Electrolytic oxygen evolution in alkaline medium on La/sub 1-x/Sr/sub x/FeO/sub 3-y/ perovskite-related ferrites. I. Electrochemical study

Oxygen evolution by electrolysis of aqueous solutions has been studied on nonstoichiometric perovskite-related ferrites of composition La/sub 1-x/Sr/sub x/Fe/sub 1-tau//sup 3+/Fe/sub tau//sup 4+/O/sub 3-y/(O < chi ≤0.95). Electrochemical measurements have been carried out according to a methodology previously proposed for ceramic-type materials. The physical chemical and geometrical parameters are preliminary fixed. A maximum of the electrocatalytic activity appears for chi ≅ 0.90, which also corresponds to the highest value of Fe/sup 4+/ ratio (tau = 0.68). Two Tafel regions have been observed and kinetic parameters show that: at low potential the acid-base reaction M(OH)/sub ads/ + OH/sup -/ → M(O/sup -//sub ads/ + H/sub 2/O is rate determining whereas at high potential it is the first electron transfer M(OH/sup -//sub ads/ → M(OH)/sub ads/ + e/sup -/. This change with potential implied that the transport properties of the materials play a decisive role in the reaction mechanism