Durability of Bilayer Bifunctional Air Electrodes Analyzed by Impedance Spectroscopy

The degradation behavior of bifunctional air electrodes featuring with a bilayer design with an oxygen reduction reaction (ORR) catalytic layer and an oxygen evolution reaction (OER) catalytic layer was investigated using electrochemical impedance spectroscopy (EIS). The impedance spectra were analyzed using an equivalent circuit model incorporating two finite diffusion terms: resistance to ionic diffusion and resistance to oxygen diffusion. The bilayer electrode demonstrated excellent stability for over 100 hours at ambient temperature, even when subjected to severe anodic treatment at 200 mA cm−2. However, analysis of the EIS signals revealed that oxygen diffusion progressively emerged as the limiting factor as the testing time was prolonged. The degradation analysis of the bilayer electrodes yields critical insights and actionable recommendations for subsequent electrode optimization and design improvements.