Silicon microwire arrays decorated with amorphous heterometal-doped molybdenum sulfide for water photoelectrolysis
Journal
Nano Energy
Journal Volume
32
Pages
422-432
Date Issued
2017
Author(s)
Abstract
Silicon is a promising photocathode material for solar hydrogen evolution because of its small band gap, negative conduction band position, and ideal theoretical current density. In this study, p-type Si microwire (p-Si MW) arrays were prepared as photocathodes because of the large surface area and high light-harvesting capability. However, Si MWs suffered from low photocatalytic activity because of slow photo-induced carriers during driving of water-splitting reaction. Therefore, molybdenum sulfide (MoS2) with appropriate band alignment with p-Si material was employed for surface modification to function as a co-catalyst for collecting photo-generated minority carriers and reducing recombination possibility. The onset potential and current density at 0 V versus reversible hydrogen electrode (RHE) of Si@MoS2 MWs were +0.122 V and ?8.41 mA cm?2. Heterometal atoms were employed to dope MoS2 co-catalyst and expose more sulfur-terminated active sites to further boost photoelectrochemical performance. Optimal activity of Si@MMoSx (M = Fe, Co, Ni) was achieved by doping Co heteroatoms, and its turn-on voltage and photocurrent density at 0 V (vs. RHE) were respectively increased to +0.192 V and ?17.2 mA cm?2. X-ray absorption spectroscopy was applied to demonstrate that Fe ions of FeMoSx were dichalcogenide materials, forming a composite with MoS2 and contributing better photoelectrolytic efficiency. By contrast, two-valent heteroatoms of CoMoSx and NiMoSx substituted the Mo4+ ions in MoS2. For charge compensation, more defects and edges were revealed as active sites of solar hydrogen production by adding Co or Ni dopants in MoS2 co-catalyst, which led to lower overpotential. ? 2017 Elsevier Ltd
Subjects
Catalyst activity; Catalysts; Doping (additives); Energy gap; Field emission cathodes; Hydrogen production; Molybdenum; Molybdenum compounds; Nickel; Photocathodes; Silicon; Solar power generation; Sulfur compounds; Surface treatment; X ray absorption spectroscopy; Co catalysts; Molybdenum sulfide; Silicon microwire; Solar hydrogen; Water splitting; Amorphous silicon
SDGs
Other Subjects
Catalyst activity; Catalysts; Doping (additives); Energy gap; Field emission cathodes; Hydrogen production; Molybdenum; Molybdenum compounds; Nickel; Photocathodes; Silicon; Solar power generation; Sulfur compounds; Surface treatment; X ray absorption spectroscopy; Co catalysts; Molybdenum sulfide; Silicon microwire; Solar hydrogen; Water splitting; Amorphous silicon
Type
journal article