The effect of additive supporting electrolytes on transport and electrochemical properties of deep eutectic solvent (DES
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ORIGINAL PAPER
The effect of additive supporting electrolytes on transport and electrochemical properties of deep eutectic solvent (DES) applied in non-aqueous redox flow batteries Ping Lu 1 & Liyu Qin 1 & Prabhuraj Balakrishnan 1 & Qiang Ma 1 & Huaneng Su 1 & Weiwei Yang 2 & Qian Xu 1 Received: 13 May 2020 / Revised: 1 June 2020 / Accepted: 6 June 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Although the utilization of deep eutectic solvents (DES) as non-aqueous electrolyte of redox flow batteries has received enormous attention, its properties like high viscosity and low conductivity always remain a matter of concern, due to their negative effect on final battery power performance. Herein, the introduction of two types of additive supporting electrolytes (one: a mixture of dimethyl carbonate (DMC) and ethylene carbonate (EC) and the other: ethyl acetate (EA)) remarkably decreasing the viscosity and impedance of the DES with iron ions is reported, especially for DMC+EC. In addition, the cyclic voltammetry results show that the reversibility of Fe(III)/Fe(II) redox couple, and the reaction kinetics are improved after adding DMC+EC, while EA has little effect on improving the electrochemical performance. From Raman spectroscopy, it is found that a distinct characteristic peak occurs at 895 cm−1 for DMC+EC mixture, whereas the intensity of this peak is weak for EA. It is highly probable that the appearance of this characteristic peak serves to improve the electrochemical properties of DES. Keywords Redox flow batteries . Non-aqueous electrolyte . Deep eutectic solvent (DES) . Supporting electrolyte . Electrolyte additives
Introduction Redox flow battery is a promising energy storage system especially suitable for large-scale energy storage system. The improvement of electrode [1, 2], electrolyte, and diaphragm is researched. The deep eutectic solvent (DES) as redox flow battery electrolyte (non-aqueous organic systems) is widely preferred due to its wide potential electrochemical window [3–5], high thermal and electrochemical stability [6, 7], higher conductivity than aqueous electrolytes [8–10], and low cost [11, 12] characteristics. Extensive studies have revealed that DES, an uncommon ionic liquid, can be ascribed to the hydrogen bond acceptors like quaternary ammonium salts on * Weiwei Yang [email protected] * Qian Xu [email protected] 1
Institute for Energy Research, Jiangsu University, Zhenjiang 212013, China
2
School of Energy and Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
one side and hydrogen bond donors compounds, for example, amides, carboxylic acids, and polyols on the other at a certain stoichiometric ratio [13, 14], yielding them suitable for use as electrolytes. However, the pure DES owns drawbacks especially in terms of high viscosity and low conductivity properties, affecting their practical applications. In this sense, improving the physical properties and electrochemical process characteristics of DES becomes a necessity. Adding vari
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