S-Block Metal Mg-Mediated Co─N─C as Efficient Oxygen Electrocatalyst for Durable and Temperature-Adapted Zn-Air Batteries.

Abstract

In the quest to enhance Zn-air batteries (ZABs) for operating across a wide spectrum of temperatures, synthesizing robust oxygen electrocatalysts is paramount. Conventional strategies focusing on orbital hybridization of d-d and p-d aim to moderate the excessive interaction between the d-band of the transition metal active site and oxygen intermediate, yet often yield suboptimal performance. Herein, an innovative s-block metal modulation is reported to refine the electronic structure and catalytic behavior of Co─NC catalysts. Employing density functional theory (DFT) calculations, it is revealed that incorporating Mg markedly depresses the d-band center of Co sites, thereby fine-tuning the adsorption energy of the oxygen reduction reaction (ORR) intermediate. Consequently, the Mg-modified Co─NC catalyst (MgCo─NC) unveils remarkable intrinsic ORR activity with a significantly reduced activation energy (Ea) of 10.0 kJ mol^-1, outstripping the performance of both Co─NC (17.6 kJ mol^-1), benchmark Pt/C (15.9 kJ mol^-1), and many recent reports. Moreover, ZABs outfitted with the finely tuned Mg_0.1Co_0.9─NC realize a formidable power density of 157.0 mW cm^-2, paired with an extremely long cycle life of 1700 h, and an exceptionally minimal voltage gap decay rate of 0.006 mV h^-1. Further, the Mg_0.1Co_0.9─NC-based flexible ZAB presents a mere 2% specific capacity degradation when the temperature fluctuates from 25 to -20 °C, underscoring its robustness and suitability for practical deployment in diverse environmental conditions.