KCS

Photoelectrochemical water splitting has been considered as the most promising technology for generating hydrogen energy. Herein, we report nickel sulfide nanocrystals (NCs) as excellent catalysts for solar-driven photoelectrochemical (PEC) hydrogen evolution. Photocathodes were fabricated by growing the NiS and NiS_1.97 NCs with controlled composition directly onto Si nanowire (NW) arrays. The deposition of NiS NCs results in excellent PEC performance in 0.5 M H₂SO₄ and 1 M KOH; the photocurrent is 10 mA cm^-2 and the onset potential is 0.2 V. In contrast, the Si-NiS_1.97 photocathode exhibit much lower photocurrent and less stability. Detailed structure analysis using X-ray photoelectron spectroscopy reveals that the NiS is more metallic than the NiS_1.97 and retains the same electronic structures during the PEC reaction. Separate NiS and NiS_1.97 NCs without Si NWs were also synthesized, and the former showed higher electrocatalytic activity toward the hydrogen/oxygen evolution reactions. The high catalytic activity of metallic NiS NCs should be the main cause of this enhanced PEC performance, promising efficient water-splitting Si-based PEC cells.