Self‑nitrogen-doped carbon materials derived from microalgae by lipid extraction pretreatment: Highly efficient catalyst for the oxygen reduction reaction.

Biomass-based nitrogen-doped carbon-based material has gradually become a premising metal alternative catalyst for oxygen reduction reaction due to their broad resources, renewable property, and low cost. However, the efficient nitrogen doping is still restricted by their low content and poor conversion efficiency. In this study, self- nitrogen -doped biomass-based carbon materials with high content of nitrogen (27.8% pyridinic-N and 40.3% graphitic-N) and hierarchical pore structure were prepared via lipid extraction pretreatment. The obtained microalgae residue carbon (MRC) catalyst exhibits superior oxygen reduction reaction performance, in terms of more preferable electrode performance and better stability, higher power density in the microbial fuel cells system compared to that of microalgae carbon (MAC). The onset potential of the MRC is 60 mV higher than that of MAC, and the maximum power density of microbial fuel cells (MFCs) with MRC as cathode catalyst reache 412.85 mW m-2. This can be attributed to the fact of that the lipid extraction was not only beneficial to the nitrogen enhancement and oriented conversion but also be conductive to the structure construction. The synergistic effect between active sites and hierarchical structure endows the catalyst excellent ORR performance and good stability in the MFCs system.