving multiple impact pathways related to atmospheric chemistry, air quality, water resources, biodiversity, and climate change [98]. The technology’s environmental performance is critically dependent on emission control effectiveness, particularly for ammonia, nitrogen oxides, nitrous oxide, and hydrogen leakage.

The environmental performance of the technology strongly depends on controls of emissions, especially ammonia, nitrogen oxides, and nitrous oxide, plus hydrogen leakage. Here are some of the key takeaways from this analysis: (1) Atmospheric Chemistry: Hydrogen leakage may indirectly influence stratospheric ozone and methane lifetime via OH radical chemistry, NO_x emissions causes to tropospheric ozone formation and N₂O has direct stratospheric ozone depletion effect [99]; (2) Air Quality: Ammonia emissions is the most important precursor for PM_2.5 formation, with strong correlations between NH₃ concentrations and SIA levels; (3) Water Quality: Nitrogen deposition leads to acidification and eutrophication in aquatic ecosystems; (4) Biodiversity: Nitrogen enrichment endangers terrestrial as well as aquatic biodiversity by changed competitive relationships and soil acidification; (5) Climate: N₂O emissions are the dominant climate impact, a greenhouse gas with a global warming potential 265–298 times higher than CO₂. To minimize these impacts, recommended measures include high-efficiency ammonia capture systems, NO_x abatement technologies, optimized plasma operating conditions to reduce N₂O formation, low-leakage hydrogen handling systems, and continuous emissions monitoring.

For the general plasma-assisted ammonia synthesis assessment, the EF 3.0 method was applied because it is the default impact assessment method available in the Devera tool and is widely used for policy-oriented environmental benchmarking. In contrast, the experimental case study employed ReCiPe 2016 to enable direct comparison with previous plasma-assisted ammonia synthesis LCA studies, which commonly use midpoint-based methods. To evaluate methodological consistency, an additional comparison between ReCiPe 2016 and EF 3.0 was also performed for the experimental case study using the same Devera assessment platform. Although both methods evaluate similar environmental mechanisms, they differ in characterization, normalization, and aggregation approaches. Therefore, quantitative comparisons should only be made within the same assessment framework rather than directly across sections. Nevertheless, the overall qualitative conclusions remain consistent, with both methods indicating substantially higher environmental impacts for current plasma-assisted ammonia synthesis compared with conventional Haber–Bosch production across most impact categories.

7.2. Future Potential and Development Pathways

Future improvements in plasma-based ammonia synthesis development could enhance efficiency and environmental performance along multiple pathways. Such as optimizing the geometry of plasma reactors and electrode configuration to maximize energy transfer, investigating other kinds of sources like microwave plasma, gliding arc discharge, or atmospheric-pressure plasma jets combined with catalysts to reduce activation energy barriers and obtain more ammonia during preparation. Additional improvements may also be achieved through process intensification strategies, including better gas mixing and residence time control, as well as through waste heat recovery and closer integration with renewable electricity systems. Together, these developments could significantly reduce energy demand and enhance the overall viability of plasma-based ammonia production.

While a significant proportion of current plasma ammonia technology remain unable to compete with Haber–Bosch for large-scale production, it may find niche applications where its unique characteristics provide value [100]: distributed agricultural production (small-scale on-farm synthesis eliminating transport infrastructure), renewable energy integration (direct coupling with intermittent wind/solar providing grid balancing), specialty chemical production (high-purity ammonia for electronics/pharmaceuticals), emergency or military applications (portable production for remote locations), and research platforms (studying nitrogen fixation mechanisms).

The potential contribution of plasma-assisted ammonia synthesis to the Sustainable Development Goals (SDGs) depends strongly on achieving major improvements in energy efficiency. Based on the break-even analysis, electricity consumption would need to decrease to ≤50 kWh/kg NH₃ using renewable electricity, representing approximately a 10.7× improvement from the predictive baseline and a 1269× improvement from the current experimental DBD case study. At present performance levels, the technology is not environmentally competitive and would likely be counterproductive to sustainable development due to its extremely high energy demand and associated environmental impacts.

If substantial efficiency improvements can be achieved, plasma-assisted ammonia synthesis could potentially support several SDGs. For SDG 2 (Zero Hunger), decentralized ammonia production may improve fertilizer accessibility in remote agricultural regions. For SDG 7 (Affordable and Clean Energy), coupling with renewable electricity could enable lower-carbon ammonia production and energy storage applications. For SDG 9 (Industry, Innovation, and Infrastructure), plasma synthesis represents a novel technological pathway that could diversify ammonia production systems. For SDG 12 (Responsible Consumption and Production), modular reactors may enable more flexible and localized production. For SDG 13 (Climate Action), reduced electricity consumption combined with renewable power could lower the carbon footprint below that of conventional Haber–Bosch production.

However, these potential benefits remain hypothetical and depend entirely on achieving substantial reductions in energy consumption. Renewable electricity alone is insufficient to offset moderate or high process inefficiency.

This work highlights the Collingridge dilemma, which describes the difficulty of regulating emerging technologies. As explained by David Collingridge in the early 1980s, the dilemma involves two conflicting challenges [101,102]. First, during the early stages of development, when a technology is still flexible and easier to modify, its long-term social and environmental impacts are difficult to predict. Second, once the technology becomes mature and its consequences become visible, it is often deeply embedded in economic systems, infrastructure, and institutional frameworks, making major changes difficult and expensive.

The best example of this dilemma is the process of plasma ammonia synthesis. Having the technology at the current state of TRL 4 adds a lot of flexibility as research focus can be adjusted, catalyst systems redesigned, and operating parameters can be completely reconceptualized. However, based on this assessment, there is considerable uncertainty regarding the environmental effects, as the current literature presents conflicting results by three orders of magnitude in performance (10³–10⁶ GJ/t-NH₃). Answering these questions on top of the absence of solid evidence is partly covered by the predictive LCA methodology because quantitative environmental baselines and performance targets are set, but only so much has been learnt about how boundary conditions change efficiency to obtain an outcome as efficient as possible when it is being done on a large scale, and how it will be able to sustain itself over time.

If the efficiency targets for plasma-based ammonia generation are achieved, the technology could progress toward TRL 9 and commercial-scale deployment. However, if these targets are not met, the technology may remain locked in an environmentally suboptimal pathway. Significant investments in plasma reactors, electricity grid capacity, and supply chain integration could create economic and institutional barriers to future reform. These sunk costs, together with established operational practices, may resist transformational changes even if later studies demonstrate that superior catalyst systems or alternative plasma configurations are more effective.

This work contributes to navigating the Collingridge dilemma by providing an early-stage quantitative environmental assessment that can inform decisions regarding the future development of the technology before it becomes technologically and institutionally entrenched. Such an assessment facilitates an evidence-based prioritization of the suite of research to be conducted by formulating clear and specific targets for performance, where plasma-catalyst synergy serves as the primary techno-economic driving force. However, above these benchmarks, we find that more R&D can only possibly be justified if it is clear to the relevant mechanistic details of catalyst integration and nitrogen activation by vibrational activation. For funding agencies, this implies considerable technical risk that may require diversified portfolio strategies. For technologists, research efforts should prioritize improvements in energy efficiency. For policymakers, plasma-assisted ammonia synthesis represents a promising long-term pathway toward decarbonization, particularly as advances in efficiency and renewable energy integration continue to emerge. For investors, continued technological progress and innovation could support future commercialization opportunities within the 2040–2050 timeframe.

8. Conclusions

In theory, plasma-assisted ammonia synthesis is attractive because it can operate under mild conditions and be powered by intermittent renewable electricity. However, the current environmental performance remains several orders of magnitude worse than that of conventional ammonia synthesis technologies. Unless major improvements in energy efficiency are achieved, the process may simply shift the environmental burden from high-temperature and high-pressure process emissions to intensive electricity consumption and its associated upstream impacts. Nevertheless, the BCS suggests that optimized plasma systems could potentially surpass conventional ammonia synthesis in terms of energy efficiency. Substantial improvements in performance may therefore be achievable through plasma-catalyst synergies and renewable electricity integration, which could significantly improve the environmental viability of the technology.

This study has several limitations that should be considered when interpreting the results. The gate-to-gate system boundary focuses only on the reactor and excludes upstream hydrogen production and downstream processes, which limits direct comparison with cradle-to-gate Haber–Bosch assessments. In addition, part of the analysis relies on literature-based data, as actual performance may vary depending on reactor design and operating conditions. Finally, this work evaluates environmental impacts only and does not consider economic feasibility, which is an important factor for real-world implementation. Even with such limitations, this study offers valuable insight into the potential environmental performance of ammonia synthesis techniques.

The Collingridge dilemma suggests that performance benchmarks and decision criteria should be established while a technology can still be fundamentally redirected, rather than allowing inertia and sunk costs to drive development toward environmentally inefficient pathways. This predictive LCA provides a quantitative foundation for evidence-based technology governance, helping researchers, funders, and policymakers make informed decisions regarding investments in plasma-based ammonia synthesis. Future research should prioritize catalyst screening, characterization of plasma-catalyst interactions, and pilot-scale experimental validation supported by environmental key performance indicators (KPIs) to reduce the risk of technological lock-in.