(449c) MoS2 Nanostructures As Efficient, Stable, and Earth-Abundant Catalysts for Hydrogen Evolution In Acid
In order to obtain a cost effective alternative to Pt for driving the hydrogen evolution reaction (HER) in acidic media, we need to develop Earth-abundant materials that are highly efficient for the HER and remain stable over long periods of use. Nanostructured MoS2 has previously shown excellent HER activity with minimal overpotentials of 150-200 mV due to the presence of a large number of highly active edge sites. Driving practically relevant geometric current densities, however, requires a high aspect ratio morphology upon which the edge sites can be vertically integrated. We produce vertically aligned α-MoO3 nanowires using a hot-wire chemical vapor deposition method followed by sulfidization over a range of temperatures from 150-700°C to create MoS2 shells of varying thicknesses. At an optimal sulfidization temperature of 200°C, these core-shell nanowires exhibit excellent activity for the HER while remaining stable over thousands of potential cycles in strong acid. The MoS2 shell further provides a protecting layer for the underlying MoO3, which is otherwise unstable in strong acid, while the n-type MoO3 provides a conductive electron pathway to the poorly conducting MoS2. The understanding of MoS2 HER activity arising from edge sites provides insight into the possibility of increasing the activity of these nanowires even further. Towards this goal, we also present work on other nanostructures of MoS2 that also drive efficient HER. Lastly, we explore the optical response properties of these nanowires in solution and their possibility for driving photoelectrochemical water splitting.