High Power Density and Stable Fuel Cells with 18‐Phosphomolybdic Acid as Oxygen Reduction Reaction Mediator

Abstract Mediated fuel cells (MedFCs) offer a promising alternative to proton exchange membrane fuel cells by addressing key challenges such as reliance on precious metal catalysts and complex water and thermal management through the use of redox mediators as efficient oxygen reduction reaction (ORR) facilitators. However, currently available mediators exhibit either low electrochemical activity or insufficient stability, which constrains the performance and durability of these fuel cells. In this study, a Dawson‐type 18‐molybdophosphoric heteropoly acid (18‐PMA) with high redox activity and stability is introduced as an ORR mediator in mediated fuel cells, utilizing ordinary carbon felt electrodes. The mediated fuel cell employing 18‐PMA achieved a maximum steady‐state power density of 600 mW cm⁻² under dry gas conditions and demonstrated stable discharge performance at current densities ranging from 100 to 500 mA cm⁻², and the long‐term stability is ensured through a simple and convenient replacement of the Fe‐N‐C catalyst in external reactor.