Numerical And Experimental Research On The Influence Of Electrode Structure On Mass Transfer Of Redox Flow Battery

Redox flow battery is one of the latest large-scale electrochemical energy storage technologies.It has many advantages such as high efficiency,simple operation,low maintenance cost,extremely long cycle life and flexible design due to the decoupling of power and energy.Therefore,it has played an important role in the field of energy storage technology.The working principle of the redox flow battery is the energy conversion and storage between electrical and chemical energy,which can be achieved by the change of valence of active materials during the process of reversible chemical reaction.However,due to the restriction of the property of its key components,the performance,reliability and cycle efficiency of the redox flow battery cannot meet current practical application requirements.It is well known that it is in the electrode where the redox reaction of energy-storage active materials occurs in the battery.Thus,it is essential to modify the electrode structure and operating conditions to improve the performance of the redox flow battery.Herein,the effects of electrode structure on mass transfer of the redox flow battery was studied by combining numerical simulation and experiment.Several important results of this study were summarized as follows:In order to investigate the influence of electrode compression,electrolyte velocity and initial concentration on the performance of the battery based on the mass transfer and electrochemical performance,a three-dimensional model of an all-vanadium redox flow battery was developed.The battery using electrodes with different electrode compression ratios was firstly performed.Results showed that the performance of the battery could be effectively improved by regulating the electrode compression ratio without additional operating costs.When the electrode compression ratio was 30%,the mass transfer and the potential of the electrolyte inside the electrode were more uniformly distributed,which improve the electrochemical performance of the all-vanadium redox flow battery.Meanwhile,the electrochemical performance of the all-vanadium redox flow battery can be optimized by appropriately increasing the flow rate and the initial concentration of electrolyte.To reduce material costs and improve environmental safety,a three-dimensional model using iron as redox reactant instead of vanadium was developed.It was found that the all-iron redox flow battery with Fe³⁺/Fe²⁺redox pair also showed good performance.Specially,internal flow and mass transfer of the electrode and the electrochemical performance of the battery have been further improved by setting the flow field structure.In addition,after comparing the mass transfer and electrochemical performance of the battery with nine sizes of flow channels,it was found that the battery with a flow channel thickness of 0.005 m showed best battery performance.These results will be helpful for designing flow channel sizes of all-iron redox flow batteries.To further improve the flow mass transfer inside the electrodes and the efficiency of the all-iron redox flow battery,slurry electrode was designed to replace the traditional porous electrode.In this case,a semi-solid all-iron redox flow battery was developed.The charging and discharging experiment of the battery was then carried out based on this semi-solid battery.Moreover,an external magnetic field was also set up in the semi-solid battery.Results showed that the addition of external magnetic field improved the mass transfer of the slurry in the battery flow channel and prolonged the battery discharge time.In addition,a three-dimensional model of the semi-solid all-iron redox flow battery was also developed and verified to be reliable by experimental data.The simulation results showed that the ion concentration distribution in the battery became more uniform with the increase of the flow rate and the initial concentration.Furthermore,it was also found that the size of the battery flow channel influenced the mass transfer efficiency of the slurry.After optimizing the flow channel,it was found that when the flow channel length of slurry inlet and outlet section was 2 cm,the operating efficiency of the semi-solid battery evidently increased.