The Hydrogen Evolution Reaction: Using Molecular Design in Transition Metal Complexes to Control Catalytic Microenvironments on Electrode Surfaces

Hydrogen gas and its production from renewable power sources will be an important part of decreasing global reliance on fossil fuels and developing a sustainable energy economy. Efficient electrocatalysis, however, relies on the delivery of both protons and electrons; ideally in a concerted fashion to avoid high energy intermediates, prevent charge build‐up, and circumvent large kinetic barriers. While this can be achieved using ligand design in homogenous molecular transition metal catalysts (specifically incorporating proton shuttles in the secondary coordination sphere), heterogeneous systems are more desirable from an industrial perspective due to their ease of use and enhanced durability. Supporting transition metal catalysts on electrode surfaces is therefore a promising approach for developing next generation electrocatalysts that retain molecular level control in interfacial environments. This review will first cover key design principles from natural systems, such as hydrogenase enzymes, and then survey some representative examples of synthetic homogeneous hydrogen evolution electrocatalysts that incorporate these important features. We will then discuss transition metal species that have been supported on electrode materials, with a focus on recent advances in the field, and the major challenges that remain. Combining the unique benefits of transition metal complexes and heterogeneous electrocatalysts is a promising strategy for developing next‐generation sustainable energy technologies. This review discusses key design principles from homogeneous hydrogen evolution catalysts in the context of molecular species that have been supported on electrode materials, with a focus on recent advances in the field and the major challenges that remain.