CO2 Electrolysis Research Articles

Roles of copper(I) in water-promoted CO2 electrolysis to multi-carbon compounds.

The membrane electrode assembly (MEA) is promising for practical applications of the electrocatalytic CO2 reduction reaction (CO2RR) to multi-carbon (C2+) compounds. Water management is crucial in the MEA electrolyser without catholyte, but few studies have clarified whether the co-feeding water in cathode can enhance C2+ formation. Here, we report our discovery of pivotal roles of a suitable nanocomposite electrocatalyst with abundant Cu2O-Cu0 interfaces in accomplishing water-promoting effect on C2+ formation, achieving a current density of 1.0 A cm-2 and a 19% single-pass C2+ yield at 80% C2+ Faradaic efficiency in MEA. The operando characterizations confirm the co-existence of Cu+ with Cu0 during CO2RR at ampere-level current densities. Our studies reveal that Cu+ works for water activation and aids C‒C coupling by enhancing formations of adsorbed CO and CHO species. This work offers a strategy to boost CO2RR to C2+ compounds in industrial-relevant MEA by combining water management and electrocatalyst design.

Hierarchically conductive electrodes unlock stable and scalable CO2 electrolysis.

Electrochemical CO2 reduction has emerged as a promising CO2 utilization technology, with Gas Diffusion Electrodes becoming the predominant architecture to maximize performance. Such electrodes must maintain robust hydrophobicity to prevent flooding, while also ensuring high conductivity to minimize ohmic losses. Intrinsic material tradeoffs have led to two main architectures: carbon paper is highly conductive but floods easily; while expanded Polytetrafluoroethylene is flooding resistant but non-conductive, limiting electrode sizes to just 5 cm2. Here we demonstrate a hierarchically conductive electrode architecture which overcomes these scaling limitations by employing inter-woven microscale conductors within a hydrophobic expanded Polytetrafluoroethylene membrane. We develop a model which captures the spatial variability in voltage and product distribution on electrodes due to ohmic losses and use it to rationally design the hierarchical architecture which can be applied independent of catalyst chemistry or morphology. We demonstrate C2+ Faradaic efficiencies of ~75% and reduce cell voltage by as much as 0.9 V for electrodes as large as 50 cm2 by employing our hierarchically conductive electrode architecture.

Controlling the Polarity of Metal–Organic Frameworks to Promote Electrochemical CO2 Reduction

AbstractThe addition of polar functional groups to porous structures is an effective strategy for increasing the ability of metal–organic frameworks (MOFs) to capture CO2 by enhancing interactions between the dipoles of the polar functional groups and the quadrupoles of CO2. However, the potential of MOFs with polar functional groups to activate CO2 has not been investigated in the context of CO2 electrolysis. In this study, we report a mixed‐ligand strategy to incorporate various functional groups in the MOFs. We found that substituents with strong polarity led to increased catalytic performance of electrochemical CO2 reduction for these polarized MOFs. Both experimental and theoretical evidence indicates that the presence of polar functional groups induces a charge redistribution in the micropores of MOFs. We have shown that higher electron densities of sp2‐carbon atoms in benzimidazolate ligands reduces the energy barrier to generate *COOH, which is simultaneously controlled by the mass transfer of CO2. Our research offers an effective method of disrupting local electron neutrality in the pores of electrocatalysts/supports to activate CO2 under electrochemical conditions.

Ionomer and Membrane Designs for Low-temperature CO2 and CO Electrolysis.

Low-temperature electroreduction of CO2 and CO (CO(2)RR) into valuable chemicals and fuels offers a promising pathway to reduce greenhouse gas emissions and achieve carbon neutrality. Today's low-temperature CO(2)RR technology relies on the use of ionomers, polymers with ionized groups, primarily as catalyst layer (CL) additives. In the meantime, ionomers can assemble into ion-exchange membranes (IEMs), serving as important components of electrolyzers. According to the ion-exchange functions, ionomer additives are classified as cation-exchange ionomers (CEIs) and anion-exchange ionomers (AEIs); similarly, IEMs are divided into cation-exchange membranes (CEMs) and anion-exchange membranes (AEMs), as well as the multilayer polymer electrolytes (MPEs). Recent studies show that ionomer additives can regulate the catalytic microenvironment and thereby enhance performance towards desired products. This Review discusses the roles of ionomer additives and IEMs in CO2 and CO reduction reactions, highlighting the latest mechanistic insights and performance advances. It outlines challenges in designing ionomer additives and IEMs to improve product selectivity, energy efficiency (EE), and operational lifetime of CO(2)RR electrolyzers, while also providing perspectives on future research directions. The aim is to connect the current status of ionomer and membrane development with performance metrics analysis, offering insights for the advancement of commercially relevant low-temperature CO(2)RR electrolyzers.

Research Progress of High-entropy Oxides for Electrocatalytic Oxygen Evolution Reaction.

High-entropy oxides (HEOs), similar to high-entropy materials (HEMs), have "four-core effects", i. e., high-entropy effect, delayed diffusion effect, lattice distortion effect and cocktail effect, which have attracted more and more attention in the scientific field of renewable energy technology due to their unique structural characteristics, variable chemical composition and corresponding functional properties. HEOs have become potential candidates for electrocatalytic oxygen evolution reaction (OER), which is a key half reaction for electrolytic CO2, nitrogen reduction, and water electrolysis. However, the precise synthesis of HEOs with a wide range of components and structures is challenging, not to mention their active and stable operation for OER. In this paper, we review the recent advancements in the electrocatalytic oxygen evolution facilitated by HEOs in water electrolysis. We analyze these developments from the perspectives of activity and stability in acid and alkaline conditions, respectively. Furthermore, we summarize the design from the aspect of element composition, structure, morphology, and catalyst-support interactions, along with related reaction mechanism of HEOs. Additionally, we discuss the current challenges faced by HEOs in the field of OER and suggest potential directions for the future development of HEOs beyond water electrolysis application.

Atomically Dispersed Ru Species Induced by Strong Metal-Support Interaction for Electrochemical Methane Reforming.

During the high-temperature oxygen evolution reaction for CO2 electrolysis in solid oxide electrolysis cells (SOECs), the key elementary process of O2- transfer is restricted by the high anodic oxygen pressure thermodynamically, thus requiring a high external voltage [open-circuit voltage (OCV)] to drive the electrolysis reaction. Herein, electrochemical CH4 reforming is introduced to the SOEC anode, which remarkably lowers the anodic oxygen pressure and OCV, finally reducing the energy demand from 3.12 to 0.11 kW h per cubic meter of CO. Meanwhile, atomically dispersed Ru species is anchored on the anode surface due to the strong metal-support interaction, which exhibits superior CH4 reforming activity (90% of CO selectivity) and stability (300 h) to the infiltrated Ru nanoparticles and doped Ru species in the bulk lattice at 600 °C. This work proposes an efficient strategy to boost the SOEC performance thermodynamically and produce value-added chemicals at both the cathode and anode of SOEC simultaneously.

The Role of Cation Exchange Membrane Characteristics in CO2 Electrolysis to CO Using Acid Anolyte

Cation exchange membranes are considered a suitable option for zero-gap CO2 electrolysis due to their potential to avoid carbonation and improve carbon efficiency. However, the use of acidic anolytes remains an issue due to high hydrogen production. This study investigates Nafion® membranes (111, 112, 115, 211, and 212) with different thicknesses produced by extrusion or solution-cast processes in a zero-gap cell with an acidic anolyte containing K2SO4. Faradaic efficiencies for CO production (FECO) are higher with thinner membranes, regardless of the manufacturing process, reaching FECO around 75% at 50 mA cm⁻². Additionally, membranes with similar thicknesses (∼50.8 µm) but produced in different ways displayed flow field carbonation after 3 hours of electrolysis at 30°C and 50 mA cm⁻². Linear sweep voltammetry (LSV) in full and half-cell configurations shows limiting diffusion current (iL) relative to proton transport for all the employed membranes, no matter the thickness. In contrast, the iL for Nafion® 115, the thicker membrane, is suppressed, indicating that proton depletion is fast and the electrode surface alkalinization primarily results from water reduction in this case. A mechanistic analysis was performed to explain the behavior of the limiting currents in the cell with Ar- and CO2-feed, indicating that CO2 reduction aids in the consumption of H+ provided by the membrane, increasing the local pH at less negative potentials. Overall, thinner membranes exhibited higher values of FECO and energy efficiency for CO (EE%CO). However, solution-cast membranes are more prone to provide K+, leading to better performance than those prepared by extrusion.

Intermittent CO2 electrolysis needs its time in the sun

Intermittent CO2 electrolysis needs its time in the sun

Study on the influence characteristics of multi-working condition parameters on membrane electrode type CO2 electrolyzer

The electrochemical conversion of carbon dioxide (CO2) into basic chemicals or carbon-based fuels is a promising new strategy for carbon resource utilization. Within this domain, solid-electrolyte CO2 electrolyzer demonstrate significant potential for the continuous production of pure formic acid solutions. This study, leveraging a 4 cm2 visualization electrolyzer, explores the impact of three working condition parameters on performance: working voltage, gas flow rate, and the intermediate chamber water flow rate. It compares the variations in current density, formic acid concentration, and the distribution of liquid water on the cathode side under different working conditions. The results indicate that the working voltage, current density, and formic acid yield are all positively correlated; overly low gas flow rates can lead to CO2 deficiency and diminished electrolyzer performance; concentration control of the formic acid solution is effectively achieved by adjusting the intermediate chamber water flow rate; and during the electrolyzer reaction process, almost all of the liquid water is positioned at the bends downstream of the cathode flow channel.

Fluorine-doped perovskite cathodes with boosted electrocatalytic activity for CO2 electrolysis

Global energy demands that have traditionally been satisfied by the use of fossil fuels have led to substantial emissions of CO2, an important greenhouse gas. Solid oxide electrolysis cells (SOECs) offer a practical approach for transforming CO2 into valuable fuels. Accordingly, creating stable electrocatalysts and perovskite cathodes capable of efficiently converting CO2 is a primary aim for the further development of SOECs. Although reconstructing active sites during CO2 electrolysis is significantly challenging, it is also constrained by our lack of understanding of this process. Herein, we introduce an innovative strategy that involves co-doping with Cu and F to better facilitate the exsolution reaction, which resulted in the formation of an advanced cathode composed of Cu-Fe alloy nanoparticles embedded in a fluorine-doped Sr2Fe1.5Mo0.5O6−δ (SFM) ceramic matrix. The in-situ electrochemical reconstruction of the SFM cathode through co-doping not only improves mass-transfer efficiency during CO2 electrolysis but also enhances the catalytic activity and durability of the ceramic cathode. A SOEC assembled with this material as a symmetrical electrode delivered 4.99 mL min−1 cm−2 of CO at 850 °C and an applied voltage of 1.8 V, which is 168 % higher than that of a pure SFM electrode. In addition, no carbon deposits were observed at the end of the reaction. The co-doping strategy delivered enhanced performance without degradation over 100 h of high-temperature operation, which suggests that it is a reliable cathode material for CO2 electrolysis. This study introduced an innovative method for improving the SOEC-electrode microstructure and developing efficient electrocatalysts for CO2 electrolysis.

Unlocking the Activity of Molecular Assemblies for CO2 Electroreduction in Zero-Gap Electrolysers via Catalyst Ink Engineering.

In recent years, CO2 electrolysis, particularly the electrochemical reduction of CO2 to CO in zero-gap systems, has gained significant attention. While Ag-coated gas diffusion electrodes are commonly used in state-of-the-art systems, heterogenized molecular catalysts like bis-coordinated homoleptic silver(I) N,N-bis(arylimino)-acenaphthene (Ag-BIAN) complexes are emerging as a promising alternative due to their tunability and high mass activity. In this study, the influence of ink composition on the performance of Ag-BIAN-based GDEs in zero-gap electrolyzers (ZGEs) are systematically explored at 60°C and 600mA cm⁻2. Sedimentation analyses across various solvents informed the selection of optimal solvent-catalyst and solvent-carbon additive combinations, streamlining the GDE optimization process and reducing associated costs and time. These results demonstrate that solvent choice and dilution state of the ink are critical factors impacting CO2 reduction, achieving faradaic efficiencies for CO production (FECO) up to 67% at 600mA cm⁻2 with catalyst loadings as low as 0.2mg cm⁻2. These findings lay the groundwork for advancing from homogeneous H-type cells to industrial ZGE systems through tailored ink engineering.

Enhanced graphitization of CO2-derived carbon anodes via Joule heating reformation for high-performance lithium-ion batteries

Molten salt electrolysis of CO2 represents a promising technology for highly efficient CO2 capture and the production of economically valuable CO2-derived carbon materials. In this study, we established a 100-A-scale molten salt CO2 electrolysis cell to synthesize hundreds of grams of CO2-derived carbon. Subsequent Joule heating at 2800 °C transformed these materials into high-quality graphite. Further composite modification with asphalt and petroleum coke effectively reduced surface area, resulting in high-performance graphite for lithium-ion battery. The CO2-derived graphite anodes demonstrated high reversible capacities ranging from 297.7 to 378.1 mAh g−1, exhibiting outstanding rate capability and stability over 300 charge-discharge cycles at a current density of 1 A g−1. Finally, we assembled a coin full-cell using AG-2/2/6 anode and LFP cathode, which demonstrated good cycling performance. XPS analysis revealed a significant reduction in oxygen content by the post-reformation, facilitating the formation of highly graphitized structures. This study not only pioneers the up-class synthesis of CO2-derived carbon but also underscores its potential for sustainable energy applications, particularly in lithium-ion battery technology.

Synergistic Interactions in a Heterobimetallic Ce(III)-Ni(II) Diimine Complex: Enhancing the Electrocatalytic Efficiency for CO2 Reduction.

In this study, we propose a practical approach for producing a heterobimetallic Ni(II)-Ce(III) diimine complex from an extended salen-type ligand (H2L) to serve as an electrocatalyst for CO2 reduction and demonstrate an outstanding overall efficiency of 99.6% of the cerium-nickel complex and integrate it into applicable cell assemblies. We optimize not only the catalyst, but the operational conditions enabling successful CO2 electrolysis over extended periods at different current densities. A comparison of electrochemical behavior in H-cell and zero-gap cell electrolyzers suggests potential applications for industrial scale-up. In the H-cell electrolyzer configuration, the most elevated efficiency in CO production was achieved with a selectivity of 56.96% at -1.01 V vs RHE, while HCOO- formation exhibited a selectivity of 32.24% at -1.11 V vs RHE. The highest TON was determined to be 14657.0 for CO formation, followed by HCOO- with a TON of 927.8 at -1.11 V vs RHE. In the zero-gap electrolyzer configuration, the most efficient setup toward CO production was identified at a current density (CD) of 75 mA cm-2, a flow rate of 10 mL min-1, operating at 60 °C and utilizing a low KOH concentration of 0.1 M to yield a maximum faradaic efficiency (FECO) of 82.1% during 24 h of stable electrocatalysis.

Synergizing autothermal reforming hydrogen production and carbon dioxide electrolysis: Enhancing the competitiveness of blue hydrogen in sustainable energy systems

With the global energy paradigm shifting towards renewable and sustainable systems, hydrogen is increasingly recognized as a promising energy carrier. In this transition, blue hydrogen is often considered a bridge solution to green hydrogen due to its economic vulnerability to carbon costs and environmental regulations related to life-cycle emissions. To expand the role of blue hydrogen, it is essential to enhance hydrogen yield, reduce production costs, and minimize greenhouse gas emissions during the production phase. This study proposes an integrated process for blue hydrogen production and CO2 electrolysis to enhance the competitiveness of blue hydrogen in sustainable energy systems. The focus of this study was to integrate autothermal reforming hydrogen production with solid oxide CO2 electrolysis and to determine the optimal configuration and operating conditions of the integrated process. The proposed process demonstrated superior performance in terms of energy efficiency, production cost, and environmental impact compared with conventional blue hydrogen production. Furthermore, considering the intermittency of renewable electricity and the uncertainties in CO2 electrolysis technology, the industrial feasibility of the proposed process was validated. The integration of autothermal reforming blue hydrogen production and CO2 electrolysis has four clear advantages: (i) the costly air separation and carbon capture units, which pose significant financial burdens in autothermal reforming blue hydrogen production, can be eliminated; (ii) the downstream separation, which is indispensable in a standalone CO2 electrolysis system, can be removed; (iii) utilization pathways for captured CO2 from blue hydrogen production have been proposed; and (iv) guidelines have been provided for the industrial utilization of CO2 electrolysis.

Flooding Control by Electrochemically Reduced Graphene Oxide Additives in Silver Catalyst Layers for CO2 Electrolysis.

Electrolyte flooding in porous catalyst layers on gas diffusion electrodes (GDE) limits the stability and high-current performance of CO2 and CO electrolyzers. Here, we demonstrate the in situ electroreduction of graphene oxide (GO) to reduced graphene oxide (r-GO) within a silver catalyst layer on a carbon GDE. The r-GO introduces hydrophobicity regions in the catalyst layer that help mitigate electrolyte flooding during high current density CO2 electrolysis to CO. The flooding-resistant r-GO/Ag-coated GDE achieves a sustained Faradaic efficiency of CO at 94% for more than 8 h, compared to a rapid drop from 95% to 66% in an Ag-coated GDE without r-GO at 100 mA·cm-2. We found that GO enhances the electrochemically active surface area of the catalyst layer during CO2 electrolysis tests because the incorporation of GO increases the roughness of the catalyst layer. The in situ method of electrochemically reducing GO to r-GO provides a low-cost, practical approach that can be applied during standard spray-deposition procedures to develop flooding-resistant GDEs.

Controlling the Polarity of Metal-Organic Frameworks to Promote Electrochemical CO2 Reduction.

The addition of polar functional groups to porous structures is an effective strategy for increasing the ability of metal-organic frameworks (MOFs) to capture CO2 by enhancing interactions between the dipoles of the polar functional groups and the quadrupoles of CO2. However, the potential of MOFs grafted to polar functional group to activate CO2 has not been investigated in the context of CO2 electrolysis. In this study, we report a mixed-ligand strategy to incorporate various functional groups in the MOFs. We found that substituents with strong polarity led to increased catalytic performance of electrochemical CO2 reduction for these polarized MOFs. Both experimental and theoretical evidence indicates that the presence of polar functional groups induces a charge redistribution in the micropores of MOFs. We have shown that higher electron densities of sp2-carbon atoms in benzimidazolate ligands reduces the energy barrier to generate *COOH, which is simultaneously controlled by the mass transfer of CO2. Our research offers an effective method of disrupting local electron neutrality in the pores of electrocatalysts/supports to activate CO2 under electrochemical conditions.

Flow-electrode capacitive separation of organic acid products and recovery of alkali cations after acidic CO2 electrolysis

Acidic CO2 electrolysis, enhanced by the introduction of alkali cations, presents a strategic approach for improving carbon efficiency compared to processes conducted in neutral and alkaline environments. However, a significant challenge arises from the dissolution of both organic acids and alkali cations in a strongly acidic feed stream, resulting in a considerable energy penalty for downstream separation. In this study, we investigate the feasibility of using flow-electrode capacitive deionization (FCDI) technology to separate organic acids and recover alkali cations from a strongly acidic feed stream (pH ~ 1). We show that organic acids, such as formic acid and acetic acid, are retained in molecular form in the separation chamber, achieving a rejection rate of over 90% under all conditions. Alkali cations, such as K+ and Cs+, migrate to the cathode chamber in ionic form, with their removal and recovery significantly influenced by their concentration and the pH of the feed stream, but responding differently to the types and concentrations of organic acids. The energy consumption for the removal and recovery of K+ is 4 to 8 times higher than for Cs+, and the charge efficiency is significantly influenced by the types of organic acid products and alkali cations. We conduct a series of electrochemical measurements and analyze the impedance spectroscopy, identifying that hindered mass transfer governed the electrode process. Our findings underscore the potential of FCDI as an advanced downstream separation technology for acidic electrocatalysis processes.

Evaluation and Upscaling of Impregnated La0.20Sr0.25Ca0.45TiO3 Fuel Electrodes for Solid Oxide Electrolysis Cells

Recent research into Rh and Ce0.80Gd0.20O1.90-impregnated La0.20Sr0.25Ca0.45TiO3 fuel electrodes for solid oxide fuel cells has demonstrated the high-stability of these material sets to a variety of harsh operating conditions at small scales (1 cm2 active area button cells), as well as commercial scales (100 cm2 cells) in short stacks (5 cells) and full micro-combined heat and power systems (60 cells). In this work, the authors present a comprehensive evaluation of the ability of these novel titanate-based materials to function as fuel electrodes in solid oxide electrolysis cells (SOECs). Short-term and durability testing of button cell scale SOECs highlighted the limited stability of lanthanum strontium manganite-based air electrodes, under CO2 and steam electrolysis conditions, with lanthanum strontium cobaltite ferrite-based air electrodes offering improved degradation characteristics. Upscaling of this optimized cell chemistry to a 16 cm2 active area SOEC and testing under CO2, CO2/H2O and H2O electrolysis conditions demonstrated encouraging performance over a period of ∼600 h, with stable co-electrolysis performance at ∼−7.5 A at 1.47 V for the first 100 h.

Electrolyte-supported solid oxide electrochemical cells for versatile operations

Electrolyte-supported solid oxide electrochemical cells (SOCs) offer advantages in terms of easier fabrication and enhanced mechanical properties, but achieving high performance and multifunctionality remains challenging. In this study, we develop high-performance and versatile electrolyte-supported SOCs using La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte materials through microstructural engineering of Sr2Fe1.5Mo0.5O6-δ (SFM)-based fuel electrodes. We evaluate the cells for power generation, hydrogen production, and carbon dioxide reduction, showcasing the diverse potential of various fuel electrode configurations. Among these, the impregnated SFM@LSGM electrode achieves the best overall performance, with a maximum power density of 739 mW cm−2 in fuel-cell mode, a current density of −0.81 A cm−2 at 1.3 V during steam electrolysis, and an unprecedented current density of −1.92 A cm−2 at 1.5 V in CO₂ electrolysis. Furthermore, it exhibits satisfactory stability across all operational modes. These findings provide valuable insights into the design of versatile electrolyte-supported SOCs and open new possibilities for their flexible applications in future low-carbon energy systems.

Zr and Y co-doped SrFe0.8Zr0.1Y0.1O3-δ perovskite oxide as a stable, high-performance symmetrical electrode for solid oxide cells

Symmetrical solid oxide cells (SSOCs), which use the same material for both anode and cathode, simplify the cell fabrication process and effectively resist carbon deposition and sulfur poisoning. In this study, Zr, Y co-doped SrFe0.8Zr0.1Y0.1O3-δ (SFZY) perovskite oxide is synthesized and evaluated its properties as an SSOFCs electrode. Density functional theory (DFT) indicates that the local state density of SFZY is lower than that of SrFeO3-δ (SFO). SFZY has good chemical compatibility with La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) electrolyte below cell operating temperature. Zr, Y co-doped SrFe0.8Zr0.1Y0.1O3-δ maintains structural stability in H2 atmosphere. At 750 ℃, the polarization resistance (Rp) of SFZY is 0.11 and 1.06 Ω cm2 in air and hydrogen atmosphere, respectively. During the Rp stability test, SFZY exhibits better stability than that of SrFeO3-δ in air and hydrogen atmosphere. At 750 ℃, the maximum power density of SFZY/LSGM/SFZY fuel cell reaches 420.1 and 258.31 mWcm−2 using H2 and wet C3H8 as fuel, respectively. In electrolytic mode, the current density of SFZY/LSGM/SFZY electrolysis cell reaches -0.55 A cm−2 at 1.3V for electrolysis of pure CO2 at 750 ℃. In summary, SFZY has a great potential as SSOCs electrode.