Efficient CO₂Electroreduction with a Monolayer Bi₂WO₆through 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 Bi₂WO₆with high bismuth exposure demonstrates excellent performance for the electrocatalytic conversion of CO₂to 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/cm²in 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 elucidatesin operandophase transition to a “metallic intermediate state” on monolayer Bi₂WO₆during the electrocatalytic process, providing the experimental evidence to the basis of satisfying performance from all Bi-based catalysts in CO₂reduction.