What Controls Activity Trends of Electrocatalytic Hydrogen Evolution Reaction?─Activation Energy Versus Frequency Factor

Renewable energy storage via water electrolysis strongly depends on the design of electrified electrode–electrolyte interfaces at which electricity is converted into chemical energy. At the core of the hydrogen evolution reaction (HER) and the oxygen evolution reaction conversion efficiency are interfacial processes with complex dynamic mechanisms, whose further acceleration is practically impossible without a thorough fundamental understanding of electrocatalysis. Here, we communicate new experimental insights into HER, which will potentially further deepen our general understanding of electrocatalysis. Of special note is the very surprising observation that the most active metals (i.e., noble metals) for HER, which exhibit the lowest overpotentials at a defined current density, exhibit the highest activation energies in comparison to the other metals from the d-block. This suggests a major, if not dominant, impact of the frequency factor on activity trends and the need for deeper reconsideration of the origins of electrocatalytic activity.