Importance of pyrolysis programs in enhancing the application of microalgae-derived biochar in microbial fuel cells

Abstract

Nitrogen-doped (N-doped) biochar was prepared by pyrolyzing lipid-extracted microalgae residues under 800 °C for 2 h with different temperature increasing rates (single-segment programs: 3–8 °C/min for room temperature-800 °C; two-segment programs: 5–8 °C/min for room temperature-500 °C and 3 °C/min for 500–800 °C). The obtained biochar was used for oxygen reduction reactions and microbial fuel cell applications. Interestingly, biochar prepared by two-segment programs achieved better performances than those prepared by single-segment programs with higher onset potentials in oxygen reduction reactions and higher maximal power densities in microbial fuel cell. This is likely because the applied two-segment programs improved the porous structure and enhanced the formation of pyridinic N in the biochar. Notably, applying the optimal program (5–8 °C/min for room temperature-500 °C and 3 °C/min for 500–800 °C) obtained biochar with a maximal oxygen reduction reactions onset potential of 0.877 V and a maximal microbial fuel cell power density of 843.6 mW·m−2, both of which are higher than values achieved using Pt/C. This study suggests that simply improving the pyrolysis program for N-rich biomass pyrolysis is promising for producing high-performance N-doped biochar for microbial fuel cells.