Electrocatalytic water oxidation at neutral pH by a nanostructured Co(PO₃)₂ Anode

Cobalt metaphosphate Co(PO₃)₂ nanoparticles are prepared via the thermolytic molecular precursor (TMP) method. A Ni form electrode decorated with Co(PO₃)₂ nanoparticles is evaluated as an anode for water oxidation electrocatalysis in pH 6.4 phosphate-buffered water. Catalytic onset occurs at an overpotential of ca. 310 mV, which is 100 mV lower than that observed for Co₃O₄ nanoparticles, with a comparable surface area under identical conditions. A per-metal turnover frequency (TOF) of 0.10-0.21 s^-1 is observed at an overpotential, η, of 440 mV, which is comparable to the highest rate reported for a first-row metal heterogeneous catalyst. Post-catalytic characterization of the catalyst resting state by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy reveals that surface rearrangement occurs, resulting in an oxide-like surface overlayer. A nanostructured Co(PO₃)₂ is prepared by the thermolytic molecular precursor method and then drop-cast onto an anode to perform water oxidation at neutral pH at a rate of 0.21 s^-1 and an overpotential of 440 mV. The catalytic onset overpotential is ca. 310 mV, which is 100 mV lower than that of comparable Co₃O₄ nanoparticles under identical conditions.