Active and Stable Nickel-Based Electrocatalysts Based on the ZnO:Ni System for Water Oxidation in Alkaline Media

The synthesis of monodisperse, surfactant-free, Ni-substituted ZnO nanocrystallites (ZnO:Ni) by the mild solvolysis of heterobimetallic Ni4-xZnxO4 cubane-like precursors (x=1-3) in benzylamine is reported. Ni4-xZnxO4 was grafted by electrophoretic deposition onto fluorine-doped tin oxide glass substrates and used as an active and stable working electrode for water oxidation. Upon the application of a voltage at the electrodes, the ZnO:Ni precatalyst leads to an active composite material that can oxidize water (>15h) with an increasing catalytic current. In contrast, the performance of homometallic NiO reference materials decreases rapidly over time and is surpassed by the composite from the ZnO:Ni precatalyst in terms of both stability and activity. Extensive characterization of the as-prepared and activated ZnO:Ni precatalyst by using hard X-ray photoelectron spectroscopy revealed that the excellent performance of the electrode material is because of the formation of a unique self-supported turbostratically disordered mixture of -NiOOH/-Ni(OH)(2)-like phases from the rapid dissolution of Zn-II in the ZnO:Ni precatalyst into the electrolyte during activation.