Photochemical CO 2 Reduction Using Zinc Vanadium Oxyhydroxide Catalysts

ABSTRACT Photochemical reduction of CO 2 into value‐added chemicals such as formic acid (HCOOH) or CO is a promising approach for solar‐to‐chemical energy conversion. Mixed‐anion compounds have attracted attention as a versatile platform for catalyst design, yet combining catalytic activity with structural robustness under reaction conditions remains a challenge. Here, we report that Zn 3 V 2 O 7 (OH) 2 ·2H 2 O (ZVO), a layered Zn‐based mixed‐anion oxyhydroxide, functions as an efficient catalyst for CO 2 reduction under visible light when coupled with [Ru(bpy) 3 ] 2+ ( RuPS ) as a photosensitizer and 1‐benzyl‐1,4‐dihydronicotinamide (BNAH) as an electron donor. ZVO synthesized hydrothermally at 353 K afforded HCOOH with an apparent quantum yield of 1.7% at 460 nm and a CO 2 reduction selectivity of 98%, while retaining its layered structure and nanosheet morphology after the photoreaction. Heat treatment of ZVO transformed the oxyhydroxide framework into the oxide phase (Zn 3 V 2 O 8 ), together with progressive loss of hydroxyl groups. Notably, samples sharing the same Zn 3 V 2 O 8 phase exhibited markedly different photochemical CO 2 reduction activities, demonstrating that the catalytic behavior cannot be explained solely by the bulk crystalline phase. Restoring surface hydroxyl groups on inactive Zn 3 V 2 O 8 increased both CO 2 uptake and CO 2 reduction activity without substantially altering the bulk crystalline phase or specific surface area. These findings highlight the importance of hydroxyl‐rich surface chemical environments in governing CO 2 adsorption and catalytic performance in mixed‐anion photocatalyst systems.