Optimization of PGM-free cathodes for oxygen reduction in microbial fuel cells

Iron-nitrogen-carbon catalyst based on iron phthalocyanine supported on nitrogen-functionalized carbon black pearls (FeBP(N)) was integrated into gas diffusion layer electrodes by hot pressing and tested at the cathode side of microbial fuel cells (MFC). As highlighted by I-V characteristics, peak power density decreased over time during MFC functioning. This was caused by an increase of charge and mass transfer resistances of the oxygen reduction reaction due to a biofilm accumulation at the cathode interface, as revealed by electrochemical impedance spectra of the cathodes. Monitoring the peak power density retention over time demonstrated that kinetic and diffusional limitations of ORR at the cathode side of operating MFCs can be minimized by tuning the hot pressing parameters, thus optimizing the cathode interface. In fact, MFCs assembled with cathode obtained by using T = 120 degrees C and p = 2 MPa as hot pressing parameters allowed achieving the highest performance in terms of peak power density (206.1 +/- 10.3 mu Wcm(-2)) and peak power retention over 100 days MFC operation (77%), as compared to the cathode prepared with different hot pressing parameters and Pt-based cathodes taken as reference. (C) 2020 Elsevier Ltd. All rights reserved.