Ternary (N, B, F)-Doped Biocarbon Derived from Bean Residues as Efficient Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions

Abstract

Development of efficient metal-free carbon-based electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are of great significance for Zn-air batteries. Herein, a porous biocarbon bifunctional catalyst (C-NBF-G) was directly synthesized via simple alkali activation and carbonization from bean residues. C-NBF-G exhibited hierarchical porous structures, ternary heteroatom (N, B, and F) doping, a large specific surface area, and a relatively high degree of graphitization. The synergistic action of these characteristics contributed to the outstanding catalytic properties of C-NBF-G for ORR and OER. The catalyst demonstrated an onset potential of 0.94 V, half-wave potential of 0.824 V, and a limiting current density of 5.92 mA cm−2, comparable to those of the commercial 20 wt% Pt/C catalysts. C-NBF-G also exhibited an OER overpotential of 333 mV at 10 mA cm−2 and a Tafel slope of 114 mV dec−1, lower than those of the commercial Pt/C and RuO2 catalysts. These results proved the promising performance of C-NBF-G as a bifunctional catalyst for the ORR and OER.