An easy synthesis of Ni-Co doped hollow C-N tubular nanocomposites as excellent cathodic catalysts of alkaline and neutral zinc-air batteries

Exploring high-activity electrocatalyst for oxygen reduction reaction (ORR) is of great significance for a variety of renewable energy conversion and storage technologies. Herein, we fabricated novel ORR electrocatalysts derived from Ni-Co nanoparticles encapsulated in hollow tubular C-N composites (ht-CN) through an easy and scalable pyrolysis route utilizing nickel acetate and cobalt acetate as metal precursors, 2-cyanoguanidine as the nitrogen source, and sucrose as the carbon source. Among the prepared nanocomposite catalysts with different molar ratios of Ni/Co, the catalyst Ni2Co3@ht-CN exhibits an outstanding ORR electroactivity comparable to Pt/C catalyst both in alkaline and neutral media. Home-made zinc-air battery with the Ni2Co3@ht-CN as cathode electrocatalyst presents excellent performance and superior durability either in neutral or alkaline medium. The Ni2Co3@ht-CN battery delivers an open circuit voltage of 1.08 V and a maximum power density of 47 mW cm(-2) in 0.5 mol L-1 KNO3 solution, while 1.51 V and 314 mW cm(-2) in 6 mol L-1 KOH solution. In addition, whether in neutral or alkaline solution, the constant current discharge curves of the Ni2Co3@ht-CN battery at different current densities exhibit higher voltage plateau and stability than the Pt/C battery. Results demonstrate the potential application of the catalysts of the present investigation to Zn-air batteries both in alkaline and neutral media.