High Performance Oxygen Reduction/Evolution Electrodes for Zinc–Air Batteries Prepared by Atomic Layer Deposition of MnOx

Oxygen reduction electrodes for zinc–air batteries (ZAB) have been prepared by depositing conformal films of MnO x directly onto high surface area gas diffusion layers (GDL) via atomic layer deposition (ALD). MnO x films were prepared by means of two deposition conditions: one using a forming gas (95% N 2, 5% H 2 ) plasma (FG-MnO x ) and one using an O 2 plasma (O 2 -MnO x ). A composite electrode of FG-MnO x + CoO x was also examined. The conformal nature of ALD films allowed for MnO x to be deposited within the porosity of the GDL, as confirmed by X-ray microanalysis. Full cell ZAB tests showed excellent performance for MnO x -coated electrodes, outperforming Pt/Ru–C at current densities larger than 100 mA cm –2 . Annealed FG-MnO x and O 2 -MnO x electrodes had maximum power densities of 170 and 184 mW cm –2, respectively. With the catalyst distributed within the structure of the GDL, performance limitations associated with electrolyte flooding and air diffusion are reduced, improving discharge potential and cycling behavior. FG-MnO x + CoO x electrodes showed good cycling stability, both in a trielectrode configuration and bifunctionally. When cycled at 20 mA cm –2 for 100 h (200 cycles), FG-MnO x + CoO x had initial and final discharge potentials of 1.18 and 1.15 V, respectively.