Molybdenum Tungsten Disulfide with a Large Number of Sulfur Vacancies and Electronic Unoccupied States on Silicon Micropillars for Solar Hydrogen Evolution.

Hydrogen energy is a promising alternative for fossil fuels because of its high energy density and carbon-free emission. Si is an ideal light absorber used in solar water splitting to produce H gas because of its small band gap, appropriate conduction band position, and high theoretical photocurrent. However, the overpotential required to drive the photoelectrochemical (PEC) hydrogen evolution reaction (HER) on bare Si electrodes is severely high owing to its sluggish kinetics. Herein, a molybdenum tungsten disulfide (MoS-WS) composite decorated on a Si photoabsorber is used as a cocatalyst to accelerate HER kinetics and enhance PEC performance. This MoS-WS hybrid showed superior catalytic activity compared with pristine MoS or WS. The optimal MoS-WS/Si electrode delivered a photocurrent of -25.9 mA/cm at 0 V (vs reversible hydrogen electrode). X-ray absorption spectroscopy demonstrated that MoS-WS possessed a high hole concentration of unoccupied electronic states in the MoS component, which could promote to accept large amounts of carriers from the Si photoabsorber. Moreover, a large number of sulfur vacancies are generated in the MoS constituent of this hybrid cocatalyst. These sulfur defects served as HER active sites to boost the catalytic efficiency. Besides, the TiO-protective MoS-WS/Si photocathode maintained a current density of -15.0 mA/cm after 16 h of the photocatalytic stability measurement.