Enhancing Thermal‐Photocatalytic Reduction of CO ₂ via H ₂ O‐H ₂ Co‐Feeding in Mg‐Doped Bismuth Catalysts

The rational design of efficient thermal‐photo CO 2 reduction catalysts necessitates synergistic integration of structural modulation and reactant activation strategies. Herein, a Mg‐doped Bi nanosphere catalyst is reported, engineered for efficient CO 2 reduction under H 2 O‐H 2 co‐feeding conditions. Mg doping not only optimizes the nanostructure by reducing the particle size but also modifies the surface charge distribution and enhances water adsorption, thereby promoting CO 2 activation and catalytic performance. Crucially, under H 2 OH 2 co‐feeding, H 2 O interacts with Bi to generate hydroxylated BiOH sites that promote CO 2 chemisorption, while H 2 supplies hydrogen species (*H) for CO 2 reduction. In situ diffuse reflectance infrared Fourier transform spectroscopy reveals a cooperative mechanism: CO 2 adsorbs on BiOH to form *CO 3 2− intermediates, which undergo sequential reduction facilitated by H 2 activation. This synergy achieves a CO production rate of 55.32 μmol·g −1 ·h −1 under 420 nm illumination with 100% selectivity, which is 2.4 times higher than that under a pure H 2 atmosphere. The work highlights the critical role of dopant‐driven active site engineering and reactant synergies (H 2 OH 2 ) in CO 2 valorization, providing a scalable strategy for catalytic performance enhancement.