Morphological Effects and Stabilization of the Metallic 1T Phase in Layered V-, Nb-, and Ta-Doped WSe₂ for Electrocatalysis

Layered transition-metal dichalcogenides (TMDs) are valued for their electrocatalytic properties toward the hydrogen-evolution reaction (HER) and oxygen-reduction reaction (ORR). One effective strategy to activate the electrocatalytic properties of TMDs is through doping. The optimistic outlook of doped-MoS₂ as an electrocatalyst witnessed in previous reports spurred us to examine the effect of doping WSe₂ with Group 5 transition-metal species, namely V, Nb, and Ta, in aspects of inherent electroactivities and catalysis. Apart from the mild reduction signal unique to the Group 5 transition-metal dopants, the Group 5 transition-metal-doped WSe₂ materials are found to possess largely identical inherent electrochemistry to the undoped WSe₂ with a characteristic anodic peak. Living up to expectations, the Group 5 transition-metal-doped WSe₂ materials exhibit improved electrocatalytic HER efficiency, as evident by the lower HER overpotentials and Tafel slopes relative to undoped WSe₂. After doping with V, Nb, or Ta species, an increased number of active sites is observed given the distinct changes in morphology from thick bulky pieces in undoped WSe₂ to thinner fragments in doped WSe₂. Although undoped WSe₂ exists in the semiconducting 2H phase, the Group 5 transition-metal-doped WSe₂ materials are dominated by the metallic 1T phase. Doping WSe₂ with V, Nb, or Ta stabilizes the catalytic 1T phase and appears to induce the transition from the 2H to 1T phase. In contrast to the enhanced HER performance of WSe₂ upon doping, Group 5 transition-metal dopants proved futile in activating the ORR electrocatalytic behavior of WSe₂, for which the ORR efficiency is unchanged. Therefore, these findings facilitate the understanding of the role of Group 5 transition-metal dopants in the electrochemical and catalytic properties of WSe₂ relative to their morphological features and provide an evaluation of the efficacy of doping TMDs in electrocatalytic applications.