Nitrogen Self-Doped Porous Carbon from Surplus Sludge\nas Metal-Free Electrocatalysts for Oxygen Reduction Reactions

Abstract

Nitrogen\nself-doped porous carbon was prepared by calcination treatment\nof surplus sludge, a toxic byproduct from microbial wastewater treatments,\nand exhibited a mesoporous structure, as manifested in scanning and\ntransmission electron microscopic measurements. Nitrogen adsorption/desorption\nstudies showed that the porous carbon featured a BET surface area\nas high as 310.8 m²/g and a rather broad range of pore\nsize from 5 to 80 nm. X-ray photoelectron spectroscopic studies confirmed\nthe incorporation of nitrogen into the graphitic matrix forming pyridinic\nand pyrrolic moieties. Interestingly, the obtained porous carbon exhibited\napparent electrocatalytic activity in oxygen reduction in alkaline\nmedia, with the optimal temperatures identified within the range of\n600 to 800 °C, where the number of electron transfers involved\nin oxygen reduction was estimated to be 3.5 to 3.7 and the performance\nwas rather comparable to leading literature results as a consequence\nof deliberate engineering of the graphitic matrix by nitrogen doping.