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–, Fe3+/Fe2+, I2/I–, Sn2–/S2–) 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 (Bi3+ reduction and S2– oxidation), (ii) protolytic reactions leading to the dissolution of the semiconductor in acidic solutions at рН < 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]·3H2O, BiOI and Bi2S3). 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.