Operando Resonant Soft X-ray Scattering Studies of Chemical Environment and Interparticle Dynamics of Cu Nanocatalysts forCO₂Electroreduction

Understanding the chemical environment and interparticle dynamics of nanoparticle electrocatalysts under operatingconditions offers valuable insights into tuning their activity and selectivity. This is particularly important to the design of Cunanocatalysts for CO2electroreduction due to their dynamic nature under bias. Here, we have developedoperandoelectrochemicalresonant soft X-ray scattering (EC-RSoXS) to probe the chemical identity of active sites during the dynamic structuraltransformation of Cu nanoparticle (NP) ensembles through 1 mu m thick electrolyte.Operandoscattering-enhanced X-ray absorptionspectroscopy (XAS) serves as a powerful technique to investigate the size-dependent catalyst stability under beam exposure whilemonitoring the potential-dependent surface structural changes. Small NPs (7 nm) in aqueous electrolyte were found to experience apredominant soft X-ray beam-induced oxidation to CuO despite only sub-second X-ray exposure. In comparison, large NPs (18 nm)showed improved resistivity to beam damage, which allowed the reliable observation of surface Cu2O electroreduction to metallicCu. Small-angle X-ray scattering (SAXS) statistically probes the particle-particle interactions of large ensembles of NPs. This studypoints out the need for rigorous examination of beam effects foroperandoX-ray studies on electrocatalysts. The strategy of using EC-RSoXS that combines soft XAS and SAXS can serve as a general approach to simultaneously investigate the chemical environmentand interparticle information on nanocatalysts.