Nanostructuring Matters: Stabilization of Electrocatalytic Oxygen Evolution Reaction Activity of ZnCoO by Zinc Leaching.

Despite the enormous attention paid to cobalt oxide materials as efficient water splitting electrocatalysts, a deep understanding of their activity discrepancy is still elusive. In this work, we showed that stabilization of the internally generated oxygen evolution reaction (OER) active phase (oxyhydroxide) is crucial for ZnCoO electrocatalysts. A systematic evaluation of the bulk and nanostructured ZnCoO system concomitant with nanostructured CoO showed that leaching of Zn is the driving force behind the near-surface transformation to the oxyhydroxide phase. The relative contribution to this near-surface reconstruction was found to be surface-sensitive. The electrochemical observations combined with Raman and impedance spectroscopy revealed that the good catalytic activity could be attributed to the formation of the cobalt oxyhydroxide phase, which was created by the dissolution of Zn from the nanostructured surface. Moreover, this study sheds light on previous contradicting postulates regarding the discrepancy of the OER activity of ZnCoO. Our finding regarding the formation of the OER active phase in spinel Zn-Co oxide will motivate researchers to focus more on the near-surface reconstruction behavior of cobalt-based oxide electrocatalysts in the future.