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A piece of commercially-available carbon cloth (CC) was treated using a simple wet method and then served as a substrate for the direct growth of MnO2 via an electrochemical process. The treated CC electrode allowed the deposition of a large amount of MnO2 while maintaining its electrochemical utilization efficiency. The optimal mass loading of MnO2 was determined to be 4.27 mg cm-2, a level that gave an areal capacitance of 568 mF cm-2 at a scan rate of 2 mV s-1. This MnO2/CC piece was employed in conjunction with an activated carbon-coated CC section as the positive and negative electrodes, respectively, in a solid-state asymmetric supercapacitor.

Multilayered manganese dioxide film intercalated with surfactant molecules was synthesized by anodic oxidation of aqueous Mn(II) ions in the presence of cetyltrimethylammonium (CTA) ions. Ion-exchange and electrochemical properties of the CTA/MnO2 nanocomposite were examined in different electrolytes (Na2SO4, sodium dodecylsulfate (NaDS), sodium benzenesulfonate (NaBS), and dodecyltrimethylammonium chloride. CTA+ cations that were incorporated between MnO2 layers during electrodeposition were not ion-exchanged with Na+ in solution, probably as a result of hydrophobic interaction between their long alkyl chains. According to XPS analysis, cationic head groups of the surfactants were coupled with not only negative charges on MnO2 layers but also Cl- anions. These Cl- anions were readily replaced with SO4 2- and BS-, which means installation of anion exchange sites in the interlayer. Only in NaBS electrolyte, the CTA/MnO2 film provided a good electrochemical response without releasing the CTA+ ions, where the electroneutrality of the film was maintained by Na+ ions.

We have fabricated birnessite-type layered manganese oxide bycathodic reduction of aqueous permanganate ions (MnO4-) in thepresence of various alkaline metals. The electrodeposition andcharge storage processes were monitored by means ofelectrochemical quartz crystal microbalance (EQCM). Molarmasses acquired for the electrodeposition process revealed thatMnO2 grows concurrently with the incorporation of the coexistingcations and water molecules. The molar mass decreases in theorder of Li > Rb ~ K ~ Cs > Na, which is in good agreement withthe order of crystallinity. Clearly, the degree of crystallinity in theformation of birnessite depends on the incorporation amount of theguest ions and water. The birnessite-modified electrode increasesand decreases in mass during cathodic and anodic scans in Na2SO4electrolyte. The molar masses obtained were 21.6 and 24.9 g permole of electrons, respectively, both of which coincide with theatomic weight of Na (23.0 g).

Multilayered manganese dioxide (MnO2) film intercalated with tris(2,2-bypyridine)ruthenium(II) ([Ru(bpy)3]2+) was synthesized by a one-step electrochemical method. The obtained film was characterized by FTIR, XRD, SEM and TEM techniques. FTIR and XRD measurements revealed that [Ru(bpy)3] ions are intercalated in the interlayer between MnO2 layers and exist as a two-layer form. After immersion in water, the two-layer form was changed into the one-layer. Electrochemistry of the resulting films in Na2SO4 solution indicated an electron transfer from/to the underlying Pt substrate to/from the incorporated complexes through the MnO2 sheets. At this situation, [Ru(bpy)3] ions were extracted to maintain the charge neutrality of the film.

Cathodic reduction of an aqueous solution of potassium permanganate in the presence of various alkaline metals except for Na+ ions led to a deposition of birnessite-type layered MnO2. Thehighest crystallinity was achieved in a bath containing 2 mMK MnO4 and 50 mM KCl by applying a constant potential of 0 V vs Ag/AgCl. The cathodic formation of birnessite was prevented by the presence of divalent cations, and Na+ ions yielded an amorphous or low crystalline product. The birnessite film thus formed showed excellent pseudocapacitive characteristics in its as-deposited state; i.e., a specific capacitance as high as 322 F g-1 at a potential scan rate of 2 mV s-1, which is much higher than that (75F g-1) of the birnessite film prepared anodically from Mn2+ ions.

Chemical processes occurring in the vapor deposition of silicon from a mixture of bromosilanes (SiHBr3:SiBr4 = 1:4) with hydrogen gas have been monitored by means of online gas chromatography, and the obtained deposits were characterized by XRD, SEM, and EDX techniques. The deposition of silicon occurred at 900 ºC, accompanied by the larger consumption of SiBr4 than SiHBr3. The numerous rugged rod-like deposits of poly-silicon were grown appearing the crystal diffractions of (111), (220), (311), and (331) planes. The diameter of deposits mainly ranged from 2 to 4 um and their lengths extended to about 10 um.

Buserite-type layered manganese oxide was prepared on Pt substrate by anodic deposition of birnessite intercalated with tetrabutyl ammonium cations and the following ion-exchange with Ni2+ ions. The resulting Ni-intercalated buserite was subjected to repetitive potential steps between +0.8 and 0.0 V in an Na2SO4 aqueous electrolyte. During the repetitive steps, the electrochemical activity of the film was enhanced drastically with increasing the step number and interval. This behavior was accompanied by an irreversible morphological transformation of the MnO2 film. The structure thus formed exhibited a specific capacitance of 225 F g-1 at a scan rate of 2 mV s-1 in Na2SO4 electrolyte. Furthermore, we fabricated a hybrid cell based on the optimized MnO2 film and activated carbon as the positive and negative electrodes, respectively. It can be cycled reversibly in the voltage region of 0.0 to +1.8 V and exhibits an energy density of 1.1 Wh kg-1.

Anodic deposition of layered manganese oxides has been carried out at various bath temperatures in the presence of cobalt ions. Crystallinity of the layered Mn oxide increased with increasing the bath temperature. In the deposition of the layered Mn oxide, Co2+ ions were not involved at room temperature, while at 70°C the presence of Co2+ exhibited a catalytic current suggesting the formation of Mn and Co composite. Addition of Co2+ did not provide any new diffraction peaks but caused broadening of the peaks due to Mn oxide. This indicates the introduction of Co ions into the Mn oxide sheets. Doping of Co into the Mn oxide framework caused a drastic increase in the specific capacitance.

Various metal ions (Na+, Ca2+, Co2+, Ni2+, and Pb2+) were intercalated between the manganese oxide layers grown anodically on a Pt substrate. The films were subjected to a repetitive charge-discharge cycle test in an aqueous electrolyte of Na2SO4 between 0 and +0.8 V (vs Ag/AgCl). When the number of cycles increased, remarkably increased capacitances due to pseudocapacitance were observed for the manganese oxide films intercalated with Co2+, Ni2+, and Pb2+, accompanying drastic morphology changes where the multilayers lying parallel to the substrate before cycling were aligned vertically.

Potentiostatic electrolysis of a mixed aqueous solution of Bu4NBr (Bu = C4H9) and MnSO4 at +1.0 V (vs Ag/AgCl) on Pt electrode resulted in the oxidation of Br- and Mn2+ ions, which was followed by the deposition of insulating crystals of bromide salt of Bu4N+ and the subsequent formation of layered manganese oxide in the interstitial spaces of the bromide grains already grown. Dissolution of the bromide crystals with water left a well-dispersed porous texture composed of manganese oxide nanosheets.

Birnessite-type layered manganese dioxide (MnO2) films intercalated with Li+, Na+ or Mg2+ ions were synthesized by a one-step electrochemical route. The oxide films were electrodeposited by applying a constant potential of 1.0 V vs. Ag/AgCl from aqueous Mn2+ solutions containing perchlorate salts of the cations. The galvanostatic charge/discharge experiments performed in 1 M LiPF6-DME/PC solution indicated that the Mg2+-containing MnO2 electrode exhibits a discharge capacity as large as 140 mAh g-1 and a better cyclability as compared with Li+- and Na+-containing MnO2 electrodes.