A pH-universal ORR catalyst with S heteroatom doping single-atom iron sites derived from a 2D flake-like MOF for superior flexible quasi-solid-state rechargeable Zn-air battery

Regulating the atomic coordination ambiance of uniformly distributed single atoms (SAs) via heteroatom doping is an up-and-coming method to facilitate the catalytic activity for oxygen reduction reactions (ORR). With the cooperative interaction of dual heteroatom doping supplied extra degrees of freedom, a greater efficiency of ORR can be realized via a reduction in intermediate energy barrier during catalytic reactions. Here, we explore a fresh approach to generate N, S co-doped Fe-SA in embedded porous carbon nanosheets/carbon nanotubes (Fe-NX@NSCST-ZL) utilizing a 2D leaf-shaped MOF as a template in this work. Taking advantage of the combined effect of carbon matrix and nanotubes as well as the abundance of Fe-NX active sites and thiophene-S, the Fe-NX@NSCST-ZL provides exceptional performance for ORRs with a half-wave potential of 0.94 V at alkaline conditions, 0.77 V at acidic conditions, and 0.74 V at neutral conditions (V vs. RHE). Furthermore, Fe-NX@NSCST-ZL-based Zn-air battery, as well as quasi solid-state flexible battery, maintain steady operation for 765 h and 30 h with a small discharge/charge interval, respectively. This work contributes perspectives on the reasonable design of economical single-atom catalysts (SACs) for applications in energy conversion that have outstanding electrocatalytic potential.