CoFe formic-acid framework derived S, N co-doped carbon nanotube composites decorated with a bimetallic sulfide as a bifunctional electrocatalyst for rechargeable zinc–air batteries

Wearable and rechargeable zinc–air batteries (ZABs) hold significant potential for applications in flexible electronics and light weight power sources due to their high energy density and excellent safety. However, the practical use of ZABs is hindered by the slow kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the air cathode. Here, we prepared S, N co-doped carbon nanotubes loaded with a cobalt–iron alloy (CoFe and Co0.72Fe0.28) and Co8FeS8 nanoparticles that can act as bifunctional electrocatalysts through one-step pyrolysis using the CoFe formic-acid framework (CoFe-FF) as the metal source. This electrocatalyst exhibited a superior electrocatalytic performance compared to commercial Pt/C (20 wt%) and RuO2. The ZAB assembled with CoFeS/SNCNT demonstrated an open-circuit voltage (OCV) of 1.47 V, a maximum power density (Pmax) of 175.3 mW cm−2, and a good cycle life. Furthermore, the flexible ZAB assembled with CoFeS/SNCNT achieved an OCV of 1.38 V and a Pmax of 77.7 mW cm−2, while maintaining stability under different bending angles. This study presents a feasible strategy for synthesizing and constructing high-performance non-noble metal bi-functional electrocatalysts for rechargeable zinc–air batteries.