Imaging the complex interactions in CuAg-PEO nanoparticles ensemble for enhanced CO2 reduction

CO₂ electrochemical reduction (CO₂ER) is a promising technology that can convert CO₂ into useful chemicals and fuels with simultaneously reducing greenhouse gas emissions. Cu nanoparticles-based catalysts are an optimal choice of CO₂ER due to its excellent conductivity and catalytic activity. In this study, we combined scanning transmission X-ray microscopy (STXM) and spectro-ptychography to investigate the chemical and electronic structural changes of the CuAg nanocatalysts before and after CO₂ER. We observed that Cu species with the same valence state self-aggregate into separated phases. For the spent CuAg nanocatalysts after CO₂ER, most Cu(I) and Cu(0) species are oxidized to Cu(II) together with CuO transforming into undetermined Cu(II) species. We believe these mechanisms are the key reason why the CuAg nanocatalysts lost catalytic activity. Such information will be highly valuable for understanding Cu nanoparticles catalyzed CO₂ER.