Engineering Heterogeneous NiS<sub>2</sub>/NiS Cocatalysts with Progressive Electron Transfer from Planar <i>p</i>‐Si Photocathodes for Solar Hydrogen Evolution
Sijie Li, Gaoliang Yang, Peng Ge, Huiwen Lin, Qi Wang, Xiaohui Ren, Shunqin Luo, Davin Philo, Kun Chang, Jinhua Ye
Abstract
Abstract The sluggish transfer of electrons from a planar p ‐type Si ( p ‐Si) semiconductor to a cocatalyst restricts the activity of photoelectrochemical (PEC) hydrogen evolution. To overcome such inefficiency, an elegant interphase of the semiconductor/cocatalyst is generally necessary. Hence, in this work, a NiS 2 /NiS heterojunction (NNH) is prepared in situ and applied to a planar p ‐Si substrate as a cocatalyst to achieve progressive electron transfer. The NNH/Si photocathode exhibits an onset potential of +0.28 V versus reversible hydrogen electrode ( V RHE ) and a photocurrent density of 18.9 mA·cm −2 at 0 V RHE , as well as a 0.9% half‐cell solar‐to‐hydrogen efficiency, which is much superior compared with those of NiS 2 /Si and NiS/Si photocathodes. The enhanced performance for NNH/Si is attributed to the contact between the sectional n ‐type semiconducting NNH and the planar p ‐Si semiconductor through a p ‐Si/ n ‐NiS/ n ‐NiS 2 manner that functions as a local pn ‐junction to promote electron transfer. Thus, the photogenerated electron is transferred from p ‐Si to n ‐NiS within NNH as the progressive medium, followed by to Ni 2+ and/or S 2 2− of the defect‐rich n ‐NiS 2 phase as the key active sites. This systematic work may pave the way for planar Si‐based PEC applications of heterogeneous metal sulfide cocatalysts through the progressive transfer of electrons.