Green synthesis of iron and nitrogen co-doped porous carbon via pyrolysing lotus root as a high-performance electrocatalyst for oxygen reduction reaction

Carbon-based oxygen reduction reaction (ORR) catalysts, especially N-doped carbon and Fe/N co-doped carbon (Fe-N-C) catalysts are the most promising substitution for Pt-based catalysts. However, most preparations of carbon-based ORR catalysts consume large amounts of fossil organic nitrogen compounds and high-cost carbon supports. Herein, this paper reports a green strategy employing nontoxic CaCl2 as an activating agent, FeCl3 as a metal source, and urea as a nitrogen source to synthesize iron and nitrogen co-doped porous carbon from lotus root. The as-synthesized lotus root-derived carbon (L1221-90) is featured by high specific surface area (899.90 m(2) g(-1)), abundant pores, highly disperse FeNx, and doped-N. The optimal L1221-900 respectively exhibits a high selectivity 4e(-) ORR route with high half-wave potential of 0.960 and 0.660 V in alkaline and acid medium, which is proximate to commercial Pt/C. It is found that graphitic-N and FeNx are the possible active sites, while abundant pores, especially the mesoporous, facilitate the O-2 diffusion. Theoretical calculations reveal that the FeNx with different coordination numbers displays different ORR activities in acid medium. The L1221-900 presumably contains some slightly active FeNx species, which leads to the relatively lower ORR activity in the acid medium. This research develops a green approach to prepare Fe-N-C catalyst for ORR.

Automated summary

This study developed a green approach to prepare iron and nitrogen co-doped porous carbon catalyst with high specific surface area and abundant pores, showing high ORR activity.