Photoelectrochemical (PEC) water splitting via semiconductors is an effective and feasible method for synthesizing renewable hydrogen (H-2) fuels. In this study, beta-In2S3 nanosheets were first grown on conductive glass. Then, we prepared P-doped beta-In2S3 nanosheets with an amorphous InPOx overlayer via the incomplete phosphorization of pristine beta-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 beta-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 beta-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 beta-In2S3 photoanode. However, there were two pathways (core/shell coupling and shallow trap states) for charge transfer in the phosphorized beta-In2S3 photoanode, which improved the performance of its PEC water oxidation. (C) 2019 Elsevier Inc. All rights reserved.