(560by) Mechanisms for Hydrogen Evolution on Transition Metal Phosphides and Pt

Water electrolysis for renewable energy storage and conversion is limited by the high cost of Pt-based catalysts used for the hydrogen evolution reaction (HER). Earth-abundant transition metal phosphides have emerged as active HER catalysts with lower cost than Pt. However, the catalytically active sites and reaction mechanisms on these catalysts remain unclear. We present models of the HER on four different transition metal phosphide surfaces (Co₂P, CoP, Fe₂P, and FeP) using cluster expansions parameterized by density functional theory. We predict the structures and energetics of adsorbed hydrogen as a function of temperature and applied potential, allowing us to determine the potential-dependent activities of different sites while fully accounting for interactions among adsorbed hydrogen atoms. For comparison, we have used the same approach to model the HER mechanisms on Pt surfaces – including Pt(111), Pt(110), and Pt(100). We demonstrate the effects of potential-dependent surface coverage on HER current density and propose mechanisms that are in good agreements with experiments. The present work provides a general and effective way to study catalytic reaction mechanisms and probe catalytically active sites on surfaces, which can facilitate the design of highly active catalysts.

*Office of Naval Research N00014-16-1-2355