Electrochemical intercalation of alkali-metal ions into birnessite-type manganese oxide in aqueous solution

A thin layer electrode of birnessite-type manganese oxide was prepared by brushing a mixed solution of KOCOCH3 and Mn(OCOCH3)(2) on a platinum substrate, followed by heating at 1073 K. The chemical composition of the electrode was KxMnOy (x = 0.33 and y similar to 2) with an interlayer spacing of c(0) = 0.697 nm. The positive-potential going sweep on the electrode in an aqueous phase caused the deintercalation of K+ with an increase in c(0). The quasi-reversible intercalation of K+ occurred with a subsequent negative-potential going sweep in a 0.2 mol/dm(3) KCl solution. The electrochemical measurements suggested that K+ is not electrochemically active in the deintercalation/intercalation reaction but H+ is. The reaction proceeds based on a mechanism consisting of an electrochemical reaction (the redox reaction between Mn3+ and Mn4+) and an ion-exchange reaction between K+ and H+. The intercalation experiments in various alkali-metal chloride solutions showed the intercalation capacity to be in the order of Na similar to K > Li > Rb > Cs.