Cyclic Voltammetry of Metallic Acetylacetonate Salts in Quaternary Ammonium and Phosphonium Based Deep Eutectic Solvents
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Seven commercially sourced acetylacetonate salts were investigated in deep eutectic solvents (DESs that were prepared from ethylene glycol and trifluoroacetamide hydrogen bond donors) by cyclic voltammetry, to identify electrolytes suitable for future applications in electrochemical energy storage devices. Although the solubilities are low and on the order of 0.02 mol·L−1 for the most soluble salts, some were found to display encouraging quasi-reversible electrochemical kinetics. For instance, the diffusion coefficients of copper(II) acetylacetonate and iron(III) acetylacetonate in the trifluoroacetamide based DES are 1.14 × 10−8 and 5.12 × 10−9 cm2·s−1, which yields rate constants of 3.16 × 10−3 and 8.43 × 10−6 cm·s−1, respectively. These results are better than those obtained with the DESs prepared from ethylene glycol. The poor kinetics of the iron(III) acetylacetonate system was possibly due to the hygroscopic nature of the DESs that resulted in a continuous build-up of moisture in the system in spite of the maintenance of an inert atmosphere by means of a plastic glove bag. Further work is thus envisaged in an inert dry box that could lead to H-type glass cell charge/discharge experiments in the future.
KeywordsAcetylacetonate Solubility Deep eutectic solvents Electrochemical energy storage
The authors are grateful to the University of Malaya and the Ministry of Higher Education in Malaysia for supporting this collaborative work via the research grants UM.C/HIR/MOHE/ENG/18 and UM.C/HIR/MOHE/ENG/25 as well as the Deanship of Scientific Research at King Saud University through group project No. RGP-VPP-108, which made possible an extended visit of MHC to the University of Southampton and Imperial College London in the UK. The authors are also grateful to the reviewers for providing useful comments that have resulted in a significant enhancement in the quality of this paper.
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