Co-generation of hydrogen and power/current pulses from supercapacitive MFCs using novel HER iron-based catalysts

In this work, four different supercapacitive microbial fuel cells (SC-MFCs) with carbon brush as the anode and an air-breathing cathode with Fe-Aminoantipyrine (Fe-AAPyr) as the catalyst have been investigated using galvanostatic discharges. The maximum power (P_max) obtained was in the range from 1.7 mW to 1.9 mW for each SC-MFC. This in-series connection of four SC-MFCs almost quadrupled P_max to an operating voltage of 3025 mV and a P_max of 8.1 mW, one of the highest power outputs reported in the literature. An additional electrode (Ad_HER) connected to the anode of the first SC-MFC and placed in the fourth SC-MFC evolved hydrogen. The hydrogen evolution reaction (HER) taking place at the electrode was studied on Pt and two novel platinum group metal-free (PGM-free) catalysts: Fe-Aminoantipyrine (Fe-AAPyr) and Fe-Mebendazole (Fe-MBZ). The amount of H₂ produced was estimated using the Faraday law as 0.86 mMd^-1cm^-2 (0.132 L day^-1) for Pt, 0.83 mMd^-1cm^-2 (0.127 L day^-1) for Fe-AAPyr and 0.8 mMd^-1cm^-2 (0.123 L day^-1) for Fe-MBZ. Hydrogen evolution was also detected using gas chromatography. While HER was taking place, galvanostatic discharges were also performed showing simultaneous H₂ production and pulsed power generation with no need of external power sources.