Carbon-air electrode with regenerative short time overload capacity: Part 1. Effect of manganese dioxide

Abstract

To increase the overload capacity of the carbon-air electrode in alkaline electrolyte, without seriously changing the electrode potential during short-time overload periods, small amounts of MnO₂ were added to carbon and the effects investigated. The potentiodynamic investigations revealed the existence of two reducible manganese species with reduction potentials of about −280 mV and −400 mV. The second potential corresponds to the known reduction process Mn(III) → Mn(II) whilst the first one corresponds to a reversible process (the product is easily reoxidized by air or anodically), not reported in literature as yet. It was explained in terms of a new redox potential for the system Mn(III)/Mn(II), both species being strongly and irreversibly adsorbed at the carbon surface. The galvanostatic discharge curves in the absence of air indicate that a sufficient overload capacity of about 40 C cm⁻² is available if 22% (wt) MnO₂ is added. Steady-state polarization curves in the presence of air indicate the catalytic effect of small amounts of MnO₂ for the oxygen reduction reaction.