Manganese oxide, proton conduction

CNTs were also demonstrated to be a perfect support for cheap transition metal oxides of poor electrical conductivity, such as amorphous manganese oxide (a-Mn02 H20) [5,96], The pseudocapacitance properties of hydrous oxides are attributed to the redox exchange of protons and/or cations with the electrolyte as in Equation 8.13 for a-Mn02 H20 [97] ... 

This paper describes the catalytic activity of various forms of manganese dioxides towards volatile organic compounds deep oxidation. Important differences in activity are evidenced for very closely related structures the most active sample is a high surface area nsutite. A parallel is drawn between the findings in the literature of battery applications and the catalytic activity results. The superior activity of nsutite is attributed to a different oxygen coordination and to the clustering of cationic vacancies in the bulk which improves electronic and protonic conductivity. 

To conclude, the comparison of the activity of manganese dioxides of different structures shows that very similar oxides can nevertheless exhibit quite different catalytic properties. As far as manganese dioxides are concerned, the changes in the catalytic activity from one oxide to another must be attributed to the difference in coordination for the oxygen anion and to the presence of (clustered) anionic vacancies which modifies the electronic and protonic conductivity of these oxides. 

The number of studies which utilize ionic liquid electrol54e in redox capacitor system is still small, probably due to the difficulty to reproduce the pseudo-capacitive reaction in ionic liquid media. While the principle of pseudo-capacitance of conductive polymer electrodes permits to utilize ionic liquid electrolytes, high viscosity and rather inactive ions of ionic liquid may make their pseudo-capacitive reaction slow. The combination of nanostmctured conductive polymer electrode and ionic liquid electrolyte is expected to be effective [27]. It is far difficult that ionic liquids are utilized in transition metal-based redox capacitors where proton frequently participates in the reaction mechanisms. Some anions such as thiocyanate have been reported to provide pseudo-capacitance of manganese oxide [28]. The pseudo-capacitance of hydrous ruthenium oxide is based on the adsorption of proton on the electrode surface and thus requires proton in electrolyte. Therefore ionic liquids having proton have been attempted to be utilized with ruthenium oxide electrode [29]. Recent report that 1,3-substituted imidazolium cations such as EMI promote pseudo-capacitive reaction of mthenium oxide is interesting on the viewpoint of the establishment of the pseudo-capacitive system based on chemical nature of ionic liquids [30]. 

Many of the important chemical reactions controlling arsenic partitioning between solid and liquid phases in aquifers occur at particle-water interfaces. Several spectroscopic methods exist to monitor the electronic, vibrational, and other properties of atoms or molecules localized in the interfacial region. These methods provide information on valence, local coordination, protonation, and other properties that is difficult to obtain by other means. This chapter synthesizes recent infrared, x-ray photoelectron, and x-ray absorption spectroscopic studies of arsenic speciation in natural and synthetic solid phases. The local coordination of arsenic in sulfide minerals, in arsenate and arsenite precipitates, in secondary sulfates and carbonates, adsorbed on iron, manganese, and aluminium hydrous oxides, and adsorbed on aluminosilicate clay minerals is summarized. The chapter concludes with a discussion of the implications of these studies (conducted primarily in model systems) for arsenic speciation in aquifer sediments. 

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