Electrochemical Reconstruction of Zn_0.3Co_2.7(PO₄)₂·4H₂O for Enhanced Water Oxidation Performance

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotentials for the water splitting reaction. Toward the oxygen evolution reaction (OER) in alkaline medium, designing pre-catalysts that could provide abundant catalytic active centers can significantly improve the electrocatalytic activity. This work demonstrates the production of active α-Co(OH)2/CoOOH species using the sacrificial pre-catalyst Znx/Co3–x (PO4)2·4H2O (ZCP) (x = 0.15–0.9), which was developed by the one-step hydrothermal method. Electrochemical activation of ZCP results in the formation of a porous cobalt catalyst with abundant active centers. Elemental analysis revealed that both Zn2+ and PO43– ions etch away during the activation process, thereby exposing a higher number of catalytically active cobalt centers that otherwise stay inactive due to their location in the bulk. The resulting materials showed promising electrocatalytic activities toward OER; especially, a material (ZCP-0.3) consisting of Zn2+ and Co2+ in a 1:7 ratio was found to deliver the best activity. The carbon paper-supported ZCP-0.3 exhibited a high current density of 50 mA/cm2 at an overpotential of 390 mV. In contrast, the material prepared without zinc (i.e., Co3(OH)2(HPO4)2) showed inferior catalytic activity, thus demonstrating the necessity for Zn2+ etching to expose the additional active sites for improved electrocatalytic activity of ZCP-0.3.