Porous CuBi 2 O 4 Photocathode with Intrinsic Cu + /Cu 2+ Redox Improves Solar C(sp 3 )‐H Bond Conversion Efficiency by an Order of Magnitude

Selective C-H activation is the most important step for organic molecule transformation. Photocatalytic radicals driven C-H activation is considered a promising route but suffers from simultaneously utilizing electron/hole pairs which are limited to broad-band gap semiconductors. Herein, a half-photocathodic reaction strategy is demonstrated to activate and oxygenate C(sp³)-H bonds of toluene toward selective benzaldehyde production using a narrow-bandgap CuBi₂O₄ (CBO) porous photocathode. The intrinsic Cu⁺/Cu²⁺ redox of porous CBO photocathode catalyzes the photocathodic oxygen reductive H₂O₂ to generate ·OH capable of oxidation which activates the C(sp³)-H bond that is further oxygenated via ·O₂ ^- formed of the photocathodic oxygen reduction. As a result, the benzaldehyde selectivity is up to 90%. Impressively, the narrow-band gap of CBO enables record-high light-driven benzaldehyde yields of 111.93 mmol m^-2 h^-1 with stability of over 20 h. This work opens a green and efficient light-driven C(sp³)-H bond oxidation strategy by using a narrow-bandgap photocathode.