The Critical Role of Initial/Operando Oxygen Loading in General Bismuth-Based Catalysts for Electroreduction of Carbon Dioxide.

Operando reconstruction of solid catalyst into a distinct active state frequently occurs during electrocatalytic processes. The correlation between initial and operando states, if ever existing, is critical for the understanding and precise design of a catalytic system. Inspired by recently established intermediate metallic state of Bi-based catalysts during electrocatalytic carbon dioxide reduction (CO 2 RR), here we investigate a series of Bi oxide catalysts (Bi, Bi 2 O 3 , BiO 2 ) and demonstrate that the operando surface/subsurface oxygen loading, positively correlated to the initial oxygen content, plays a critical role in determining Bi-based CO 2 RR performance. Higher initial oxygen loading indicates a better electrocatalytic efficiency. Further analysis shows that this conclusion generally applies to all Bi-based electrocatalysts reported up to date. Following this principle, cost-effective BiO 2 nanocrystals demonstrated the highest formate Faradaic efficiency (FE) and current density compared to Bi/Bi 2 O 3 , further allowing a pair-electrolysis system with 800 mA/cm 2 current density and an overall 175% FE for formate production.