Band edge modulation via a hydrogen-bond-free cation in hybrid bismuth iodine for overall photocatalytic CO2 reduction

Abstract

Overall photocatalytic CO₂ reduction (PCR) which transforms CO₂ with H₂O into value-added products without sacrificial reagents has attracted tremendous interest but is hindered by the large overpotential of the H₂O oxidation half-reaction. We propose organic cation engineering by employing a “hydrogen-bond-free” cation instead of a “hydrogen bond” cation to optimize the band edges and PCR performance of hybrid bismuth halides. (H₂biz)BiI₄·H₂O (Hbiz = benzimidazole, 1) and (Me₂biz)BiI₄ (2) were designed. The methylation modification on Hbiz affords a “hydrogen-bond-free” cation (Me₂biz)⁺ in 2 with a greatly increased VB edge of 1.31 eV (0.53 eV larger than that of 1), which activates the H₂O oxidation half-reaction thermodynamically. Theoretical calculations disclose that the methylation modification greatly increases the highest occupied molecular orbital energy of the cation, thereby increasing the VB edge of 2. This study on 2 represents the first report of a hybrid bismuth-based photocatalyst for an overall PCR reaction in pure water.