Single Unit Cell Bismuth Tungstate Layers Realizing Robust Solar CO2 Reduction to Methanol

Solar CO₂ reduction into hydrocarbons helps to solve the global warming and energy crisis. However, conventional semiconductors usually suffer from low photoactivity and poor photostability. Here, atomically‐thin oxide‐based semiconductors are proposed as excellent platforms to overcome this drawback. As a prototype, single‐unit‐cell Bi₂WO₆ layers are first synthesized by virtue of a lamellar Bi‐oleate intermediate. The single‐unit‐cell thickness allows 3‐times larger CO₂ adsorption capacity and higher photoabsorption than bulk Bi₂WO₆. Also, the increased conductivity, verified by density functional theory calculations and temperature‐dependent resistivities, favors fast carrier transport. The carrier lifetime increased from 14.7 to 83.2 ns, revealed by time‐resolved fluorescence spectroscopy, which accounts for the improved electron‐hole separation efficacy. As a result, the single‐unit‐cell Bi₂WO₆ layers achieve a methanol formation rate of 75 μmol g^?1 h^?1, 125‐times higher than that of bulk Bi₂WO₆. The catalytic activity of the single‐unit‐cell layers proceeds without deactivation even after 2 days. This work will shed light on designing efficient and robust photoreduction CO₂ catalysts.