Extending the CO₂ Value Chain: Formic Acid as a Bridge Chemical Toward a Net-Zero Circular Carbon Economy

Abstract

Reaching net-zero emissions requires more than displacing fossil combustion with renewable electricity; several of the largest industrial emitters—cement, steel, chemicals, and aviation—cannot be fully electrified with current technology, and captured carbon dioxide (CO₂) itself must find a productive destination rather than remain a permanent liability. Converting CO₂ into formic acid (HCOOH) has emerged as one of the more mature answers to that second problem. Formic acid combines a respectable hydrogen content (4.4 wt%), a stable liquid state at ambient conditions, and comparatively benign handling relative to gaseous or cryogenic hydrogen, positioning it as both a chemical feedstock and an energy carrier. This review synthesizes the current state of CO₂-to-HCOOH conversion across thermochemical, electrochemical, photocatalytic, and biocatalytic routes; examines formic acid’s performance as a liquid organic hydrogen carrier (LOHC) and direct fuel-cell fuel; and evaluates the technology through a recently published pilot-scale case study of a photocatalytic reactor, branded RK-X, developed by the author’s employer—presented here as a single illustrative example rather than a representative benchmark—to show both the promise and the unresolved energetic and economic questions still facing the field. We conclude that formic acid-based CO₂ utilization is technically credible and policy-relevant, but that claims of net energy or carbon benefit must be assessed pathway-by-pathway, powered overwhelmingly by low-cost renewable electricity, and confirmed through independent life-cycle assessment before the technology can be considered a settled pillar of the net-zero toolkit.

1. Introduction

The net-zero transition is often narrated as a story about electricity: replace coal and gas power plants with wind, solar, and storage, and electrify transport and heating on top. That narrative is accurate for a large share of global emissions, but it leaves an awkward remainder. Cement, steel, chemicals, and aviation together account for roughly a third of global CO₂ emissions, and each faces process chemistry or energy-density requirements that renewable electricity alone does not solve. For these hard-to-abate sectors, carbon capture is frequently the only near-term lever available—but capture only becomes economically self-sustaining once the captured CO₂ has somewhere useful to go.

This is the distinction between carbon capture and storage (CCS) and carbon capture and utilization (CCU). CCS treats CO₂ as waste to be sequestered permanently underground; it reduces emissions but generates no direct revenue and requires durable, publicly underwritten infrastructure. CCU instead treats CO₂ as a feedstock, converting it into marketable fuels, chemicals, or materials and thereby creating an economic incentive to capture it in the first place. Reframing carbon as a resource rather than a liability is the conceptual core of what is increasingly called the circular carbon economy: a system in which carbon already in circulation is cycled through value chains instead of being extracted anew from the ground and released once [1].

Among the many CO₂-derived products under investigation, formic acid occupies an unusually favorable niche. It has an established industrial market as a preservative, antibacterial agent, and animal-feed additive, so a portion of any new production capacity does not depend on new demand being created from scratch. More importantly for the net-zero conversation, formic acid contains 4.4 wt% hydrogen, releases that hydrogen through mild catalytic dehydrogenation, and remains a stable, transportable liquid under ordinary ambient conditions—a combination that positions it as both a chemical product in its own right and a liquid organic hydrogen carrier (LOHC) for a hydrogen economy that still lacks cheap, safe, energy-dense storage and transport options.

Formic acid is not the only liquid e-fuel competing for attention and renewable electricity in this space. Green methanol and e-methane (synthetic methane from CO₂ methanation) are both further along in announced commercial capacity and already ride on existing chemical and gas-grid infrastructure, while green ammonia is being pursued chiefly as a hydrogen carrier and marine fuel. Formic acid enters this competition from a much smaller demand base: global formic acid consumption is on the order of 0.8–1 Mt per year [2], roughly two orders of magnitude below methanol demand. That smaller market cuts both ways for a net-zero assessment—it means CO₂-to-formic-acid conversion can realistically absorb only a low single-digit share of the multi-gigatonne CO₂ streams that hard-to-abate sectors need to manage, even at full market saturation, but it also means new capacity is comparatively easy to site against existing, non-speculative demand while the broader market for CO₂-derived fuels continues to grow.

This review has three aims: first, to summarize the principal routes by which CO₂ is converted to formic acid—thermochemical hydrogenation, electrochemical reduction, photocatalysis, and biocatalysis—and the catalytic advances that have brought each closer to industrial relevance; second, to examine formic acid’s downstream role as a hydrogen carrier and direct fuel-cell fuel, and to compare it honestly against competing carriers; and third, to use a recently published pilot-scale engineering study of a photocatalytic reactor (the RK-X platform) as a critical, single-case illustration of what “scaling up” CO₂-to-formic-acid conversion looks like in practice, reading comparatively against the other three routes surveyed in Section 3 and including the parts of that story that remain unresolved or unverified by independent parties. The intention throughout is not to present formic acid as a silver bullet, but to give as accurate a picture as the current literature allows of where this chemistry can realistically contribute to a net-zero world, and where it cannot yet.

This review follows a narrative rather than a systematic design, appropriate for a focused synthesis of one bridge chemical rather than an exhaustive meta-analysis of CO₂ utilization. Sources were located through Web of Science, Scopus, and Google Scholar searches (through July 2026) by combining terms such as formic acid, CO₂ utilization, CO₂ hydrogenation, electrochemical and photocatalytic CO₂ reduction, liquid organic hydrogen carriers, and techno-economic or life-cycle assessment, supplemented by patent and industry-report searches and by citation-chasing from key papers. Peer-reviewed studies from 2014 onward reporting quantitative performance, cost, or life-cycle data were prioritized, alongside a small number of earlier foundational papers and current policy documents needed for context.

2. Why Formic Acid? The Physicochemical Case for a CO₂-Derived Energy Vector

Any candidate hydrogen carrier is judged against a small set of practical criteria: how much hydrogen it holds by weight and by volume, whether it is liquid (and therefore compatible with existing tanker, pipeline, and fueling infrastructure) at ordinary temperature and pressure, how toxic or flammable it is, and how much energy is lost charging and discharging the carrier. Table 1 places formic acid alongside methanol, ammonia, a representative aromatic LOHC (toluene/methylcyclohexane), and compressed hydrogen gas [3,4,5].

Table 1. Formic acid against competing hydrogen carriers.

Carrier	Gravimetric H2 (wt%)	Volumetric Energy Density	Ambient State	Key Handling Trait
Formic acid (HCOOH)	4.4	~1.8−1.9 kWh/L *	Liquid	Corrosive, low flammability
Methanol	12.6	~4.4 kWh/L	Liquid	Toxic, flammable
Ammonia	17.8	~3.5 kWh/L	Liquid (pressurized)	Toxic, pungent, needs pressure
Toluene/MCH (LOHC)	6.2	~1.9 kWh/L	Liquid	Requires high-T dehydrogenation
Compressed H2 (700 bar)	100	~1.3 kWh/L	Gas, high pressure	Heavy tanks, energy-intensive compression

Note: * Reported volumetric energy densities for formic acid vary across the literature depending on whether the figure reflects the heat of combustion of pure HCOOH or the usable hydrogen content after dehydrogenation; both values are cited here because published sources are not fully consistent on this point. Correcting for formic acid’s density (1.22 kg/L) and the lower heating values of H₂ (33.3 kWh/kg) and HCOOH (5.53 MJ/kg), the two bases converge on a narrow physical range of approximately 1.8−1.9 kWh/L; wider figures occasionally seen in secondary sources appear to conflate volumetric and gravimetric bases and should not be relied upon.

Formic acid does not win outright on any single metric as seen in Figure 1. Its gravimetric hydrogen content is the lowest of the liquid carriers shown, and it is corrosive enough to require compatible materials of construction. Its case rests instead on the combination of properties: it is non-flammable under most storage conditions, it dehydrogenates at far lower temperatures (60−120 °C) than aromatic LOHCs (which typically require 300 °C or more), and unlike ammonia it is not acutely toxic at the concentrations typically handled. The low-temperature release is particularly relevant to a circular energy system, since it can be driven by waste heat recovered from a fuel cell rather than by additional primary energy input.

Figure 1. Formic acid trades hydrogen density for handling simplicity.

3. Production Pathways from CO₂ to Formic Acid

Four broad families of chemistry convert CO₂ into formic acid or its conjugate base, formate: thermochemical catalytic hydrogenation, electrochemical reduction, photocatalysis, and biocatalysis [6]. Table 2 summarizes typical operating conditions and representative performance benchmarks reported for each; the subsections that follow discuss the underlying chemistry and recent advances.

Table 2. Operating conditions, representative performance, and main bottlenecks for the four CO₂-to-formic-acid production pathways.

Pathway	Typical Conditions	Representative Performance	Main Bottleneck
Thermochemical hydrogenation	30−50 bar, 30−80 °C, homogeneous Ru/Ir/Fe or heterogeneous catalysts	Turnover numbers up to ~12,700 with recyclable base-free Ir systems	Green H2 sourcing; catalyst/solvent recovery
Electrochemical CO2 reduction	Ambient temperature, aqueous or acidic electrolyte, Sn/Bi/In-based cathodes	Faradaic efficiency > 90% and industrial-level current densities (~1 A/cm2) reported for phase-engineered tin sulphide	Electricity demand; long-term catalyst/membrane stability
Photocatalytic/photoelectrochemical	Ambient temperature, low pressure, visible-light illumination	Formation rates on the order of tens of µmol/h reported for microbubble gas–water interface systems; kg-scale rates reported for LED-driven pilot reactors	Low quantum efficiency; light penetration at scale
Biocatalytic (formate dehydrogenase)	Ambient temperature and pressure, aqueous buffer, enzymatic cofactor regeneration	High selectivity; limited by enzyme stability and cofactor cost	Enzyme lifetime; cofactor recycling economics

Figure 2 synthesizes these same qualitative comparisons across four dimensions to make the trade-offs between pathways visually explicit. No single pathway dominates: electrochemical reduction is the most balanced performer, while the photocatalytic and biocatalytic routes trade scale and maturity for milder operating conditions.

Figure 2. Schematic, qualitative comparison of the four CO₂-to-formic-acid pathways across operating mildness, reported performance, scale/maturity, and bottleneck manageability. Scores (1−5) are assigned by the author from the ranges reported in Table 2 and the primary sources cited in Section 3.

Beyond the qualitative comparison in Figure 2, it is useful to sketch the technological arrangement each pathway implies. Thermochemical hydrogenation calls for a pressure-rated stirred-tank or trickle-bed reactor fed with compressed H₂ and CO₂ (30–50 bar, 30–80 °C), followed by a flash separator that recycles unreacted gas to the reactor inlet and downstream distillation/extraction to concentrate the aqueous formic acid product, with spent ionic liquid or leached metal as the main waste stream requiring disposal; the hazard here is dominated by the compressed hydrogen inventory and rises with both operating pressure and temperature. Electrochemical reduction instead uses an electrolyzer stack (gas-diffusion cathode, ion-exchange membrane, anode compartment evolving O₂) run near ambient temperature and pressure, with a separator recovering formate/formic acid from the catholyte and a recycle loop returning unconverted CO₂ and electrolytes to the stack; its hazards are chiefly electrical and chemical (corrosive electrolyte) rather than pressure-related. Photocatalytic and biocatalytic reactors follow the same generic block flow—illuminated or enzyme-loaded reactor, product separator, recycle of unconverted CO₂ and catalyst/enzyme, disposal of spent catalyst or cofactor—but at ambient temperature and pressure, their hazard profile is comparatively mild, with light penetration and catalyst/enzyme lifetime being the binding practical constraints rather than containment of a pressurized or corrosive stream.

3.1. Thermochemical (Catalytic) Hydrogenation

Direct hydrogenation of CO₂ with molecular H₂ is thermodynamically uphill in the gas phase but becomes favorable in solution, particularly in the presence of a base or an appropriately designed catalyst. Homogeneous catalysts built around ruthenium, iridium, and increasingly iron have been studied for decades; a longstanding challenge has been that many such systems require a stoichiometric base to pull the equilibrium toward product, complicating downstream isolation of free formic acid [7]. The thermodynamics of this step deserve explicit comment: gas-phase hydrogenation of CO₂ to formic acid is overall endothermic once the unfavorable entropy of converting two moles of gas into one mole of condensed product is included, so elevated pressure is a thermodynamic requirement rather than only a kinetic convenience—it is what shifts the equilibrium toward formic acid and is a first-order reason for the 30–50 bar operating window in Table 2, with the compressed hydrogen inventory becoming the dominant process-safety concern as pressure and temperature both increase [8]. The alternative route of reacting CO₂ directly with water rather than H₂ is thermodynamically even less favorable and more energy-demanding, which is part of why electrochemical reduction (Section 3.2) rather than water-mediated hydrogenation has attracted the greater share of recent industrial interest. More recent designs have overcome this: heterogenized iridium catalysts supported on solid phosphines operating in an ionic-liquid solvent have achieved turnover numbers above 12,000 under base-free conditions, with the ionic liquid and catalyst both recoverable and reusable across multiple cycles [9]. Separately, catalytic systems operating in acidic aqueous media without any additive have demonstrated that base-free, high-purity formic acid synthesis is achievable directly from CO₂ and H₂, removing one of the traditional cost and complexity barriers to industrial deployment [10].

3.2. Electrochemical CO₂ Reduction

Electrochemical CO₂ reduction to formate/formic acid (CO₂RR) has attracted the most sustained recent attention, in large part because it couples naturally to renewable electricity and can, in principle, be switched on and off to follow variable wind or solar generation [11]. A thermodynamic accounting is equally relevant here: the standard potential for CO₂ reduction to formate (−0.61 V vs. SHE, close to that of the competing hydrogen evolution reaction) means high Faradaic efficiency is fundamentally a selectivity problem fought over a narrow thermodynamic margin, not merely a kinetic one; once an integrated CO₂-capture step is coupled to the reduction, the combined transport, kinetic, and thermodynamic penalties are larger than a treatment of the reduction potential in isolation would suggest [12]. Catalyst design has moved from early bismuth- and tin-based electrodes toward finely tuned surface chemistries: phase-engineered tin sulphide catalysts operating in acidic media have reached Faradaic efficiencies above 90% at industrially relevant current densities near 1 A/cm², addressing a longstanding criticism that lab-scale CO₂RR results do not translate to commercially useful throughput [13]. Electronic microenvironment engineering of bismuth single-site catalysts has likewise been used to suppress the competing hydrogen evolution reaction and sharpen selectivity toward the desired formate product [14]. Beyond metal catalysts, metal-free molecular approaches—such as recyclable organohydride mediators stabilized by added salts—have demonstrated proof-of-concept formate yields around two-thirds under quantum-chemistry-guided design, illustrating that the field is diversifying beyond precious-metal electrocatalysis [15]. Continuous-flow reactor engineering has become as important a research question as the catalyst itself, since sustained, industrially relevant operation depends on managing gas–liquid mass transfer, product crossover, and electrolyte stability over long duty cycles.

3.3. Photocatalytic and Photoelectrochemical Routes

Photocatalytic CO₂ reduction uses light, rather than electrical potential, to drive the redox chemistry, typically via a heterogeneous semiconductor or metal-complex photocatalyst under visible-light illumination. A notable recent demonstration achieves selective CO₂-to-formic-acid conversion at the gas–water interface of CO₂ microbubbles bubbled through a copper–phenanthroline photocatalyst solution, with formation rates enhanced substantially by the addition of iodide as a co-catalyst [16]. Photocatalysis has historically lagged electrochemical routes in overall energy efficiency because visible-light photon-to-product conversion (quantum efficiency) remains low and because light penetration becomes a genuine engineering constraint once reactors are scaled beyond laboratory glassware. Section 4 examines one attempt to address that scale-up problem directly.

3.4. Biocatalytic Routes

Enzymatic reduction of CO₂ to formate using formate dehydrogenase, typically with an NAD(P)H cofactor, offers very high selectivity under mild aqueous conditions and has attracted interest in integrating CO₂ capture with biological or hybrid bio-electrochemical systems. Its industrial relevance remains constrained chiefly by enzyme operational stability and the cost of regenerating the reduced cofactor at scale, and to date it has been demonstrated mainly at laboratory rather than pilot scale.

4. A Scale-Up Case Study: The RK-X Photocatalytic Reactor

Moving any of these chemistries from a laboratory beaker to an industrially relevant reactor is where much of the remaining uncertainty in the field lives. A 2025 study by Köntös and Masason [17] is instructive precisely because it attempts that jump explicitly. The authors describe a 1600 L continuous stirred-tank photoreactor (branded “RK-X”), agitated by the pressurized flow of CO₂ gas itself rather than a mechanical stirrer, and illuminated by LED panels to drive photocatalytic reduction of dissolved CO₂ over a fulvic-acid-based homogeneous catalyst [18]. Framed around a notional feedstock of 10,000 tonnes of CO₂ per year, the study reports an 85% conversion yield with stable catalyst performance over roughly 25 h of continuous operation, translating—under the authors’ assumptions—to a hydrogen energy content on the order of 11−14 GWh depending on the efficiency figure used.

The study is a useful illustration of the engineering questions that dominate scale-up: managing reactor pressure and liquid level with automated control loops, dosing CO₂ to maintain solubility as it is consumed, and balancing light intensity against energy input across three simulated LED power levels. It also usefully reports a mass balance (0.956 t CO₂ and 0.391 t H₂O consumed per tonne of HCOOH produced) and a specific energy consumption figure (roughly 2−2.7 kWh per kg of HCOOH depending on operating mode) on Figure 3, that can be compared against other production routes.

Figure 3. Mass and energy balance reported for the RK-X pilot-scale photoreactor, as reported in Köntös & Masason (2025) [17] and Köntös (2023) [18].

The reported EROI of approximately 0.7 can be reconstructed explicitly from the study’s own figures. Formic acid contains 4.4 wt% recoverable hydrogen; at the lower heating value of H₂ (33.3 kWh/kg), this corresponds to an energy content of 0.044 × 33.3 = 1.47 kWh per kg of HCOOH produced. Against the study’s reported electrical energy consumption of 2.0−2.7 kWh per kg HCOOH (LED illumination plus auxiliary loads), EROI (energy recovered as H₂, divided by electrical energy input) works out to 1.47/2.7 = 0.54 at the higher end of reported consumption, and 1.47/2.0 = 0.74 at the lower end. This range brackets the study’s reported EROI of ~0.7: even on its own numbers, the RK-X configuration as tested uses more electricity than it recovers as usable hydrogen.

Several aspects of the study also call for a measure of caution before its figures are treated as representative of the field. Köntös and Masason disclose that both are paid employees of the company that manufactures the proprietary catalyst used, a conflict of interest that does not invalidate the reported measurements but does mean independent replication carries extra weight before the results are generalized. This review treats the RK-X case as one illustrative data point among several possible scale-up routes, not as evidence that photocatalytic or vendor-led scale-up outperforms alternatives; readers seeking a catalyst-agnostic view of the broader industrial CO₂ electrolysis scale-up landscape, including electrochemical pilot and demonstration plants for formate and other C1 products, are directed to recent independent reviews of that field [19,20].

The authors’ own energy-return-on-investment calculation—roughly 0.7, meaning more electrical energy is consumed producing the hydrogen than is later recovered from it—is itself a caution against overstating the net energy benefit of the specific configuration studied, even though Köntös and Masason argue the balance improves once cheap renewable electricity and the value of avoided CO₂ emissions are factored in. The study has already been cited as the technical basis for a follow-on feasibility analysis of in situ CO₂ utilization on Mars, an application that further illustrates both the versatility of the underlying chemistry and the importance of validating the base case before building further conclusions on top of it [21].

The appropriate reading of this case study, in other words, is as a demonstration that engineers are actively solving the practical control-systems and reactor-design problems standing between laboratory photocatalysis and continuous industrial operation—not as proof that any specific configuration is already net energy- or carbon-positive at scale. That distinction matters for a Special Issue readership evaluating which sustainable chemistry claims are ready for investment and which still require independent verification.

5. Formic Acid as a Liquid Organic Hydrogen Carrier and Fuel-Cell Fuel

Once produced, formic acid’s value as an energy vector depends on how efficiently its stored hydrogen can be recovered. Two routes dominate: catalytic dehydrogenation to release gaseous H₂ for use in a conventional hydrogen fuel cell, or direct electro-oxidation of formic acid itself in a direct formic acid fuel cell (DFAFC) [22]. The patent literature illustrates this same loop in device form: a US patent for a formic-acid-fueled electricity generation device includes process diagrams that depict the capture-to-power arrangement in hardware terms, offering a useful visual complement to the schematic process flows described above [23].

Dehydrogenation is typically catalyzed by palladium, ruthenium, or iridium complexes and proceeds at 60−120 °C, a temperature window low enough to be driven by waste heat recovered from a downstream polymer electrolyte fuel cell, improving the overall system’s round-trip efficiency [24]. A persistent engineering challenge is selectivity: formic acid can decompose along two competing pathways, one yielding H₂ and CO₂ (the useful pathway) and the other yielding CO and water, with even trace CO contamination poisoning downstream fuel-cell electrodes. Catalyst and support design continues to focus on suppressing this dehydration pathway and maintaining activity over extended operating lifetimes.

DFAFCs avoid the separate dehydrogenation step by oxidizing formic acid directly at the anode, offering a high theoretical open-circuit potential (1.48 V) and comparatively low fuel crossover through Nafion-type membranes relative to direct methanol fuel cells [25,26]. Reported power densities vary widely by design and operating mode, from a few mW/cm² under passive, air-breathing operation to over 100 mW/cm² with actively pumped, temperature-controlled reactant flow, and palladium-black anode catalysts remain the dominant choice for suppressing the competing CO-forming pathway [27]. DFAFCs have found their clearest niche in portable and small-scale power applications rather than grid-scale storage, where their moderate power density is less of a constraint.

A combined techno-economic analysis and life-cycle assessment of formic acid as an LOHC offers a useful reality check on both routes [28]: it finds that, evaluated on full life-cycle terms, formic acid is currently less competitive than delivering liquefied hydrogen directly, though formic acid produced specifically via electrochemical CO₂ reduction retains the lowest global-warming potential among the CO₂-derived pathways considered. This is an important qualifier for any “new economy” narrative built around formic acid: its climate case is strongest when the CO₂ reduction step itself is powered by low-carbon electricity, and weakest when it is compared against hydrogen delivered by other already-mature logistics chains.

6. Techno-Economic Reality Check

Cost sensitivity analyses of formic acid production presented on Figure 4. consistently identify the same two levers: the cost of the CO₂ feedstock itself (which depends heavily on whether it comes from concentrated flue gas or from more dilute, energy-intensive direct air capture) and the price of the electricity or hydrogen used to drive the reduction chemistry. Modeling of the levelized cost of formic acid across both flue-gas capture and direct air capture pathways shows that costs competitive with conventional, fossil-derived formic acid production (below roughly €450 per tonne) are only reached when renewable electricity is cheap and CO₂ capture costs are moderate; direct air capture in particular remains expensive enough today that flue-gas-sourced CO₂ is the more realistic near-term feedstock for cost-competitive formic acid.

Figure 4. Schematic techno-economic sensitivity of CO₂-to-formic-acid production cost.

Reported production-cost figures in the low hundreds of euros per tonne of formic acid, alongside CO₂ capture costs on the order of €50 per tonne, suggest the economics are not far from break-even under favorable renewable-electricity pricing, but they are also sensitive enough to input assumptions that independent, standardized techno-economic comparisons across studies—rather than any single paper’s headline figures—should guide investment decisions. The broader point for a net-zero strategy is that CO₂-to-formic-acid conversion is not automatically cheap or automatically clean; it inherits the carbon intensity and cost of whatever electricity source powers it, which is precisely why its deployment is usually discussed alongside renewable buildout rather than as a standalone solution.

Formic acid’s techno-economic position should also be read against competing e-fuel investment cases operating under the same EU policy signals. Green ammonia and e-methanol currently attract far larger capital commitments and benefit from established shipping-fuel and chemical-feedstock offtake respectively, while e-kerosene is pulled forward by RefuelEU Aviation’s sub-mandates rather than by formic acid’s smaller preservative and animal-feed niches. Under the EU’s Carbon Border Adjustment Mechanism (CBAM) [29] and the recast Renewable Energy Directive (RED III) [30], all of these routes compete for the same scarce input—additional, low-cost renewable electricity—and RED III’s additionality and temporal-correlation rules for renewable fuels of non-biological origin apply to CO₂-derived formic acid in the same way they apply to e-ammonia or e-methanol. Formic acid is therefore competing less against other formic-acid producers than against every other electricity-intensive decarbonization pathway for the same constrained pool of renewable electrons, which is why techno-economic claims for any single pathway—including the one examined in Section 4—should be read alongside, not instead of, that broader competition.

7. Toward a New Circular Carbon Economy

The policy environment around CO₂ utilization has moved quickly. The European Union’s Carbon Border Adjustment Mechanism took effect for covered sectors in 2026, extending a carbon-price signal to imported goods and creating fresh commercial pressure on carbon-intensive exporters to either decarbonize or absorb the border cost—a pressure that strengthens the business case for converting captured CO₂ into sellable products rather than treating it purely as a compliance cost. International bodies including the IEA and the Global CCS Institute continue to frame carbon capture, utilization, and storage collectively as accounting for a meaningful share—on the order of one-fifth—of the emissions reductions needed by 2050, precisely because hard-to-abate sectors such as cement, steel, and chemicals cannot fully decarbonize through electrification alone [31,32].

CCU’s distinguishing appeal within this policy landscape is that it converts a captured-carbon liability into a marketable commodity, which is what makes the phrase “circular carbon economy” more than a slogan: carbon already extracted and in circulation is cycled through additional value-generating steps—formic acid production, hydrogen release, fuel-cell power generation—before any of it is ultimately re-released or permanently stored. Formic acid’s dual identity as both an established industrial chemical and a candidate hydrogen carrier gives it a practical advantage here over purely novel CO₂-derived products: a portion of its market already exists, which lowers the demand-creation risk that many circular-economy technologies face. The patent literature cited in Section 5 for its fuel-cell hardware diagrams [23] is equally suggestive here: its capture-to-power process schematic is a useful visual template for illustrating the closed CO₂-to-formic-acid-to-power loop that defines this circular carbon economy concept.

8. Challenges and Outlook

Several open problems stand between the current state of the art and formic acid playing a settled role in net-zero infrastructure:

• Catalyst durability and poisoning. Long-duration operation without loss of selectivity or activity—whether in electrochemical, thermochemical, or photocatalytic systems—remains less proven at industrial timescales than at laboratory scale.
• CO₂ capture cost. Direct air capture in particular remains too expensive for most techno-economic scenarios to close; near-term deployment will likely concentrate on concentrated point-source flue-gas capture.
• Energy return and carbon accounting. As the RK-X case study illustrates, a process can be technically elegant while still consuming more energy than it recovers under a specific set of operating assumptions; independent, standardized life-cycle assessment—not vendor-reported figures alone, and following recognized methodology such as ISO 14040/14044 [33,34]—should underpin investment and policy decisions.
• Standardization and certification. As with “green” hydrogen and “green” ammonia, the market will need agreed certification standards, for the carbon intensity of the electricity and CO₂ feedstock used, to prevent “CO₂-derived” from becoming a marketing label detached from verified climate benefit.
• Integration with variable renewables. Electrochemical and photocatalytic routes are well suited in principle to following intermittent wind and solar output, but demonstrating this coupling at the reactor-control level, rather than only in techno-economic models, remains an active engineering task.

None of these challenges is disqualifying; each is the kind of problem that incremental catalyst, reactor, and policy engineering has a track record of solving over a decade-long horizon. But an “outstanding” contribution to this Special Issue is better served by stating that horizon honestly than by presenting formic acid as an already-solved pillar of the net-zero transition.

9. Conclusions

Formic acid sits at a genuinely useful intersection of carbon management and hydrogen storage: it gives captured CO₂ an economically productive destination, and it gives the hydrogen economy a liquid, low-toxicity, ambient-temperature carrier compatible in large part with existing chemical logistics. The chemistry to make it—thermochemical, electrochemical, photocatalytic, and biocatalytic—has matured substantially over the past decade, and pilot-scale engineering efforts such as the RK-X reactor demonstrate that the practical reactor-control problems of scale-up are being actively addressed rather than merely theorized about.

At the same time, this review’s closer look at the techno-economic and life-cycle literature counsels against treating CO₂-to-formic-acid conversion as an automatic net-zero win. Its climate and economic case depends entirely on the carbon intensity and price of the electricity that drives it; current life-cycle assessments find it less competitive than direct liquefied-hydrogen delivery on a full life-cycle basis, and at least one detailed pilot-scale study reports an energy return below unity under its own stated assumptions. The honest and, we would argue, more durable case for formic acid in a net-zero world is not that it is already a finished solution, but that it is one of a small number of CO₂ utilization pathways mature enough to deserve continued investment, independent verification, and integration with the broader buildout of low-cost renewable electricity—the resource on which its entire climate benefit ultimately rests.