Long-Term Operation of Perovskite-Catalyzed Bifunctional Air Electrodes in Rechargeable Zinc-Air Flow Batteries

Abstract

Rechargeable zinc-air flow batteries are investigated as promising stationary energy storage system due to compact system design and low cost materials. Bifunctional air electrodes employing a La0.6Sr0.4Co0.2Fe0.8O3 perovskite catalyst for O2-reduction and O2-evolution are manufactured in small scale (4 cm2) and in up-scaled sizes (50–55 cm2) and tested in unit cell configuration with flowing electrolyte. Stable operation of 1000 h is achieved in the small set-up with an overall 1800 h of operation over 700 cycles at high voltage efficiencies of >50 % (air electrode) at 50 mA cm−2. The up-scaled flow cell reaches nearly the same performance for 320 h and 130 h, respectively, proving the successful scale-up. Slowly decreasing hydrophobicity is found to be the main reason of initially increasing but then decreasing performance. This is confirmed by electrochemical impedance spectroscopy. Although many problems are suppressed with flowing electrolyte, zinc morphology proves to be the major challenge especially in larger cells in long-term operation of a few hundred hours.