Electrochemical and structural study on a FEIII-ionic liquid redox electrolyte Christian Balischewski 1 , Biswajit Bhattacharyya 1 , Josh Bailey 2 , Jiyong Kim 3 , Shashank Gahlaut 1 , Yann Garcia 4 , Eric Sperlich 1 , Christina Günter 5 , and Andreas Taubert 1 1 University of Potsdam, Germany, 2 Queen’s University Belfast, BT7 1NN, UK 3 Fraunhofer Institute of Applied Polymer Research (IAP) Germany Ionic Liquids (ILs) are generally understood as salts with melting points below 100°C, which are easy to handle due to their non-flammability and non-volatility. They also exhibit high thermal and electrochemical stabilities with high ionic conductivities. Their physical properties can be altered to fit a specific purpose by changing (parts of) the ions, which means they can be regarded as “task-specific materials”. Introducing metals into ILs can further change the individual properties by inducing new optical or electrical mechanisms and qualities. Furthermore, metal-containing ILs (also called MILs) are currently investigated as precursor materials for syntheses of different metal compounds, such as chalcogenides or perovskites. Due to these qualities, MILs are therefore studied as promising candidates for the synthesis of active energy materials and direct use in energy devices, such as batteries and sensors. 1 In the last decade, due to the increasing cost of resources and severe impact on the environment, a growing focus has been put on new energy production and storage technologies with sustainable material development. In this regard MILs can contribute to both aspects like the transition from using fossil fuels to renewable energy sources with novel design of energy harvesting molecules and switching from rare and expensive materials to more cost-efficient, environmentally friendly and readily available systems for the fabrication of energy storage systems. 4 Institute of Condensed Matter and Nanosciences, Belgium 5 Institute of Geosciences, University of Potsdam, Germany In this study we are presenting a Fe III -based MIL for the direct use in energy devices as an electrolyte. The MIL (BuPy)[FeCl 4 ] has been synthesized and its structural properties are analyzed using single crystal X-ray analysis, X-ray powder diffraction, Infrared spectroscopy, as well as X-ray photoelectron spectroscopy and Mössbauer spectroscopy, showing that the compound consists of one N -butylpyridinium cation and one [Fe III Cl 4 ] - anion. The anions organize themselves in tilted anion chains, which is a reason for the low melting temperature of just 35°C. Additionally Cyclic voltammetry in MeCN and water was used to identify redox processes. In MeCN the system shows a reversible redox couplet with E 1/2 =-0.419V vs. Fc + /Fc with ΔE p =87mV. This can be attributed to the redox processes between [Fe II Cl 4 ] 2- and [Fe III Cl 4 ] - . 2 This reversible process indicates that (BuPy)[FeCl 4 ] is a promising candidate for an electrolyte application in the growing field of Fe-based redox flow batteries (RFBs). References 1. Y. Kim, et al . J. Chem. Phys. 2018. 148 (19): 193818. DOI: 10.1063/1.4991622 M. Yamagata, et al . Electrochimica Acta. 2007. 52 (9): 3317-3322. DOI: 10.1016/j.electacta.2006.10.008
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