Nitrogen self-doped porous carbon from surplus sludge as metal-free electrocatalysts for oxygen reduction reactions

Nitrogen self-doped porous carbon was prepared by calcination treatment of surplus sludge, a toxic byproduct from microbial wastewater treatments, and exhibited a mesoporous structure, as manifested in scanning and transmission electron microscopic measurements. Nitrogen adsorption/desorption studies showed that the porous carbon featured a BET surface area as high as 310.8 m(2)/g and a rather broad range of pore size from 5 to 80 nm. X-ray photoelectron spectroscopic studies confirmed the incorporation of nitrogen into the graphitic matrix forming pyridinic and pyrrolic moieties. Interestingly, the obtained porous carbon exhibited apparent electrocatalytic activity in oxygen reduction in alkaline media, with the optimal temperatures identified within the range of 600 to 800 °C, where the number of electron transfers involved in oxygen reduction was estimated to be 3.5 to 3.7 and the performance was rather comparable to leading literature results as a consequence of deliberate engineering of the graphitic matrix by nitrogen doping.