Synthesis and electrochemical properties of mesostructured 12-phosphotungstic acid thin films with hierarchical structur
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Synthesis and electrochemical properties of mesostructured 12-phosphotungstic acid thin films with hierarchical structures by triblock copolymer templating a
Hui-suk Yun, a Makoto Kuwabara, b Haoshen Zhou, b Itaru Honma*
a
Department of Materials Science, Graduate School of Engineering, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan b National Institute of Advanced Industrial Science and Technology(AIST), Tsukuba Central 2, Energy Electronics Institute, 1-1-1, Umezono, Tsukuba, Ibaraki, 305-8568, Japan, *E-mail: [email protected]
ABSTRACT Hexagonally mesostructured 12-phosphotungstic acid (PWA) thin films with both large pore size and hierarchical structures have been successfully prepared by using triblock copolymer templates for the first time. The films is composed by three kind of structures; PWA Keggin anion, monoclinic crystal structure consisting of PWA Keggin anion and organic part (hydrophilic component) of block copolymers, and the hexagonal mesostructure of self-arrayed PWA and block copolymers. The calcined PWA films show better electrochemical properties such as a faster faradic processes and larger specific capacity than normal PWA clusters.
INTRODUCTION Heteropoly oxometalates (designated HPOM) have been numerously studied in various research area since Berzelius described ammonium 12-molybdophosphate in 1826.[1] Thereafter the field developed rapidly and the wide applicable points were summarized by several reviews.[2-4] The applications of HPOM are centered primarily on their redox properties, photochemical response, ion charge, and conductivity. Nevertheless, general HPOM have very low surface area and this presents the major obstacle to applications.[5] Very recently, several research groups have tried to prepare mesoporous HPOM for improving efficiency of HPOM and they have succeeded to obtain mesostructural H2W12O40/surfactant composite materials.[6-8] However, almost all HPOM mesostructure were collapsed by removing the templates, and consequently those surface areas were very small (10m2·g-1). Moreover, the mesostructure of the reported HPOM was only powdery materials and the pseudo-crystal of polyanions composed by cation surfactant and anion HPOM although the control of materials states as a film is necessary to maximize the utility of HPOM in electrode and sensor devices.[9] Whereas, we have successfully synthesized mesostructured various HPOM as thin film state. The mesostructure can be adjusted to various mesophase by controlling block copolymer architecture. Here we report the structural properties of firstly synthesized mesostructured 12-phosphotungstic acid films having hierarchical structures. The electrochemical properties of calcined 12-phosphotungstic acid film as electrode materials in Li-ion batteries have been
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also studied. Mesoporous HPOM provide the high specific capacity and the fast faradic process supposedly due to their unique structural properties such as the large surface area, thin framework structure and the continuous pore
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