A benzoquinone-mediated fuel cell in alkaline conditions with a packed-bed reactor for enhanced performance and efficiency

Hydrogen fuel cells, which produce electrical energy and only water as a byproduct, are evaluated for their use in eco-friendly technology. However, there are challenges with using abundant precious metal catalysts for electrodes, particularly regarding hydrogen gas crossover and managing the moisture of the polymer electrolyte membrane. To overcome these challenges, a mediated fuel-cell (MedFC) system, in which hydrogen fuel cells are combined with a redox-flow battery using an oxidation–reduction reaction of an electrolyte, has been recently developed. In a MedFC system, the reduced ions of redox-active materials generated by the oxidation of hydrogen in a packed-bed reactor are fed to the fuel cell electrode as a mediator. In this study, 2,5-dihydroxy1,4-benzoquinone (DHBQ) was used as a anode mediator to operate MedFCs under alkaline conditions. DHBQ and hydrogen were injected with an upward flow into the packed-bed reactor to reduce DHBQ via a chemical reaction. On the anode side of the fuel cell, DHBQ oxidized and transferred the electrons to the cathode. By contrast, an oxygen reduction reaction (ORR) occurred at the cathode under alkaline conditions. The reduction potential of DHBQ was −0.72 V (vs. SHE), and that of ORR was 0.4 V (vs. SHE); thus, the theoretical potential of the cell was 1.12 V. During the MedFC operation, a maximum power density of 282 mW/cm2 was obtained.