Anodic expulsion of Cu nanoparticles from a polycrystalline Cu substrate: a novel corrosion and single entity study approach

Cu is the dominant heterogeneous metal catalyst for CO₂ reduction (CO₂R) in combatting climate change, which often relies on Cu oxides (CuO or Cu₂O). This is complicated by the relatively facile reduction of Cu oxides to metallic Cu that precedes CO₂R, leading to potential morphological surface restructuring and lowered electrocatalysis. Herein, the anodic ejection of Cu/Cu oxide nanoparticles (NPs) from polycrystalline Cu is tracked through scanning electrochemical microscopy in substrate generation/tip collection (SECM-SG/TC) mode. Single entity electrochemical (SEE) detection of Cu⁰ and Cu oxide NPs was recorded through the electrocatalytic amplification (ECA) of the CO₂R and O₂ evolution reaction (OER). The frequency (<i>f</i>) of NP impacts decreases concomitantly with increasing tip-substrate distance, while increasing the absolute value of the ultramicroelectrode (UME) tip potential (<i>E</i>_tip, negatively for CO₂R and positively for OER) resulted in an increase in stochastic NP impact peak current (<i>i</i>_p) commensurate with increasing overpotential. Complementary finite element simulations provide insight into the NP catalyzed CO₂R catalytic rate constants as well as the rate of passivation. If substrate oxidation is entirely avoided and cathodic <i>E</i>_sub maintained, then no NP ejection was observed. Anodic potentials are often used to oxidize Cu substrates making them more electrocatalytically active as well as to regenerate Cu oxide catalyst layers. We demonstrate that SEE detection offers a potential means of monitoring corrosion/loss of Cu material as well as quantitative kinetics measurement.