Bismuth Oxysulfide Photoelectrodes with Giant Incident Photon‐to‐Current Conversion Efficiency: Chemical Stability in Aqueous Solutions

Abstract Bismuth oxysulfide (BOS) films demonstrate giant incident photon‐to‐current conversion efficiency (IPCE≫100 %) under cathodic polarization. Their photoelectrochemical behavior and corrosion stability in aqueous solutions containing different redox systems ([Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− , Fe 3+ /Fe 2+ , I 2 /I − , S n 2− /S 2− ) has been investigated. We established that the chemical stability of the BOS is controlled mainly by three factors: i) potentials of cathodic and anodic destruction of the BOS (Bi 3+ reduction and S 2− oxidation)L ii) protolytic reactions leading to the dissolution of the semiconductor in acidic solutions at pH<3; iii) presence in solutions of anions, capable to participate in ion exchange reactions with the semiconductor forming poorly soluble compounds (K[BiFe(CN) 6 ] ⋅ 3H 2 O, BiOI and Bi 2 S 3 ). The enrichment of the BOS surface with sulfur atoms (formation of S‐terminated surface) gives rise to the substantial increase in the electrocatalytic activity of [Fe(CN) 6 ] 3− cathodic reduction, which is accompanied by up to order increase of IPCE.