(27e) Role of OH* in the Alkaline Hydrogen Evolution Reaction

The mechanism of the alkaline hydrogen evolution and oxidation reactions (HER/HOR), important in water electrolyzers and hydrogen fuel cells, has been hotly debated. Recent evidence suggests another activity descriptor beyond hydrogen binding strength (which is sufficient in an acid electrolyte) is needed. Subbaraman et al. decorated Pt(111) with nano-size transition metal hydroxide clusters, and found the rate of hydrogen evolution was additionally correlated to the binding strength of hydroxide [1]. However, they did not provide a mechanistic explanation as to why the hydroxide binding strength should be important for HER. Using a combination of detailed experiments on single-crystal electrodes and density functional theory (DFT) simulations, we examine the role of adsorbed hydroxide in the alkaline HER. We create a model catalyst which has constant hydrogen binding strength, variable hydroxide binding strength, controllable interfacial area, and is sufficiently easy to model with DFT such that the hydroxide adsorption strength can be directly calculated. We also use DFT to simulate potential dependent activation energies for water dissociation to adsorbed hydrogen and identify the role of OH* in the reaction mechanism. Using this combination of experiment and theory we will provide specific design criteria for more active catalysts for alkaline hydrogen evolution. We additionally will discuss the role of interfacial water reorganization and electrode potential of zero charge [2].

1) R. Subbaraman, D. Tripkovic, K.-C. Chang, D. Strmcnik, A.P. Paulikas, P. Hirunsit, M. Chan, J. Greeley, V. Stamenkovic, N.M. Markovic, Nature Materials, 11, 550-557 (2012).

2) I. Ledezma-Yanez, W. David Z. Wallace, P. Sebastián-Pascual, V. Climent, J.M. Feliu, M. T.M. Koper, Nature Energy, 2:17031 (2017).