Regulating the coordination environment of atomically dispersed Fe-N4 moieties in carbon enables efficient oxygen reduction for Zn-air batteries

Fe-N-C single-atom catalysts exhibit the highest oxygen reduction reaction catalytic activity among reported transition metal-based SACs. However, the intrinsic activity of atomically dispersed Fe-N4 moieties in carbon limits the ORR catalytic activity of current Fe-N-C. This work describes a simple method for synthesizing single-atom catalysts with atomically dispersed FeN4CxSy active sites, referred to as FeZ-N/S0.6-C. It also developed a radical polymerization approach to encapsulate ZnCl2 and [Fe(Phen)3]3+ within a polyacrylamide matrix. Due to abundant -CO and –NH2 groups in polyacrylamide, the Zn2+ and Fe complexes could be evenly distributed throughout the polymer. Subsequent one-step pyrolysis allowed the generation of nitrogen-sulfur co-doped catalysts with well-defined pore structures and uniform active sites. The introduction of S atoms by ammonium persulfate extended the Fe-N bond of the Fe-N4 moiety, while the ZnCl2 template aided in fine-tuning the channels within the catalyst. As a result, the FeZ-N/S0.6-C catalyst showed a record high half-wave potential (E1/2 = 0.93 V vs. RHE) among the reported non-noble metal catalysts regulated by S elements. Moreover, FeZ-N/S0.6-C-based aqueous Zn-air and quasi-solid Zn-air batteries achieved excellent performance and showed great application potential in energy storage and conversion devices. This work provides a new approach to encapsulate metal ions in polymers and optimize the single-atom catalyst structure by heteroatom doping to enhance the performance for sustainable applications.