The γ-MnO₂ electrode: the electrochemical de-insertion of the (H⁺, e^–) couple from the partly reduced grain

Abstract

A considerable understanding of the re-oxidation properties of partly reduced γ-MnO₂ is gained through simple phenomenological analysis of the experimental results and exploitation of the advances in the science of carrier injection in semiconductors. It is essentially demonstrated that the de-insertion reaction is still possible if the free or untrapped charges (H⁺, e^–) in the bulk of the host material remain the majority carriers. In contrast, in the existence zone (r _d>0.80) of δ-MnOOH the trapped particles become the majority (the free ones become minority) carriers and the flux may be stopped or gives rise to further types of reaction (complex formation, oxygen regeneration, etc.). Besides being of interest in themselves, these results are useful in studying the properties of electrode materials or semiconductors in which they occur.