Alkali metal cations at work: Enhancing CO₂ electroreduction to CO on ZnO nanorods

Abstract

Oxide-derived zinc, an abundant and cost-effective electrode material alternative to gold and silver, has exhibited high activity for the electroreduction of CO2 to CO (CO2RR). However, the impact of cations on the CO2RR activity remains unexplored. In this study, we investigated the effect of three alkali metal cations (Cs+, K+, and Li+) on the CO2RR over a ZnO nanorod electrode, using a rotating ring disk electrode (RRDE) technique. Cyclic voltammetry of the Pt ring in the RRDE tip reveals a consistent trend in the buffering capacity of these cations (Cs+ > K+ > Li+), as evidenced by the availability of OH- ions for CO electrooxidation and hydrogen oxidation reactions (HOR). Cs+ showed a pronounced effect on the activity of the CO2RR to CO since it can regulate OH- concentration and maintain the local pH. This study addresses the ongoing debate concerning the effects of cations;interfacial electric field and buffering capacity;and elucidates the relationship among electrolyte/cation, local pH dynamics, and the CO2RR activity towards CO over the active oxide-derived Zn electrodes, all derived from the fast and facile RRDE technique.