Reversible bismuth reduction-driven dark photoelectrochemistry

Current research in photoelectrochemical (PEC) systems focuses on designing photoelectrodes with light-enhanced charge transfer efficiency at the solid-liquid interface, which leads to the oxidation of various reductant molecules at the anode, posing a challenge in terms of selectivity. In this study, we introduce an original concept of dark-enhanced PEC system (dark-PEC) based on bismuth oxybromide (BiOBr)-photocathode. The reversible bismuth reduction causes the passivation and regeneration of oxygen reduction sites on the photocathode, thereby leading to an unconventional reverse photocurrent (|I_dark | > |I_light | ) signal under air conditions. Significantly, owing to the selective binding and charge transfer between glutathione and BiOBr, the reversibility of bismuth reduction is increased, with a 10-fold enhancement of reverse photocurrent. Compared to traditional PEC systems, the dark-PEC system enables the selective recognition of reductant molecules by photocathodes, unveiling an original PEC reaction mechanism. This study will offer valuable insights into device design and redox processes in the PEC field.