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.