Influence of CO2 on the stability of bifunctional oxygen electrodes for rechargeable zinc/air batteries and study of different CO2 filter materials

Abstract

The stability of bifunctional oxygen electrodes used in electrically rechargeable zinc/air batteries was investigated as a function of the CO₂ concentration in the feed gas. Using pure oxygen as feed gas, the oxygen evolving electrode was life limiting being stable up to 2500 h. However, by increasing the CO₂-concentration in synthetic air up to 10000 ppm, the life limiting electrode is changed to the oxygen reducing electrode and the lifetime is reduced due to poisoning by carbonate precipitation inside the pores of the gas diffusion electrode. Furthermore, the CO₂ filtering efficiency of several alkaline filter materials has been tested. It has been found that the filter capacity was strongly dependent on the humidity ratio of the feed gas. 9.2 g of LiOH–Ca(OH)₂ mixture were able to filter 2500 l ambient air (90% RH, 409 ppm CO₂) with a rest concentration of less than 20 ppm.