AC impedance analysis of bifunctional air electrodes for metal-air batteries

The activity and stability of bifunctional air electrodes for electrically rechargeable metal air batteries were investigated using ac impedance spectroscopy The poly(tetrafluoroethylene) bonded electrodes consisted of a perovskite-type catalyst (La0.6Ca0.4CoO3) dispersed on high surface area carbon (Ketjen black) or on graphitized carbon (Vulcan XC 72). The impedance spectra were analyzed using an equivalent circuit contaning two finite diffusion terms. The diffusing species were shown to be oxygen dissolved in the electrolyte solution and the peroxide ion generated at the electrode by the electrochemical reaction. The electrode deterioration occurring during anodic oxygen evolution was also studied using impedance analysis. The degradation, mainly carbon corrosion, resulted in a loss of electrochemically active surface area of the electrode. High catalyst loadings improved the electrode stability. The electrode characteristics are discussed using the electrochemical parameters obtained From the impedance spectra analysis. (C) 2000 The Electrochemical Society. S0013-4651(99)06-071-1. All rights reserved.