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Mechanism–structure–performance relationship of porous single-phase La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and dual-phase La0.6Sr0.4Co0.2Fe0.8O3−δ–Sm0.2Ce0.8O1.9 (LSCF–SDC) composites.

Possible rate-limiting steps of oxygen reduction reaction for porous materials at various temperatures by comparing oxygen consumption fluxes (Js) and oxygen supply fluxes (Jg).

Fe-SDC formed Fe nanoparticles on the ceria surface through the exsolution reaction, which significantly improved its electrochemical properties.

In situ Fe exsolution under SOEC working conditions remarkably facilitates CO2 reduction, enabling high-efficiency CO2 electrolysis at lower temperatures.

Improving proton conduction in cathodes is regarded as one of the most effective methods to accelerate the sluggish proton-involved oxygen reduction reaction (P-ORR) for proton-conducting solid oxide fuel cells (P-SOFCs). In this work, K+ dopant was used to improve the proton uptake and migration ability of SrCo0.9 Nb0.1 O3-δ (SCN). K+ -doped SCN (KSCN) demonstrated great potential to be a promising cathode for P-SOFCs. Density functional theory calculations suggested that doping with K+ led to more oxygen vacancies and more negative values of hydration enthalpy, which was helpful for the improvement of proton concentration. Importantly, the proton migration barriers could be depressed, benefiting proton conduction. Electrochemical investigations signified that the cell using KSCN cathode had a peak power density of 967 mW cm-2 at 700 °C, about 54.1 % higher than that using a SCN cathode. This research highlights the K+ -doping strategy to improve electrochemical performance of cathodes for P-SOFCs.

Triple-conducting (H

Reversible protonic ceramic cells (R-PCCs) have attracted intensive attention, as they can operate efficiently for both power generation and fuel production. The practical application of R-PCCs is, however, limited by the poor catalytic activity and stability of the air electrode. Here, we report a novel electrochemical catalyst of 10 mol% La substituted Ba0.5Sr0.5Co0.8Fe0.2O3−δ , showing improved stability under typical R-PCCs working conditions. XRD patterns confirm that La0.1Ba0.4Sr0.5Co0.8Fe0.2O3−δ maintains the cubic structure after heat treatment in humid air (3% H2O) at 700 °C for 100 h. In addition, the assembled full cells using this novel material as air electrode catalyst present outstanding performance. At 700 °C, the peak power density reaches 650 mW cm−2 (fuel cell mode); and in electrolysis mode the maximum current density reaches 1840 mA cm−2 at 1.5 V. We speculate that the much-improved stability and electrochemical performance of the La0.1Ba0.4Sr0.5Co0.8Fe0.2O3−δ air electrode may result from the higher electronegativity of La, which is beneficial for reducing the basicity and improving the chemical stability in acidic atmospheres; from the smaller ionic radius of La, which can alleviate the lattice distortion of BSCF; and from the stronger interaction between La and lattice oxygen inhibiting the structural degradation caused by Sr segregation.

Perovskite oxide Sr2Fe1.5Mo0.5O6−δ (SFM) has attracted much attention as a potential ceramic anode material for solid oxide fuel cells. In this work, antimony is primarily proposed to partially replace the Mo element in order to improve its electrochemical performance. Sb doping significantly reduces oxygen vacancy formation energy and hybridization between Fe 3d and O 2p electrons, promotes the reduction process for anode application, greatly increases the oxygen vacancy concentration and the content of adsorbed oxygen species, and effectively improves the surface reaction rate constant for the hydrogen oxidation reaction and chemical oxygen diffusion coefficient. Consequently, Sb doping greatly improves the anode performance by a factor of 2.4 through decreasing the area specific interfacial polarization resistance from 0.184 to 0.075 Ω cm2 at 800 °C. The performance is much higher than those ever reported for SFM doped with various metal elements, and is even higher than those of SFM-based composite electrodes. In addition, Sb doping greatly improves fuel cell performance such as increasing the peak power density from 681 to 920 mW cm−2 at 800 °C with H2 as the fuel. Meanwhile, improvement is also achieved with syngas and ethanol fuels, generating peak power densities of 765 and 557 mW cm−2, respectively.

Nowadays, effective utilization of CO2 has been a worldwide issue. Among numerous CO2 conversion devices, solid oxide electrolysis cells (SOECs) have drawn special attention due to their high energy conversion efficiency, great potential in carbon cycling, and low environmental impacts. Compared with the typical ones taking asymmetrical configuration, symmetrical SOECs adapting the same oxide materials as both the cathode and anode have the advantages of simplified fabrication procedures, reduced processing costs and minimized compatibility issues. As the appropriate sites for CO2 conversion, cathodes play the key role in determining the performance of symmetrical SOECs, and thus, attract more attention to improve their electrocatalytic behaviors and endurance via exploring novel materials. In this work, Eu-doped Ruddlesden–Popper (R–P) oxide, SrEu2Fe2O7 (SEF), is applied as an electrode material for symmetrical SOECs to directly electrolyze pure CO2. The outstanding structural stability and excellent electrochemical activity of the SEF electrode under both oxidizing and reducing atmospheres are demonstrated, and relatively low polarization resistances of 0.07 Ω cm2 in air and 0.48 Ω cm2 in 2CO2–CO mixtures at 800 °C are observed. A great current density of 1.27 A cm−2 at an applied voltage of 1.5 V and 800 °C is achieved on this symmetrical SOEC. An extremely low polarization resistance of 0.27 Ω cm2 is also observed under open circuit conditions. Further, the symmetrical button cell has demonstrated excellent stability within 260 h of the long-term CO2 electrolysis test.

Tungsten-doped strontium ferrite (SrFe1-xWxO3-δ, SFW) is prepared and characterized as the electrode materials for symmetrical solid oxide electrochemical cell. X-ray diffraction refinement reveals the symmetrical structure transform from cubic ( p m 3 ¯ m ) for x = 0.1 to tetragonal (I4/m) when x = 0.2. According to the analysis including electrical conductivity, Hydrogen temperature-programmed reduction (H2-TPR), thermal expansion and X-ray photoelectron spectra (XPS), it suggests that the decrease in conductivity, content of Fe2+ and oxygen vacancy concentration with the increase of W content is attributed to the stronger lattice framework. The oxygen vacancy can be dramatically activated around 600 °C. Using SrFe0.8W0.2O3-δ as the electrodes, symmetrical single cells supported on doped ceria electrolytes can achieve acceptable power density (0.19 W cm−2 at 750 °C) and considerable stability. Meanwhile symmetrical cells with La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte substrates can achieve 0.75 A cm−2 at 800 °C under the voltage of OCV (open circuit voltage) +0.5 V when it is operated in electrolysis mode. SrFe0.8W0.2O3-δ can gain a considerable stability and electrochemical activity under both oxide and reductive atmospheres. Oxygen vacancy formation energy (Evac) and electron density distribution are computed to verify the enhancement on crystal structure stability by doping W. The Evac critically depends on the distance from the W atom.

Protonic ceramic fuel cells (PCFCs) have been proved as an efficient energy converter at intermediate temperatures. To accelerate the kinetics of the proton-involved oxygen reduction reaction (p-ORR), developing efficient and durable cathodes is of great importance for improving PCFCs. In this work, a new triple-layered Ruddlesden-Popper (R-P) structure oxide, Sr3 EuFe2.5 Co0.5 O10-δ (3-SEFC0.5 ), was developed as a potential single-phase cathode for PCFCs, showing high oxygen non-stoichiometry and desirable structural thermal stability. By employing this highly active and stable single-phase cathode, the PCFC demonstrated unprecedented low polarization resistances and exceptionally great peak power densities, which were approximately 0.030 Ω cm2 and 900 mW cm-2 measured at 700 °C, respectively. These findings not only manifest the effectiveness of optimal doping in improving the structural stability and electrocatalytic activity in the multi-layered perovskite family, but also highlight the great potential of using multi-layered R-P series oxides as highly active and durable catalysts for PCFCs.

As a typical Ruddlesden-Popper oxide, La2NiO4+δ draws special attention for its high oxygen ion conducting behavior and special interstitial oxygen defects which enables it a promising electrocatalyst toward oxygen reduction reaction. In this work, Ca-doped La2NiO4+δ samples are prepared and their structure and defect evolution are investigated as Ca content. Electrical conductivity and electron conduction relaxation (ECR) investigations suggest that La1.9Ca0.1NiO4+δ has the great electronic conductivity and the highest oxygen surface exchange coefficient and oxygen bulk diffusion coefficient at intermediate temperatures. These results may imply that more gas oxygen has inserted into La1.9Ca0.1NiO4+δ sample, suggesting the native interstitial oxygen defects in it. X-ray photon spectroscopy (XPS) results confirm that La1.9Ca0.1NiO4+δ have more active oxygen species when compared with La2NiO4+δ and La1.8Ca0.2NiO4+δ. The great oxygen exchange and bulk diffusion properties along with its great stability in steam involved atmosphere enables it a promising for cathode for H–SOFCs. Compared with that using La2NiO4+δ cathode, peak powder density of H–SOFC using La1.9Ca0.1NiO4+δ single phase cathode improves about 30.5% at 700 °C, suggesting that accelerating oxygen reduction reaction can effectively improve cathode performance of H–SOFCs.

The grievous carbon deposition in Ni-based anode limits its practical application in solid oxide fuel cells for methane conversion. In this work, nano-layer MgO decorated Ni-based anode is successfully prepared by in-situ reduction of Ni0.9-xCu0.1MgxO solid solution. Peak power density of 670 mW cm−2 at 700 °C in humid methane is achieved using Ni0.875Cu0.1-0.025MgO/Sm0.2Ce0.8O2 anode thanks to the improved active surface and the special modulation effect of MgO nano-layer on anode reactions. Interestingly, synchrotron vacuum ultraviolet photoionization mass spectra and high temperature X-ray photoelectron spectra jointly suggest that the effect of MgO on carbon resistance differs with the operating temperatures, which accelerates the steam reforming of CH4 via improving dissociative adsorption of acidic gas H2O at ∼500 °C, while depresses CH4 cracking to carbon and improves the formation of light olefin at ∼700 °C. In addition, possible methane reaction paths over such anode are derived.

Direct utilization of hydrocarbon fuels in solid oxide fuel cells (SOFCs) has drawn special attention for high energy conversion efficiency, low cost, and simple devices. However, when fueled with hydrocarbons, SOFCs encountered great difficulty in both performance and stability, which should be attributed to the sluggish hydrocarbon oxidizing reactions, the severe carbon deposition reactions, and the possible sulfur poisoning reactions in the anode. This review summarizes potential anode reactions in hydrocarbon-fueled SOFCs and discusses the possible anode deactivation mechanisms. Further, various strategies to improve the anode performance and stability are reviewed, including substituting alloys or increasing oxide basicity for nickel-based anodes, adopting oxide anodes, and adding catalyst layers. The advantages and challenges of each strategy are discussed. Special attention is paid on properties and models of novel oxide anodes, of which nano-metal catalysts are in-situ exsolved. The publications concerning SOFC anodes, mainly in recent 5 years, are listed and compared in this article.

Direct internal reforming of methanol is applied as fuel for a Ni-YSZ anode-supported solid oxide fuel cell with a flat tube based on double-sided cathodes. It achieves a power density (PD) of 0.25 W/cm2 at 0.8 V, reaching about 90% of that is fueled by H2. And the cell has been operated for more than 120 h by the direct internal reforming of methanol. The durability and apparent advantage for using humidified methanol may lead to widespread applications by direct internal reforming method for this new designed SOFC in the future.

High-temperature catalytic and transport properties of porous ionic–electronic conducting materials (MIECs) are vital for device-level performance and are sensitive to microstructure, however they are indirectly characterized using dense MIECs with simple geometry. The structure–property relationship can be misinterpreted, as the fabrication procedures and microstructures of the dense MIECs are different from those of the porous MIECs. Here, the distribution of characteristic times (DCT) is proposed to resolve chemical relaxation (CR) kinetics in porous MIECs. The peak in a DCT spectrum has a clear physical origin, with its integral area being the fractional volume involved. In contrast to previous treatments that assume surface exchange-limited kinetics, the DCT spectra of porous La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) show that gaseous oxygen diffusion can dominate the CR kinetics in 0–40 percent volume, depending on the sintering temperature of the sample. The surface exchange coefficient and its thermal activation energy are much lower than those of the dense bulk LSCF. These findings indicate a different catalytic mechanism on the internal surface of porous LSCF, compared to in the dense bulk material. The DCT approach opens up a way to reveal the CR kinetics in porous MIECs, and can readily be extended from e−/O2− to e−/H+ and e−/H+/O2− conducting oxides.

Improving proton conduction in cathodes is regarded as one of the most effective methods to accelerate the sluggish proton-involved oxygen reduction reaction (P-ORR) for proton-conducting solid oxide fuel cells (P-SOFCs). In this work, K

Gold is generally considered to be inert for electrochemical reactions in solid oxide fuel cells (SOFCs). It is thus used as the standard current collector to characterize the catalytic activity of various cathode materials including the state-of-the-art lanthanum strontium cobalt iron oxide (LSCF). This work shows that gold is not inert but active for oxygen reduction reaction (ORR) via LSCF. Electrical conductivity relaxation measurement shows that scattered gold particles on LSCF surface can greatly increase the ORR rate. Gold improves the chemical oxygen surface exchange coefficient by a factor up to 27.5. The improvement is much high at reduced temperature from 800 to 650 °C. In addition, gold particles with smaller size show better performance in enhancing the ORR activity.

Nano-structuring methods are actively applied to solid oxide fuel cell electrodes to reduce the operating temperature while preserving a high electro-catalytic activity. The unique nanoscale microstructure is vital to electrochemical performance, yet not well quantified in three dimensions. Here, with a multi-stage recovering principle of distance correlation functions, the three-dimensional microstructures of La0.8Sr0.2MnO3-δ nanoparticles infiltrated porous Y0.16Zr0.84O2-δ electrodes are reconstructed with a dimension of 1024 × 1024 × 1024 voxels at a resolution of 7.5 nm from one two-dimensional micrograph. The key geometric characteristics, such as tortuosity factors, active surface/interface areas and three-phase boundary length, are calculated from the reconstructed three-dimensional microstructures at various loadings of La0.8Sr0.2MnO3-δ. Combining with the analysis of distribution of relaxation times, the active three-phase boundary length is shown to be the main factor governing the electrode impedance, and is related quantitatively to the electrochemical process at high frequency. The accuracy of capturing nanoscale features is validated by the focused ion beam sectioning dataset of a Ni-Y0.16Zr0.84O2-δ electrode at nanoscale resolution. This work provides a promising strategy for reconstructing three-dimensional heterogeneous nanostructures from one super-resolution two-dimensional micrograph, and demonstrates a quantitative approach for uncovering processing-structure-property relationships of nanostructured electrodes and beyond.

CO2 conversion plays a critical role in sustainable carbon cycling. In this work, reduction of CO2 over three Pt-decorated/undecorated CeO2-based catalysts (partially reduced CeO2(111), Pt decorate...

The objective of this study was to build an efficient outer-inner looping redox reaction mechanism called steam recycled biomass chemical looping gasification (SR-BCLG) for H2 production by using BaFe2O4 as an oxygen carrier (OC). The X-ray diffraction (XRD) results showed the phase changes of BaFe2O4 in the SR-BCLG process can be oxidized to its initial state stimulated by steam. In addition, the impacts on the temperature, water injection rate (steam/biomass ratio) and OC loading were investigated. The maximum H2 production of 28.5 mol/kg· biomass was achieved in the 60 min of gasification with a BaFe2O4 load amount of 10 wt%, which is an increase in H2 production of 109.6% compared with the no-OC biomass gasification process under the optimal conditions. Durative high production of H2-enriched syngas was obtained during the cyclic stability tests, indicating the significant redox durability and high H2-generation properties of BaFe2O4. The XRD, scanning electron microscopy (SEM), and thermo-gravimetric analyzer (TG) characterizations revealed the high stability of BaFe2O4, which can be ascribed to the existence of Ba2+. The bimetal functional BaFe2O4 allows for an innovative method of outer-inner looping redox reactions for continuous H2-enriched syngas generation in the SR-BCLG process.

Ruddlesden−Popper type oxide, La0.5Sr1.5MnO4+δ, is investigated as a potential electrode material for symmetrical solid oxide fuel cells. This work improves its electrochemical catalytic activity through over doping nickel to form a B-site excess oxide, (La0.5Sr1.5Mn)Ni0.1O4+δ. X-ray diffractometry shows that the over doped oxide has the Ruddlesden−Popper structure when heated up to 800 °C in air and hydrogen atmospheres. Investigations with scanning electron microscopy, transmission electron microscopy and temperature-programmed reduction clearly demonstrate the exsolution of Ni nanoparticles from the parent Ruddlesden-Popper phase in hydrogen atmospheres. The Ni nanoparticles significantly improve the catalytic activity for hydrogen electro-oxidation reaction, reducing the interfacial polarization resistance at 800 °C by >40%. Meanwhile, the B-site excess design improves the electro-catalytic activity for oxygen reduction reaction, reducing the interfacial polarization resistance at 800 °C by >20%. As a result, the nickel enrichment design improves the peak power density at 800 °C by a factor of ∼4 for the electrolyte supported model cells with symmetrical electrodes based on (La0.5Sr1.5Mn)Ni0.1O4+δ. The Ni enrichment design displays great prospects in improving the electrochemical performance for Ruddlesden−Popper type oxide as the electrode for symmetrical solid oxide fuel cells.

CO2 electrolysis was carried out by using flat-tube solid oxide electrolysis cells (SOECs) with double-sided air electrodes. Redox cycles were employed to study the mechanical and performance stabilities. The cell was cycled 10 times and then the electrolysis was performed at a current density of −0.33 A/cm2 for 50 h at 750 °C. The results demonstrate that the unique SOEC structure leads to a stable performance for the electrolysis of pure CO2, reaching electrolysis efficiencies >30%. Compared to conventional cells, the redox performance of the cell is remarkably enhanced.

Ruddlesden-Popper-type strontium-doped lanthanum cuprates are unique in oxygen defects because of the oxygen-deficient composition. This work increases the oxygen vacancy concentration through bismuth-doping and thus promotes the electrochemical performance for oxygen reduction reaction (ORR) in solid oxide fuel cells. X-ray diffraction shows that up to 10% A-site elements can be doped with bismuth. The doping improves the catalytic activity through (1) increasing oxygen vacancy concentration by 87.5 and 65.5% at room temperature and 800 °C, respectively, as demonstrated by iodometric titration and thermogravimetric analysis, (2) greatly reducing the energy for oxygen vacancy formation as shown by density functional theory calculation, (3) forming additional reactive oxygen species at the near surface region as suggested with X-ray photoelectron spectroscopy, and (4) enhancing the oxygen transport properties as exhibited with electrical conductivity relaxation. In addition, bismuth doping reduces the thermal expansion coefficient to a level that could exactly match the thermal expansion behavior to the electrolytes. Consequently, the interfacial polarization resistance for ORR is decreased by 43% at 800 °C for the cuprate-based composite electrodes. The decrease is greatly attributed to the enhancement in the charge-transfer process, the rate-limiting step. Further, the peak power density for a model cell is increased from 530 to 630 mW·cm

Stochastic heterogeneous microstructures are widely applied in structural and functional materials, playing a crucial role in determining their performance. X-ray tomography and focused ion beam serial sectioning are frequently used methods to reconstruct three-dimensional (3D) microstructures, yet are demanding techniques and are resolution-limited. Here, a high-throughput multi-stage 3D reconstruction method via distance correlation functions is developed using a single representatively large-sized 2D micrograph for stochastic microstructures, and verified by X-ray micro-tomography datasets of isotropic and anisotropic solid oxide fuel cell electrodes. This method provides an economic, easy-to-use and high-throughput approach for reconstructing stochastic heterogeneous microstructures for energy conversion and storage devices, and can readily be extended to other materials.

Driven by the increasing global energy demand, the development of innovative energy conversion and storage systems is becoming more and more urgent. As one of the attractive means, water splitting has attracted widespread attention because of its great potential in storing electricity in the form of chemical fuel which also makes it a promising solution to the utilization of non-grid electricity generated by solar or wind. The oxygen evolution reaction (OER) is generally deemed as the key rate-limiting step of water splitting, and thus studying efficient OER electrocatalysts with a low overpotential and good stability is of vital importance. Here, we successfully prepared an OER catalyst with excellent electrochemical performance through a simple anion doping. Firstly, a stable cubic perovskite SrCoO3−δ was prepared by anion F-doping instead of traditional A and/or B site doping. Secondly, SrCoO2.85−δF0.15 demonstrates excellent OER activity superior to its parent hexagonal compound H-Sr2Co2O5 and those perovskites prepared via complicated A- and/or B-site doping. DFT calculations and XPS investigations reveal that the cubic structure and the highly oxidative oxygen species (O22−/O−) via F− doping jointly contribute to the better OER properties of SrCoO2.85−δF0.15. Our work brings forth a promising strategy to stabilize cubic structures from hexagonal ones via a simple anion doping strategy, which may open a new avenue for the development of even more effective OER catalysts and may be applied in many other fields related to structure transformation, in addition to energy and catalysis fields.

An open question for interpretation of impedance spectra of electrochemical cells is how to decouple the electrochemo-structural interactions. Reduced-dimensional models, such as equivalent circuits, face challenges in capturing the impacts of inhomogeneities (e.g. roughness and constriction effects) in three-dimensional microstructures, where mean-field assumption breaks down. Here we report a new method to analyze the impedance spectra of the reaction-diffusion process in an electrode based on a distribution of reaction-diffusion streamlines (DRDS) connected parallelly with different lengths (representing the roughness effects) and shapes (representing the constriction effects). Demonstrations on (La,Sr)(Co,Fe)O3−δ electrodes show that the DRDS method can explicitly capture the geometric inhomogeneities and the multiple rate-determining steps in the multi-scale features of the electrode microstructure. Furthermore, the kinetic parameters for the reaction-diffusion process can be extracted accurately from the DRDS analysis, and ‘direct three-phase-boundary reactions’, a well-known open hypothesis in solid oxide cells, are monitored clearly by using the DRDS pattern. This method is generally applicable to many electrochemical systems involving a reaction-diffusion process in the electrode.

Suppression of carbon deposition and sulfur poisoning without sacrificing electrochemical performance is crucial for operating solid oxide fuel cells (SOFCs), especially at intermediate temperatures (IT). In this work, nickel-doped A-site deficient perovskite oxides (PrBa)0.95Fe1.9−xNixMo0.1O6−δ (PBFMNix, x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized and investigated as potential anodes for IT-SOFCs. With increased amounts of Ni2+, the ratios of Fe2+/Fe3+ and Mo5+/Mo6+ in as-prepared PBFMNix continuously decreased under a charge-compensating mechanism, which simultaneously depressed the formation of the impurity phase (BaMoO4). Interestingly, the substitution of Ni2+ benefits the reduction of Fe3+ to Fe2+ and Mo6+ to Mo5+, and small portions of Fe and Ni elements are exsolved from the parent oxides, forming FeNi3 alloy nano-particles that greatly accelerate the chemical adsorption and surface reaction kinetics of H2, and thus improve the electrochemical performances of oxide-based anodes. Transformation of the electrical conduction from p-type to n-type after reduction was also observed. A very small polarization resistance of 0.028 Ω cm2 at 750 °C was achieved for the cell with the PBFMNi0.3 anode. Importantly, fueled with syngas with 50 ppm H2S, the maximum power density of a button cell based on the PBFMNi0.3 anode and an Sm0.2Ce0.8O1.9 (SDC) electrolyte-supporting configuration can reach 498 mW cm−2 at 750 °C, and long-term stability over 100 hours can be demonstrated with negligible performance decay. All these results indicate that PBFMNi0.3 is a promising high-performance anode material with good coking resistance and sulfur tolerance in intermediate temperatures.

This work investigates the kinetics of CO2 electrolysis on Cu-SDC (samaria-doped ceria) composite electrodes supported on YSZ (yttria-stabilized zirconia) electrolytes. The Cu-SDC electrode was achieved by impregnating Cu into porous SDC with a copper nitrate solution. The electrochemical characteristics including polarization curves and AC impedance spectra were measured at different temperatures and applied biases, and in different atmospheres. The exchange current densities and charge transfer coefficients at various temperatures were obtained by applying nonlinear curve-fitting analysis to the current–overpotential curves. The polarization resistance derived from the I–V curve is consistent with that from the impedance spectrum, which indicates good reliability for fitting the Butler–Volmer equation to the I–V curve. The activation energy of CO2 electrolysis derived from the Arrhenius behavior of exchange current density is not affected by the atmosphere; however, it is decreased with the increase of impregnated Cu. The determined rate-limiting step is related to oxygen vacancies that play a vital role in CO2 electrolysis.