Preparation of a high-yield Fe–N4 site-containing hierarchical porous carbon eletrocatalyst for effective oxygen reduction and zinc-air battery: The effect of dual protection-exposure mechanism

Abstract

Iron-based catalysts are considered highly promising as non-noble metal catalysts for oxygen electroreduction. However, the optimization of iron-based catalysts is limited by the well-designed carbon support and high-efficiency catalytic sites. Furthermore, achieving high production yield on an industrial scale while maintaining high performance would also be highly encouraged. Therefore, a dual-protection-exposure mechanism was employed for a hierarchical porous carbon (HPC) embedded with Fe–N4 sites (Fe–N4/HPC) catalysts, which were prepared through the ionothermal carbonization of Fe/ZnTBrPP@MgCl2 [5, 10, 15, 20-tetrakis (4′-bromophenyl) porphyrinato iron (FeTBrPP) mixed with ZnTBrPP on MgCl2·6H2O template]. Apart from self-protection-exposure of the Fe/ZnTBrPP itself, the hydrated salt template provided a secondary protection and exposure simultaneously. As a result, the Fe–N4/HPC retains more Fe–N4 sites and a larger BET surface, resulting in excellent ORR activity and durability in alkaline (0.922 V vs. RHE). Interestingly, under the conditions of using hydrated magnesium salt as a soft template, the yield rate of the Fe–N4/HPC significantly higher than the product without hydrated salt. Furthermore, the utilization of Fe–N4/HPC as the cathode in a zinc-air battery demonstrated remarkable performance, achieving an high peak power density (94 mW cm−2) and good stability.