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

Abstract 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(sp 3 )‐H bonds of toluene toward selective benzaldehyde production using a narrow‐bandgap CuBi 2 O 4 (CBO) porous photocathode. The intrinsic Cu + /Cu 2+ redox of porous CBO photocathode catalyzes the photocathodic oxygen reductive H 2 O 2 to generate ·OH capable of oxidation which activates the C(sp 3 )‐H bond that is further oxygenated via ·O 2 − 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(sp 3 )‐H bond oxidation strategy by using a narrow‐bandgap photocathode.