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

Oxygen reduction electrodes for zinc–air batteries (ZAB) have been prepared by depositing conformal films of MnOx directly onto high surface area gas diffusion layers (GDL) via atomic layer deposition (ALD). MnOx films were prepared by means of two deposition conditions: one using a forming gas (95% N2, 5% H2) plasma (FG-MnOx) and one using an O2 plasma (O2-MnOx). A composite electrode of FG-MnOx + CoOx was also examined. The conformal nature of ALD films allowed for MnOx to be deposited within the porosity of the GDL, as confirmed by X-ray microanalysis. Full cell ZAB tests showed excellent performance for MnOx-coated electrodes, outperforming Pt/Ru–C at current densities larger than 100 mA cm–2. Annealed FG-MnOx and O2-MnOx 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-MnOx + CoOx 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-MnOx + CoOx had initial and final discharge potentials of 1.18 and 1.15 V, respectively.