Global Transition of Energy Vectors in the Maritime Sector: Role of Liquefied Natural Gas, Green Hydrogen, and Ammonia in Achieving Net Zero by 2050

Abstract

The global transition toward net-zero emissions by 2050, encompassing the International Energy Agency’s Roadmap for the energy sector, the IMO’s revised strategy for the maritime industry, and broader climate guidelines, necessitates a profound transformation of both global energy systems and the shipping sector. In this context, energy vectors such as Liquefied Natural Gas, Green Hydrogen, and Ammonia are emerging as key elements for this shift. This review article proposes a comprehensive analysis of these vectors, contrasting their roles: Liquefied Natural Gas as a transitional solution and Hydrogen and Ammonia as long-term pillars for decarbonization. The research moves beyond a simple comparative analysis, offering a detailed mapping and evaluation of the global port infrastructure required for their safe handling, cryogenic storage, and bunkering operations. We examine their technical specifications, decarbonization potential, and the challenges related to operational feasibility, costs, regulation, and sustainability. The objective is to provide a critical perspective on how the evolution of maritime ports into energy hubs is a sine qua non condition for the secure and efficient management of these vectors, thereby ensuring the sector effectively meets the Net Zero 2050 climate goals.

1. Introduction

The Intergovernmental Panel on Climate Change (IPCC) aims to provide rigorous and transparent assessments of climate change science, offering reliable information for the formulation of climate, energy, and transport policies [1,2,3,4], with various stakeholders interested in its findings [1,2,3,4,5,6].

The IPCC’s First Assessment Report (FAR) confirmed that anthropogenic activities increase atmospheric greenhouse gases (GHG), intensifying the greenhouse effect. Even then, the complexity of emission reduction policies was recognized, given that primary sources originate from end-use energy and land-use sectors [7,8]. To date, six assessment reports and other documents covering sectors such as industry, transport, and construction have been published [7,8,9,10,11,12,13].

Following the publication of IPCC reports, sectors like energy [14] and maritime transport [15] have intensified efforts to assess and mitigate their contribution to GHG emissions, developing calculation methodologies and scenario analyses to achieve carbon neutrality in the coming decades.

In the energy sector, the International Energy Agency (IEA) [16] and British Petroleum (BP) [17] play complementary roles in analyzing the global energy system. BP has evolved since the late 90s, investing in renewable energy [18] and publishing reports such as the Statistical Review of World Energy [19,20], which includes emissions data. In 2020, BP committed to reaching net-zero emissions by 2050 [21], intensifying its publications on the energy transition and developing decarbonization scenarios [19,20,21,22].

The IEA [16] has recognized the central role of the energy sector in meeting climate goals [16,23]. It has published roadmaps [24,25] that establish a detailed trajectory for carbon neutrality. These documents signal the suspension of investments in new oil or gas fields and a significant decrease in global demand for fossil fuels [23,24,25].

Maritime transport has gained relevance in climate studies due to its contribution to GHG emissions and high energy consumption [26,27]. Despite being an efficient system [28], the predominant use of heavy fossil fuels makes it a major source of emissions [29]. This sector has intensified efforts to evaluate its environmental impact and advance toward decarbonization through calculation methodologies, scenario analysis, and roadmaps to transform its energy vectors and achieve carbon neutrality [26,27,28,29,30,31].

Since 2018, international and regional institutions have published strategies for climate neutrality in emission-intensive sectors such as energy and maritime transport. The International Maritime Organization (IMO) established its initial strategy for reducing GHG emissions in shipping with Resolution MEPC.304(72) [32], reinforced in 2023 with Resolution MEPC.377(80) [33], moving toward Net Zero by 2050, which updates its commitments in alignment with the goals of the Paris Agreement [34]. Concurrently, the European Union (EU) has implemented an ambitious legislative framework, including the European Green Deal [35], the Fit for 55 package [36], and specific regulations on alternative fuel infrastructure [37] and directives [38]. Furthermore, in the energy field, the IEA has published fundamental roadmaps [24,25,39,40], mapping global pathways to maintain the 1.5 °C goal. Initiatives like the RNC2050 [41] reflect national commitments to climate neutrality. Together, these instruments form a strategic framework guiding the transformation of energy vectors and the decarbonization of maritime transport and other sectors [32,33,34,35,36,37,38,39,40,41].

The regulatory framework promoted by the IMO seeks to reduce the environmental impact of maritime transport. Through various strategies, it aims to limit GHG emissions and optimize the energy consumption of ships and port infrastructure. These initiatives align with global climate commitments, encouraging the adoption of clean technologies, alternative fuels, and energy management systems to move toward carbon neutrality. This includes increasing ship efficiency and establishing Green Shipping Corridors and strengthening cooperation between the port and energy sectors, as described in the concept note of the 30th session of the Conference of the Parties (COP30) in Belém, Brazil [42]. This approach would enable the transport of low-emission fuels from production sites to high-energy demand centers, also facilitating the supply of these fuels for ships.

Within this framework, Liquefied Natural Gas (LNG), Hydrogen (H₂), and Ammonia (NH₃) have been identified [24,25] as crucial energy vectors for achieving carbon neutrality by 2050 [43,44]. For energy chains, these energy vectors have gained significance in research and development due to their potential for storage and their ability to connect producers with end-users, generally through maritime transport. This is possible because they can be transported and stored in liquid form at cryogenic temperatures [24,25,43,44,45].

Recent literature highlights a clear need for research on the maritime energy transition. Since 2023, it has been identified that the introduction of multiple alternative fuels for decarbonization demands careful governance and additional investigation [46]. This recognition coincides with the observation that ports play a critical role in the energy transition, serving as essential nodes that must evolve into renewable energy centers [47]. Furthermore, while fuels such as hydrogen, ammonia, and methanol are considered promising, their deployment requires urgent research [48], primarily to overcome technical and economic barriers [49]. Finally, the vision for 2025 reiterates that critical energy infrastructure in maritime ports is essential to enable their role as hubs [50]. This consensus reveals a central knowledge gap: while the necessity for ports to transform into hubs and adopt new fuels is indisputable, detailed research on the governance, infrastructure implementation, and transition required to materialize this change on a global and comparative scale remains incomplete.

Primarily, LNG is conceived as a transition fuel, necessary to displace coal in electricity generation in the short term [51]. However, its use must be gradually reduced as renewable sources expand. In contrast, hydrogen and ammonia are envisioned as zero- or low-emission solutions for the long term. Furthermore, the use of hydrogen is projected to decarbonize energy-intensive industries (significantly the steel and chemical industries) and for the production of synthetic fuels [52,53,54,55]. On the other hand, ammonia is planned as an essential and clean fuel, particularly for the maritime transport sector [56,57,58]. Methanol has not been considered in this study because, unlike other energy vectors, its role in global decarbonization still depends on carbon-intensive production processes derived from natural gas or coal [59,60,61]. Although clean methanol pathways exist (bio-methanol and e-methanol), their development is still in the research phase [52,53,54,55,56,57,58,59,60,61,62].

The aspects related to the necessity of emission reductions by the energy and maritime transport sectors highlight the leading role that energy vectors will play in achieving Net Zero by 2050, with ports becoming the new energy hubs in the coming years. This intensifies the need for research involving the analysis, synthesis, and evaluation of the participation of these vectors in the global energy transition.

The primary contribution of this study lies in offering an integrated framework for the transition of energy vectors within the maritime sector. This research goes beyond a simple comparative analysis of fuels by articulating the transformative role of maritime ports as energy hubs. Specifically, it provides an analysis that contrasts LNG as a transition fuel with Green Hydrogen and Ammonia as long-term Net Zero solutions. This articulation is crucial because the feasibility of decarbonization depends directly on how port infrastructure evolves to safely and efficiently manage the complex supply chain, cryogenic storage, handling, and bunkering of these new vectors. This integrated approach offers a strategic guide to ensure that the maritime sector meets global climate goals by 2050.

2. Materials and Methods

The purpose of this work is to analyze, synthesize, and evaluate the participation of LNG, Hydrogen, and Ammonia as energy vectors in the global energy transition to achieve Net Zero by 2050. To this end, a semi-systematic literature review method [63,64] has been employed, as it does not utilize all the structured steps required in a systematic review [65]. This review integrates the analysis of scientific literature with the evaluation of documentation from key official sources (intergovernmental reports, IEA/IMO roadmaps, and corporate/port strategies). This approach is fundamental to demonstrating the rapid regulatory and technological progress defining the maritime energy transition. The analytical contribution of this research focuses on three interconnected pillars that, until now, have not been synthesized together [62,63,64]:

• Mapping of Port Infrastructure for Energy Vectors: An updated mapping of the infrastructure for handling LNG, Hydrogen, and Ammonia in ports and maritime terminals globally is provided. This synthesis identifies the current presence of reception, storage, and bunkering capabilities for each energy vector, establishing an empirical baseline on the current state of the port energy transition. To classify the information, the terms in the tables have been grouped based on the following definitions [65]:
  • Operational (OPE): The port actively offers bunkering services (supply) for this fuel to ships on a regular and established basis.
  • Operational/Scaling (OPSC): The port not only offers the service but is also investing in or has implemented measures to drastically increase the supply volume.
  • Project (PRO): Financing has been secured, and the engineering or construction phase of specific infrastructure (for example, a terminal, a dedicated pipeline, or a bunkering barge) has formally commenced. The project has a budget, a schedule, and a defined location.
  • Project/Pilot (PRP): The project involves an experimental trial operation (pilot) to validate technology and supply chains, and crucially, to develop or adjust the safety regulatory framework before large-scale commercialization.
  • Project/Planning (PRPL): The feasibility study has been approved, and the port has allocated funds or formed consortia for the preliminary design or construction of the infrastructure, with an initial schedule and budget.
  • Planning (PLA): The fuel has been identified as a future priority in the port strategy, but specific investment, feasibility studies, or fund allocations for the infrastructure have not yet been publicly finalized.
  • Planning/Strategic (PLS): The fuel is part of the future national or port decarbonization strategy. It is a long-term goal, but dedicated infrastructure has not yet entered the public design or investment phase.
  • Planning/Study (PLST): The port is conducting technical feasibility studies, risk analyses, and demand studies to determine if the project is viable and how it would be implemented. The process is moving from the conceptual stage to scientific validation
• Technical and Other Characteristics: An analysis of the characteristics of each energy vector has been conducted, covering its entire life cycle. This includes a detailed evaluation of its technical and operational specifications. This analysis is complemented by research into the global production and demand dynamics for each fuel, a comparison of their emission profiles, and the impact of their adoption on the maritime industry. This compilation is essential to inform decision-making regarding the standardization and regulation of future port infrastructure.

In the preparation of this paper, the Gemini generative artificial intelligence (developed by Google) was utilized to assist in the synthesis and structuring of specific sections. Specifically, this AI model was employed to refine the synthesis of the study’s conclusions, ensuring alignment with the research findings across the categorized port groups. Additionally, Gemini was used to assist in the restructuring of the abstract and the thematic organization of technical characteristics regarding ammonia and hydrogen as energy vectors. All AI-generated outputs were critically reviewed, verified for technical accuracy, and edited by the authors to ensure the academic integrity and originality of the final manuscript.

3. Results and Discussion

While the total number of maritime ports worldwide is estimated at more than 8000 [66], they represent an indispensable node for international trade. In fact, United Nations Conference on Trade and Development (UNCTAD) underscores that global merchandise trade relies on the traffic of merchant ships for more than 80% of its volume [67]. The importance of a maritime port is distinguished by its position and the centrality of its activities [68]. Furthermore, due to their role in the supply chain, generation, governance, and other factors, official sources do not indicate an exact number of existing ports. The Appendix A shows the top 50 ports according to Twenty-foot Equivalent Unit (TEU) moved for the 2023/2024 period [69]. For greater ease in data management, the ports have been grouped according to the following thresholds [70,71]:

• Group 1: Greater than 10,000 TEU
• Group 2: Between 5000 and 9900 TEU
• Group 3: Below 4990 TEU

3.1. Mapping of Port Infrastructure for Energy Vectors

As previously mentioned, a mapping of the port infrastructure for LNG, Hydrogen, and Ammonia has been conducted for the 50 ports categorized into Groups 1, 2, and 3.

Group 1: In total, this group is composed of 14 ports. Their geographic location illustrates the dominance of Asia in global maritime trade. Ten of these ports are located in Asia, including seven of the primary megahubs in China (Shanghai, Ningbo-Zhoushan, Shenzhen, Qingdao, Guangzhou, Tianjin, and Xiamen), along with Singapore (Southeast Asia), Busan (South Korea), Hong Kong, and Klang (Malaysia). The remaining four ports are distributed across other key regions: two in Europe (Rotterdam and Antwerp-Bruges), serving as the main gateways to the continent, and one in the Middle East (Jebel Ali, United Arab Emirates).

Table 1. Energy Infrastructure of Maritime Ports: Group 1.

Port	LNG				Hydrogen						Ammonia
	OPE	OPSC	PRO	PRP	PRO	PRP	PRPL	PLA	PLS	PLST	PRO	PRP	PRPL	PLA	PLS	PLST
Shanghai [72]	•							•						•
Singapore [73]		•							•			•
Ningbo-Zhoushan [74]		•
Shenzhen [75]		•						•						•
Qingdao [76]	•							•						•
Guangzhou [77]	•							•						•
Busan [78]	•								•						•
Tianjin [79]	•						•							•
Hong Kong [80]				•						•						•
Rotterdam [81]	•					•							•
Jebel Ali (Dubai) [82]				•	•						•
Antwerp-Bruges [83]	•				•							•
Klang [84]	•							•						•
Xiamen [85]	•							•						•
Average (%)	50.0	21.4	0.0	14.3	7.1	7.1	0.0	50.0	7.1	7.1	0.0	7.1	0.0	50.0	0.0	14.3

Note: The dot (•) symbol indicates a correlation between the corresponding row and column.

presents the analysis of these ports and demonstrates a clear division in infrastructure maturity among alternative maritime fuels. LNG has firmly established itself as the current transition fuel, as ports offer or have committed to OPE or PRP status for bunkering. This confirms LNG as the immediate response of the sector to short-term decarbonization goals, with infrastructure development that is already consolidated. Conversely, Hydrogen and Ammonia remain largely in the PLS phase within the dominant Asian ports. PRO or Pilots dedicated to these zero-emission fuels are primarily concentrated in the West, led by European and Middle Eastern strategic hubs (Rotterdam, Antwerp-Bruges, and Jebel Ali) that are actively investing in import terminals and regulatory frameworks. This geographic disparity indicates that, while the industry is committed to LNG today, the physical infrastructure investment and regulatory development required for the widespread adoption of other vectors are lagging, posing a considerable challenge to achieving Net Zero goals by 2050.

Group 2: This group encompasses ports with an annual container traffic between 5 and 9.9 million TEU (including Kaohsiung, Los Angeles, Hamburg, Valencia, and others) and constitutes the category of Major Regional Gateways and Key-Level Transshipment Centers. These are essential as they play a crucial role as focal points of entry and exit for major economies (North America and Europe) and as strategic hubs for intra-Asian trade and Indian Ocean routes. Their relevance is high: they are the spearhead in the PRO/PRP phases, investing in the validation of Hydrogen and Ammonia infrastructure under strict regulatory frameworks. This is often driven by ambitious local zero-emission targets (as in the case of Los Angeles/Long Beach [86] and Valencia [87]) or by national energy security strategies (as in Kaohsiung [88] and New York/New Jersey [89]), making them fundamental testing centers for global decarbonization, as shown in

Table 2. Energy Infrastructure of Maritime Ports: Group 2.

Port	LNG				Hydrogen						Ammonia
	OPE	PRO	PLS	PLST	PRO	PRP	PRPL	PLA	PLS	PLST	PRO	PRP	PRPL	PLA	PLS	PLST
Kaohsiung [90]		•			•						•
Los Angeles [86,91]	•				•						•
Tanjung Pelepas [92]	•								•						•
Hamburg [93]	•						•						•
Long Beach [86,94]	•					•						•
Laem Chabang [95]				•				•						•
New York/New Jersey [96]	•								•						•
Colombo [97]			•							•					•
Valencia [98]	•					•							•
Ho Chi Minh [99]			•					•						•
Yantian (Shenzhen) [100]		•							•						•
Average (%)	45.5	9.1	9.1	9.1	9.1	18.2	9.1	9.1	18.2	9.1	9.1	18.2	9.1	9.1	18.2	9.1

Note: The dot (•) symbol indicates a correlation between the corresponding row and column.

.

Group 3: This group is composed of 26 ports handling container traffic volumes below 4.99 million TEU, positioning them as Crucial Regional Ports, National Gateways, and Specialized Transshipment Centers. Geographically, this group is the most diverse, with significant representation in Latin America (Manzanillo, Colon, Callao, and Cartagena), Europe (Algeciras, Bremerhaven, Valencia, Genoa, Sines, and Marsaxlokk), Asia/Middle East (Chennai, Dalian, Rizhao, Manila, Jeddah, Said, and Salalah), and other regions such as North America (Halifax, Montreal, Philadelphia, and Baltimore), Australia (Sydney), and Africa (Durban and King Abdullah). Unlike the other groups, these ports focus on regional transshipment and feeder operations, serving as vital links between megahubs and domestic markets. Their participation in the energy transition is characterized by being predominantly in the PLA/PLST phases, with investments in alternative fuel infrastructure often limited to LNG projects or subject to national maritime development strategies, given the smaller scale of bunkering demand and the need to prioritize investment in the efficiency of national gateways. The review of these ports revealed that only 8 of them present evidence of active infrastructure, projects, or plans for energy vectors, as shown in

Table 3. Energy Infrastructure of Maritime Ports: Group 3.

Port	LNG				Hydrogen						Ammonia
	OPE	OPSC	PLA	PLST	PRO	PRP	PRPL	PLA	PLS	PLST	PRO	PRSC	PRPL	PLA	PLS	PLST
Algeciras [101]	•									•	•
Bremerhaven [102]	•							•						•
Génova [103]	•									•						•
Sines [104]	•				•					•
Montreal [105]		•						•						•
Colón [106]	•									•						•
Salalah [107]			•		•						•
Durban [108]				•					•						•
Average (%)	15.4	3.8	3.8	3.8	7.7	0.0	0.0	7.7	3.8	11.5	7.7	0.0	0.0	7.7	3.8	11.5

Note: The dot (•) symbol indicates a correlation between the corresponding row and column.

.

The comparative analysis of the three port groups reveals a clear correlation between traffic volume and the maturity of alternative fuel infrastructure. Global Megahubs (Group 1) lead the implementation of LNG, with more than 85% possessing operational infrastructure, consolidating this fuel as the dominant short-term transition solution. However, their focus on the other two vectors is cautious, primarily concentrated on Planning. For their part, the Major Regional Gateways (Group 2) emerge as the spearhead of the Pilot and Project phases, showing a balanced distribution, with 27.3% of the ports already maintaining active projects for both hydrogen and ammonia, indicating an earlier commitment to zero-emission technologies. Finally, Group 3 (Regional Ports) exhibits the most significant lag; considering the total base of 26 ports, only 7.7% have active projects for these two vectors. Although LNG is operational in nearly 20% of the sample, the group is predominantly in the initial Study and Planning phases.

3.2. Technical and Other Characteristics

3.2.1. Liquefied Natural Gas

• Technical Characteristics: LNG is cryogenic methane. Its liquid state is achieved through a liquefaction process that reduces the temperature of natural gas to approximately −162 °C. This transition results in a volumetric reduction of approximately 600:1, which is fundamental for transport and storage. Its transportation is carried out in specialized ships of the LNG carrier type with insulated double-hull tanks, specifically designed to contain the gas cargo at a cryogenic temperature of −169 °C and a pressure slightly above atmospheric, approximately 0.3 barg. The energy content (MJ/kg) corresponds to 48.62 for the lower heating value (LHV) and 55.19 for the higher heating value (HHV) [109].
• Demand: LNG constitutes a strategic pillar for global energy security and the diversification of supply sources. Demand is on a sustained growth trajectory, primarily driven by the substitution of fuels with higher environmental impacts (coal and fuel oil) and industrial expansion in emerging markets. Europe has significantly increased its dependence on LNG, securing supply through the signing of new long-term contracts and the activation of spot capacities. Projections indicate a notable increase in global LNG demand until 2030, requiring a parallel expansion of liquefaction capacity [110]. Global gas demand is projected to grow by 1.5% annually through 2030, with LNG trade exceeding 400 million tonnes (MT) in 2024 [111]. The maritime sector is a key driver of this expansion; LNG bunkering demand is expected to reach approximately 16 MT by 2030, supported by an increasing fleet of over 600 operational vessels and a growing order book of dual-fuel ships [112].
• Production: LNG production is characterized by geographic diversification that mitigates supply risks. The main exporters by volume and installed liquefaction capacity include the United States, Qatar, and Australia. Other relevant producers: global export capacity is complemented by significant volumes from countries such as Russia, Malaysia, Nigeria, and Norway [113].
• Costs and Market Structure: The final value of this fuel depends on natural gas production (upstream), midstream liquefaction, transportation (in cryogenic tanker ships), downstream regasification, and end-use markets [114]. Table 4 shows the final value provided across three markets. While market prices are dictated by regional Hubs (Table 4), the economic viability of LNG supply depends on the breakdown of liquefaction costs. Capital Expenditures (CAPEX) for liquefaction facilities typically range from 1000 to 1500 USD/tpa, while Operating Expenditures (OPEX) stay between 0.30 and 0.80 USD/MMBtu. Consequently, a total liquefaction fee of 2.50–3.50 USD/MMBtu is usually required to reach the break-even point, significantly increasing the final value over the raw gas price at the Hub [115].

  Table 4. Approximate LNG Prices for End-Users in 2025.

  Hub	Prices (Approximate)	Unid
  Henry Hub (HH) [116]	4.11–4.14	USD/MMBtu
  Dutch TTF [117]	∼9.50	USD/MMBtu
  GNL Spot (JKM) [118]	10.66	USD/MMBtu

  Table 4. Approximate LNG Prices for End-Users in 2025.

  Hub	Prices (Approximate)	Unid
  Henry Hub (HH) [116]	4.11–4.14	USD/MMBtu
  Dutch TTF [117]	∼9.50	USD/MMBtu
  GNL Spot (JKM) [118]	10.66	USD/MMBtu

• Emissions: Its combustion in power generation produces approximately 50–60% less CO₂ than the combustion of coal. However, the environmental impact analysis must be comprehensive (life cycle). Methane is a potent GHG. Methane slip occurring during extraction, liquefaction, and transport represents a critical challenge [119]. The mitigation of these leaks is essential to validate the lower-impact credentials [120]. Additionally, its combustion drastically reduces emissions of local atmospheric pollutants, such as sulfur oxides (SOx), nitrogen oxides (NOx), and particulate matter, compared to coal and heavy fuel oil, contributing to the improvement of air quality. While LNG is a key transition fuel, its adoption reconfigures the emission profile without entirely eliminating the carbon footprint. Current projections may underestimate the net climate impact [5], as highlighted by the Fourth IMO GHG Study [121], which notes a significant rise in methane emissions. However, these estimates remain conservative because they often fail to account for fugitive emissions and the lower operational efficiency of auxiliary engines under real load profiles at maritime nodes [122]. This methane slip remains a critical challenge that must be addressed to validate the fuel’s environmental credentials [123].
• Port Infrastructure: The maritime industry is undergoing an active transition from Heavy Fuel Oil (HFO) toward LNG as the preferred fuel for the main and auxiliary engines of merchant ships. This adaptation is primarily materialized in the construction of new ships that incorporate dual-fuel systems designed from the outset to utilize LNG or liquid fuel. LNG is compatible with both high- and low-speed propulsion engines as well as auxiliary generator units, allowing for the reduction in emissions of sulfur oxides, particulate matter, and nitrogen oxides on board. High-pressure propulsion engines are preferred in new constructions due to their efficiency and their capacity to mitigate the risk of methane slip [124]. Although the retrofitting of existing ships is technically feasible, this option is costly and complex, as it requires the installation of bulky cryogenic tanks and the adaptation or replacement of existing machinery, a process that must strictly comply with the IGF Code [119] for operational safety [120]. LNG bunkering requires the creation of an LNG-to-Ship supply chain (Ship-to-Ship, Shore-to-Ship, etc.) at the maritime port or terminal and the implementation of safety protocols according to the IGF Code [123], as shown in

  Table 5. Bunkering Method from LNG in port area.

  Bunkering Method	Description	Key Port Infrastructure Requirement
  Ship-to-Ship (STS) [126,127]	LNG is transferred from a dedicated bunker ship (barge) to the receiving ship. This is the most flexible and high-capacity method.	Quay Requirements: Reinforced mooring points and ample exclusion zones (safety perimeters) to accommodate the simultaneous maneuvering of two ship. Logistics: Centralized LNG storage facility required to supply the bunker ship.
  Pipe-to-Ship (PTS) [128]	LNG is transferred directly from a fixed shore storage tank or terminal to the ship via piping.	Specialized Terminals: Installation of permanently installed cryogenic piping along the berth (or loading arms) capable of safely handling LNG
  Truck-to-Ship (TTS) [129]	Multiple cryogenic road tankers connect to the ship to supply LNG. Used for smaller ship and limited volume transfers.	Dedicated Transfer Area: Requires a designated land area on the quay with easy road access to safely park and connect multiple cryogenic trucks simultaneously.

  [125].

3.2.2. Green Hydrogen

• Technical Characteristics: Hydrogen possesses challenging technical characteristics due to its physical and energetic state. It has the highest energy content of all known fuels, with an LHV of 119.96 MJ/kg and HHV of 141.88 MJ/kg. Regarding storage, it requires highly complex solutions. Storage in gaseous form demands high-pressure tanks (350–700 bar). For liquid storage, extreme cryogenic conditions of −253 °C are required due to its boiling point of −252.8 °C. Although its density in a liquid state is 70.79 kg/m³, the liquefaction process involves a high energy cost, consuming 12 to 13.3 kWh/kg, which is significantly higher than compression (2.3 to 3 kWh/kg) [130].
• Demand: The global demand for Green Hydrogen and its derivatives is projected to exceed 100 million tons by the year 2030. This strong demand is reflected in the growth of its market value: estimated at 7980 million dollars in 2024 and projected to reach 60,560 million dollars by 2030. The primary driver of this demand stems from the need to decarbonize heavy industrial processes and hard-to-abate sectors [131].
• Production: Green Hydrogen is defined by its production method: the electrolysis of water using 100% renewable energy. The Green Hydrogen Standard (GH₂) accreditation establishes that this energy must come from sources such as hydroelectric, solar, wind, geothermal, or ocean energy. However, current production is minimal: by 2020, only 3% of global production was green, and in 2023, it represents less than 1% of global use. To meet the Net Zero Emissions Scenario for 2050, this production must increase at least 100-fold by 2030 [132].
• Costs and Market Structure: The economic valuation of Green Hydrogen is primarily defined by the Levelized Cost of Hydrogen (LCOH), which is highly sensitive to the capacity factor and the cost of renewable electricity. Unlike the LNG market, which operates through mature global hubs (e.g., Henry Hub [133], Title Transfer Facility-TTF [134], and Japan Korea Marker [135]), the hydrogen market currently lacks a unified price discovery mechanism. Instead, prices are established through Over-the-Counter (OTC) bilateral contracts and long-term agreements. Now, the LCOH is the most reliable proxy for market value, reflecting local resource availability rather than global supply-demand dynamics. For instance, in Brazil, specifically in the state of Bahia, the LCOH varies significantly by energy source: solar PV-based electrolysis ranges from 2.16 to 2.28 USD/kgH₂, while offshore wind units present higher costs, between 3.57 and 3.81 USD/kgH₂ [136]. To bridge the gap with fossil fuels, current industry targets aim for a cost reduction towards 2.00 USD/kgH₂ by 2030. Table 6 summarizes the LCOH data for Green Hydrogen, highlighting the cost variance between solar and wind-powered electrolysis as discussed in the previous section.

  Table 6. Representative Green Hydrogen Production Costs for 2025.

  Production Context/Source	Price/Cost Range (Approximate)	Unit	References
  Solar PV (Brazil, 50–100 MW)	2.16–2.28	USD/kgH2	[136]
  Offshore Wind (Brazil, 50–100 MW)	3.57–3.81	USD/kgH2	[136]
  EU Benchmark (Estimated OTC)	5.50–8.00	USD/kgH2	[132,137]
  Target for Global Competitiveness	~2.00	USD/kgH2	[138]

  Table 6. Representative Green Hydrogen Production Costs for 2025.

  Production Context/Source	Price/Cost Range (Approximate)	Unit	References
  Solar PV (Brazil, 50–100 MW)	2.16–2.28	USD/kgH2	[136]
  Offshore Wind (Brazil, 50–100 MW)	3.57–3.81	USD/kgH2	[136]
  EU Benchmark (Estimated OTC)	5.50–8.00	USD/kgH2	[132,137]
  Target for Global Competitiveness	~2.00	USD/kgH2	[138]

• Emissions: The primary environmental advantage of Green Hydrogen lies in its production via electrolysis powered by renewable energy, resulting in near-zero life-cycle GHG emissions. Unlike conventional fuels, its use eliminates the emission of hydrocarbons and particulate matter [139]. However, its NO₂ emission profile is strictly dependent on the conversion technology employed: while fuel cells achieve zero-emission operation through a low-temperature electrochemical process, the use of hydrogen in internal combustion engines (H₂-ICE) can lead to the thermal oxidation of atmospheric nitrogen, potentially generating nitrogen oxides that require mitigation strategies [140].
• Port Infrastructure: The integration of Green Hydrogen in the maritime industry is primarily linked to fuel cell development [141] and adapted internal combustion engines [142]; however, its widespread adoption faces critical barriers due to extreme storage conditions at −253 °C. Its low volumetric energy density requires a storage capacity approximately four times larger than HFO to maintain energy parity, which limits vessel autonomy and cargo space, making it more viable for short-sea shipping or high-frequency bunkering routes [139]. Onboard implementation requires costly retrofitting and strict compliance with the IGF Code [123] to mitigate risks associated with leaks and extreme cryogenic handling [143]. Accordingly, port infrastructure must evolve through the construction of terminals equipped with high-pressure, double-walled cryogenic tanks and high-capacity cooling systems [144]. Currently in the pilot phase, hydrogen bunkering is managed as a cryogenic liquid (LH₂) using transfer methods that require specialized vacuum-insulated piping and advanced Boil-off Gas (BOG) management systems to handle temperatures near absolute zero, as synthesized in

  Table 7. Bunkering Methods for Liquid Hydrogen (LH₂) in Port Areas.

  Bunkering Method	Description	Key Port Infrastructure Requirement
  STS [139]	Transfer from a dedicated LH2 bunker vessel to the receiving ship. Best for large-scale oceanic ship.	Bunker Barges: Specialized ships with high-vacuum insulation. Safety: Enhanced exclusion zones due to hydrogen’s high flammability and leak rate.
  PTS [139]	Direct transfer from a fixed land-based cryogenic storage tank via a loading arm or flexible hose.	Cryogenic Terminals: Permanent vacuum-insulated pipelines. BOG Recovery: Advanced systems to recapture hydrogen gas displaced during transfer.
  TTS [141]	Mobile cryogenic road tankers connect to the ship. Suitable for small ferries or inland waterway vessels.	Transfer Manifolds: Dedicated quay areas with hydrogen sensors and grounding systems. Limited by the low capacity of individual trucks.

  .

3.2.3. Ammonia

• Technical Characteristics: Ammonia is distinguished by its storage conditions and high energy density. It can be stored at a relatively low pressure of 11.72 bar or at a temperature of −33 °C, conditions that are much less extreme than those of LNG or hydrogen, which significantly reduces operational costs. Its energy content corresponds to 22.5 MJ/kg [109]. Green Ammonia is a substance less flammable than hydrogen; therefore, it is considered safer, and its leaks are detected with greater ease, offering clear advantages for transport and storage [130,145].
• Demand: The projected demand for green ammonia (NH₃) as a zero-emission energy vector is fundamentally driven by its dual-use potential as both a maritime fuel and an industrial feedstock. Unlike hydrogen, ammonia benefits from a pre-existing global trade infrastructure tied to the fertilizer industry, which serves as a market anchor to mitigate early-investment risks. According to the IEA [146], ammonia is expected to account for approximately 45% of the total maritime energy demand by 2050, particularly for long-haul ships where the volumetric density of liquid hydrogen proves prohibitive. This demand surge is further reinforced by strategic co-firing initiatives in the Asian power sector, creating cross-sectoral synergies that stabilize port infrastructure investments. However, the transition from current gray production to a large-scale green ammonia market remains contingent on the stabilization of the Levelized Cost of Ammonia (LCOA) and the full implementation of safety protocols for toxicity management, as outlined in the most recent regulatory updates [33]. Ultimately, the scaling of this market is tied to the adoption of global market-based measures, such as a carbon levy, intended to bridge the price gap between ammonia and fossil-based benchmarks [33].
• Production: In the European context, with a prominent projection in Spain, various energy and chemical corporations have taken a leading role in the transition toward carbon-neutral fuels. These entities are concentrating efforts on the production of low-carbon ammonia and green hydrogen, leveraging electrolysis powered by renewable sources [147]. The production process relies on the Haber-Bosch synthesis, where nitrogen is separated from the air and combined with green hydrogen, requiring significant renewable energy input to eliminate the carbon footprint of traditional steam methane reforming.
• Costs and Market Structure: The global Green Ammonia market was valued at 47.41 million USD in 2023 and is projected to reach 44,299.43 million USD by 2032. This growth is driven by the decarbonization of agriculture and, especially, maritime transport [136,148]. While market demand is projected to reach 125 Mton in the energy sector by 2050, its economic valuation is currently defined by the LCOA. Unlike LNG, there are no global hubs for green ammonia; prices are based on production costs and bilateral agreements. Currently, the LCOA ranges from 720 to 1200 USD/t, significantly higher than conventional fossil-based ammonia (300–450 USD/t). Table 8 synthesizes these production costs and market targets for 2025.

  Table 8. Representative Green Ammonia Production Costs (LCOA) for 2025.

  Production Context/Source	Cost Range (Approximate)	Unit	Reference
  Renewable-intensive regions (e.g., Chile, Australia)	720–850	USD/t	[149]
  EU/High-cost regions (e.g., Spain pilot projects)	900–1200	USD/t	[150]
  Conventional Ammonia (Fossil-based benchmark)	300–450	USD/t	[151]
  Target for Maritime Competitiveness (2030)	450	USD/t	[152]

  Table 8. Representative Green Ammonia Production Costs (LCOA) for 2025.

  Production Context/Source	Cost Range (Approximate)	Unit	Reference
  Renewable-intensive regions (e.g., Chile, Australia)	720–850	USD/t	[149]
  EU/High-cost regions (e.g., Spain pilot projects)	900–1200	USD/t	[150]
  Conventional Ammonia (Fossil-based benchmark)	300–450	USD/t	[151]
  Target for Maritime Competitiveness (2030)	450	USD/t	[152]

• Emissions: While ammonia is a prominent carbon-free candidate due to its high energy density and existing transport infrastructure, its implementation as a marine fuel faces severe safety and environmental hurdles [153]. Unlike hydrogen, ammonia is highly toxic to humans even at low concentrations and is classified as a hazardous substance for marine ecosystems in the event of a leakage or operational spill [154]. Furthermore, its corrosive nature requires specialized materials for storage and piping systems [155]. From a combustion perspective, ammonia also presents challenges due to its low flame speed and the potential for increased N₂O (a potent GHG) and NOx emissions, necessitating advanced engine management and after-treatment systems to mitigate its environmental impact.
• Port Infrastructure: A significant advantage of Green Ammonia is that its storage requirements are much less extreme than those of hydrogen, offering clear safety advantages for on-board storage as it is less flammable and leaks are more easily detected [156]. Furthermore, its current use in internal combustion processes accelerates its operational viability [157], supported by a globally developed distribution network that provides substantial logistical savings in transport and supply infrastructure [158]. However, despite these advantages, ammonia bunkering is inherently complex due to its high toxicity. Unlike LNG or hydrogen, ammonia operations require strict exclusion zones based on toxic gas dispersion modeling to protect port personnel. Port terminals must be equipped with specialized vapor recovery units (VRU) and scrubber systems to neutralize any accidental releases. These transfer methods while mirroring the logistical flow of LNG, demand unique chemical safety protocols as synthesized in

  Table 9. Bunkering Methods for Ammonia in Port Areas.

  Bunkering Method	Operational Description	Key Safety and Infrastructure Requirements
  STS [157,159]	Transfer via dedicated ammonia bunker vessels or Liquefied Petroleum Gas (LPG)-derived carriers.	Double-walled hoses and dry-break couplings. Onboard scrubbers to manage toxic vapors during connection/disconnection.
  PTS [159,160]	Direct transfer from refrigerated terminal storage via loading arms.	Closed-loop systems with Vapor Return Lines (VRL). Automated leak detection and water curtain systems to knock down potential gas clouds.
  TTS [161]	Delivery via pressurized or semi-refrigerated road tankers.	Limited to small-scale vessels. Requires mobile exclusion zones and specific Personal Protective Equipment (PPE) for toxicity.

  .

3.2.4. Comparation

The analysis reveals a dichotomy between energy density and logistical complexity.

Table 10. LNG, Green Hydrogen, and Ammonia comparation.

Feature	LNG (Liquefied Natural Gas)	Green Hydrogen (H2)	Ammonia (NH3)
Physical State	Cryogenic Liquid (−162 °C)	Cryogenic Liquid (−253 °C) or Compressed Gas	Refrigerated Liquid (−33 °C) or Low Pressure
LHV (MJ/kg)	48.62	119.96	22.50
TRL [162]	9 (Commercial)	6-7 (Demonstration)	7 (Early adoption)
Storage Complexity	High (Cryogenic)	Extreme (Cryogenic/High Pressure)	Moderate (Standard Refrigeration)
Infrastructure Status	Operational/Consolidated	Planning/Pilot Phase	Planning/Strategic Phase
Volume Factor (vs. HFO)	~2.4x	~7.6x	~4.1x
Emissions Profile	20–25% CO2 reduction vs. HFO	Near-Zero GHG emissions	Zero CO2/Potential N2O risk
Main Advantage	Established global supply chain	Highest energy per unit of mass	Lower storage cost than H2
Main Barrier	Methane slip and fossil origin	Low volumetric energy density	High toxicity and NOx emissions
Regulatory Framework	IGF Code (Established) [123]	IGF Code (Under adaptation) [163]	IGF Code (Under development) [163]

presents a comparison between the three vectors, categorized by their Technology Readiness Level (TRL), utilizing a scale adapted by the European Commission [162] for the evaluation of alternative fuels.

LNG (TRL 9) represents a fully mature technology with established supply chains. Green Ammonia (TRL 7) is moving toward full-scale operational demonstration, with the first commercial engine deliveries expected by 2025–2026. Conversely, Green Hydrogen (TRL6-7) remains in the pilot and validation phase for large-scale maritime applications due to persistent challenges in cryogenic storage and volumetric efficiency.

LNG remains the current efficiency benchmark with a TRL 9, allowing for an autonomy comparable to traditional fossil fuels. However, its primary disadvantage is methane slip, which can account for 1 to 3% of total emissions, potentially compromising its net climate benefit [121]. In contrast, LH₂ possesses the highest energy content by mass, but its low volumetric density imposes a critical spatial penalty: it requires 7.6 times more storage volume than HFO to deliver the same amount of energy. This limits its future deployment to short-sea shipping or ferries. On the other hand, NH₃ emerges as a viable solution for long-distance transport. Although its LHV is the lowest among the three, its volumetric density is more manageable (requiring ~4.1 times more space than HFO), and its storage conditions drastically reduce infrastructure costs compared to hydrogen.

A fundamental finding of this review is the regulatory gap acting as an entry barrier. While the IGF Code [123] is fully consolidated for LNG, the frameworks for Hydrogen and Ammonia are currently in the Interim Guidelines [162].

The future demand projected for 2050 shows a clear segmentation based on end-use:

○

LNG: Demand is driven by the replacement of coal and fuel oil assets. Its role is that of an energy security guarantor, with an infrastructure that allows for cargo diversion according to the needs of port nodes [110,111,112].

○

Green Hydrogen: Demand in ports will not only be as a marine fuel but also as an industrial raw material (chemical and steel industries). This creates a synergy: ports acting as hydrogen import hubs will reduce ship bunkering costs through economies of scale [131].

○

Green Ammonia: Demand is intrinsically linked to the fertilizer sector and, increasingly, to power generation in Asia (co-combustion) [130]. This dual demand stabilizes investment in port infrastructure, as ammonia terminals can serve multiple industrial sectors simultaneously [33].

A determining factor differentiating these three vectors is the maturity of their commercial ecosystem. While LNG operates under a consolidated global market architecture, hydrogen and ammonia are transitioning from a niche economy to an industrial scale, as shown in

Table 11. Market Indicators for LNG, Green Hydrogen, and Ammonia.

Feature	LNG (Liquefied Natural Gas)	Green Hydrogen (H2)	Ammonia (NH3)
Price Architecture	Global Hubs/Gas Indexation	LCOH + Subsidy Premiums	LCOA + Offtake Contracts
Market Liquidity	Very High	Very Low (Pilot Projects)	Low (Growing via Fertilizers)
Primary Drivers	Energy Transition/Security	Industrial Decarbonization	Heavy Transport/Agriculture

.

The LNG market is the only one featuring transparent price discovery through regional hubs. This structure allows shipowners to utilize financial instruments to mitigate volatility. In contrast, Green Hydrogen and Green Ammonia lack liquid hubs. Their current prices are defined through long-term bilateral contracts (OTC) and offtake agreements, where the price is heavily indexed to the local cost of production (LCOH/LCOA) rather than global supply and demand.

Three deployment scenarios are projected based on the infrastructure evolution mapped:

○

2030 Horizon (Dominant Transition): LNG will lead the market due to the maturity of hubs (Henry Hub in the US [133], TTF in Europe [134], and Japan Korea Marker in Asia [135]) and the existence of a fleet of over 600 operational ships [163].

○

2040 Horizon (Ammonia Deployment): Ammonia will capture the heavy-duty segment (bulk carriers and tankers) once safety protocols for toxicity exclusion zones are standardized and existing LPG terminals are repurposed [164].

○

2050 Horizon (Hydrogen Specialization): Liquid hydrogen will consolidate in Short Sea Shipping routes and specific Green Corridors, conditioned on the reduction of LCOH toward 2.00 USD/kg [165].

Finally, the prolonged latency in large-scale capital allocation for zero-emission energy vectors (Green Hydrogen and Ammonia), in stark contrast to the rapid scaling of LNG, is driven by four systemic and interrelated barriers:

• Market Coordination Asymmetry: A significant misalignment exists between the investment cycles of shipowners and port infrastructure providers. The absence of a synchronized order book for zero-emission ships creates a market stalemate where bunkering infrastructure development is stalled by the lack of guaranteed demand, while fleet renewal is hindered by the absence of supply security. Unlike the LNG transition, which capitalized on pre-existing industrial gas networks, green hydrogen and ammonia necessitate the development of entirely new, high-CAPEX supply chains from production to the final maritime node [166].
• Technoeconomic Disparity and Market-Based Measures: As evidenced in Table 10, the LCOH and LCOA present a substantial premium over fossil-based benchmarks. Without the implementation of global, mandatory Market-Based Measures (MBM) to internalize environmental externalities and bridge the price gap, the Internal Rate of Return (IRR) for zero-emission infrastructure remains below the threshold required for private capital mobilization.
• Technological Hedging and Regulatory Lag: The maritime industry is currently navigating a period of high technology lock-in risk [167]. The wait-and-see strategy adopted by many stakeholders is a rational response to the risk of asset obsolescence should a competing vector emerge as the dominant standard. This uncertainty is exacerbated by the current lag in the IGF Code [123] regarding toxicity management and high-pressure cryogenic handling, which introduces significant legal and insurance-related hurdles for port permitting.
• Volumetric Constraints and Port Land-Use Opportunity Cost: The unfavorable energy-to-volume ratio of zero-emission fuels imposes a double penalty. Beyond reducing a ship’s effective cargo capacity, it necessitates a vast expansion of port storage footprints. For high-density maritime hubs, this represents a significant Opportunity Cost in terms of land utilization, further discouraging the transition from the more compact and established LNG infrastructure [168].

4. Conclusions

The comparative analysis of LNG, Green Hydrogen, and Ammonia reveals that the maritime energy transition is not a linear process but a segmented evolution governed by energy density, infrastructure readiness, and market maturity. The following points summarize the final findings:

• Technological Maturity vs. Decarbonization Potential: LNG (TRL 9) remains the only viable commercial benchmark for the 2030 horizon, supported by a consolidated fleet of over 600 ships and a transparent pricing architecture (Henry Hub, TTF, and JKM). However, its role is strictly transitional due to methane slip risks [163,168]. In contrast, Green Ammonia (TRL 7) and Green Hydrogen (TRL6-7) offer near-zero emission profiles but face significant penalties in volumetric density—requiring 4.1x and 7.6x more storage volume than HFO, respectively—which imposes a double burden on both ship cargo capacity and port land utilization [130,168].
• Strategic Segmentation of Future Demand: The study projects a clear division of the maritime market by 2050. Ammonia is positioned as the primary vector for heavy-duty, long-haul segments (bulk carriers and tankers), leveraging its manageable storage conditions and the potential to repurpose existing LPG infrastructure [165,166]. Conversely, liquid hydrogen will likely specialize in Short Sea Shipping and Green Corridors, where its volumetric constraints are less prohibitive, provided the LCOH reaches the competitive threshold of 2.00 USD/kg [165].
• Structural Investment Asymmetry and Coordination Failure: A fundamental barrier to the scaling of zero-emission vectors is the systemic misalignment between the capital investment cycles of shipowners and port infrastructure providers. This reciprocal dependency creates a market stalemate—often characterized in the literature as a coordination failure—where the absence of a synchronized order book for green vessels disincentivizes the deployment of bunkering infrastructure, while simultaneously, the lack of supply security hinders fleet renewal [118]. Unlike the LNG transition, which leveraged pre-existing industrial gas networks and mature midstream assets, green hydrogen and ammonia necessitate the development of entirely new, high-CAPEX supply chains. These nascent markets currently lack the sophisticated price discovery mechanisms and financial hedging instruments—such as those found in established global gas hubs—required to mitigate long-term investment risks [165].
• Regulatory and Safety Imperatives: The transition is currently hindered by a regulatory lag in the IGF Code [123] regarding toxicity management for ammonia and high-pressure cryogenic handling for hydrogen. The standardization of safety protocols and toxicity exclusion zones is a prerequisite for private capital mobilization and port permitting [154,164].
• Policy Recommendation: To bridge the technoeconomic gap identified in the LCOH/LCOA analysis, the implementation of global MBM, such as a carbon levy, is essential. Without these measures to internalize environmental externalities, the IRR for zero-emission infrastructure will remain insufficient to trigger the massive capital allocation required for the 2050 Net Zero scenario [33,131].