Power Generation Characteristics of Metal-Fueled Redox Flow Polymer Electrolyte Fuel Cells Employing Heteropolyanions As Anode Redox Mediators

In this study, the heteropolyanion of [PW12O40]3- is applied as an anode redox mediator in the redox flow polymer electrolyte fuel cells (PEFCs). This system enables continuous power generation by the electrochemical oxidation of the heteropolyanions over the carbon anode and subsequent re-reduction of the oxidized heteropolyanions in the anode tank. Currently, effective reduction methods alternative to biomass are required to achieve both high performance and long-term stability. In this study, a novel reduction method of heteropolyanions utilizing the corrosion reaction of metals (aluminum, iron, nickel, cobalt) in strong acid aqueous solutions is investigated. Current passage tests reveal that the hydrogen evolution reaction, which competes with the re-reduction of the oxidized heteropolyanions, affects the fuel efficiency. Among metals studied, aluminum is able to effectively re-reduce oxidized heteropolyanions while suppressing the consumption of protons and metals associated with the hydrogen evolution reaction. On the other hand, cobalt consumes a large amount of metal in the hydrogen evolution reaction and is found to be inferior to aluminum in fuel efficiency. This study provides an innovative approach to the reduction method of the anode redox mediator in the redox flow PEFCs.