Nitrogen/Phosphorus/Boron-Codoped Hollow Carbon Spheres as Highly Efficient Electrocatalysts for Zn-Air Batteries

Considering the shortage of platinum resources and its high price, it is crucial to explore its substitutes to satisfy the market demand of metal-air batteries. Thence, N/P/B-codoped hollow carbon nanospheres were synthesized by doping B and P into polydopamine spheres. Thanks to the abundance of defects in the hollow carbon sphere shell, the large active area, the high content of pyrrolic N, and B-C, C-N, and other electrocatalytic active sites, NHCS@B1P2 exhibits excellent oxygen reduction reaction (ORR) catalytic perform-ance. Electrochemical tests show that NHCS@B1P2 has outstanding ORR electroactivity in alkaline electrolytes, with a half-wave potential (E-1/2) 60 mV higher than Pt/C and a limiting diffusion current density 0.97 mA cm-2 greater than Pt/C. Meanwhile, NHCS@B1P2 (E-1/2 = 0.86 V) still exhibits superior electrochemical performance to Pt/C in neutral media. It is noteworthy that a Zn-air battery (ZAB) using NHCS@B1P2 as the ORR catalyst exhibits a higher peak power density (158.5 mW cm(-2) for an alkaline ZAB and 104.6 mW cm-2 for a neutral ZAB) than Pt/C (136/46.7 mW cm-2) in both alkaline and neutral electrolytes. In step discharge at different current densities, it still has a stable voltage value comparable to (even higher than) Pt/C. In addition, NHCS@B1P2 exhibits a more durable and stable voltage plateau than Pt/C at 10 mA cm(-2). This work provides a practical and valuable avenue for the application of heteroatom-doped carbon-based ORR catalysts in ZABs.