An altered nanoemulsion assembly strategy for in-situ synthesis of Co2P/NP-C nanospheres as advanced oxygen reduction electrocatalyst for zinc-air batteries

The design of highly active and stable non-noble metal catalysts for oxygen reduction reaction (ORR) is indispensable for metal-air batteries. Herein, an altered nanoemulsion assembly approach is developed to synthesize fine Co2P dispersed in N, P doped carbon nanospheres (Co2P/NP-C) as prominent ORR electrocatalyst for zinc-air batteries (ZABs). A high half-wave potential of 0.81 V vs. RHE and a limiting current density of 4.54 mA cm−2 is exhibited for Co2P/NP-C, which are comparable with those of commercial Pt/C, indicating excellent ORR electrocatalytic activity. Moreover, a big peak power density of 152.4 mW cm−2 and a high gravimetric energy density of 1286.0 Wh kgZn−1 are delivered for the assembled primary ZAB using Co2P/NP-C as cathode catalyst with a high open circuit voltage of 1.448 V. The excellent performance should be attributed to the in-situ formed Co2P nanoparticles and N, P heteroatoms in nanospherical carbon matrix with high accessible surface area, which both provide sufficient catalytic active sites and ensure efficient mass/charge transport in ORR process.