Oxygen Evolution Reaction Electrocatalysis on Transition Metal Oxides and (Oxy)hydroxides: Activity Trends and Design Principles

Poor oxygen evolution reaction (OER) catalysis limits the efficiency of H2 production from water electrolysis and photoelectrolysis routes to large-scale energy storage. Despite nearly a century of research, the factors governing the activity of OER catalysts are not well understood. In this Perspective, we discuss recent advances in understanding the OER in alkaline media for earth-abundant, first-row, transition-metal oxides and (oxy)­hydroxides. We argue that the most-relevant structures for study are thermodynamically stable (oxy)­hydroxides and not crystalline oxides. We discuss thin-film electrochemical microbalance techniques to accurately quantify intrinsic activity and in situ conductivity measurements to identify materials limited by electronic transport. We highlight the dramatic effect that Fe cationsadded either intentionally or unintentionally from ubiquitous electrolyte impuritieshave on the activity of common OER catalysts. We find new activity trends across the first-row transition metals, opposite of the established ones, and propose a new view of OER on mixed-metal (oxy)­hydroxides that illustrates possible design principles and applications.