Efficient CO2 Electroreduction with a Monolayer Bi2WO6 through a Metallic Intermediate Surface State

Electrocatalytic conversion of carbon dioxide to high-value fuels and chemical feedstocks represents a promising solution toward carbon neutrality. Ongoing efforts have been directed to the development of high-performance, mass production, and cost-efficient catalysts, which, in turn, requires a more precise understanding of the operando details of the catalytic interface and fine control over the reaction pathway. Here, we report that a two-dimensional (2D) monolayer Bi2WO6 with high bismuth exposure demonstrates excellent performance for the electrocatalytic conversion of CO2 to formic acid, including the high Faradic efficiency (FE) over a broad potential range (over 90% from 0.9 to 1.3 V vs RHE, >98% FE at 1.0 V vs RHE) and a high current density over 250 mA/cm2 in a flow cell equipped with a gas diffusion electrode (>97% FE). The distinct reaction pathway observed in the electrocatalytic process, in contrast to the photocatalytic reactions, was investigated by density functional theory. Additionally, the mechanistic investigation further elucidates in operando phase transition to a "metallic intermediate state" on monolayer Bi2WO6 during the electrocatalytic process, providing the experimental evidence to the basis of satisfying performance from all Bi-based catalysts in CO2 reduction.