Objective evaluation of the performance of electrocatalysts for CO2 reduction has been complicated by a lack of standardized methods for measuring and reporting activity data. In this perspective, we advocate that standardizing these practices can aid in advancing research efforts toward the development of efficient and selective CO2 reduction electrocatalysts. Using information taken from experimental studies, we identify variables that influence the measured activity of CO2 reduction electrocatalysts and propose procedures to account for these variables in order to improve the accuracy and reproducibility of reported data. We recommend that catalysts be measured under conditions which do not introduce artifacts from impurities, from either the electrolyte or counter electrode, and advocate the acquisition of data measured in the absence of mass transport effects. Furthermore, measured rates of electrochemical reactions should be normalized to both the geometric electrode area as well as the electrochemically active surface area to facilitate the comparison of reported catalysts with those previously known. We demonstrate that, when these factors are accounted for, the CO2 reduction activities of Ag and Cu measured in different laboratories exhibit little difference. Adoption of the recommendations presented in this perspective would greatly facilitate the identification of superior catalysts for CO2 reduction arising solely from changes in their composition and pretreatment.

The electrochemical CO₂ reduction reaction (CO₂RR) using Cu-based catalysts holds great potential for producing valuable multi-carbon products from renewable energy. However, the chemical and structural state of Cu catalyst surfaces during the CO₂RR remains a matter of debate. Here, we show the structural evolution of the near-surface region of polycrystalline Cu electrodes under in situ conditions through a combination of grazing incidence X-ray absorption spectroscopy (GIXAS) and X-ray diffraction (GIXRD). The in situ GIXAS reveals that the surface oxide layer is fully reduced to metallic Cu before the onset potential for CO₂RR, and the catalyst maintains the metallic state across the potentials relevant to the CO₂RR. We also find a preferential surface reconstruction of the polycrystalline Cu surface toward (100) facets in the presence of CO₂. Quantitative analysis of the reconstruction profiles reveals that the degree of reconstruction increases with increasingly negative applied potentials, and it persists when the applied potential returns to more positive values. These findings show that the surface of Cu electrocatalysts is dynamic during the CO₂RR, and emphasize the importance of in situ characterization to understand the surface structure and its role in electrocatalysis.