Ionic Liquid–Heteropolyacid: Synthesis, Characterization, and Supercapacitor Study of Films Deposited by Electrophoresis

Abstract

Hybrid materials based heteropolyacids, silicotungstic acid ͑H 4 SiW 12 O 40 ·nH 2 O͒ or phosphomolybdic acid ͑H 3 PMo 12 O 40 ·nH 2 O͒, and a room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ͓͑BMIM͔ ͓BF 4 ͔͒ were synthesized. Carbon analysis showed that 1 mol of ͓SiW 12 O 40 ͔ 4− reacts with 4 mol of ͓BMIM͔ + and 1 mol of ͓PMo 12 O 40 ͔ 3− reacts with 3 mol of ͓BMIM͔ + . 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 ͑SS͒ wires from aqueous suspensions at 30 Supercapacitors, also called ultracapacitors, are electrochemical capacitors that are able to store and deliver a huge amount of energy in a short period of time.1,2 Current research in electrochemical capacitors is focused on the development of new electrode materials.3-5 Three different types of supercapacitors can be found: high surface area carbons, 6 metal oxides, 7-12 and conducting polymers. [13][14][15][16] Novel alternative materials such as hybrid organicinorganic nanocomposites are being considered due to their potential for synergic behavior. In this respect, we can mention a recent report of supercapacitor electrodes based on conducting polymers and metal oxides 17 and conducting polymers and heteropolyacids. 18,19 Heteropolyacids have been applied as electrolyte components in several patents [20][21][22] and as electrolyte in electrochemical supercapacitors.23 Their use as active materials for electrochemical supercapacitors in combination with Ru, conducting polymers, or carbon nanotubes and nanofibers has been recently reported.24-32 On the other hand, ionic liquids have been studied extensively for batteries and fuel cells, [33][34][35][36][37][38] and hybrids of ionic liquid-heteropolyacid based especially on Keggin structures have been reported recently for applications in photochromism, 39 homogeneous catalysis, 40 and as fast proton conductors. 41,42 In this paper, we have investigated the use of ionic liquidheteropolyacid hybrids for applications as supercapacitor electrodes in an environmentally friendly neutral pH electrolyte. The hybrids were synthesized using silicotungstic acid ͑H 4 SiW 12 O 40 ·nH 2 O͒ or phosphomolybdic acid ͑H 3 PMo 12 O 40 ·nH 2 O͒ and the room temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. The hybrid materials were characterized by Fourier transform infrared ͑FT-IR͒, thermogravimetric analysis ͑TGA͒, and cyclic voltammetry. The performance of the films deposited on stainless steel ͑SS͒ electrodes using alternating current electrophoretic deposition ͑AC-EPD͒ from aqueous suspensions was evaluated for use as supercapaci...

Synthesis and properties of new materials with cobalt(II), iron(III) and manganese(III)-substituted Keggin polyoxotungstates and 1-alkyl-3-methylimidazolium cations

“…The FTIR bands corresponding to the organic cations are located at 1100−1600 cm -1 and 2700−3200 cm -1 and are in conformity with what is observed for the pure (Bmim)Br ionic liquid [52,53], and other Bmim or Omim salts containing Keggin [21,32] or other anions [43]. Thus, both TMSP and the chosen cations seem to be present in the solid compounds without noticeable changes.…”

“…Yet, several compounds with these cations and Keggin-type anions have been synthetized. The majority contains parent Keggin anions, like [PW 12 O 40 ] 3- [14][15][16][17][18], [SiW 12 O 40 ] 4- [19][20][21] or [PMo 12 O 40 ] 3- [18,[21][22][23][24][25][26][27].…”

Polyoxometalate‐coupled Graphene via Polymeric Ionic Liquid Linker for Supercapacitors

“…Note that the maximum specifi c capacitance value of POM/PIL/RGO was higher than those Adv. A maximum energy density of 56 Wh kg −1 (with a power density of 0.8 kW kg −1 ) and a maximum power density of 52 kW kg −1 (with an energy density of 50 Wh kg −1 ) were obtained from SCs based on two symmetric POM/PIL/RGO electrodes with an operating voltage of 1.0 V. These values are superior compared to presently available SCs and other POM-based symmetrical supercapacitors, including POM/polypyrrole (PPy)//POM/PPy (1.44 Wh kg −1 at 18.90 W kg −1 ), [ 38 ] POM/MWNT//POM/MWNT (57 Wh kg −1 at 120 W kg −1 ), [ 39 ] POM/polyaniline (PANI)// POM/PANI (24 Wh kg −1 at 240 W kg −1 ), [ 20 ] POM/ionic liquid (IL)//POM/IL (8.6 Wh kg −1 at 1.75 kW kg −1 ), [ 40 ] and POM/activated carbon (AC)//POM/AC (4.96 Wh kg −1 at 115 kW kg −1 ). Mater.…”

Electrophoretic deposition under modulated electric fields: a review

“…Recently, the theory of nonlinear electrophoresis was tested experimentally and found to successfully produce thick deposits of inorganic, 95,96 organic-inorganic particles 97 and enzymes and biological cells. 24,28,29,[98][99][100]103 Using asymmetrical triangular waves, Neirinck et al 95,96 deposited thick and uniform alumina coatings with higher green density from low aqueous conductivity suspensions at 50 Hz and 500 V p-p .…”