Redox-Mediated Metal-Air Fuel Cells

Electrochemical energy conversion and storage technologies have been pivotal in propelling global sustainable development. However, traditional electrochemical processes which are centered on intricate "electrode-electrolyte interface" confront substantial challenges when applied to emerging large-scale applications with open systems and distributed resources, for which the system generally involves evolving interfaces with the formation of new phases or requires the supply of feedstock and removal of products. This is especially the case for metal-air battery systems. Metal-air batteries present an alternative approach to achieving high power generation. Besides considerably higher volumetric energy density, the storage and transportation of solid fuels in metal-air systems are more practical compared to that of hydrogen fuel cells. However, metal-air systems face formidable challenges from both the metal and air electrodes, regardless of electrolyte conditions. The redox-mediated approach offers an elegant solution by directing the oxygen reaction from the cell compartment to a separate reactor tank. This approach has been exemplified in Li/Zn/Fe-air battery chemistries, showing the feasibility of loading solid fuels in external tank, which greatly facilitates the refueling process. While the concept has been successfully demonstrated, the development of viable devices necessitates systematic studies on the materials aspects (redox mediators, membranes, and catalysts) and engineering optimizations.