Iron phthalocyanine and MnOx composite catalysts for microbial fuel cell applications

A low cost iron phthalocyanine (FePc)-MnOx composite catalyst was prepared for the oxygen reduction reaction (ORR) in the cathode of microbial fuel cells (MFCs).The catalysts were characterised using rotating ring disc electrode technique. The n number of electrons transferred, and H₂O₂ production from ORR was investigated. The FePc-MnOx composite catalyst showed higher ORR reduction current than FePc and Pt in low overpotential region. MFC with composite catalysts on the cathode was tested and compared to Pt and FePc cathodes. The cell performance was evaluated in buffered primary clarifier influent from wastewater treatment plant. The membrane-less single chamber MFC generated more power with composite FePcMnOx/MON air cathodes (143mWm^-2) than commercial platinum catalyst (140mWm^-2) and unmodified FePc/MON (90mWm^-2), which is consistent with the RRDE study.The improvement was due to two mechanisms which abate H₂O₂ release from the composite. H₂O₂ is the reactant in two processes: (i) chemical regeneration of MnOx after electro-reduction to Mn²⁺, and (ii) peroxide undergoing chemical disproportionation to O₂ and H₂O on an electrochemically aged manganese surface retained in the film. Process (i) has the potential to sustain electrochemical reduction of MnOx at cathode potentials as high as 1.0V_RHE.