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The design and fabrication of efficientand inexpensive electrodesfor use in the oxygen evolution reaction (OER) is essential for energy-conversiontechnologies. In this study, high OER performance is achieved usingnovel hierarchical ZnxCo3–xO4nanostructures constructed with smallsecondary nanoneedles grown on primary rhombus-shaped pillar arrays.The nanostructures have large roughness factor, high porosity, andhigh active-site density. Only a small overpotential of ∼0.32V is needed for a current density of 10 mA/cm2with a Tafelslope of 51 mV/decade. The nanostructures are also found to performsignificantly better than pure Co3O4and a commercialIr/C catalyst and to perform similarly to the best OER catalysts thathave been reported for alkaline media. These merits combined withthe satisfactory stability of the nanostructures indicate that theyare promising electrodes for water oxidation. [ABSTRACT FROM AUTHOR]