Towards a mechanically rechargeable solid fuel flow battery based on earth-abundant materials

Metal-air batteries are a promising energy storage solution, but materials limitations (e.g., metal passivation, low active material utilization) have stymied their adoption. We investigate a solid fuel flow battery (SFFB) architecture that combines the energy density of metal-air batteries with the modularity of redox flow batteries. Specifically, a metallic solid electrochemical fuel (SEF) is spatially separated from the anodic current collector; a dissolved redox mediator shuttles charge between the two, and an oxygen reduction cathode completes the circuit. This modification decouples power and energy system components while enabling mechanical recharging and mitigating the effects of non-uniform metal oxidation. We conduct an exploratory study showing that metallic SEFs can chemically reduce organic redox mediators repeatedly. We subsequently operate a proof-of-concept SFFB cell for ca. 25 days as an initial demonstration of technical feasibility. Overall, this work illustrates the potential of this storage concept and highlights scientific and engineering pathways to improvement.