| The extensive use of highly polluting fossil fuels and the rapid depletion of fossil mineral energy have a huge impact on the already severe environmental and energy problems facing our planet today.Solving the increasingly energy shortage problem and serious environmental pollution is a challenge to the global scientific and technological community,and various energy storage technologies will play their due roles and values in the future human society.The large-scale application of energy storage technology in the energy field will also have a profound impact on all links of modern energy production,transportation,distribution and consumption,and effectively promote the implementation of Chinese renewable energy and energy Internet strategy.The load of the power grid has peaks and valleys.Effective storage and utilization of low valley electric energy is very important for China.The most effective way to store low-valley electric energy is to use electrochemical(battery)energy storage technology.Emerging battery energy storage technologies currently applicable to off-grid and microgrid systems include fuel cells,sodium/sulfur cells,redox flow batteries,etc.Among them,the redox flow battery is regarded as the one of most important new energy storage technologies in the future,due to its advantages of free site location,large-scale energy storage,fast response,safety and reliability,no cross-contamination,flexible structural design and recyclable battery materials.However,current development of redox flow batteries has not yet entered the practical application market,mainly because of their low energy density and high capital cost.In order to solve the problems faced by redox flow batteries,it is proposed to use nonaqueous electrolytes instead of conventional aqueous electrolytes.Such electrolytes have a wide electrochemical reaction window and improve the solubility of active materials.In this thesis,a new type of non-aqueous electrolyte—Deep Eutectic Solvent(DES)is used in the redox flow battery.The external magnetic field and the use of magnetic field-temperature synergistic effect to improve the mass transfer characteristics of the non-aqueous redox flow battery are studied.The specific research contents are listed as follows:1.The effect of external magnetic field on the physical and electrochemical characteristics of Fe-V DES electrolyte was studied.The experimental results showed that the external magnetic field increased the conductivity of the iron-vanadium DES electrolyte,decreased the viscosity,increased the redox peak current,decreased the ohmic resistance and electrochemical reaction resistance of the solution.It was worth mentioning that the conductivity of vanadium DES electrolyte after adding 605 m T magnetic field can be increased by 19.10%,viscosity can be reduced by 10.85%,and its redox peak current density can be increased by 41.56% and 30.74% respectively.The increase of the diffusion coefficient and the reaction rate constant showed that the external magnetic field can promote the diffusion of the components in the DES electrolyte,enhance its mass transfer capacity,affect the electrochemical activity of iron and vanadium ions,and make the electrochemical reaction easier.Therefore,applying a magnetic field to the DES electrolyte can not only improve the relative physical properties of the DES electrolyte(viscosity and conductivity,etc.),but also can make the electrochemical reaction activity of the two redox couples Fe(II)/Fe(III)and V(III)/V(II)be improved.At the same time,it also can have a positive effect on the mass transfer capacity of DES electrolyte.2.The effect of external magnetic field on the charging and discharging performance and power density of nonaqueous DES redox flow battery was studied.Two types of ion exchange membranes(Nafion 115 membrane and Nafion 212membrane)were used for the assembly of the DES redox flow battery.Through experimental test comparison,it was found that the internal resistance of the DES redox flow battery assembled with Nafion 212 membrane was smaller and had better transmission characteristics during battery operation.When a magnetic field was added to the DES flow battery,the limiting current density and maximum power density of the battery were increased,the charging voltage of the battery was reduced,the discharge voltage was increased,the internal resistance of the battery was reduced by18.96%,and the energy efficiency was significantly improved(14.98%).It showed that the external magnetic field accelerated the electrochemical reaction inside the battery,reduced the internal loss of the battery,and improved the working performance of the DES redox flow battery.3.Since the property of DES is greatly affected by temperature,the synergistic effect of magnetic field and temperature on the physical and electrochemical characteristics of DES electrolyte were studied.The results of the experiment found that the synergistic effect of temperature and magnetic field reduced the viscosity of the DES electrolyte(up to 13.57%)and increased the conductivity(up to 17.70%).The experimental results of the ion diffusion characteristics in DES electrolyte showed that the synergistic effect of magnetic field and temperature increased the diffusion coefficient of iron ions and vanadium ions,increased the electrochemical reaction rate,enhanced the oxidation-reduction reaction capacity(up to 25.07%),and enhanced the mass transfer capacity.So the synergistic effect of magnetic field and temperature is an effective method to improve the physical and electrochemical characteristics of DES electrolyte. |
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