Phosphorus modification of cobalt-iron nanoparticles embedded in a nitrogen-doped carbon network for oxygen reduction reaction

For the electrochemical reduction of oxygen the development of heteroatom-doped carbon-based transition metal catalysts has become a recognized strategy to replace traditional noble metal catalysts. In this work a catalyst consisting of CoFe nanoparticles encapsulated in N-doped carbon-based materials (NC) supported by carbon nanotubes (CNTs), i.e. Fe₃Co₁@NC/CNTs, was modified via treatment with a phosphate salt to synthesize a P-Fe₃Co₁@NC/CNTs catalyst. The P-Fe₃Co₁@NC/CNTs exhibits with 5.29 mA cm^-2 an enhanced current density which is comparable to a Pt/C catalyst. In addition, a stability and methanol resistance better than the Pt/C catalyst were observed which is ascribed to the carbon encapsulation and the synergies between the two transition metals. Finally, the reaction mechanism of P-doping was studied and discussed. These results provide possible directions for carbon-based catalysts and doping with heteroatoms for the improvement of catalytic activity. Moreover, the zinc-air battery assembled with P-Fe₃Co₁@NC/CNTs as the air-cathode exhibited a high-power density of 73 mW cm^-2, which is comparable to that of Pt/C (71 mW cm^-2) and a specific capacity of 763 mA h g^-1. The prepared catalyst could potentially serve to take the place of precious metal catalysts in rechargeable Zn-air batteries.