Toward a Mechanically Rechargeable Solid Fuel Flow Battery Based on Earth-Abundant Materials

Abstract

Metal–air batteries are a promising energy storage solution, but material limitations (e.g., metal passivation and 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 (RM) shuttles charges 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 nonuniform metal oxidation. We conduct an exploratory study showing that metallic SEFs can chemically reduce organic RMs 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.

A Redox‐Mediated Iron‐Air Fuel Cell for Sustainable and Scalable Power Generation

“…Consequently, the capacity for energy storage and conversion is essentially limited by the electrode compartment volume and the degradation and passivation of the electrode during operation. [5] The concept of redox targeting (RT) of energy storage materials offers a feasible solution to address the above issues by employing redox mediators (RMs) dissolved in the electrolyte. [6] To tackle the above challenges, here we develop a redoxmediated iron-air fuel cell (RM-IAFC) based on the RT reactions of Fe 2+/3+ with O 2 in the catholyte and an RM with iron metal in the anolyte, respectively.…”

“…Consequently, the capacity for energy storage and conversion is essentially limited by the electrode compartment volume and the degradation and passivation of the electrode during operation. [ 5 ] The concept of redox targeting (RT) of energy storage materials offers a feasible solution to address the above issues by employing redox mediators (RMs) dissolved in the electrolyte. [ 6 ]…”

Phenomenological observations of quinone-mediated zinc oxidation in an alkaline environment

“…In a device analogue to a metal-air battery, a redox-mediated approach was previously explored within our group, where soluble redox species discharge a metallic zinc anode in a separate compartment (tank), resulting in a system where the capacity of the anodic half-cell could be mechanically increased by replacing the zinc metal in the external tank. 5 This system used water-soluble quinone derivatives commonly employed as charge-storage materials in conventional RFBs 6,7 , due to their standard redox potentials which are controllable through molecular engineering and sufficiently disparate from the zinc substrate as to induce a reaction. Zinc anodes are an ideal chemistry to explore for redox-mediated processes, as they are ubiquitous in primary alkaline "dry-cells", providing a well-developed research area from which to draw information.…”

“…To serve as redox-mediators, we explored several quinone derivatives as candidates, identical to the prior work. 5 A discussion of cell performance for these molecules in similar operating circumstances can be found elsewhere. [5][6][7] We elected to use an alkaline electrolyte (1 M KOH), in common with primary zinc batteries, and in which these quinone derivatives are soluble and kinetically facile.…”

“…5 A discussion of cell performance for these molecules in similar operating circumstances can be found elsewhere. [5][6][7] We elected to use an alkaline electrolyte (1 M KOH), in common with primary zinc batteries, and in which these quinone derivatives are soluble and kinetically facile. All selected mediators are believed to undergo 2-electron reduction reactions, 9 resulting in soluble and moderately stable dianion species which appear chemically reversible on inert electrodes (e.g., platinum).…”