Coverage, Repulsion, and Reactivity of Hydrogen on High-Entropy Alloys

Graphical abstract

Modeling hydrogen evolution reaction (HER) probability on IrPdPtRhRu(111) high-entropy alloys. Determining hydrogen coverages based on ligand effects and generalized hydrogen-hydrogen repulsion.

Authors:  Frederik Cornelius Østergaard, Frank Abild-Pedersen, Jan Rossmeisl

The rate of H2 formation is highly impacted by the level of hydrogen coverage on the catalyst surface. In search of optimal catalytic properties high-entropy alloys (HEA) are promising candidates that utilize the compositional space of multiple elements. Based on simulations of HEA, model (111) surfaces with a range of hydrogen coverages, distributions of binding energies are used to construct a framework that approximates the probability that adsorbed hydrogen leads to the formation of  H2 as a function of applied potential.

By optimizing the alloy compositions for the highest reaction probability at given potentials the best and most efficient catalyst candidates for HER can be identified. Treating hydrogen-hydrogen repulsion effects and binding energy separately, we find that the repulsion is larger for HEAs than for pure metals. Differing isotherm slopes in the mean adsorption and desorption energies demonstrate a possible hysteresis for hydrogen adsorption on HEAs.

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