Unusual In-Electrolyte Stability of Doped Molybdenum Sulfide in pH Universal Hydrogen Evolution Reaction Conditions

With a layered structure, molybdenum disulfide (MoS2) has become a prudent alternative to platinum in hydrogen evolution reactions (HERs). In particular, choosing the 2H crystal phase is known to be advantageous because of its thermodynamic stability, even though it is catalytically less active phase. This demands a more rational approach to facilitate the electronic properties and understanding of the in-reaction phase stability rather than developing a new catalyst. Here, a vanadium (V)-doped 2H-MoS2 solid-solution cathode material is prepared for activity and phase stability screening under pH universal conditions. The cathodic preconditioning shows a substantial change in the phase after alkaline and neutral HERs but not in acidic HER. The catalytic activity follows an order of acidic > alkaline > neutral. The performance stability is poor in a neutral medium, which shows a monotonic decrease over 24 h, which is not the case for acidic and alkaline media. The local charge transfer effect of V4+ doping and its impact on the HER are discussed using theoretical calculations. This study does not aim to provide an explicit idea of activity performance but rather gives a standard but easy protocol to investigate the catalytically active phase.