Coupling of Fe-Nx sites and Fe nanoparticles on nitrogen-doped porous carbon for boosting oxygen electroreduction in Zn-air batteries

Fe and nitrogen co-doped carbon (Fe-N-C) catalysts have emerged as attractive materials to substitute Pt-based catalysts for the oxygen reduction reaction (ORR) in Zn-air batteries (ZABs). However, the Fe-N-C catalysts with monotypic active component usually endow suboptimal catalytic performance and stability under both acid and alkaline medium. Herein, a nano ZnO template and two-step pyrolysis co-assisted strategy is proposed to achieve the coupling of Fe-Nx sites and metallic Fe nanoparticles in hierarchically porous N-doped carbon for ORR. The nano ZnO template contributes to the formation of meso/macropores structure, while the secondary pyrolysis is beneficial to the creation of more micropores. Besides the advanced hierarchical porosity, the combination of dispersed Fe-Nx sites and dominated metallic Fe nanoparticles is also conducive to boost ORR activity in both acid and alkaline solution. Impressively, the prepared Fe@FeHPNC-P2 electrocatalyst exhibits an excellent half-wave potentials (E-1/2) of 0.88 V and 0.79 V in alkaline and acidic electrolyte, respectively. Meanwhile, the assembled liquid Zn-air battery using Fe@FeHPNC-P2 delivers a peak power density of 149.3 mW cm(-2) and a maximum energy density of 957.1 Wh kg(Zn)(-1) along with long-term stability for 1000 cycles.