Journal of the Electrochemical Society vol:158 issue:1 pages:A14-A21
Hybrid materials based heteropolyacids, silicotungstic acid (H4SiW12O40 center dot nH(2)O) or phosphomolybdic acid (H3PMo12O40 center dot nH(2)O), and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM] [BF4]) were synthesized. Carbon analysis showed that 1 mol of [SiW12O40](4-) reacts with 4 mol of [BMIM](+) and 1 mol of [PMo12O40](3-) reacts with 3 mol of [BMIM](+). Fourier transform infrared spectra showed the presence of both 1-butyl-3-methylimidazolium cations and the Keggin anion. Cyclic voltammetry illustrated that the reduction peak potentials of the Keggin anion in the hybrid materials shift toward negative values. The hybrid materials can be suspended in ultrapure water to form true suspensions. Alternating current electrophoretic deposition was used to obtain thick homogeneous films of the hybrid materials in few minutes over stainless steel (SS) wires from aqueous suspensions at 30 Hz and 200 Vp-p. [BMIM](4)SiW12O40/SS and [BMIM](3)PMo12O40/SS previously treated at 370 degrees C for 15 min were subjected to cyclic voltammetry and galvanostatic charge-discharge cycling in 0.5 M Na2SO4 (pH 7) and observed to exhibit capacitance behavior between 0 and -0.6 V vs AgCl/Ag. In 0.5 M Na2SO4 (pH 7) and in this range of potentials, the hybrid [BMIM](4)SiW12O40 material had an ideal behavior with a stable specific capacitance close to 172 F g(-1) and good cyclability at 7 mA/cm(2) over 1100 cycles. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3507254] All rights reserved.