Bringing rechargeable metal�air batteries to practical fruition intersects all of the challenges inherent to fuel cells, electrolyzers, and batteries. For energy stored in the metal anode to be released (battery function), oxygen must be catalytically reduced at a porous air cathode (fuel-cell function); for the battery to be recharged, oxygen must be catalytically regenerated from the products of metal oxidation (electrolyzer function). Redesigning the air cathode via an architectural, nanoscopic, and three-dimensional (3D) perspective has brought technologically relevant O2-reduction activity to carbon nanofoam paper derived from nanoscopic coatings of manganese oxide (~10-nm thick MnOx) at the carbon walls plus a new function difficult to achieve in metal�air cells: pulse power from the pseudocapacitance of the oxide paint. Converting standard Zn powder composite anodes to a 3D form factor (we use the aperiodic sponge) ensures that an inner core of Zn remains at all times to facilitate long-range electronic conductivity throughout charge/discharge and provide more uniform current distribution. Such Zn sponges can be charged and discharged without generating the dendrites that can direct short metal-based batteries. The final piece of the puzzle lies in bringing a third functionality to the air cathode (in addition to O2-reduction catalysis and pseudocapacitive pulse power): O2-evolution catalysis. Our efforts on this final, but critical, step to create fully rechargeable Zn�air cells will be described.

Metal�air batteries: Architecturally rewriting energy storage as enabled by catalyzing energy conversion reactions

246th National Meeting (2013)

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