Selective CO2 Electroreduction Research Articles

Selective and stable CO2 electroreduction at high rates via control of local H2O/CO2 ratio

Controlling the concentrations of H2O and CO2 at the reaction interface is crucial for achieving efficient electrochemical CO2 reduction. However, precise control of these variables during catalysis remains challenging, and the underlying mechanisms are not fully understood. Herein, guided by a multi-physics model, we demonstrate that tuning the local H2O/CO2 concentrations is achievable by thin polymer coatings on the catalyst surface. Beyond the often-explored hydrophobicity, polymer properties of gas permeability and water-uptake ability are even more critical for this purpose. With these insights, we achieve CO2 reduction on copper with Faradaic efficiency exceeding 87% towards multi-carbon products at a high current density of −2 A cm−2. Encouraging cathodic energy efficiency (>50%) is also observed at this high current density due to the substantially reduced cathodic potential. Additionally, we demonstrate stable CO2 reduction for over 150 h at practically relevant current densities owning to the robust reaction interface. Moreover, this strategy has been extended to membrane electrode assemblies and other catalysts for CO2 reduction. Our findings underscore the significance of fine-tuning the local H2O/CO2 balance for future CO2 reduction applications.

Anchoring Cs+ Ions on Carbon Vacancies for Selective CO2 Electroreduction to CO at High Current Densities in Membrane Electrode Assembly Electrolyzers

Electrolyte cations have been demonstrated to effectively enhance the rate and selectivity of the electrochemical CO2 reduction reaction (CO2RR), yet their implementation in electrolyte‐free membrane electrode assembly (MEA) electrolyzer presents significant challenges. Herein, an anchored cation strategy that immobilizes Cs+ on carbon vacancies was designed and innovatively implemented in MEA electrolyzer, enabling highly efficient CO2 electroreduction over commercial silver catalyst. Our approach achieves a CO partial current density of approximately 500 mA cm−2 in the MEA electrolyzer, three‐fold enhancement compared to pure Ag. In‐situ Raman and theoretical analyses, combined with machine learning potentials, reveal anchored Cs induces an electric field that significantly promotes the adsorption of *CO2− intermediates through performing muti‐point energy calculations on each structure. Furthermore, reduced adsorption of *OH intermediates effectively hampers competing hydrogen evolution reaction, as clarified by disk electrode experiments and density functional theory studies. Additionally, coupling our system with commercial polysilicon solar cells yields a notable solar‐to‐CO energy conversion efficiency of 8.3%. This study opens a new avenue for developing effective cation‐promoting strategy in MEA reactors for efficient CO2RR.

Highly Selective CO2 Electroreduction to C2H4 Using a Dual-Sites Cu(II) Porphyrin Framework Coupled with Cu2O Nanoparticles via a Synergetic-Tandem Strategy.

Low *CO coverage on the active sites is a major hurdle in the tandem electrocatalysis, resulting in unsatisfied C2H4 production efficiencies. In this work, we developed a synergetic-tandem strategy to construct a copper-based composite catalyst for the electroreduction of CO2 to C2H4, which was constructed via the template-directed polymerization of ultrathin Cu(II) porphyrin organic framework incorporating atomically isolated Cu(II) porphyrin and Cu(II) bipyridine sites on a carbon nanotube (CNT) scaffold, and then Cu2O nanoparticles were uniformly dispersed on the CNT scaffold. The presence of dual active sites within the Cu(II) porphyrin organic framework create a synergetic effect, leading to an increase in local *CO availability to enhance the C-C coupling step implemented on the adjacent Cu2O nanoparticles for further C2H4 production. Accordingly, the resultant catalyst affords an exceptional CO2-to-C2H4 Faradaic efficiency (FEC2H4) of 71.0% at -1.1 V vs reversible hydrogen electrode (RHE), making it one of the most effective copper-based tandem catalysts reported to date. The superior performance of the catalyst is further confirmed through operando infrared spectroscopy and theoretic calculations.

Amine-Functionalized Metal-Free Nanocarbon to Boost Selective CO2 Electroreduction to CO in a Flow Cell.

Highly efficient electrochemical CO2-to-CO conversion is a promising approach for achieving carbon neutrality. While nonmetallic carbon electrocatalysts have shown potential for CO2-to-CO utilization in H-type cells, achieving efficient conversion in flow cells at an industrial scale remains challenging. In this study, we present a cost-effective synthesis strategy for preparing ultrathin 2D carbon nanosheet catalysts through simple amine functionalization. The optimized catalyst, NCNs-2.5, demonstrates exceptional CO selectivity with a maximum Faradaic efficiency of 98% and achieves a high current density of 55 mA cm-2 in a flow cell. Furthermore, the catalyst exhibits excellent long-term stability, operating continuously for 50 h while maintaining a CO selectivity above 90%. The superior catalytic activity of NCNs-2.5 is attributed to the presence of amine-N active sites within the carbon lattice structure. This work establishes a foundation for the rational design of cost-effective nonmetallic carbon catalysts as sustainable alternatives to metals in energy conversion systems.

Theoretical study on CO production mechanism from CO2 reduction on Cu–catalyst surface with different oxidation states

The rational design of copper (Cu)-based catalysts with different oxidation states is essential to achieve highly selective and efficient CO2 electroreduction. However, the effect of different oxide states of Cu-based catalysts has rarely been studied. Herein, the reaction mechanism of CO2 hydrogenation into CO on Cu-based catalysts with different oxidation states, such as Cu(111), Cu2O(111) and CuO(111), was studied using the density functional theory. The most favored pathway for CO production and the rate-controlling step on the three catalyst models were determined. The results show that, Cu2O (111) shows the best catalytic activity among the three catalysts due to the lowest activation barrier. The electronic structure analysis shows that Cu2O has the proper electronic structure to activate CO2 which is further reduced to CO. This work provides an important insight on the effect of oxidation state of Cu-based catalysts on the reduction of CO2 to CO.

Tailoring the catalytic microenvironment of CuO with hydrophobic CuSA2 for selective CO2 electroreduction to C2+ products

Advancing the Faraday efficiency (FE) and current density of Cu catalyzed electrochemical CO2 reduction (ECR) reaction to produce C2+ products is important for its practical applications. Constructing a hydrophobic interface to regulate the local reaction environment is an effective method to improve the selectivity of C2+ products, but it is limited by the low reaction current density. In this work, we fabricated a novel hydrophobic and ECR active copper stearate (CuSA2) decorated CuO nanoparticle catalyst (CuO/CuSA2) for ECR reaction toward C2+ products. As a result, the CuO/CuSA2 catalyst achieved an FE of 61.33 % and a partial current density of 429.33 mA cm−2 for C2+ products. The CuSA2 and CuO nanoparticle cooperate very well for the formation of C2+ products. The in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and electrochemical adsorption experiment indicated that the hydrophobic CuSA2 regulated the local ECR reaction environment. The local ∗CO2.- and *CO adsorption were strengthened by hydrophobic CuSA2 modification while the H2O adsorption was inhibited. CuO nanoparticle promotes *CO coupling reaction and enhances C2 intermediates (*OCCOH and *OC2H5) adsorption. Hydrophobic CuSA2 and CuO nanoparticle synergistically promote the generation of C2+ products. This work provides new insights into the design of hydrophobic CO2 reduction electrocatalysts for the preparation of C2+ products.

Oxygen-affinity engineering on single-site catalysts for selective CO2 electroreduction

Oxygen-affinity engineering on single-site catalysts for selective CO2 electroreduction

Modulating local environment for electrocatalytic CO2 reduction to alcohol

The fundamental drivers for the selective CO2 electroreduction reaction (CO2RR) to alcohol (e.g. C2H5OH) or alkene (e.g. C2H4) still remain unexplored. Previous studies mainly focus on catalyst engineering to enhance electrocatalytic performance, while the selectivity to alcohol has reached a bottleneck. Here, we modulate local environment to reveal the contribution of *CO and *H reaction intermediates in the selectivity of CO2 to alcohol/alkene on Cu electrocatalyst. Through modifications on local CO2 concentration, varied *CO/*H coverage ratios can be achieved. Based on the reaction kinetics analysis, we find that there is a direct connection between local CO2 concentration and interfacial *CO and *H coverage, which finally affects the selectivity of CO2 to alcohol or alkene. To verify this principle, polyvinylidene fluoride (PVDF), a hydrophobic binder, were selected and introduced into the catalyst surface for further enhancement of interfacial *CO/*H coverage. With PVDF decoration, alcohol/alkene ratio increased from 0.69 to 1.35. The Faradic Efficiency of alcohol is up to 37.5 % under a high current density of 800 mA cm–2 (a partial current density of 300 mA cm–2), surpassing most reported Cu-based materials. Our findings provide a fundamental guidance for CO2RR to alcohol under an industrial-level current density.

Promoting CO2 Electroreduction to Ethane by Iodide-Derived Copper with the Hydrophobic Surface.

Electrochemical reduction of CO2 to value-added products provides a feasible pathway for mitigating net carbon emissions and storing renewable energy. However, the low dimerization efficiency of the absorbed CO intermediate (*CO) and the competitive hydrogen evolution reaction hinder the selective electroreduction of CO2 to ethane (C2H6) with a high energy density. Here, we designed hydrophobic iodide-derived copper electrodes (I-Cu/Nafion) for reducing CO2 to C2H6. The Faradaic efficiency of C2H6 reached 23.37% at -0.7 V vs RHE over the I-Cu/Nafion electrode in an H-type cell, which was about 1.7 times higher than that of the I-Cu electrode. The hydrophobic properties of the I-Cu/Nafion electrodes led to an increase in the local CO2 concentration and stabilized the Cu+ species. In situ Raman characterizations and density functional theory calculations indicate that the enhanced performances could be ascribed to the strong *CO adsorption and decreased the formation energy of *COOH and *COCOH intermediates. This study highlights the effect of the hydrophobic surface on Cu-based catalysts in the electroreduction of CO2 and provides a promising way to adjust the selectivity of C2 products.

Dynamically Reconstructed Triple-Copper-Vacancy Associates Confined in Cu Nanowires Enabling High-Rate and Selective CO2 Electroreduction to C2+ Products.

Electrochemically reconstructed Cu-based catalysts always exhibit enhanced CO2 electroreduction performance; however, it still remains ambiguous whether the reconstructed Cu vacancies have a substantial impact on CO2 -to-C2+ reactivity. Herein, Cu vacancies are first constructed through electrochemical reduction of Cu-based nanowires, in which high-angle annular dark-field scanning transmission electron microscopy image manifests the formation of triple-copper-vacancy associates with different concentrations, confirmed by positron annihilation lifetime spectroscopy. In situ attenuated total reflection-surface enhanced infrared absorption spectroscopy discloses the triple-copper-vacancy associates favor *CO adsorption and fast *CO dimerization. Moreover, density-functional-theory calculations unravel the triple-copper-vacancy associates endow the nearby Cu sites with enriched and disparate local charge density, which enhances the *CO adsorption and reduces the CO-CO coupling barrier, affirmed by the decreased *CO dimerization energy barrier by 0.4eV. As a result, the triple-copper-vacancy associates confined in Cu nanowires achieve a high Faradaic efficiency of over 80% for C2+ products in a wide current density range of 400-800mA cm-2 , outperforming most reported Cu-based electrocatalysts.

Selective and Efficient CO2 Electroreduction to Formate on Copper Electrodes Modified by Cationic Gemini Surfactants

AbstractElectroreduction of CO2 into valuable chemicals and fuels is a promising strategy to mitigate energy and environmental problems. However, it usually suffers from unsatisfactory selectivity for a single product and inadequate electrochemical stability. Herein, we report the first work to use cationic Gemini surfactants as modifiers to boost CO2 electroreduction to formate. The selectivity, activity and stability of the catalysts can be all significantly enhanced by Gemini surfactant modification. The Faradaic efficiency (FE) of formate could reach up to 96 %, and the energy efficiency (EE) could achieve 71 % over the Gemini surfactants modified Cu electrode. In addition, the Gemini surfactants modified commercial Bi2O3 nanosheets also showed an excellent catalytic performance, and the FE of formate reached 91 % with a current density of 510 mA cm−2 using the flow cell. Detailed studies demonstrated that the double quaternary ammonium cations and alkyl chains of the Gemini surfactants played a crucial role in boosting electroreduction CO2, which can not only stabilize the key intermediate HCOO* but also provide an easy access for CO2. These observations could shine light on the rational design of organic modifiers for promoted CO2 electroreduction.

Selective and Efficient CO2 Electroreduction to Formate on Copper Electrodes Modified by Cationic Gemini Surfactants.

Electroreduction of CO2 into valuable chemicals and fuels is a promising strategy to mitigate energy and environmental problems. However, it usually suffers from unsatisfactory selectivity for a single product and inadequate electrochemical stability. Herein, we report the first work to use cationic Gemini surfactants as modifiers to boost CO2 electroreduction to formate. The selectivity, activity and stability of the catalysts can be all significantly enhanced by Gemini surfactant modification. The Faradaic efficiency (FE) of formate could reach up to 96 %, and the energy efficiency (EE) could achieve 71 % over the Gemini surfactants modified Cu electrode. In addition, the Gemini surfactants modified commercial Bi2 O3 nanosheets also showed an excellent catalytic performance, and the FE of formate reached 91 % with a current density of 510 mA cm-2 using the flow cell. Detailed studies demonstrated that the double quaternary ammonium cations and alkyl chains of the Gemini surfactants played a crucial role in boosting electroreduction CO2 , which can not only stabilize the key intermediate HCOO* but also provide an easy access for CO2 . These observations could shine light on the rational design of organic modifiers for promoted CO2 electroreduction.

Steering the Selectivity of Carbon Dioxide Electroreduction from Single-Carbon to Multicarbon Products on Metal-Organic Frameworks via Facet Engineering.

Although metal-organic frameworks (MOFs) have attracted more attention for the electrocatalytic CO2 reduction reaction (CO2RR), obtaining multicarbon products with a high Faradaic efficiency (FE) remains challenging, especially under neutral conditions. Here, we report the controlled synthesis of stable Cu(I) 5-mercapto-1-methyltetrazole framework (Cu-MMT) nanostructures with different facets by rationally modulating the reaction solvents. Significantly, Cu-MMT nanostructures with (001) facets are acquired using isopropanol as a solvent, which favor multicarbon production with an FE of 73.75% and a multicarbon:single-carbon ratio of 3.93 for CO2RR in a neutral electrolyte. In sharp contrast, Cu-MMT nanostructures with (100) facets are obtained utilizing water, promoting single-carbon generation with an FE of 63.98% and a multicarbon: single-carbon ratio of only 0.18. Furthermore, this method can be extended to other Cu-MMT nanostructures with different facets in tuning the CO2 reduction selectivity. This work opens up new opportunities for the highly selective and efficient CO2 electroreduction to multicarbon products on MOFs via facet engineering.

Highly selective and low-overpotential electrocatalytic CO2 reduction to ethanol by Cu-single atoms decorated N-doped carbon dots

Selective, low-overpotential and high Faradaic efficiency electroreduction of CO2 to ethanol is in prominent global demand and lies in structuring, loading, and modulating the coordination states of Cu single atom catalysts (SACs) with support matrix. Here, the low-temperature (160 °C) synthesis of Cu–SACs–N-doped carbons dots (Cu–SACs–N–CQDs) is reported via Cu–dopamine complex process. The optimized Cu–SACs–N–CQDs electrocatalyst brings remarkably high Faraday efficiency (> 80%) and selectivity for ethanol with 50 h operation stability, which far exceeds previous results in terms of overpotential, stability, and Faraday efficiency. Surprisingly, the Faraday efficiency and selectivity of ethanol are highly sensitive to the coordination states of copper SACs with variation of Cu loadings. Operando X-ray absorption spectroscopy indicates in situ-generated neighboring metallic Cu–Cu atom coordination as real catalytic active sites from isolated single Cu atom during CO2 reduction, which favors the ethanol selectivity.

Gas-induced controllable synthesis of the Cu(100) crystal facet for the selective electroreduction of CO2 to multicarbon products.

Electrocatalytic CO2 reduction (ECR) to high value-added chemicals is an excellent method to attenuate the impact of greenhouse effect caused by CO2. At the same time, multicarbon products (C2+) get extensive attention in view of their relatively high energy density and market price. At present, Cu is an important metal electrocatalyst to convert CO2 into multicarbon products (e.g. ethylene, ethanol, and n-propanol); however, its poor selectivity impedes its practical application. It is well-known that the Cu(100) crystal facet can enhance the selectivity toward multicarbon products among different Cu crystal facets. Herein, the Cu nanoparticles were firstly prepared using the inductive effect of different gases (CO2, CO, Ar, N2, and air) during the Cu electrodeposition processes, in which the CO2-induced Cu catalyst (Cu-CO2) showed the largest normalized content of the Cu(100) crystal facet and the highest C2+ faradaic efficiency of 69% at a current density of 80 mA cm-2 in ECR. Subsequently, the different CO2 pressures during the Cu electrodepositions were studied to reveal the optimal CO2 pressure in the CO2-induced Cu synthesis for improved Cu(100) content as well as C2+ faradaic efficiency. Finally, density functional theory (DFT) calculations confirmed that CO2 molecules preferred to get adsorbed on the Cu(100) crystal facet, which resulted in not only the presence of dominant Cu(100) during the CO2-induced Cu synthesis but also the good electrocatalytic performance in ECR.

Highly selective electroreduction of CO2 to CO with ZnO QDs/N-doped porous carbon catalysts.

ZnO quantum dots (QDs) supported on porous nitrogen-doped carbon (ZnOQDs/P-NC) exhibited excellent electrochemical performance for the electroreduction of CO2 to CO with a faradaic efficiency of 95.3% and a current density of 21.6 mA cm-2 at -2.2 V vs. Ag/Ag+.

Restructuring multi-phase interfaces from Cu-based metal-organic frameworks for selective electroreduction of CO2 to C2H4.

Multi-phase interfaces are promising for surmounting the energy barriers of electrochemical CO2 reduction involving multiple electron transfer steps, but challenges still remain in constructing interfacial micro-structures and unraveling their dynamic changes and working mechanism. Herein, highly active Ag/Cu/Cu2O heterostructures are in situ electrochemically restructured from Ag-incorporating HKUST-1, a Cu-based metal-organic framework (MOF), and accomplish efficient CO2-to-C2H4 conversion with a high faradaic efficiency (57.2% at -1.3 V vs. RHE) and satisfactory stability in flow cells, performing among the best of recently reported MOFs and their derivatives. The combination of in/ex situ characterizations and theoretical calculations reveals that Ag plays a crucial role in stabilizing Cu(i) and increasing the CO surface coverage, while the active Cu/Cu2O interfaces significantly reduce the energy barrier of C-C coupling toward the boosted ethylene production. This work not only proves MOFs as feasible precursors to derive efficient electrocatalysts on site, but also provides in-depth understanding on the working interfaces at an atomic level.

Recent advances in nanoscale engineering of Pd-based electrocatalysts for selective CO2 electroreduction to formic acid/formate

Electrochemical conversion of carbon dioxide (CO2) into high-value chemicals and fuels driven by electricity derived from renewable energy has been recognized as a promising strategy to achieve carbon neutrality and create sustainable energy. Particularly from the viewpoint of the product values and the economic viability, selective CO2 reduction to formic acid/formate has shown great promise. Palladium (Pd) has been demonstrated as the only metal that can produce formic acid/formate perfectly near the equilibrium potential; yet, it still suffers from CO poisoning, poor stability and competitive CO pathway at high overpotentials. Herein, recent progress of Pd-based electrocatalysts for selective CO2 electroreduction and their mechanistic understanding are reviewed. First, the fundamentals of electrochemical CO2 reduction and the reaction pathway of formic acid/formate on Pd are presented. Then, recent advances in the rational design and nanoscale engineering strategies of Pd-based electrocatalysts for further improving CO2 reduction activity and selectivity to formic acid/formate product, including size control, morphology and shape control, alloying, heteroatom doping, surface-strain engineering, and phase control, are discussed from the perspectives of both experimental and computational aspects. Finally, we discuss the pertinent challenges and describe the future prospects and opportunities in terms of the development of electrocatalysts, electrolyzers and characterization techniques in this research field.

FePc/MXene as an efficient catalyst for the selective electroreduction of CO2 into CO in a flow cell

Recently, the exploration of MXene-based catalysts has become a hot topic in the electrocatalytic field. Herein, an electrocatalyst of decorating FePc on MXene (called FePc/MXene) was prepared and applied to CO2 reduction reactions (CO2RR) in a flow cell. The results show that CO is the main product of CO2RR on the as-prepared FePc/MXene electrocatalyst, and H2 is the only by-product (small part). Notably, the optimal of FePc/MXene (1:3) (mass ratio) has a high selectivity for CO with a CO Faraday efficiency (FECO) of 98.23%. After 24 h of continuous electrolysis, the FECO remained at a high level of 96.31%. This study would provide a promising catalyst for CO2RR, giving a good reference to developing the MXene-based electrocatalyst.

In situ dynamic re-structuring and interfacial evolution of SnS2 for high-performance electrochemical CO2 reduction to formate

The conversion of CO2 to value-added fuels and chemicals through electrochemical reduction has garnered substantial traction as an environmentally friendly approach toward a carbon-neutral society. Surface re-structuring of catalysts stands as one of the dynamic behaviors exhibited by electrocatalytic systems, exerting a significant influence on the catalysts' chemical, electronic, and physical characteristics, and thereby impacting their catalytic capabilities. Herein, we have discovered that the re-structured SnS2 nanoflowers with in situ formed Sn nanoclusters exhibit an enhanced Faradic efficiency of up to 93% with long-term stability for selective electroreduction of CO2 to formate with dynamic surface re-structuring. The in situ generated Sn nanoclusters on SnS2 nanoflowers at negative potential were found to play a vital role in facilitating over 90% CO2 electroreduction efficiency to formate. The presence of key intermediate OCHO* was proved through in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. It was also guided by first-principal calculations that the interfacial region between Sn nanoclusters and SnS2 nanosheet acts as the most favorable catalytic site for the formation of OCHO*. This work unveils the significance of surface re-structuring behaviors of electrocatalysts under in situ environment for the pathway and mechanism of CO2 electroreduction, demonstrating the promise of structure-modulated SnS2 as a candidate for formate production.