3D Networks of CoFePi with Hierarchical Porosity for Effective OER Electrocatalysis

A series of amorphous 3D Co-based phosphate networks with hierarchical porosity, including the CoPi, the binary CoM₁ Pi and the trinary CoM₁ M₂ Pi (M_i  = Ni^II , Fe^III , Ce^III ) are produced via a novel bitemplate coprecipitation approach at room temperature. Interestingly, the integration of Fe^III and Co^II in the same network is found to significantly influence both the porosity and the electronic state of Co^II . The CoFePi with a Fe^III to Co^II mole ratio of 0.91 has a specific surface area of 170 m² g^-1 and average pore size of 12.3 nm, larger than those of the CoPi network; furthermore, the Co^II within such CoFePi exhibits a higher oxidation state than that in the CoPi. Due to such structural and compositional merits, the binary CoFePi network shows superior oxygen evolution reaction (OER) electrocatalytic activity, which gives an overpotential as low as 0.315 V at 10 mA cm^-2 and a Tafel slope of 33 mV dec^-1 in 0.10 m KOH. Additionally, the trinary CoFeNiPi demonstrates similar OER catalytic performance. The two phosphate networks also exhibit remarkable catalytic stability. In view of their easy preparation, superior activity, high stability, and low cost, such transition metal phosphate networks are promising catalysts for practical OER processes.