Metal-air batteries store more energy per mass (specific energy) and per volume (energy density) than Li-ion batteries, but the rates of oxygen reduction and oxidation at metal anodes impede metal-air batteries from delivering energy quickly enough for power-hungry devices. We hypothesize that the specific power of metal-air batteries, as a class, would increase if the electrochemically accessible interfacial areas of metal anodes were greatly enlarged by supporting the redox-active metal component on nanostructured, porous current collectors. In such a design, a greater percentage of a metal's atoms would be expressed on an electrode's surface and would be simultaneously accessible to a liquid electrolyte that transports ions through a continuous pore network that is coupled with electronically conductive pore walls. We report a method to prepare sheets of carbon nanofoams that comprise a nanostructured carbon skeleton and micron-sized macropores within a bed of interleaved carbon fibers. A uniform coating of FeOx deposits from dilute K2FeO4 solution throughout the porous solid onto the pore walls of carbon nanofoams, and this rust coating can be electrochemically converted into iron metal. We demonstrate that these electrodes reversibly discharge and charge over several cycles, and that dilute additions of K2S to the electrolyte solution reduces the rate that the capacity fades upon cycling. In our study, iron-coated carbon nanofoams discharged more energy than similarly prepared, but nonporous electrode analogues at current densities between 0.01 � 1 mA cm-2.

Carbon nanofoams as porous scaffolds for iron-air battery electrodes

247th National Meeting (2014)

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