Charge self-regulation in 1T'''-MoS 2 structure with rich S vacancies for enhanced hydrogen evolution activity.

Active electronic states in transition metal dichalcogenides are able to prompt hydrogen evolution by improving hydrogen absorption. However, the development of thermodynamically stable hexagonal 2H-MoS 2 as hydrogen evolution catalyst is likely to be shadowed by its limited active electronic state. Herein, the charge self-regulation effect mediated by tuning Mo-Mo bonds and S vacancies is revealed in metastable trigonal MoS 2 (1T'''-MoS 2 ) structure, which is favarable for the generation of active electronic states to boost the hydrogen evolution reaction activity. The optimal 1T'''-MoS 2 sample exhibits a low overpotential of 158 mV at 10 mA cm -2 and a Tafel slope of 74.5 mV dec -1 in acidic conditions, which are far exceeding the 2H-MoS 2 counterpart (369 mV and 137 mV dec -1 ). Theoretical modeling indicates that the boosted performance is attributed to the formation of massive active electronic states induced by the charge self-regulation effect of Mo-Mo bonds in defective 1T'''-MoS 2 with rich S vacancies.