Cobalt Incorporated Hydroxyapatite Catalyst for Water Oxidation

We report the novel oxygen evolution reaction (OER) catalyst based on cobalt incorporated hydroxyapatite (CoHAP). Our catalyst is prepared on the surface of hydroxyapatite by ion exchange reaction in Co2+ aqueous solution. The cobalt content is approximately 1 wt. % based on ICP-AES and XPS experiments. XRD, TEM, EDX experiments suggest that individual cobalt ions are adsorbed on the HAP surface in non-aggregated manner. The cyclic voltammetry (CV) of CoHAP exhibits a weak oxidation peak at 1.10 V which is comparable to CV of in-situ formed Co-Pi in previous literature. Tafel slope is approximately 80 mV/decade which is independent on the loading amount of CoHAP. The Faradaic efficiency is 94 % measured by quantitative analysis of O-2 using gas chromatography. Bulk electrolysis verifies that CoHAP can be utilized OER catalyst at neutral pH with high stability. Our preparation method using hydroxyapatite as a solid phase phosphate source offers a new strategy to fabricate the OER catalysts.