Mechanistic pathways of copper catalyst reconstruction in CO2 electroreduction

Surface reconstruction is a common and critical process in copper catalysts during electrochemical CO2 reduction reaction (CO2RR), continuously reshaping their structures and compositions into states distinct from the pristine material. Although recognized as central to catalyst performance, the mechanistic pathways and chemical identities of the dissolved Cu species remain unclear. Employing clean and well-defined Cu nanoparticle arrays as a model platform, we directly visualize morphological evolution and simultaneously track reaction intermediates by in situ surface-enhanced Raman spectroscopy (SERS). We resolve three distinct dissolution-redeposition pathways of Cu catalyst: (i) *CO-mediated Cu+ dissolution and facet-selective redeposition at moderate potentials; (ii) field-assisted leaching of neutral Cu0 species at strongly negative potentials; and (iii) oxidative Cu+ dissolution at open-circuit potential, followed by redeposition into Cu2O cubes enabled by CO2RR-generated active sites. These findings reveal a nonlinear, potential-dependent behavior of Cu reconstruction, and provide guiding principles for directing catalyst evolution through control of adsorbates, potential windows, and bias protocols.