Numerical Simulation And Electrode Modification Of Redox Flow Battery With Deep Eutectic Solvent As Electrolyte

The shortage of resources and environmental pollution caused by the excessive consumption of fossil fuels has prompted the increasing demand for renewable energy.In view of the intermittent and discontinuous nature of renewable energy,designing an efficient,low-cost energy storage system is crucial for the application of renewable energy.Among various energy storage technologies,redox flow battery technology is considered to be the most promising technology for independent output power and energy storage capacity and high energy efficiency.However,for the commonly used aqueous flow batteries,low energy density and narrow electrochemical window limit their commercialization.Therefore,in recent years,non-aqueous flow batteries have rapidly developed.The electrolyte of non-aqueous flow batteries not only provides a wide potential window,but also the greater solubility of active materials in non-aqueous solvents,which increases the energy density.In this study,one of the non-aqueous solvents—deep eutectic solvent(DES)was used as the non-aqueous electrolyte.The experimental method was used to compare the transport of active ions in DES under different conditions.The influence of temperature on the DES flow battery was also studied.Finally,the influence of gradient electrode on the performance of battery was discussed.First,cyclic voltammetry and other methods were used to study the physical and electrochemical properties of iron ions in ethylene glycol-based DES and urea-based DES and the effect of crystal water on the physical and electrochemical properties of iron ions in ethylene glycol-based DES.It is found that the diffusion coefficient of iron ions in ethylene glycol-based DES is slightly larger than that of urea-based DES;the presence of crystal water makes the reversibility and reaction rate constant of iron ions in DES increase.Single cell test found that the flow battery can obtain higher power density in the presence of crystal water.The results of this study can provide key parameters and test methods for the numerical simulation of DES flow batteries.In view of the large viscosity of reline DES,which could be influenced by the temperature,a steady two-dimensional model was established to study the effect of temperature on reline DES flow battery and the physical parameters of reline DES were determined by the test method above.The results show that as the temperature rises,the over-potential of the battery gradually decreases;the pump power loss decreases by 85.71% from 25 °C to 55 °C.The numerical simulation results agree well with the experimental results.Therefore,it can be applied to predict the performance of DES-based flow batteries,and further provide theoretical guidance for the research on non-aqueous flow batteries.The numerical simulation of the battery found that the concentration of active ions at the inlet and outlet of the electrolyte and the polarization over-potential change greatly.In view of this situation,the uniform distribution can be improved by two-part modified electrode.The half-cell test shows that the reversibility of the two-part graphite felt electrode is improved,and the ohmic resistance and charge transfer resistance are reduced;the polarization curve and the charge-discharge curve also prove that the modified electrode is beneficial to improve the performance of the redox flow battery.