Publications

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A redox flow battery utilizing two, three-electron polyoxometalate redox couples (SiVV3WVI9O 407-/SiVIV3WVI 9O4010- and SiVIV3W VI9O4010-/SiVIV 3WV3WVI6O 4013-) was investigated for use in stationary storage in either aqueous or non-aqueous conditions. The aqueous battery had coulombic efficiencies greater than 95% with relatively low capacity fading over 100 cycles. Infrared studies showed there was no decomposition of the compound under these conditions. The non-aqueous analog had a higher operating voltage but at the expense of coulombic efficiency. The spontaneous formation of these clusters by self-assembly facilitates recovery of the battery after being subjected to reversed polarity. Polyoxometalates offer a new approach to stationary storage materials because they are capable of undergoing multi-electron reactions and are stable over a wide range of pH values and temperatures.

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A series of redox flow batteries utilizing mixed addenda (vanadium and tungsten), phosphorus-based polyoxometalates (A-α-PV3W 9O40^6-, B-α-PV3W 9O40^6-, and P2V3W 15O62^9-) were prepared and tested. Cyclic voltammetry and bulk electrolysis experiments on the Keggin compounds (A-α-PV3W9O40^6- and B-α-PV3W9O40^6-) established that the vanadium centers of these compounds could be used as the positive electrode (PV^IV3W^VI9O 40^9-/PV^V3W^VI 9O40^6-), and the tungsten centers could be used as the negative electrode (PV^IV3W^VI 9O40^9-/PV^IV3W ^V3W^VI6O40^12-) since these electrochemical processes are separated by about 1 V. The results showed that A-α-PV3W9O40^6- (where A indicates adjacent, corner-sharing vanadium atoms) had coulombic efficiencies (charge in divided by charge out) above 80%, while the coulombic efficiency of B-α-PV3W9O40^6- (where B indicates adjacent edge-sharing vanadium atoms) fluctuated between 50% and 70% during cycling. The electrochemical yield, a measurement of the actual charge or discharge observed in comparison with the theoretical charge, was between 40% and 50% for A-α-PV3W9O40 ^6-, and ³¹P NMR showed small amounts of PV 2W10O40^5- and PVW11O 40^4- formed with cycling. The electrochemical yield for B-α-PV3W9O40^6- decreased from 90% to around 60% due to precipitation of the compound on the electrode, but there were no decomposition products detected in the solution by ³¹P NMR, and infrared data on the electrode suggested that the cluster remained intact. Testing of P2V3W15O62 ^9- (Wells-Dawson structure) suggested higher charge density clusters were not as suitable as the Keggin structures for a redox flow battery due to the poor stability and inaccessibility of the highly reduced materials. © The Royal Society of Chemistry 2013.

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An iron-based ionic liquid, Fe((OHCH2CH2) 2NH)6(CF3SO3)3, is synthesized in a single-step complexation reaction. Infrared and Raman data suggest NH(CH2CH2OH)2 primarily coordinates to Fe(iii) through alcohol groups. The compound has Tg and Td values of -64°C and 260°C, respectively. Cyclic voltammetry reveals quasi-reversible Fe(iii)/Fe(ii) reduction waves. © 2010 The Royal Society of Chemistry.

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