https://nova.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:651 5 M), where alpha-MnO2 is formed, and high temperatures (>80degreesC) where beta-MnO2 is formed. The structural variety of gamma-MnO2 in this domain of stability is interpreted in terms of: (i) the fraction of De Wolff defects (P,), which is found to increase as the H2SO4 concentration is decreased and the temperature is increased; (ii) microtwinning (T-w), which despite being less statistically significant, is found to follow a similar trend; (iii) the cation vacancy fraction; (iv) the Mn(III) fraction. Both the latter structural properties decrease as the temperature is increased; but decreasing the H2SO4 concentration leads to a decrease in cation vacancy fraction and an increase in Mn(III) fraction. These structural characteristics, in particular the De Wolff defects, are interpreted on a molecular level in terms of soluble Mn(III) intermediate condensation, in which the electrolyte conditions determine the relative proportions of equatorial-axial edge sharing (ramsdellite domains only), and equatorial-axial corner sharing (both ramsdellite and pyrolusite domains) that occurs. Morphological differentiation is easily established due to the different characteristics of each phase. gamma-MnO2 exists as fine needles (250 nm x 50 nm), beta-MnO2 is formed as much larger columns (1 mum x 100 nm), while alpha-MnO2 is present as small spheres of up to 400 nm in diameter. Electrochemical characterization by voltammetry in an aqueous 9 M KOH electrolyte demonstrates that the performance of gamma-MnO2 Samples is comparable with that of commercial EMD, whereas alpha- and beta-MnO2 suffer from diffusional limitations which lower their operating voltage. For gamma-MnO2, superior performance results when lower temperatures and H2SO4 concentrations are used. This corresponds to intermediate levels of De Wolff defects and microtwinning, and to a cation vacancy fraction minimum.]]> Thu 25 Jul 2013 09:10:27 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:26580 2·g^-1) with a hierarchical macro-meso-micro-pore structure and oxygen-enriched surface. The electrochemical performances of the ACs as electrode materials for electrochemical capacitors (ECs) were assessed by galvanostatic charge-discharge, cyclic voltammetry and cycling durability tests. It was demonstrated that the mesoporous ACs produced in this study possessed a maximum specific capacitance of 355F·g^-1 and 196F·g^-1 in 3M KOH aqueous and 1M (C₂H₅)₄NBF₄/PC organic electrolytes, respectively, at a current density of 50mA·g^-1, and exhibited a desirable energy and power density with a superior cycling performance. The excellent capacitive behavior of the prepared mesoporous ACs in aqueous system is attributed to their unique macro-meso-micro-hierarchical pore structure with high surface area and oxygen-containing surface. Their superb electrochemical performance in the organic electrolyte is attributed to their well-developed mesoporous structure.]]> Sat 24 Mar 2018 07:26:12 AEDT ]]>