Role of Hydride Formation in Electrocatalysis for Sustainable Chemical Transformations

The electrochemical potential of numerous reduction reactions corresponds to hydrogen pressures that thermodynamically favor the formation of many metal hydrides. Whether a catalyst remains metallic with hydrogen on the surface (H_ads) or absorbs hydrogen into its lattice (H_abs), forming a metal hydride, results from a balance between not only this thermodynamic driving force but also the kinetics of concurrent surface reactions and equilibrium surface coverage. Drawing parallels with thermal catalytic processes, we provide examples of how hydride formation impacts electrocatalysis in H₂ evolution, organic and CO₂ reduction, and N₂ and NO₃^- reduction reactions. Hydride formation not only changes catalyst activity and selectivity but also can impact durability. We highlight techniques capable of identifying hydride formation under reaction conditions, imperative for an understanding of electrocatalyst kinetics. Hydrides offer many possibilities in electrocatalysis, including unique reaction mechanisms involving the catalyst lattice and innovative reactor architectures, beneficial for applications in chemical transformations and energy.