Inserting Co and P into MoS2 photocathodes: enhancing hydrogen evolution reaction catalytic performance by activating edges and basal planes with sulfur vacancies

Abstract

The production of hydrogen using solar energy via a photoelectrochemical system is an effective technique for meeting present clean energy needs. Owing to the small bandgap and highly negative conduction band edge (−0.46 V) of Si, it is considered a promising photocathode material for solar hydrogen evolution reaction (HER). However, because of sluggish HER kinetics on the Si surface, bare Si electrodes have a high overpotential. Molybdenum disulfide (MoS₂) has attracted wide interest as a promising alternative to Pt-based catalysts for producing hydrogen. Nevertheless, it suffers from sluggish kinetics for driving the process of HER because of its inert basal plane. Herein, HER performance was enhanced by doping a metal (cobalt) and a nonmetal (phosphorus) into MoS₂. Doping MoS₂ (CoPO-MoS₂) on Si photocathodes with cobalt and phosphorous provides a current density of about 21.6 mA cm⁻² at 0 V (vs. RHE) and a reduced Tafel value of 54.3 mV dec⁻¹. The doped catalyst shows good stability up to 3 h with retention of about 85%. The flat surface of the Si photocathode has been chemically etched into pyramidal structures (SiMP) to reduce the loss due to reflection and enhance the catalytically active surface. Raman, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure reveal that Co and P strongly coordinated with the MoS₂ materials. Furthermore, the catalytic performance was enhanced by the defect sites on MoS₂, thereby stimulating more S vacancies on the basal planes and S-edge sites. Defect engineering will hopefully provide a new research direction for the innovation and development of more active sites of CoPO–MoS₂.