Covalent organic framework-derived Fe, Co-nitrogen codoped carbon as a bifunctional electrocatalyst for rechargeable efficient Zn–air batteries

Abstract

The development of cathode materials with controllable physicochemical structures and explicit catalytic sites is important in rechargeable Zn–air batteries (ZABs). Covalent organic frameworks (COFs) have garnered increasing attention owing to their facile synthesis methods, ordered pore structure, and selectivity of functional groups. However, the sluggish kinetics of oxygen evolution reaction (OER) or oxygen reduction reaction (ORR) inhibit their practical applications in ZABs. Herein, nucleophilic substitution is adopted to synthesize pyridine bi-triazine covalent organic framework (denoted as O-COF), and meanwhile, ionothermal conversion synthesis is employed to load MO_x (M=Fe, Co) onto carbon nanosheet (named as FeCo@NC) to modulate the electronic structure. The Fe, Co-N codoped carbon material possesses a large portion of pyridinic N and M-N, high graphitization, and a larger BET surface area. An outstanding bifunctional activity has been exhibited in FeCo@NC, which provides a small voltage at 10 mA cm⁻² for OER (E₁₀ = 1.67 V) and a remarkable half-wave voltage for ORR (E_1/2 = 0.86 V). More impressively, when assembling ZABs, it displays notable rate performance, significant specific capacity (783.9 mAh g_Zn⁻¹), and satisfactory long-term endurance. This method of regulating covalent organic framework and ionothermal synthesis can be extended to design diverse catalysts.