Boosting Electrochemical CO₂ Reduction to Methane via Tuning Oxygen Vacancy Concentration and Surface Termination on a Copper/Ceria Catalyst

Abstract

Metal oxides are a promising material for designing highly active and selective catalysts for the electrochemical reduction of carbon dioxide (CO 2 RR). Here, we designed a Cu/ceria catalyst with high selectivity of methane production at single-atomic Cu active sites. Using this, we report favorable design concepts that push the product selectivity of methane formation by combining detailed structural analysis, density functional theory (DFT), in situ Raman spectroscopy, and electrochemical measurements. We demonstrate that a higher concentration of oxygen vacancies on the catalyst surface, resulting from more available Cu + sites, enables high selectivity for methane formation during CO 2 RR and can be controlled by the calcination temperature. The DFT calculation and in situ Raman studies indicate that pH controls the surface termination; a more alkaline pH generates hydroxylated surface motifs with more active sites for the hydrogen evolution reaction. These findings provide insights into designing an efficient metal oxide electrocatalyst by controlling the atomic structure via the reaction environment and synthesis conditions.

Efficient Electromethanation from CO2 on Monodisperse Cu-Based Catalysts

“…In comparison to the recently published electromethanation of CO 2 (Figure a), Cu–DCD 40 demonstrates high selectivity (FE) and activity (partial current density) of electromethanation. ,− To evaluate the stability of the as-prepared catalyst, “pause electrolysis” to suppress the carbonate issue is adopted in this work . The pause electrolysis is shown in Figure b.…”

In Situ Carbon-Encapsulated Copper-Doped Cerium Oxide Derived from MOFs for Boosting CO2-to-CH4 Electro-Conversion

“…46,47 Figure 2b shows the Ce 3d spectrum of Cu/ CeO 2 @C. The splitting of the peaks in 3d 5/2 and 3d 3/2 is identified as v and u, respectively. The 10 characteristic peaks of Ce 3d spectra can be indexed as Ce 4+ (v, 882.1; v″, 888.6; v′″, 897.9; u, 900.6; u″, 907.3; u′″, 916.3) and Ce 3+ (v 0 , 880; v′, 884.3; u 0 , 898.9; u′, 902.5), 30,48 illustrating that the major valence in Cu/CeO 2 @C is Ce 4+ , consistent with the PXRD data.…”

“…Cerium oxide (CeO 2 ) has been successfully applied in the CO 2 RR due to its unique characteristics that are conducive to the formation of a metal–CeO 2 nanointerface, thus improving the molecular activation, dispersion, and catalytic performance. ,− On the other hand, carbon confinement would not only inhibit the agglomeration of metal-based nanoparticles and the reduction of the high valent state of metal active sites , but also provide robust charge-transfer channels for improving the catalytic efficiency. − Additionally, metal–organic frameworks (MOFs) can be used as attractive precursors or templates to generate carbon-confined metal hybrid materials due to the regular framework structures and uniform pores constructed by coordination between the bridging organic ligands and metal centers. − Therefore, it is reasonable to propose that the strategy of incorporating Cu into CeO 2 with carbon through pyrolysis of MOF precursors may modify the surface structures and suppress the reduction of Cu-based catalysts during CO 2 RR, as a result, to improve the selectivity of CH 4 with a high current density.…”

CO2electrolysis towards large scale operation: rational catalyst and electrolyte design for efficient flow-cell

“…10a). 40 At low OH À concentration (o0.4 M KOH), CO becomes the major CO 2 RR product with significantly low cathodic current density. However, a higher concentration of KOH (Z0.5 M) alters the reaction pathway and favors the formation of methane with a concurrent increase in cathodic current.…”