Schiff-Base-Polymer-Derived N/S-Codoped Carbon Nanoflowers as Efficient Metal-Free Oxygen Reduction Reaction Catalysts Applied in Zn–Air Batteries

Carbon-based composites, especially for heteroatom incorporation including P, S, N, and B, show excellent performance in the ORR and are promising alternatives in place of Pt/C catalysts. However, complex procedures are necessary for the synthesis of the precursors acting as suitable carbon-based electrocatalysts. Herein, a simple method, based on the Schiff-base reaction, offering the privileges of devising the N-containing precursors, is developed to synthesize an efficient ORR catalyst. In this study, a Schiff-base polymer with nanoflower morphology (CNF-P) is synthesized via the reaction of 3,5-diaminobenzoic acid and terephthalaldehyde at room temperature. Subsequently, the N/S-codoped carbonaceous nanoflower electrocatalyst derived from its polymer counterpart (N/S-CNF900) is fabricated through high-temperature pyrolysis of CNF-P with thiourea. Benefitting from the dopants of N and S atoms, the N/S-CNF900 sample demonstrates exceptional ORR activity, offering an E1/2 of 0.87 V, Eonset of 1.02 V, and jm of 6.05 mA cm–2, as well as excellent durability and methanol resistance. When utilized as the air electrode in ZABs, N/S-CNF900 demonstrates superior power output of 178 mW cm–2 coupled with exceptional charge–discharge durability spanning 282 h. The superior electrochemical performance stems from the abundant active sites created by heteroatomic N/S doping with a very high specific surface area and the multilevel porous architecture, thereby ensuring effective exposure of active sites. These findings suggest that the catalyst synthesized through the Schiff-base reaction holds promising potential applications in alkaline zinc–air batteries (ZABs).