Templating synthesis of hierarchically meso/macroporous N-doped microalgae derived biocarbon as oxygen reduction reaction catalyst for microbial fuel cells

N-doped carbons have been hailed as cost effective catalysts for the large-scale commercialization of microbial fuel cells (MFCs). In this paper, we developed a hierarchically meso/macroporous N-doped biocarbon by templating approach using Chlorella pyrenoidosa as precursor. The results showed that graphitic-N was the dominating functional group contributing to oxygen reduction reaction (ORR) performance. In addition, the role of pore structure was identified and the results suggested that mesopores exhibited a nearly linear correlation with limiting current density and half-wave potential, while electrochemical surface area almost linearly varied with macropores in the carbon materials. These results implied that mesopores play a dominating role in facilitating ion and oxygen supply and creating accessible active sites for ORR, while macropores mainly served as an electrolyte buffering reservoir shortening the electrolyte diffusion distances in the prepared catalysts. The optimized meso/macro pore structure enhanced the accessibility of the active sites and facilitated the mass transport of ion and oxygen, and consequently improved ORR performance of catalyst. The as-prepared catalyst exhibited a remarkably higher power generation than that of the commercial Pt/C in MFCs. This paper offered an insight into the effect of pore structure on the ORR performance of catalysts, and also provided an alternative avenue for synthesizing meso/macroporous carbon catalysts for the applications of MFCs. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.