Enhanced bifunctional electrocatalysis of Co5.47N nanocrystals in porous carbon nanofibers for high-efficiency zinc-air batteries

As a promising energy conversion and storage device, recently, rechargeable zinc-air batteries (ZABs) have developed rapidly, and the exploitation of excellent electrode catalysts to improve the energy efficiency and long-term performance of ZABs has become a focus of current research. Herein, the Co_5.47N nanocrystals embedded in porous carbon nanofibers (Co_5.47N PCNFs) were designed to act as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and iodide oxidation reaction (IOR), which occur on the electrode in the charging-discharging process of ZABs. The electrochemistry results showed that the ORR activity of Co_5.47N PCNFs is comparable to the commercial Pt/C electrocatalyst, and the IOR activity and stability are higher than those of the Pt/C electrocatalyst. Importantly, Co_5.47N PCNFs electrocatalyst endows ZABs with a low charge–discharge voltage difference (0.49 V), a high round-trip energy efficiency (72.1 %), as well as a large specific capacity (791.5 mAh g_Zn⁻¹), surpassing the performance of Pt/C electrocatalyst. Density functional theory calculation demonstrates that Co_5.47N PCNFs have lower Gibbs free energy for the formation of IOR intermediate species, thereby displaying outstanding IOR catalytic performance compared to that of Pt/C electrocatalyst. These findings offer crucial insights into the rational design of cobalt nitride-based electrocatalysts for application in ZABs with high energy efficiency.