Hollow polyhedral Fe-N-C nanostructures derived from ZIF-8 highlighting markable morphology effect on electrochemical oxygen reduction and carbon dioxide reduction

Abstract

Iron and nitrogen co-doped carbon materials (Fe-N-C) have been identified as one promising class of electrocatalysts toward both electrochemical oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR), which are profoundly influenced by both intrinsic and extrinsic factors. Herein a well-defined hollow polyhedral Fe-N-C nanostructure (FeNC-H) is obtained by pyrolyzing ZIF-8 precursor involving FeCl3 absorption and KOH treatment. In comparison, direct pyrolysis of FeCl3-absorbed ZIF-8 only leads to densely fused carbon particles (FeNC-R). Albeit similar pore characteristics between FeNC-H and FeNC-R, FeNC-H exhibits superior ORR and CO2RR performance to FeNC-R due to its markable hollow morphology effect. In O2-saturated 0.1 M KOH solution, FeNC-H delivers an onset potential of 0.966 V (vs. RHE) and a half-wave potential of 0.865 V (vs. RHE), surpassing the benchmark Pt/C. Meanwhile, FeNC-H achieves 91.8 % FE of CO at − 0.5 V (vs. RHE) in CO2-saturated 0.5 M KHCO3 solution. It is found that the unique hollow morphology endows FeNC-H with high surface area, large pore volume and fast mass transfer kinetics, thus boosting both ORR and CO2RR.