Facile Conversion of Radish to Nitrogen-Doped Mesoporous Carbon as Effective Metal-Free Oxygen Reduction Electrocatalysts

An activation step is essential for yielding nitrogen-doped mesoporous carbon (NMCs) oxygen reduction reaction (ORR) electrocatalysts from biomass. Though many solely KOH or ZnCl2 activated carbon materials have been synthesized with fine ORR activity, there a deep discussion of activated-carbon-based electrocatalysts obtained from different activation processes is still lacking. In this paper, we systemically compare radish-derived NMCs that underwent different activation processes, and reveal the relationship between structure and activity of these activated carbons. We showed that though ZnCl2 is not an effective porogen compared with KOH, owing to a more open pore structure along with effective preservation of nitrogen heteroatoms, ZnCl2 assisted activated carbon could show significantly improved ORR activity, with an onset potential of 0.91 V (vs. RHE), close to benchmark Pt/C catalysts and even better extended operation stability and stronger tolerance to methanol crossover compared with commercial Pt/C catalysts. Thus we proved that ZnCl2 assisted activation is better than exclusively self-activation or KOH assisted activation in preparing biomass-derived ORR catalysts.