Electrochemical Intercalation of Alkali-Metal Ions into Birnessite-Type Manganese Oxide in Aqueous Solution

Abstract

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 ∼ 2) with an interlayer spacing of c0 = 0.697 nm. The positive-potential going sweep on the electrode in an aqueous phase caused the deintercalation of K+ with an increase in c0. The quasi-reversible intercalation of K+ occurred with a subsequent negative-potential going sweep in a 0.2 mol/dm3 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 ∼ K > Li > Rb > Cs.