Sustainable Production of Succinic Acid through CO₂ Conversion

Abstract

Succinic acid is an important industrial platform chemical with broad applications, and its sustainable production has become increasingly critical. Converting carbon dioxide (CO₂) into succinic acid through integrated electrothermal catalytic routes offers a promising alternative to fossil-based and biological methods while contributing to carbon mitigation. This paper summarizes emerging pathways that utilize key CO₂-electrocatalytic products, including gas-phase (C₂H₄/CO/H₂), liquid-phase (acetic acid/acetate), and gas–liquid-phase (alcohols), as intermediates for thermocatalytic upgrading to succinic acid. By establishing a unified CO₂ → intermediate → succinic acid reaction framework and evaluating the feasibility, conditions, and bottlenecks of each pathway. Among the proposed pathways, the C₄ route via maleic anhydride shows the highest near-term feasibility, while gas–liquid oxidative carbonylation offers strong integration potential. This work provides guidance for the development of sustainable, scalable CO₂-based succinic acid production.

1. Introduction

Succinic acid is a four-carbon dicarboxylic acid compound with a wide range of applications and significant research value in many areas. It plays a pivotal role in the synthesis of 1,4-butanediol, tetrahydrofuran, and polybutylene succinate, which is a biodegradable plastic. Furthermore, succinic acid is widely employed in pharmaceuticals, food additives, and deicing agents. The global market for succinic acid is projected to reach $1.8 billion by 2025. Its green production is of significant importance for the promotion of sustainable development and environmental protection.

The most prevalent production methods for succinic acid are those based on petrochemical processes and biological methods. The conventional petrochemical techniques for the synthesis of succinic acid encompass paraffin oxidation, the hydrogenation of maleic anhydride, and maleic anhydride electrochemical reduction. However, these methodologies are dependent on nonrenewable fossil resources, resulting in elevated energy consumption and considerable carbon emissions. Furthermore, the fluctuating global energy prices give rise to elevated production costs, thereby posing significant sustainability challenges. In order to address these issues, modern industry has increasingly turned to alternative production methods, with biological fermentation gaining significant attention. This method entails the microbial conversion of renewable carbon sources, including glucose, glycerol, and lignocellulose, into succinic acid under anaerobic or semianaerobic conditions. , Recent work has demonstrated enhanced CO₂ utilization in biobased succinic acid fermentation by coupling CO₂ micronano-bubble delivery with biofilm-assisted systems, leading to higher yield and improved effective CO₂ utilization. In comparison to conventional petrochemical processes, biological fermentation offers a number of environmental benefits, including a reduction in greenhouse gas emissions and the utilization of renewable resources. However, the large-scale application of biological fermentation is confronted with a number of challenges, including low production yields, issues with microbial stability and tolerance, rigorous fermentation conditions, and the high costs associated with separation and purification. , Recent advances have demonstrated the conceptual feasibility of fully electrochemical cascade systems for CO₂-to-C₄ conversion. For example, a two-step electro–electro strategy coupling CO₂ reduction to C₂H₄ with subsequent C₂H₄ electrocarboxylation has been reported to produce succinic acid under ambient conditions. However, in the integrated tandem configuration, the overall CO₂-to-succinic acid yield was only 0.12 μmol over 5 h. These results highlight both the emerging possibility of electricity-driven C₄ production from CO₂ and the significant efficiency losses that currently arise from system-level integration.

The implementation of coupled electrocatalytic and thermal catalytic techniques in the synthesis of value-added chemicals represents a significant area of interest in recent times. In this process, the disruption of CO₂ stability through external energy input is a pivotal step in its conversion into other carbon-containing substances. , If the external energy source is a clean energy source, such as solar energy, the process can be completely green and “zero carbon”. As the costs of renewable energy sources like solar and wind continue to decline, considerable progress has been made in the electrochemical reduction of CO₂ to value-added chemicals using electrolyzers. − Studies have shown that different designs of cathode catalysts can effectively reduce CO₂ to produce carbon monoxide (CO), multicarbon hydrocarbons, alcohols, and other value-added products. − The efficient production of C₂₊ products, including acetic acid (CH₃COOH) and ethylene (C₂H₄), has now been successfully achieved by connecting CO₂ and CO electrolyzers in a tandem system on a kilowatt scale. −

In previous studies on CO₂ conversion, it has been demonstrated that CO₂ can be effectively converted into C₂₊ products by means of electrothermal catalytic combination. Thermochemical processes can effectively convert the simpler products of electrocatalytic reduction, such as C₂H₄/CO/Hydrogen (H₂), into more complex multicarbon and oxygenated compounds. C₂H₄ plays a critical role in electrocatalytic and thermocatalytic hybrid systems, serving both as a primary product of CO₂ reduction and as an efficient intermediate for thermochemical reactions. A tandem CO₂ electrocatalytic and thermocatalytic process has been demonstrated to be an effective method for the production of C₃ oxygenates and aromatics. , As illustrated in Figure , the utilization of electrothermal coupling systems facilitates the separation of products, enabling the direct feeding of intermediate products derived from CO₂ reduction reactions (CO₂RR) or CO reduction reactions (CORR) into thermochemical reactors. Recent advances have demonstrated that reactor-level product management, including porous solid-state electrolyte systems and integrated capture–conversion architectures, can directly generate high-purity liquid products while reducing downstream separation burdens. , This approach has the potential to reduce production costs, effectively utilize CO₂ as a feedstock, and reduce dependence on fossil resources, with the possibility of achieving CO₂ reduction or even negative emissions. Electrothermal coupling systems are regarded as a promising production model, offering a means of combining the advantages of electrocatalytic and thermochemical processes in chemical synthesis. This approach provides a potential solution for the development of sustainable chemical production.

1.

Combination of electrochemical and thermochemical to produce succinic acid.

In this work, we develop a unified electro-thermal reaction framework that maps CO₂ to succinic acid through its key electrocatalytic intermediates, including gas-phase (C₂H₄/CO/H₂), liquid-phase (acetic acid/acetate), and gas–liquid-phase (alcohols) products, and systematically examine the C₄, C₃, and C₂ thermocatalytic upgrading pathways leading to succinic acid. The novel pathways to succinic acid after electrothermal catalysis can effectively address the issues of high pollution and nonrenewable fossil energy in the chemical synthesis method as well as the challenges of instability and low productivity in the bioprocess method. This approach has the potential for sustainable development and scalability and demonstrates promise for facilitating the transition to green chemistry.

2. Electrocatalysis-Thermocatalysis Coupling for CO₂-to-Succinic Acid Conversion

On the basis of the physical state of the electrocatalytic products that can be further converted into succinic acid, they are categorized into gas-phase, liquid-phase, and gas–liquid two-phase species. This classification facilitates a systematic discussion of their current research status, key challenges, and potential solutions.

2.1. Gas-Phase Pathways

2.1.1. Electrocatalytic Production of Gas-Phase Intermediates (CO/C₂H₄/H₂)

The upstream electrocatalytic process produces different gas products, containing C₂H₄ (mainly), CO, and H₂. These gases can either be individually produced and subsequently blended in desired ratios or cogenerated as a mixed stream that is directly utilized in the downstream thermocatalytic process.

CO is one of the most mature products in CO₂ electroreduction, with Ag as the prototypical catalyst. Numerous studies and demonstration systems have established performance benchmarks directly applicable to engineering evaluation. For example, Liu et al. reported continuous stable operation for 3800 h at a CO Faradaic efficiency of 90%, and Krause et al. achieved 95% CO selectivity at ∼300 W on a 300 cm² electrode area, maintaining stability for 650 h. Industrial implementations of electrochemical CO production coupled with gas separation are already in place; for instance, TOPSOE, leveraging high-performance solid oxide electrolysis (SOEC) with downstream separation, produces carbon monoxide at 99.995 vol % purity. The main challenges in CO production are salt precipitation, cathode flooding, and high cost. Salt precipitation from CO₂–OH^– reactions blocks pores and raises resistance but can be mitigated by potential cycling, catholyte injection, or BPM/CEM membranes to suppress carbonate formation. Flooding disrupts the three-phase interface and enhances HER, which can be avoided through hydrophobic layer optimization and pressure control. High catalyst and membrane costs limit scalability but can be reduced via non-noble catalysts, lower loadings, and durable low-cost membranes.

C₂H₄ is a representative product of copper-catalyzed C–C coupling, and, in recent years, advances in electrodes and reactor integration have brought it close to device-scale operation. Huang et al. used an In/Cu catalyst with a high-pressure MEA to achieve 85% ethylene selectivity at 600 mA cm^–2 and stable operation for 1500 h. On the deployment side, Dioxycle and eChemicles are advancing large-scale electrochemical ethylene production, and the EU FlowPhotoChem project is pushing CO₂-to-ethylene electrocatalysis toward industrial demonstration. In CO₂/CO electroreduction to ethylene, several effective strategies have been established to improve both performance and cost efficiency. Cu-based catalyst engineering enhances intermediate coupling, enabling high selectivity and energy efficiency at high current densities. CEMs or BPMs suppress carbonate crossover, and tandem CO₂ → CO → C₂H₄ systems reduce carbon loss and improve utilization. Meanwhile, low-cost durable membranes, non-noble catalysts, and integrated gas–liquid separation with stackable reactor designs further lower system costs, advancing ethylene electrosynthesis toward efficient, low-carbon, and scalable production.

Regarding hydrogen production and supply, the hydrogen evolution reaction (HER) in CO₂ electrolysis competes with target product formation, depressing carbon utilization and increasing downstream separation costs. So, H₂ suppression via electrode/electrolyte engineering is a common focus. By contrast, water electrolysis provides an independent and stable source of high-purity hydrogen. Commercialization began in the early 20th century and has grown with the development of proton-exchange-membrane and solid–electrolyte technologies and the wider availability of renewable electricity. It has been noted that gigawatt-scale projects can have lifetimes of up to ∼40 years, while electrolyzer stacks are replaced every 8–10 years. The International Energy Agency projects ∼4.2 Mt H₂ yr^–1 of low-emissions hydrogen by 2030, with a further ∼6 Mt possible under supportive policies. Water electrolysis is steadily overcoming challenges of cost, durability, and system limitations. Advances in low-cost non-noble catalysts and zero-gap, high-conductivity electrodes have reduced cell voltage and energy use, while stable AEM/PEM membranes and membrane-free designs enhance lifetime and safety. Coupling with thermal, photonic, or organic oxidation reactions further lowers energy demand and enables coproduction of hydrogen and value-added chemicals. Emerging systems such as seawater and solid oxide electrolysis also broaden resource utilization, pushing the technology toward efficient, low-cost, and long-lasting green hydrogen production.

The production of CO, C₂H₄, and H₂ has already reached an industrial scale, providing key feedstocks for thermocatalytic upgrading. To reduce the energy loss from product separation and remixing, directly coupling electrochemical and thermochemical steps, where the mixed gas from the electrolyzer feeds the thermocatalytic reactor, offers the most efficient route. Recent studies have demonstrated this concept: Biswas et al. coupled a Cu-based electrocatalyst with a Rh₁Co₃/MCM-41 thermocatalyst to produce C₃ oxygenates (1-propanol, propanal), validating its scalability on a 25 cm² cell; Lv et al. integrated electrocatalytic oxygen extraction and water electrolysis with CO₂ + CH₄ dry reforming in one reactor, achieving nearly 100% selective syngas (CO + H₂) production. These electro-thermal coupled systems highlight a promising strategy for designing energy-efficient CO₂-to-succinic acid conversion pathways.

2.1.2. Thermocatalytic Upgrading: C₄, C₃, C₂ Routes

As shown in Figure , the conversion pathways of gas-phase CO₂-electrolysis products (primarily C₂H₄, CO, and H₂) to succinic acid can be organized by their key thermocatalytic intermediates (C₄, C₃, and C₂). Two practical modes exist: (i) generate CO, C₂H₄, and H₂ separately and blend to a target ratio or (ii) cogenerate a mixed stream and feed it to downstream thermocatalytic upgrading after minimal conditioning. Engineering viability is governed by achievable product concentrations and stability at the device scale and by the conditioning steps required to meet downstream purity, dryness, and pressure specifications.

2.

Conversion of CO₂ derivatives in the gas phase to succinic acid (CO₂ derivatives in the gas phase are primarily C₂H₄/CO/H₂; the parenthetical CO₂/O₂/CO/H₂/H₂O represent the reactants to be introduced in each reaction pathway. The red pathway is designed to yield succinic acid via a C₄ intermediate, the blue pathway is intended to produce succinic acid through a C₃ intermediate, and the green pathway is devised to obtain succinic acid via a C₂ intermediate.).

The C₄ intermediates derived from C₂H₄, mainly C₄H₈ and C₄H₁₀, are promising precursors for succinic acid via maleic anhydride (Figure ). Recent work demonstrated direct feeding of CO-containing electrolysis gases into a thermocatalytic reactor, achieving up to 95% C₄H₁₀ dimerization selectivity and ∼16.5% single-pass CO-to-C₄H₁₀ conversion at ambient pressure. The CO/C₂H₄ ratio is critical, an optimal value around 3.5 strongly favors C₄H₁₀ formation (with near-unity selectivity within the C₄ products), while lower ratios lead to mixed C₄ products. This highlights the need for precise control of gas composition in the electrochemical step.

3.

CO₂ derivatives to succinic acid by C₄H₁₀/C₄H₈ under typical conditions (Selective oxidation of C₄ to maleic anhydride, followed by hydrogenation and hydrolysis to succinic acid).

Stable production of tailored syngas (CO/C₂H₄/H₂) requires optimizing catalyst design, cell current or potential, and operating parameters (pH, temperature, pressure, and gas flow) to dynamically adjust product ratios. In addition, gas conditioning units, including dehumidification, CO₂ recycling, and O₂/impurity removal, are necessary to manage byproduct water, oxygen, and unreacted CO₂ from the upstream process.

For the subsequent conversion of C₄H₁₀, in the context of contemporary commercial applications, the conversion of C₄H₁₀ to maleic anhydride has been observed to reach 80–86% at 1 bar, utilizing V–P series catalysts and a fixed-bed thermal catalytic reactor at temperatures between 400 and 450 °C. The maleic anhydride liquid-phase selective hydrogenation to succinic acid can achieve 98% maleic anhydride conversion and 99% succinic acid selectivity at 353 K and 1.0 MPa when catalyzed by Pd/Al₂O₃ and 99.7% succinic acid selectivity at 150 °C when Pd/BN catalysts are used. , The aforementioned technological route has already established a theoretical foundation and practical experience for the production of succinic acid, which can be integrated by electrothermal catalysis to form an overall reaction system of C₁ → C₂ → C₄ → succinic acid. In the petroleum industry, following a lengthy period of research and experimentation, the process from C₄H₁₀ to succinic acid via maleic anhydride has reached a relatively advanced stage of development. Consequently, the aforementioned pathway, which is based on the enhancement of the technology used for the electrothermal catalytic production of C₄H₁₀, offers a considerable scope for scale-up and commercialization.

Among the C₃ substances that can be converted by C₂H₄, CH₂CHCOOH and CH₃CH₂CHO have the greatest potential to generate succinic acid via succinic anhydride, as illustrated in Figures and . The synthesis of CH₂CHCOOH via the combination of CO₂ and C₂H₄ has long been regarded as a highly desirable reaction in the field of catalysis. Recent studies have demonstrated the feasibility of this process, leading to the production of acrylic acid derivatives. , Subsequent hydrolysis treatment of these derivatives results in the formation of CH₂CHCOOH. At a CO to H₂ ratio of 95:5, CH₂CHCOOH can react under superior reaction conditions with a cobalt catalyst in 96% yield of succinic anhydride, which can then be utilized to obtain succinic acid through hydrolysis. This pathway necessitates purified CO₂ and C₂H₄ at the initial stage, requiring the separation of other products from the gaseous system, which incurs a separation cost.

4.

CO₂ derivatives to succinic acid by CH₂CHCOOH under typical conditions (Selective carbonylation of C₃ to succinic anhydride, followed by hydrolysis to succinic acid).

5.

CO₂ derivatives to succinic acid by CH₃CH₂CHO under typical conditions (selective oxidation and carbonylation of C₃ to succinic anhydride, followed by hydrolysis to succinic acid).

The conversion of CH₃CH₂CHO to succinic acid offers the advantage of avoiding the costs of separating various types of reactants through direct coupling of the catalytic reactors. Furthermore, this approach reduces the risk associated with the transportation and storage of the products. Nevertheless, this additional step of converting CH₃CH₂CHO to CH₂CHCOOH is required. The electrocatalytic products C₂H₄/CO/H₂ can be introduced into the thermal reactor to obtain CH₃CH₂CHO at ambient pressure via a hydroformylation reaction, which demonstrates a selectivity of up to 18.4% for C₃₊. ,− The gas-phase oxidative dehydrogenation of CH₃CH₂CHO with the use of molybdenum and vanadium as catalysts has the potential to facilitate the conversion of the products to the high-quality CH₂CHCOOH. The intermediate product of succinic acid, CH₂CHCOOH, possesses considerable value for commercial applications in its own right and exhibits significant potential for market growth. It is, therefore, of great significance to achieve a technological breakthrough and to scale up this pathway in order to facilitate the wide application of CH₂CHCOOH and succinic acid.

The conversion of C₂H₂/C₂H₄O/CH₃CHO in the C₂ stage products into succinic acid via a thermocatalytic process is a feasible process. The C₂H₂ obtained following the dehydrogenation of C₂H₄ holds the promise of forming succinic anhydride via the intermediate CH₂CHCOOH or dicarbonylation, which in turn allows for the formation of succinic acid. , C₂H₄ epoxidation results in the formation of C₂H₄O, whereas C₂H₄ oxidation leads to the generation of CH₃CHO. Both C₂H₄O and CH₃CHO can undergo carbonylation and subsequent conversion to succinic acid via CH₂CHCOOH. − In addition to selectivity and conversion, it is essential to consider the cost implications of purified C₂H₄, which is a requisite for the reactions in the C₂ stage pathway. The introduction of O₂ during the reaction not only poses a safety hazard but also influences the outcome of subsequent reaction steps. Moreover, the separation of O₂ after the reaction is also a costly process.

2.1.3. Direct and Indirect Electrosynthetic Routes to Additional Succinic Acid-Relevant Intermediates

The previous sections mainly discussed electrochemical routes from CO₂ to CO, ethylene, acetate, and ethanol, which can serve as primary feedstocks for the downstream thermocatalytic upgrading. In some proposed succinic acid pathways, however, more specific intermediates, such as propionaldehyde (CH₃CH₂CHO), acetylene (C₂H₂), ethylene oxide (EO), and acetaldehyde (CH₃CHO), are involved. Therefore, this section briefly evaluates whether these intermediates can be produced directly or indirectly by electrocatalysis and whether such routes are practically relevant for electrothermal coupling.

The C₃ aldehyde route is attractive because propionaldehyde can be oxidized to acrylic acid and further converted through succinic acid-related pathways. Direct CO₂ electroreduction to propionaldehyde has been observed on Cu-based catalysts, but its selectivity remains limited. , C₂-unsaturated and oxidized intermediates provide another possible route family. Acetylene can act as a reactive C₂ building block for carbonylation or oxidative functionalization toward C₄-oxygenates. The molten-salt CO₂-to-carbide-to-acetylene pathway demonstrates that CO₂ can be converted to acetylene, but the need for high-temperature operation and carbide hydrolysis makes integration with low-temperature CO₂ electrolysis difficult. Ethylene oxide (EO) is also relevant because it can undergo ring-opening or carbonylation-type reactions. However, current EO electrosynthesis generally relies on ethylene oxidation rather than direct CO₂ reduction to EO. Therefore, its practical value depends on efficient CO₂ to ethylene production and selective downstream oxidation.

Acetaldehyde represents a C₂ oxygenate route. High acetaldehyde selectivity has been reported on Cu–Ag alloys, undercoordinated Cu sites, and specific Cu facets. , However, direct CO₂ or CO electroreduction to acetaldehyde still faces challenges in product concentration, separation, and long-term selectivity. Ethanol dehydrogenation provides an alternative high-selectivity route to acetaldehyde, but this shifts the key challenge from CO₂ reduction selectivity to ethanol feedstock availability.

Overall, direct electrosynthesis of these specific aldehyde or unsaturated intermediates is scientifically attractive because it could shorten the overall process. However, most direct routes are still limited by broad product distributions, low intermediate concentrations, competing hydrogenation or C–O cleavage pathways, and difficult separation. In contrast, indirect or stepwise electro-thermal routes are currently more feasible because the electrochemical and thermocatalytic steps can be optimized separately and better matched to downstream feed requirements.

2.2. Liquid-Phase Pathways

2.2.1. Electrocatalytic Production of Acetic Acid/Acetate

Acetic acid/Acetate is a promising liquid product in CO₂ electrolysis and can be formed via either direct CO₂ reduction or indirect pathways through CO intermediates (CORR). In the direct route, multiple parallel and still-debated reaction networks have been proposed, involving different C–C coupling motifs and oxygen retention mechanisms. Rather than converging on a single dominant pathway, current studies suggest that acetate formation is highly sensitive to the local electronic structure, intermediate coverage, and interfacial reaction environment. Accordingly, diverse catalyst design strategies have been explored to steer selectivity and stability by tuning Cu-oxidation states, local coordination environments, and reaction microenvironments. For instance, Serafini et al. fabricated Cu₂O–Cu⁰ nanostructured electrodes via integrated electrodeposition/oxidation on carbon paper GDLs, achieving acetate Faradaic efficiency of up to ∼76%. Similarly, De et al. developed a Mn-corrole molecular catalyst that selectively reduced CO₂ to acetate in aqueous solution, achieving an acetate Faradaic efficiency of up to 63%. From an engineering perspective, optimization of the direct route focuses on precise interfacial control to enhance CO coverage and C–C coupling efficiency, while employing weakly alkaline or nonalkaline electrolytes, short-path mass-transfer electrodes, and segmented reactor designs to mitigate carbonate scaling and downstream separation costs in alkaline systems.

In contrast, the indirect route (CO₂ → CO → acetate) has been widely adopted owing to its clearer mechanistic framework and improved process controllability. This pathway is commonly rationalized by the ketene mechanism, in which adsorbed CO undergoes C–C coupling and proton-coupled electron transfer to form *C₂O and *HCCO intermediates, followed by ketene (H₂CCO) desorption. The desorbed ketene subsequently reacts with OH^–/H₂O near the electrode–electrolyte interface, yielding acetate or acetic acid.

Similar to direct reduction, the CORR pathway relies on Cu-based catalysts, with research focusing on valence-state engineering, defect modulation, and alloying to boost acetate selectivity. For example, Wang et al. developed a Cd–Cu catalyst, achieving 86% acetate Faradaic efficiency under pressurized conditions. At the process scale, Crandall et al. demonstrated a kilowatt-scale CO electrolyzer stack operating stably for 125 h at 300 A, producing ∼98 L of 1.2 M acetate solution with 96% molar purity. To mitigate contamination from soluble electrolytes such as KOH, porous solid electrolyte (PSE) reactors enable the continuous extraction of electrolyte-free liquid products. Using this approach, Zhu et al. achieved an acetate Faradaic efficiency of up to 43% and continuous accumulation of pure acetic acid solutions with concentrations reaching 2 wt %. Because acetate often coexists with alcohol byproducts that can permeate and degrade conventional AEM/CEM membranes, Deng et al. employed a Zirfon separator, achieving ∼700 h of stable operation and ∼50% acetate selectivity. Overall, the CORR-to-acetate process has established a coherent progression from mechanistic understanding to system-scale demonstration, providing a robust and scalable acetate feedstock for downstream thermocatalytic upgrading.

2.2.2. Hybrid Photo- and Thermo-Catalytic Upgrading to Succinic Acid

The high concentration of CH₃COOH and acetate in the electrocatalytic liquid-phase products has the potential to undergo conversion to succinic acid via a light-driven dehydrogenative coupling, as illustrated in Figure . In this photocatalytic step, the conversion of CH₃COOH to succinic acid results in the retention of all carboxylate groups and the release of H₂, representing an intriguing and atom-economical pathway. Concurrently, the reaction process can be conducted in an environmentally benign and gentle manner to transform low-value monocarboxylic acids into dicarboxylic acid molecules. The synthesis of succinic acid via a light-driven dehydrogenation coupling reaction using a 0.01% Pt/TiO₂ catalyst has demonstrated selectivity of up to 25% and 38% for succinic acid and total acid products under optimal operating conditions. This pathway is currently being further developed.

6.

CO₂ derivatives to succinic acid by CH₃COOH under typical conditions.

In parallel, another representative electrocatalytic product, C₂H₄, can be selectively oxidized to CH₃COOH via thermocatalytic gas-phase oxidation with O₂ in the presence of a Pd/V₂O₅/TiO₂ catalyst and water, at atmospheric pressure, and in the temperature range of 100–200 °C. The combination of CH₃COOH produced during electrocatalysis with CH₃COOH converted from C₂H₄ for the photocatalytic reaction can result in a higher selectivity and yield of succinic acid from the electrocatalytic product through the conversion of CH₃COOH.

2.3. Integrated Gas–Liquid Two-Phase Systems

2.3.1. Alcohol Formation

Alcohols constitute an important class of high-value products in the CO₂/CO electroreduction. Their formation is generally associated with high surface *CO coverage, C–C coupling, and subsequent hydrogenation steps that preserve the carbonyl functionality. In widely discussed pathways, CO₂ is first reduced to surface-adsorbed CO, followed by C–C coupling to form C₂ oxygenated intermediates. These species can undergo sequential proton–electron transfer steps to yield acetaldehyde, which may be further hydrogenated to ethanol, while continued CO insertion or chain growth can lead to higher alcohols such as propanol. Overall, alcohol selectivity is highly sensitive to catalyst surface structure, interfacial electronic environment, and local reaction conditions, with C–C coupling and carbonyl hydrogenation commonly regarded as key selectivity-determining processes. ,

Gu et al. reported defect-site-rich Cu catalysts that achieved ∼60% C₂₊ alcohol Faradaic efficiency at 200 mA·cm^–2 in a membrane-electrode assembly electrolyzer. Sun et al. synthesized hierarchical V-doped Cu₂Se nanotubes that achieved a Faradaic efficiency of 68.3% toward ethanol in a flow-cell configuration. Anthony Robb et al. introduced an ethylcellulose-carbon black hydrophobic overlayer onto a Cu/PTFE cathode, which reduced water transport and facilitated ethanol evaporation toward the gas channel. This strategy increased the ethanol concentration in the cathodic product stream from ∼4.3 wt % to 12.4 wt %, reaching levels comparable to those required for industrial ethanol separation.

Current engineering bottlenecks in CO₂/CO electroreduction to alcohols include limited product selectivity and substantial alcohol crossover across ion-exchange membranes, which together result in low recoverable concentrations and downstream dilution. To mitigate these challenges, Papangelakis et al. combined a cation-exchange membrane to reverse electro-osmotic water transport with multistage condensation, enabling CORR scale-up in an 800 cm² electrolyzer with a combined alcohol production rate of ∼200 mL day^–1 (96 mL day^–1 ethanol and 84 mL day^–1 propanol). These results highlight the importance of coupling membrane selection with downstream separation engineering to improve alcohol retention and enable scalable COR-based alcohol electrosynthesis.

2.3.2. Oxidative Carbonylation to Succinic Acid Derivatives

As shown in Figure , the oxidative carbonylation of C₂H₄/CO/alcohols (ROH) in the presence of a palladium catalyst under optimal operating conditions of 100 °C and 10–40 bar resulted in valuable succinic acid derivatives, and the scaled-up reaction was successfully tested. , Once the succinic acid derivatives have been obtained, the synthesis of succinic acid can be achieved through a hydrolysis separation. This approach is relatively simple and straightforward, necessitating only a basic separation of the initial electrocatalytic product and enabling the conversion of the target-product derivative in a single step. Meanwhile, the polybutylene succinate sources can be obtained by optimizing the conditions using the corresponding ROH and catalysts. Succinic acid was further obtained after hydrolysis.

7.

CO₂ derivatives to succinic acid by one-step process under typical conditions.

3. Vision for the Future of Succinic Acid

In the context of succinic acid conversion, there are several issues that require focused attention and further investigation. These include the precise control of reaction conditions and the optimization of the catalyst choice to reduce the occurrence of side reactions. Additionally, the potential for catalyst deactivation during each reaction cycle should be considered. Further research is required for composite catalysts or the development of new and stable catalysts. The generation of byproducts and the presence of unreacted feedstock gases should be addressed. Meanwhile, the lack of systems-oriented standardization and durability is one of the main bottlenecks slowing down progress in the lab-to-prototype-to-market pathway of CO₂ electroreduction technologies. Thermal catalysis also faces similar challenges. In this section, we analyze the cost drivers, assess the environmental impact, examine the current challenges, and provide an outlook on the future development of this technology.

3.1. Cost-Driven Analysis

Conventional succinic acid is produced either petrochemically (e.g., maleic anhydride hydrogenation) or via fermentation. Biobased production can be economically attractive under favorable assumptions (e.g., low-cost sugars and efficient downstream processing), whereas petrochemical routes benefit from established infrastructure and mature catalysts. Reported costs are ∼2.86 USD kg^–1 for petrochemical production versus ∼1.17 USD kg^–1 for biobased routes under favorable assumptions, but both are highly sensitive to a small set of cost drivers. In fermentation, pH control requires substantial base input, generating equimolar salt streams that add material handling and recovery burdens, while downstream purification (evaporation, crystallization, and ion-exchange) is typically energy- and capital-intensive. These pathways therefore remain largely constrained by neutralization-separation penalties, motivating integrated electro-thermal routes that could reshape cost structure by altering intermediate composition, impurity profile, and separation duty.

For electro-thermal succinic acid production, the major cost drivers can be grouped into electrolysis-related costs, intermediate conditioning and separation costs, and thermocatalytic upgrading costs. The electrolysis stage is mainly governed by electricity price, cell voltage, Faradaic efficiency, current density, electrolyzer utilization, and catalyst or membrane lifetime. Reported techno-economic analyses identify electricity price as a dominant variable. In a representative CO₂ electrolyzer model, an optimistic case assumed an electricity price of 0.03 USD kWh^–1, while sensitivity analysis examined a range of 0.02–0.04 USD kWh^–1. These values should therefore be viewed as scenario-dependent benchmarks rather than universal break-even thresholds. For higher-electron products such as ethylene and ethanol, low-cost electricity alone is insufficient; high Faradaic efficiency, low cell voltage, sufficient current density, and stable operation are also required. Current density reduces stack-related capital cost by decreasing the required electrode area, but once it exceeds approximately 250–300 mA cm^–2, further increases provide diminishing economic benefit. In contrast, cell voltage and Faradaic efficiency remain highly influential because they directly determine electricity consumption, byproduct formation, and downstream separation load.

Different electrothermal pathways impose different cost structures depending on the intermediate. CO is relatively attractive because it is a two-electron product, and its reported electrolysis cost is lower than that of C₂ products. However, its overall feasibility depends on CO purity requirements, CO₂ recycling, gas compression, and whether downstream catalysts can tolerate mixed CO/CO₂ feeds. C₂ gas-phase routes, involving ethylene or related C₂ intermediates, are more economically challenging because of their high electron demand, mixed gas products, gas separation, and recycling requirements. Liquid acetate/acetic acid routes avoid some gas-compression costs but suffer from dilute product streams, electrolyte contamination, salt accumulation, and water removal. Alcohol/aldehyde routes face additional challenges associated with low oxygenate selectivity, product crossover, mixed liquid products, and thermocatalyst compatibility.

Thermocatalytic upgrading further contributes to pathway cost through catalyst lifetime, regenerability, impurity tolerance, and material compatibility. Electrolyzer effluents may contain residual CO₂, moisture, oxygenates, salts, or trace contaminants that differ from conventional thermocatalytic feedstocks. These species can accelerate catalyst poisoning, sintering, phase transformation, or selectivity loss, increasing replacement cost, regeneration frequency, and process downtime. Therefore, catalyst stability under realistic coupled electrochemical–thermochemical feed conditions should be considered a key techno-economic parameter.

The pathway-level comparison in Table S1 shows that electro-thermal routes do not automatically lower succinic acid production cost. Instead, they shift the dominant cost drivers from fermentation-related neutralization and salt removal toward electricity consumption, electrolyzer performance, intermediate purification, separation intensity, and catalyst durability. Their current economic risks are high because integrated electrochemical–thermochemical systems remain immature, but these risks arise from identifiable and potentially reducible bottlenecks. Key cost-reduction directions include lowering cell voltage, improving Faradaic efficiency and product selectivity, increasing single-pass conversion and intermediate concentration, reducing intermediate purification requirements, improving downstream tolerance to impure feeds, and extending catalyst and membrane lifetimes. Future techno-economic studies should integrate the electrochemical stage, intermediate conditioning, thermocatalytic upgrading, and final succinic acid purification under consistent boundary conditions.

3.2. Environmental Impact Assessment

To enable a direct comparison, conventional and electrothermal routes can be evaluated in terms of global warming impact (GWI), energy intensity, water footprint, and salt waste generation. Petrochemical production via maleic anhydride hydrogenation typically exhibits reported GWI values of 3.27–12.1 kg CO₂e kg^–1, with cumulative fossil energy demand ranging from 59.2 to 124 MJ kg^–1, reflecting its direct reliance on fossil carbon feedstocks. Conventional fermentation routes reduce fossil feedstock dependence but require stoichiometric base addition for pH control. As a result, approximately 1 kg of neutralization salt is generated per kilogram of succinic acid, increasing wastewater treatment intensity and separation-related energy consumption.

In contrast, the electro-thermal architecture shifts the primary environmental driver toward the generation of multicarbon intermediates. In the electrocatalytic stage, taking CO and ethylene production from CO₂ as examples, life cycle assessments report GWI values of approximately 1.66–2.13 CO₂e kg^–1 syngas (CO-rich stream) and 2.00–2.94 kg CO₂e kg^–1 under low-emission electricity assumptions. Climate benefits are realized when the electricity carbon intensity falls below approximately 0.25 kg CO₂ kWh^–1. , Importantly, because electricity is a decarbonizable input, the climate impact of this stage is not structurally fixed and can progressively decrease as the power grid decarbonizes.

On the thermocatalytic side, upstream conditioning steps, most notably dewatering and blowdown driven by salt accumulation, can materially increase the process-wide water footprint and the intensity of wastewater treatment. In addition, solvent losses and the associated recovery and regeneration operations should be explicitly accounted for, as they can impose meaningful resource burdens and potential toxicity impacts. Moreover, thermocatalytic upgrading is often highly sensitive to oxygenated impurities in the feed (e.g., through effects on the selectivity, catalyst deactivation, and process safety). As a result, deoxygenation as well as separation and compression duties and their associated energy demand and EHS requirements constitute environmental hotspots in their own right.

3.3. Current Challenges and Integration Considerations

For the electrocatalytic stage, substantial progress has been achieved in reaching high current densities and improved selectivity in MEA systems. However, durability under industrially relevant conditions remains a major concern. Catalyst restructuring, electrolyte-induced degradation, membrane failure, and carbonate accumulation can gradually reduce performance and CO₂ utilization efficiency. In addition, many liquid products are generated at low concentrations, and their separation requires significant energy input. As a result, electrochemical performance is directly linked to process feasibility. High intrinsic activity alone is not sufficient. Stable operation at high conversion and high single-pass utilization remains a key challenge. Long-term stability remains unevenly documented across the upgrading routes reviewed here. Therefore, Table S2 summarizes representative catalytic systems in the CO₂-to-succinic-acid electro–thermal network, focusing on degradation mechanisms, regeneration or mitigation strategies, and current lifetime expectations. This summary provides a practical basis for comparing the durability limitations of mature and emerging routes.

For mature heterogeneous steps such as V–P–O-catalyzed n-butane oxidation for industrial maleic anhydride production, catalyst charges are reported to operate on the order of months, with performance maintenance via regeneration practices described in the technology and patent literature. In contrast, for many downstream upgrading transformations, especially those employing homogeneous catalysts, durability is more commonly reported as recyclability, TON, or metal leaching rather than continuous time on stream, which limits direct cross-route comparisons and highlights a need for standardized durability reporting.

Beyond stability and conversion, the choice of the electrocatalytic intermediate introduces an additional layer of uncertainty. Direct ranking of intermediates such as CO, C₂H₄, acetate, or alcohols in terms of overall succinic acid production efficiency is currently not possible. Most studies report Faradaic efficiency and current density but rarely quantify downstream carbon retention, impurity profiles, or separation requirements. From an integration perspective, each intermediate presents trade-offs.

Gaseous CO is easy to separate and handle but requires extensive downstream C–C bond formation through established thermochemical upgrading routes. C₂ intermediates such as C₂H₄ and acetate provide higher carbon order and partial functionalization but often increase the separation burden or upgrading complexity. In tandem electrocatalytic-thermocatalytic systems, the ratio of CO, H₂, and C₂H₄ must be tuned to meet downstream reaction requirements rather than maximizing single-product selectivity. More advanced oxygenated intermediates, such as aldehydes, may simplify thermocatalytic C–C coupling due to their carbonyl functionality. However, their instability in aqueous electrolytes and sensitivity to operating conditions introduce additional constraints. These trade-offs indicate that intermediate selection must be evaluated within an integrated electrothermal framework rather than based solely on electrochemical selectivity.

The integration of electrocatalytic and thermocatalytic processes remains a significant challenge. Its feasibility depends not only on the intrinsic reactivity of intermediates but also on their physical state, concentration, impurity profile, and compatibility with downstream catalytic requirements. For gas-phase pathways, product ratio control and gas pretreatment are particularly important. Thermocatalytic upgrading reactions, such as hydroformylation, carbonylation, and C₄ coupling, are highly sensitive to the feed composition, pressure, and water content. As a result, intermediate streams often require drying, CO₂ removal, impurity purification, and gas compression prior to thermocatalytic conversion. In contrast, liquid-phase intermediates such as acetate and acetic acid avoid gas compression but introduce challenges, including electrolyte contamination, salt accumulation, and low product concentration. Gas–liquid intermediate pathways face additional challenges. Alcohol crossover in the electrocatalytic unit reduces product recovery, while efficient oxidative carbonylation in the thermocatalytic unit requires the precise control of CO and C₂H₄ partial pressures. Despite these limitations, this route offers strong integration potential because C₂H₄, CO, and alcohols can all be coproduced directly from CO₂ electrolysis, reducing reliance on external feedstocks and process logistics.

Therefore, pathway evaluation should not rely solely on the electrocatalytic selectivity or thermocatalytic conversion efficiency. Instead, it must consider the compatibility between upstream intermediate generation and downstream upgrading as well as the need for intermediate conditioning steps such as purification, drying, compression, and composition adjustment.

3.4. Comparative Assessment and Future Research Directions

Future research should be prioritized according to both technology readiness and potential process impact to improve the electrothermal succinic acid production. In the near term, a minimum comparable data set should be established under consistent conditions, including single-pass conversion, selectivity, stability window, product concentration, and feedstock specifications. These metrics are essential for comparing different electrocatalytic intermediates under equivalent boundaries and for determining whether mature intermediates such as CO or more functionalized intermediates such as C₂ species and aldehydes offer better overall process efficiency.

Medium-term efforts should focus on integrated reactor and process design because upstream electrolytic streams rarely meet downstream thermal processing requirements directly. Key priorities include feedstock treatment, circulation operation, carbonate management, electrolyte control, membrane durability, and gas–liquid mass transport. For thermal catalysis, catalyst durability and impurity tolerance should be emphasized under coupled feed conditions containing electrolyte residues, salts, water, or mixed organic products.

In the long term, transformative advances may come from highly integrated electrothermal systems, selective generation of functionalized C₂–C₄ intermediates, and intensified reactor architectures that reduce intermediate purification and improve carbon and energy efficiency. Forward-looking technoeconomic and life cycle analyses should also include water use, solvent and electrolyte consumption, material footprints, and separation demands.

Table provides a comprehensive overview of the advanced CO₂ electroreduction products, their corresponding reaction pathways, operating conditions (including electrode materials, active surface area, and current density), and performance metrics, such as Faradaic efficiency and stability.

1. Overview of the Gas and Liquid Product from CO₂ Electrolysis.

				active area	Faradaic efficiency	current density	stability	s
product	electrolysis pathway	cathode	anode	cm2	%	mA/cm2	hr	reference
CO	CO2–CO	Ag/GDE	IrOx/Ti felt	100	∼80 to ∼90	100	4500
CO	CO2–CO	Ag-TEL	Ni foam	1	92	3370	210
CO	CO2–CO	Ag-TEL	Ni foam	100	90	900	50
CO	CO2–CO	Ag + PSMIM	IrO2/GDL	6.25	98	200	3800
CO	CO2–CO	Ag + PSMIM	IrO2/GDL	6.25	95	200	1000
C2H4	CO2–C2H4	In/Cu	Ni foam (NiFe hydroxide)	1	85	600	1500
C2H4	CO2–C2H4	DVL-Cu	Ni foam (NiFe hydroxide)	5	70	150	55
C2H4	CO2–C2H4	molecular film Cu	IrOx/Ti mesh	5	64	120	190
C2H4	CO–C2H4	Cu-nc	Ir ink/Ti foam	4	44	1000	150
C2H4	CO–C2H4	Cu-nc	Ir ink/Ti foam	100	40	1000	32
acetate	CO2–CO–acetate	Cu/GDE	Ni foam (NiFe hydroxide)	500	40	300	125
acetate	CO–acetate	Cu/GDE	Ni foam (NiFe hydroxide)	100	50	200	700
acetate	CO–acetate	Cu/Ag-DA	Ni foam	1	80	100	820
ethanol	CO2–ethanol	N–C/Cu	IrOx/Ti mesh	5	52	160	15
ethanol	CO2–ethanol	Cu3Sn	IrO2/Ni mesh	4.84	40	900	48
alcohols	CO–alcohols	CuO	IrOx/Ti felt	5	35	100	100

Table presents a comprehensive overview of the reaction conditions, methods, catalyst systems, and conversion indicators associated with the more effective pathway for the production of succinic acid from CO₂ derivatives under typical operating conditions.

2. Overview of the Succinic Acid Production from CO₂ Derivatives by Different Thermocatalytic Pathways under Typical Conditions.

reactants	method	catalyst system/amount	reaction condition	ratio of reactants/GHSV/volume	target product	conversion indicators	references
Gas Phase Pathway for Succinic Acid Production through C4H10
C2H4/CO/H2	dimerization	Ni–NiO–SiO2	room temperature and pressure	CO/C2H4 = 3.5; CO flow rate 5 sccm	C4H10	S = 95%
C4H10	thermal catalysis	V–P–O; 4–6 mm tablets	400–450 °C/1 bar	2 mol % of n-butane in air; 1400–2100 h–1	maleic anhydride	C = 80–86%
maleic anhydride	hydrogenation reaction	Pd/Al2O3; 0.1 g, containing 8.5 × 10–3 mmol Pd	353 K/1 MPa	maleic anhydride = 7.35 g, 1,4-dioxane = 50 mL; (WHSV = 0.61 h–1)	succinic acid	C > 98%; S > 99%
maleic anhydride	hydrogenation reaction	Pd/BN; 0.1 g catalyst	150 °C/2 MPa	2 g of maleic anhydride, 40 mL of 1,4-dioxane; n-tetradecane 0.18 g; 100 mL autoclave	succinic acid	S = 99.7%
Gas Phase Pathway for Succinic Acid Production through CH2CHCOOH
CO2/C2H4	thermal catalysis	Pd-based: (COD)PdCl2/dcpe/Zn; 0.10 mmol (COD)PdCl2, 0.11 mmol dcpe, 10 mmol Zn	145 °C/autoclave 20 h	10 bar C2H4, 20 bar CO2, sodium 2-fluorophenolate 20 mmol; THF 30 mL	acrylic acid derivatives	TON = 29
CH2CHCOOH	thermal catalysis	Co-based: 17.1 mg [Co2(CO)8]; 21.1 mg dcpe; both 5 mol %	90 °C/16 bar	acrylic acid = 68 μL 1 mol·L–1, CO/H2 = 95:5; toluene 2 mL; mesitylene 14 μL	succinic anhydride	Y = 96%
Liquid Phase Pathway for Succinic Acid Production through CH3COOH
CH3COOH	dehydrogenation coupling	Pt/TiO2; 10 mg of photocatalyst	UV-light/60 °C	3.5 mL of acetic acid, 1.5 mL of water, CH3COOH/H2O = 7:3	succinic acid	S = 25%
Gas–Liquid Phase Pathway for Succinic Acid Production
CO/C2H4/MeOH	oxidative carbonylative esterification	Pd-based: [Pd (Allyl)Cl]2 0.0125 mmol 4.6 mg, poly-PPh3 3 mg, BQ 2 mmol 216.2 mg	100 °C/10–40 bar	40 bar CO, 10 bar C2H4, alcohols 2 mL, 4 mL vial in 300 mL autoclave	succinic acid derivatives	TON = 75.2

^aIn conversion indicators, S: selectivity; C: conversion rate; Y: yield; TON: The turnover number corresponds to the number of moles of substrate that a mole of catalyst can convert before becoming inactivated.

^bIn catalyst system, Ni–NiO–SiO₂: nickel–nickel oxide-silica composite; V–P–O: vanadium–phosphorus-oxygen phase system; Pd: palladium; BN: boron nitride; Co: cobalt; Pt: platinum.

Building on the representative electrochemical and thermocatalytic examples summarized in Tables and , Table further compares the major CO₂-to-succinic-acid pathways from a process-oriented perspective. While the selectivity and yield of some of the aforementioned pathways have not yet reached a level suitable for commercialization or scale-up, the potential for the development of these novel succinic acid generation pathways is significant. Current studies validate the feasibility of each pathway. Once the corresponding technological bottlenecks have been overcome, succinic acid can be produced economically and efficiently, in a sustainable and environmentally friendly manner, with considerable development potential. Among the proposed routes, the C₄ pathway via maleic anhydride appears to have the highest near-term feasibility because the maleic anhydride-to-succinic-acid segment is technically mature and industrially established. In contrast, the gas–liquid oxidative carbonylation route is particularly attractive from an integration perspective because C₂H₄, CO, and alcohols can all be derived from electrolysis.

3. Comparison of Major CO₂-to-Succinic-Acid Pathways and Representative Experimental Scales.

pathway (references)	overall conceptual route	theoretical carbon yield to succinic acid	thermodynamic and kinetic feasibility	separation and conditioning burden	process complexity	practical promise
C4 route via maleic anhydride −	CO2 → C2H4/CO/H2 → C4H10 or C4H8 → maleic anhydride → succinic acid	high in principle if C2/C4 coupling and oxidation are fully selective	thermodynamically favorable after C4 formation; kinetically mature for n-butane oxidation and maleic anhydride hydrogenation	requires C2H4/CO/H2 ratio control, C4 separation, and maleic anhydride recovery	high, but many, steps are industrially familiar	highest near-term feasibility: the maleic anhydride → succinic acid is mature
C3 route via acrylic acid −	CO2 + C2H4 → acrylic acid derivative → acrylic acid → succinic anhydride → succinic acid	high in principle if C2H4, CO2, and CO are all derived from CO2 and no decarboxylation occurs	ethylene carboxylation with CO2 is fundamentally difficult because CO2 is stable and C–C carboxylation has kinetic barriers	requires relatively pure C2H4 and CO2; acrylic acid derivative hydrolysis and purification	high	promising chemically, but less mature than C4 route; sensitive to purification and catalyst recycling
C3 route via propionaldehyde ,−	CO2 → C2H4/CO/H2 → propionaldehyde → acrylic acid → succinic anhydride → succinic acid	potentially high, but not yet quantified at route level	feasible at the step level but integration-limited; hydroformylation is feasible	lower initial separation if mixed gas is directly fed; oxidation and carbonylation requires purification	very high	conceptually attractive, but limited by low C3 selectivity and multiple downstream steps
C2 route via acetylene, ethylene oxide, acetaldehyde −	CO2 → C2H4 → C2H2, C2H4O, or CH3CHO → acrylic acid or succinic anhydride → succinic acid	potentially high, but highly route-dependent	individual C2 transformations are known, but multistep coupling to succinic acid is not yet demonstrated as an integrated process	requires purified C2H4; O2 introduction creates safety and removal burdens	very high	lower priority unless a direct and selective C2-to-C4 process is demonstrated
liquid acetate and acetic acid coupling route ,−	CO2/CO → acetate and acetic acid → succinic acid via dehydrogenative coupling	theoretically high from two C2 units	kinetically challenging due to selective C–C coupling; competing decarboxylation likely	concentration and salt removal from dilute streams	low step count but low selectivity	promising as a green liquid-phase concept, but far from commercial relevance
gas–liquid oxidative carbonylation to succinic acid derivatives ,	CO2 → C2H4/CO + ROH → succinic acid derivatives → hydrolysis → succinic acid	high in principle; alcohol can be recycled after hydrolysis depending on process design	chemically feasible; catalyst lifetime and stability remain key unknows	CO/C2H4 control, alcohol management, hydrolysis, and catalyst recovery	medium	potentially strong integration route because C2H4, CO, and alcohols can all be electrolysis-derived

^aTheoretical carbon yield refers to the ideal retention of carbon atoms in the succinic acid based on the conceptual reaction sequence and not the experimentally demonstrated overall carbon efficiency.

^bThermodynamic feasibility, separation burden, process complexity, and practical promise are qualitative assessments based on the cited representative studies and the integration requirements discussed in the text.

4. Conclusions and Outlook

As previously stated, succinic acid possesses considerable commercial value. However, both biological and petrochemical methods of succinic acid are subject to certain limitations in the present day. A comprehensive strategy combining electrocatalytic and thermocatalytic technologies was presented with the objective of exploring and optimizing the production pathway of succinic acid. This strategy combines the advantages of electrocatalysis, which efficiently converts CO₂ to specific chemicals under mild conditions, with the ability of thermocatalysis to promote complex chemical reactions under high-temperature and high-pressure (atmospheric pressure) environments. CO₂ is first electrochemically upgraded into key intermediates, C₂H₄/CO/H₂ mixtures, acetate, and multicarbon alcohols, which are then thermocatalytically converted through C₄ (C₄H₁₀ → maleic anhydride), C₃ (acrylic acid → succinic anhydride), or C₂ (acetaldehyde/ethylene oxide/acetylene → succinic anhydride) routes to produce succinic acid. Overall, the C₄ route via maleic anhydride appears to be the most feasible near-term pathway, whereas gas–liquid oxidative carbonylation offers strong long-term integration potential because its key feedstocks can be generated electrochemically. To comprehensively assess the feasibility and sustainability of these emerging production pathways, the intermediates, conversion conditions, costs, and potential scale-up limitations of each pathway were analyzed. This is not only important for promoting the green and sustainable production of biobased chemicals, such as succinic acid, but also provides new ideas and solutions to achieve the efficient utilization of CO₂ and the goal of global carbon neutrality.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/cbe.6c00021.

• Details of cost comparison and key cost-reduction targets of conventional and electro-thermal pathways for succinic acid production and details of stability considerations for representative catalytic systems in CO₂-to-succinic-acid electro–thermal routes (PDF)

Miao Miao conceived the original concept and outline design, performed analysis, and wrote the first draft of this manuscript. Zhaoxi Wang assisted with the draft of the electrocatalytic part and updated the figures. Miao Miao and Zhaoxi Wang contributed equally to this work. All authors edited and approved the manuscript.

The authors declare no competing financial interest.