P-doped In2S3 nanosheets coupled with InPOx overlayer: Charge-transfer pathways and highly enhanced photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting via semiconductors is an effective and feasible method for synthesizing renewable hydrogen (H2) fuels. In this study, β-In2S3 nanosheets were first grown on conductive glass. Then, we prepared P-doped β-In2S3 nanosheets with an amorphous InPOx overlayer via the incomplete phosphorization of pristine β-In2S3 nanosheets. When we used this material as photoanode in a PEC cell for water splitting, the photocurrent density drastically increased to 2.2 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (vs. RHE). It enhanced 15 times as the pristine β-In2S3 nanosheets, which was only 0.15 mA cm−2 at 1.23 V vs. RHE (solar standard spectrum, 100 mW cm−2). The photoelectric conversion efficiency as high as 0.65% at a low potential of 0.81 V vs. RHE was achieved for the phosphorized β-In2S3 nanosheets. A series of experiments proved that the P-doping accelerated semiconductor charge-transport and the InPOx overlayer played cocatalyst role. We penetratingly investigated the pathway of charge transfer via femtosecond transient absorption. The results showed one pathway of charge transfer in pristine β-In2S3 photoanode. However, there were two pathways (core/shell coupling and shallow trap states) for charge transfer in the phosphorized β-In2S3 photoanode, which improved the performance of its PEC water oxidation.