Electrode Modification And Pore-scale Reaction Transport Properties Of Redox Flow Battery With Deep Eutectic Solvent As Electrolyte

The indirect renewable energy,such as solar and wind,will have unstable energy output in large-scale direct grid utilization.Therefore,the development of efficient energy storage system can guarantee the rational utilization of renewable energy.In recent years,redox flow batterie（RFB）has been regarded as a large-scale energy storage technology with great development potential due to their advantages of good safety and high energy efficiency.Some of these aqueous RFBs have entered the stage of commercial development,but due to the narrow electrochemical window of water,the batteries cannot achieve higher energy density.Therefore,the development of efficient non-aqueous RFB is one of the research hotspots.Deep eutectic solvent（DES）is a promising non-aqueous electrolyte with wide electrochemical window and easy biodegradation.At present,the non-aqueous RFB based on DES is still in the initial stage of research,and the electrode as the core component limits the development of battery.This paper takes the carbon-based electrode as the research object,and aims to obtain a high-performance electrode to improve the performance of non-aqueous RFB by surface modification and structure optimization.At the same time,numerical simulation is used to investigate the reaction transport process in porous electrode at pore scale,which provides a theoretical basis and technical approach for the development of high-efficiency non-aqueous RFB.The specific research contents are as follows:1.Combining impregnation and high-temperature calcination,Cr₂O₃ nanoparticles are introduced into the surface of graphite felt for its modification,and physical characterization and electrochemical tests are carried out on the modified graphite felt.The results show that compared with the blank graphite felt,the wettability and active sites of the graphite felt modified by Cr₂O₃ are improved.Meanwhile,the modified electrode has higher electrochemical performance to the Fe（II）/Fe（III）and V（II）/V（III）.In addition,the modified electrode is used to test the Fe-V DES redox flow battery.The experimental results show that the energy efficiency of the battery reaches 87.19%at a current density of2 m A·cm^-2,and the peak power density is 11.22 m W·cm^-2.Compared with the unmodified electrode,the energy efficiency and power density are increased by 7.67%and 14.98%respectively.2.Based on the non-uniformity of reaction transport inside the porous electrode of DES flow battery,a direct splicing double-layer composite electrode is designed and fabricated by using graphite felt and carbon paper with different porosity as substrate materials.The electrode is composed of low-porosity carbon paper that has been heat-treated at 480°C for 12 h on the membrane side and high-porosity graphite felt deposited by copper nanoparticles particles on the flow channel side.Among them,the carbon paper electrode with low porosity has good hydrophilicity and a specific surface area several times higher than that of graphite felt,which can effectively promote the electrochemical reaction on the membrane side.In addition,the high porosity graphite felt electrode containing copper after electrodeposition has high permeability,conductivity and good interfacial catalytic efficiency at low potential,which is beneficial to reduce the electrolyte flow/ion/charge transfer resistance on the negative side of the battery.The composite electrode is applied to the negative side of the Fe-V DES redox flow battery.Due to the synergistic optimization of the internal transport performance and electrochemical performance of the electrode,the power density and energy efficiency of the battery are improved.3.Based on the above experiments,a three-dimensional multi-relaxation time lattice-Boltzmann model is established to explore the pore scale reaction transport characteristics of porous electrodes（including graphite felt,carbon paper and composite electrodes）during the discharge process of DES redox flow battery.The simulation results show that the flow distribution of the electrolyte inside the porous electrode is prone to non-uniformity when the interdigitated flow field is used at a low electrolyte flow rate,which will lead to the decline of the convective mass transfer performance on the membrane side.However,the convective mass transfer effect on the membrane side can be effectively improved by increasing the inlet electrolyte flow rate.At the same time,the composite electrode battery with interdigitated flow field has the lowest total power loss compared with the single-layer electrode at high electrolyte flow rate.