Speaker
Description
The hydrogen evolution reaction (HER) is the most prominent electrocatalytic reaction. It is needed to generate green hydrogen from water and simultaneously serves as the test reaction for general electrocatalyst function in aqueous media. Despite this, it remains poorly understood. Attempts have been made to describe HER kinetics according to Brønsted-Evans-Polanyi relationships for which the hydrogen binding energy with the surface is the primary activity descriptor (1). However, this approach has been increasingly challenged (2,3). It has been pointed out that catalyst surfaces on the descending volcano branch (such as for W, Mo, Ti) are covered with amorphous oxides under operation, preventing reliable calculations3. Furthermore, even for the ascending branch, barriers of ion (de)solvation are neglected.
Here, we present our extensive study on the temperature dependent HER kinetics across a large set of nanoparticle catalysts in acidic and alkaline membrane electrolyzer environments4. When we extract the bias dependent activation entropy and enthalpy, we discover distinct kinetic fingerprints between the iron triad (Fe, Ni, Co), platinum-group metals (PGMs; Pt, Rh, Ir, Pd) and coinage metals (Au, Co, Ag). Strikingly, except for the PGMs, none of the other groups displays simple Butler-Volmer type behavior - not even in acid. Furthermore, we highlight the importance of bias dependent activation entropy in the pre-exponential factor. Consistent with our recent results (5,6), we separate the entropic changes into changes in the interfacial solvent that can differ between H+ and OH solvation, and surface configurational entropy changes that show how a bias dependent H coverage impacts HER kinetics at higher current densities.
Our results are key to update electrocatalyst research and education and for developing novel electrocatalyst design strategies. Importantly, besides developing faster HER catalysts in alkaline conditions from earth-abundant metals, understanding the slow HER kinetics of the coinage metals, is a first step toward understanding the competing CO2 reduction to C2+ products on the same catalyst surfaces.
References
- Noerskov, J. K. et al. Trends in the Exchange Current for Hydrogen Evolution. ChemInform 36, chin.200524023 (2005).
- Schmickler, W. & Trasatti, S. Comment on “Trends in the Exchange Current for Hydrogen Evolution” [J. Electrochem. Soc., 152, J23 (2005)]. J. Electrochem. Soc. 153, L31 (2006).
- Quaino, P., Juarez, F., Santos, E. & Schmickler, W. Volcano plots in hydrogen electrocatalysis – uses and abuses. Beilstein Journal of Nanotechnology 5, 846–854 (2014).
- Gisbert-Gonzalez, J. M., Gomez-Rodellar, C., Roldan Cuenya, B. & Oener, S.Z. Entropy-Enthalpy Relationships of the Hydrogen Evolution Reaction. in review (2024).
- Rodellar, C. G., Gisbert-Gonzalez, J. M., Sarabia, F., Roldan Cuenya, B. & Oener, S. Z. Ion solvation kinetics in bipolar membranes and at electrolyte–metal interfaces. Nature Energy 1–11 (2024).
- Sarabia, F., Gomez Rodellar, C., Roldan Cuenya, B. & Oener, S. Z. Exploring dynamic solvation kinetics at electrocatalyst surfaces. Nat Commun 15, 8204 (2024).
