Engineering Substrate Interaction To Improve Hydrogen Evolution Catalysis of Monolayer MoS2 Films beyond Pt.

MoS2 holds great promise as a cost-effective alternative to Pt for catalyzing the hydrogen evolution reaction (HER) of water, but its reported catalytic efficiency is still worse than that of Pt, the best HER catalyst but too rare and expensive for mass production of hydrogen. We report a strategy to enable the catalytic activity of monolayer MoS2 films that are even better than that of Pt via engineering the interaction of the monolayer with supporting substrates. The monolayer films were grown with chemical vapor deposition processes and controlled to have an optimal density (7-10%) of sulfur vacancies. We find that the catalytic activity of MoS2 can be affected by substrates in two ways: forming an interfacial tunneling barrier with MoS2 and modifying the chemical nature of MoS2 via charge transfer (proximity doping). Following this understanding, we enable excellent catalytic activities at the monolayer MoS2 films by using substrates that can provide n-doping to MoS2 and form low interfacial tunneling barriers with MoS2, such as Ti. The catalytic performance may be further boosted to be even better than Pt by crumpling the films on Ti coated flexible polymer substrates, as the Tafel slope of the film is substantially decreased with the presence of crumpling-induced compressive strain. The monolayer MoS2 films show no degradation in catalytic performance after being continuously tested for over 2 months.