Exploring the role of ZnS as passivation layer on SrTiO3/Bi2S3 heterojunction photoanode for improved solar water splitting

Abstract

Sustainable energy harvesting has emerged as a frontier research area and relentless efforts are being put in to tackle the tenacious issues of global warming and energy crisis. Photoelectrochemical (PEC) water splitting is regarded as a promising technology to produce H2. In this study, we report facile fabrication of ZnS modified SrTiO3/Bi2S3 (STO) heterojunction photoanode for PEC water splitting. Ternary heterojunction photoanode was fabricated using sol-gel followed by SILAR methods. Coupling of wide band gap STO with narrow band gap Bi2S3 photosensitizer extends the absorption edge while the ZnS passivation layer improves electrode stability by preventing direct contact of Bi2S3 with electrolyte and providing an active energy state for facile charge transfer to improve charge separation. Decreased rate of recombination and elongated lifetime of photogenerated charge carriers resulted in enhanced charge carrier dynamics. STO/Bi2S3/ZnS photoanodes displayed a photocurrent density (J) of 1.89 mA.cm−2 at 1.23 V vs RHE and HC-STH of 1.19% at 0.42 V vs RHE in neutral medium while the corresponding values in basic medium were J = 5.08 mA cm−2 at 1.23 V RHE and HC-STH 4.8% at 0.71 V vs RHE; considerably higher than bare STO and binary STO/Bi2S3 electrodes. The superior performance in basic medium could be attributed to the presence of hole scavengers. The improved photostability >3000 s was attributed to ZnS deposition. To better under the role of hole scavengers the quantification of O2 and H2 was undertaken.