Spectroelectrochemical investigations of cation-insertion reactions at sol-gel-derived nanostructured, mesoporous thin films of manganese oxide

Sol-gel-derived manganese oxide can readily be prepared as highly porous, n anostructured materials, including ambigel or aerogel monoliths and thin fi lms supported on conductive, transparent glass. The electrochromic properti es of manganese oxide, a mixed electron-cation conductor, provide an indepe ndent measure of the electronic state of the manganese in the oxide during the electrochemically driven cation-insertion process. Sol-gel-derived thin films of birnessite-type manganese oxide, NadeltaMnO2. xH(2)O, which is a layered polymorph of MnO2, were characterized by spectroelectrochemistry. D uring nonaqueous electroinsertion reactions of Li+, Mg2+, and tetrabutylamm onium cation, the spectral and electrochemical signatures are temporally di stinguished and electrochemical site specificity can also be discerned. The rate of coloration of the oxide (recovery of the Mn(IV) state) is approxim ately 4-fold more rapid than the rate of decoloration as Mn(III) centers ar e electrogenerated and electrolyte-derived cations are concomitantly insert ed. The electrochromic efficiency for Li+ insertion into thin films of birn essite-type manganese oxides is 36 cm(2) C-1.