Transition-Metal-Modified Vanadoborate Clusters as Stable and Efficient Photocatalysts for CO 2 Reduction.

Photocatalytic carbon dioxide reduction (CO ₂ RR) is considered to be a promising sustainable and clean approach to solve environmental issues. Polyoxometalates (POMs), with advantages in fast, reversible, and stepwise multiple-electron transfer without changing their structures, have been promising catalysts in various redox reactions. However, their performance is often restricted by poor thermal or chemical stability. In this work, two transition-metal-modified vanadoborate clusters, [Co(en) ₂ ] ₆ [V ₁₂ B ₁₈ O ₅₄ (OH) ₆ ]·17H ₂ O (V ₁₂ B ₁₈ -Co) and [Ni(en) ₂ ] ₆ [V ₁₂ B ₁₈ O ₅₄ (OH) ₆ ]·17H ₂ O (V ₁₂ B ₁₈ -Ni), are reported for photocatalytic CO ₂ reduction. V ₁₂ B ₁₈ -Co and V ₁₂ B ₁₈ -Ni can preserve their structures to 200 and 250 °C, respectively, and remain stable in polar organic solvents and a wide range of pH solutions. Under visible-light irradiation, CO ₂ can be converted into syngas and HCOO ^- with V ₁₂ B ₁₈ -Co or V ₁₂ B ₁₈ -Ni as catalysts. The total amount of gaseous products and liquid products for V ₁₂ B ₁₈ -Co is up to 9.5 and 0.168 mmol g ^-1 h ^-1 . Comparing with V ₁₂ B ₁₈ -Co, the yield of CO for V ₁₂ B ₁₈ -Ni declines by 1.8-fold, while that of HCOO ^- increases by 35%. The AQY of V ₁₂ B ₁₈ -Co and V ₁₂ B ₁₈ -Ni is 1.1% and 0.93%, respectively. These values are higher than most of the reported POM materials under similar conditions. The density functional theory (DFT) calculations illuminate the active site of CO ₂ RR and the reduction mechanism. This work provides new insights into the design of stable, high-performance, and low-cost photocatalysts for CO ₂ reduction.