Exploring Fe Retention in Oxygen Evolution Reaction Catalysts Via Composition Engineering

Abstract

The oxygen evolution reaction (OER) is an electrochemical half-reaction critical to electrolyzer and metal-air battery technologies. It is well established that Ni (oxy)hydroxides are state-of-the-art electrocatalysts for the OER in basic media when Fe impurities are present in these systems. Morphological studies have shown that these catalysts are prone to dramatic nanoscale reconstruction under electrochemical conditions, implying dissolution, migration and redeposition processes of the catalyst’s components. Processes involving the displacement of Fe are especially important to understand, as these impurities, while essential for high activity at the anode, are often associated with cathode fouling. Describing the parameters that govern Fe leaching is thus of interest for the design of materials aimed toward the maintenance of device performance and longevity. To study how the degree of restructuring relates to Fe dissolution and redeposition, we have prepared a series of electrolyte accessible Ni(z)Co(1-z)O(x)H(y) (z = 0, 0.2, 0.4, ...) thin film catalysts, whereby increased amounts of Co limit the material’s dynamic behavior. By introducing tertiary cations with trackable redox features, we map a parameter space of catalyst composition more or less capable of retaining surface active phases. Parallels with Ni-Co + Fe catalysts are then carried out in Fe-free electrolyte to disrupt absorption-desorption equilibria and connect host-structure dynamics to equilibrium concentrations of electrolyte impurities.