On-Chip 2D Monolayer Cr-Doped WSe₂ Microcells for Overall Water Splitting in Neutral Media

Chun-Hao Chiang^1*, Yueh-Chiang Yang², Yung-Chang Lin³, Kazu Suenaga³, Po-Wen Chiu², Chun-Wei Chen¹

¹Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan
²Department of Electrical Engineering, Nation Tsing Hua University, Hsinchu, Taiwan
³National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

* Presenter:Chun-Hao Chiang, email:d08527008@ntu.edu.tw

Electrochemical water splitting is an efficient method to generate hydrogen. In general, strong acid and base are utilized to overcome high activation energy barriers of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, the strong acid and base are corrosive to apparatus and harmful to the environment. Consequently, the employment of neutral media is an urgent task. The transition metal-based compounds have been extensively investigated and have shown outstanding performances for HER and OER. In particular, several bifunctional electrocatalysts, which can activate both HER and OER, in neutral media have been reported. For example, the CoO/Co₄N on nickel foam, prepared through hydrothermal treatments in bulk forms, performs sufficient electrocatalytic activities. Nevertheless, the fundamental studies of these bifunctional electrocatalysts for overall water splitting in neutral media are still rare. Compared to the conventional electrochemical water splitting cells with bulk electrocatalysts, the microcell with two-dimensional (2D) ultrathin catalysts is a perfect platform for deeper understanding. However, most of the microcells are half cells for either HER or OER in acid and base. Until now, there is still no report based on microcells for water splitting in neutral media.
To achieve the ultimate goal, a bifunctional electrocatalyst with high activity for water splitting in neutral media is highly desirable. Considering the strong correlation between the type of semiconductor catalysts and catalytic performance, a 2D tungsten diselenide (WSe₂) monolayer with bipolar transport properties can be a potential candidate to further study. Herein, by employing atomic doping and contact engineering on 2D WSe₂ microcells, the overall water splitting performance in neutral media can be greatly enhanced. Through the atomic Cr doping by a site-selective approach, the overpotential and Tafel slopes decrease in both HER and OER; hence, the cell voltage of the microcell substantially reduces. Additionally, the graphene-contact Cr-doped WSe₂ microcells are fabricated through the direct-growth technique of WSe₂ on a pre-patterned graphene substrate. Finally, the cell voltage of graphene-contact Cr-doped WSe₂ microcell can reduce to 1.79 V at 10 mA cm^-2.

Keywords: 2D Monolayer, Atomic engineering, On-Chip Microcells, Water Splitting, Neutral Media