Tea-leaf-residual derived electrocatalyst: Hierarchical pore structure and self nitrogen and fluorine co-doping for efficient oxygen reduction reaction

Abstract The heteroatom-doped carbon materials as metal-free catalysts show great potential for oxygen reduction reaction (ORR) due to the high electrocatalytic activity, low cost, long-term stability, and environmental friendliness. Utilizing biomass as precursors has offered facile and extremely low-cost strategy to large-scale fabrication of highly efficient carbon materials with abundant pore structures and elements. In this work, tea residue was used as precursor to synthesize nitrogen (N) and fluorine (F) co-doped porous carbon materials via one-step annealing process without any activation or post-treatment. The morphology, pore structure, elemental composition of our sample as well as its electrocatalytic performance in ORR were studied. This biomass-based carbon materials has high specific surface area (855.6 m 2  g −1 ) and hierarchical pore structure, which can offer abundant active sites and meanwhile is favorable to ion diffusion of liquid electrolyte. Secondly, the heteroatoms (especially F) doping can induce charge redistribution thanks to the electronegativity difference, which can facilitate electron transfer in ORR. When compared to commercial Pt/C, our catalyst shows a higher limited current density and a high electron transfer number of about 3.8. Finally, the catalyst also demonstrates excellent methanol tolerance in the alkaline medium. Our work provides an economical and facile strategy to synthesize efficient electrocatalyst for ORR.