Mn 2+ Doping in In 2 S 3 Increases Photoanodic Activity for Photoelectrochemical Water‐Splitting

The photoelectrochemical (PEC) water-splitting process emerges as a significant pathway for solving global energy demands for hydrogen (H2) generation. Here, a visible light-active semiconductor, indium sulfide (In2S3), is explored. The interconnected nanosheets of In2S3 can generate a photocurrent density of 3.18 mA/cm2 at 1.2 V versus RHE in Na2SO4. To improve the PEC activity of In2S3, Mn2+ is incorporated into In2S3 through an in-situ hydrothermal method. Mn-In2S3 exhibits a photocurrent density of 4.49 mA/cm2 at 1.2 V versus RHE. It demonstrates a separation efficiency of 51.2%, 1.58 times higher than In2S3 (32.4%) at 1.2 V versus RHE. Mn-doping facilitates the charge transportation, keeping excitons apart, suppressing their recombination. Mott-Schottky analysis indicates 3.23 times carrier density enhancement in Mn-In2S3. For practical applicability, the PEC performance of In2S3 and Mn-In2S3 is also determined in 3.5 wt% saline water. The Mn-In2S3 shows the photocurrent density of 5.23 mA/cm2 at 1.2 V versus RHE, ∼1.5 fold higher than the bare In2S3 (3.40 mA/cm2). Doping with Mn2+ effectively alters the band edge positions of In2S3, further supported by ultraviolet photoelectron spectroscopy (UPS) analysis, which indicates upward and downward shifting of the valence and conduction bands, respectively, resulting in narrowing of the band gap.