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 KOCOCH 3 and Mn(OCOCH 3 ) 2 on a platinum substrate, followed by heating at 1073 K. The chemical composition of the electrode was K x MnO y ( x = 0.33 and y ∼ 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 Mn 3+ and Mn 4+ ) 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.