MoS2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. The intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s–1 (65–75 mV/dec), 3.2 s–1 (65–85 mV/dec), and 0.1 s–1 (120–160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7–10%, and the number of sulfur vacancies in high crystalline quality MoS2 is higher than that in low crystalline quality MoS2, which may be related with the proximity of different local crystalline structures to the vacancies. we also demonstrate that monolayer MoS2 films may be enabled to be better than Pt for HER catalysis by optimizing the density of sulfur vacancies and leveraging its interaction with substrates. Pt substrate may be used to provide the proper interaction. The substrate does not participate the catalytic reaction, but may boost the activity of the film by forming a lower interface tunneling barrier and affecting the electronic structure of the film through charge transfer. A minimal amount of Pt like 1 nm thick is enough to enable the superior performance at the film, and the performance is very stable with no degradation after reaction for more than two months. The result opens up a new avenue for the development of ideal HER catalysts to enable affordable hydrogen production from water.

Engineering MoS2 for high-performance electrocatalytic hydrogen evolution

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.