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

Chih-Jung Chen; Chia-Yu Yeh; Chia-Hsien Chen; Anirudha Jena; Da-Hua Wei; Ho Chang; Shu-Fen Hu; Ru-Shi Liu

doi:10.1021/acsami.0c15905

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

ACS Appl Mater Interfaces. 2020 Dec 9;12(49):54671-54682. doi: 10.1021/acsami.0c15905. Epub 2020 Nov 26.

Authors

Chih-Jung Chen¹, Chia-Yu Yeh², Chia-Hsien Chen³, Anirudha Jena^{1

3}, Da-Hua Wei³, Ho Chang³, Shu-Fen Hu², Ru-Shi Liu¹

Affiliations

¹ Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan.
² Department of Physics, National Taiwan Normal University, Taipei 11677, Taiwan.
³ Department of Mechanical Engineering and Graduate Institute of Manufacturing Technology, National Taipei University of Technology, Taipei 10608, Taiwan.

PMID: 33242954
DOI: 10.1021/acsami.0c15905

Abstract

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 H₂ 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 (MoS₂-WS₂) composite decorated on a Si photoabsorber is used as a cocatalyst to accelerate HER kinetics and enhance PEC performance. This MoS₂-WS₂ hybrid showed superior catalytic activity compared with pristine MoS₂ or WS₂. The optimal MoS₂-WS₂/Si electrode delivered a photocurrent of -25.9 mA/cm² at 0 V (vs reversible hydrogen electrode). X-ray absorption spectroscopy demonstrated that MoS₂-WS₂ possessed a high hole concentration of unoccupied electronic states in the MoS₂ 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 MoS₂ constituent of this hybrid cocatalyst. These sulfur defects served as HER active sites to boost the catalytic efficiency. Besides, the TiO₂-protective MoS₂-WS₂/Si photocathode maintained a current density of -15.0 mA/cm² after 16 h of the photocatalytic stability measurement.

Keywords: electronic unoccupied states; molybdenum tungsten disulfide; photoelectrochemical hydrogen production.; silicon micropillars; sulfur vacancies.