Micro-engineered Cu–Ag catalysts as analytical tools for direct observation of hetero-interfaces and surface structures

The development of technologies for analyzing electrochemical catalysts is crucial for improving catalytic performances, including productivity and product selectivity. However, in conventional composite catalysts, directly observing local reaction sites and structures is challenging due to the size and random positioning of nanoparticles. In this study, we investigated hetero-interfacial reaction sites and surface structures before and after the electrochemical CO2 reduction reaction using a micropatterned Cu–Ag catalyst. The scalable catalyst design enabled direct analysis of oxygen adsorption on the Cu surface near the Cu–Ag hetero-interface following the electrochemical reduction reaction. The artificial flatness of the patterned catalyst also allowed for the quantitative evaluation of surface roughness changes on Cu and Ag, corresponding to the nanoparticle surfaces of composite catalysts. Furthermore, we demonstrated the potential for reaction product selectivity by microengineering the length of local reaction sites, such as the Cu–Ag hetero-interface. Our platform provides a valuable analytical toolset and framework for revealing catalytic reaction phenomena and enhancing catalytic performance.