Thin films of birnessite-type layered manganese oxides with various interlayer spacings have been prepared on a platinum electrode by a one-step electrochemical procedure. The process involves a potentiostatic oxidation of aqueous Mn(2+) ions at around +1.0 V (Ag/AgCl) in the presence of tetraalkylammonium cations with different alkyl chain lengths. X-ray diffraction indicates that the films deposited with tetrabutylammonium (TBA), tetrapropylammonium (TPA), and tetraethylammonium (TEA) ions are composed of a single phase where unhydrated tetraalkylammonium ions are accommodated as a monolayer between manganese oxide layers. The interlayer spacing of the products increases in an order of TEA < TPA < TBA. The film deposited with tetramethylammonium (TMA) is a mixture of two phases relating to hydrated and unhydrated guest cations, the former being predominant probably as a result of less hydrophobic property of TMA compared to that of other tetraalkylammonium ions. The TBA(+)-intercalated Mn oxide film-coated electrode exhibits a good charge/discharge property in a KCl solution between 0 and +0.8 V. In this case, TBA(+) ions between the Mn oxide layers are rapidly replaced with K(+) in solution by ion exchange, accompanying a shrinkage of the interlayer. The incorporated K(+) ions as well as protons play an important role in the electrochemical conversion between Mn(4+) and Mn(3+) in the oxide layer. In the TBACl solution, the interlayer TBA(+) ions can be excluded electrochemically during the positive-going scan, concomitant with the oxidation of Mn(3+) sites. This causes an anodic current and the accompanying shrinkage of the interlayer. On the reverse scan, however, the compressed interlayer does not allow the incorporation of bulky TBA(+) ions from the electrolyte, with virtually no cathodic current observed. Such an obvious difference in electrochemical behavior between the two electrolytes can be recognized by considering that most of the Mn oxide surface is present inside the layered structure, not on the external surface. This indicates that the layered structure is formed over the entire film.

Thin films of layered manganese oxides with alkylammonium and alkali-metal ions in the interlayer were formed on a platinum electrode by a one-step electrochemical route. The interlayer distance was determined by the size of the electrolyte cations used.

A layered nanocomposite with poly(diallyldimethylammonium), PDDA, intercalated between manganese oxide layers can be formed on a platinum electrode in a thin film form through a direct electrochemical route. The process involves a potentiostatic oxidation of aqueous Mn(2+) precursors in the presence of PDDA by applying a constant potential (+1.0 V vs Ag/AgCl).

Multilayered manganese oxide films were prepared on a platinum electrode by potentiostatic oxidation of aqueous Mn2+ ions in the presence of n-tetra-alkylammonium compounds. Alkylammonium cations were intercalated between manganese oxide layers to balance the negative layer charge. Effects of several preparative parameters such as the size of alkylammonium molecules, counteranions, and bath composition on the structure of products were investigated. The interlayer distance of the products increased with increasing alkyl chain length up to C4, and the change became obviously small among C4–C6 compounds. The multilayer formation was achieved only when the manganese concentration was lower than 10 mM, and the highest crystallinity was obtained from a bath composed of 2 mM manganese sulfate and 50 mM alkylammonium chloride. At low concentrations of alkylammonium (<10 mM), a product intercalated with hydrated protons was formed, in which the protons were generated by anodic oxidation of Mn2+ with H2O.

Thin films of mixed manganese (mainly 4+) and vanadium (5+) oxides deposited electrochemically on a platinum substrate have been heat-treated under vacuum at various temperatures between 25 and 400°C. Electron spin resonance and x-ray photoelectron spectroscopy revealed that the reductive formation of Mn 2+ occurs at 300°C only in the presence of vanadium within the film. This phenomenon can be regarded as a result of electron transfer from V 4+ ions generated thermally to neighboring Mn sites. Voltammetric response of the heat-treated Mn/V oxide film in borate solution was enhanced with increasing the number of potential cycles, and the steady-state current was much larger than that of pure manganese oxide. Vanadate ions were diffused from the film to maintain the charge balance during the repetition cycles. The resultant porous structure can allow easier mass transport of protons to electrically conductive Mn oxide surface, offering the improved charge-discharge performance of the electrode. II. EXPERIMENTALAll chemicals were of reagent grade (Wako Pure Chemicals, Osaka, Japan) and used as received. All