Preparation Of Electrodes For High-performance All-vanadium Flow Battery

With the adjustment of energy structure,liquid flow battery,as a safe and effective long-term energy storage,has attracted the attention of researchers.Liquid flow batteries have advantages such as high safety,long service life,and flexibility in use,making them suitable as long-term energy storage facilities for solar and wind power generation.Among them,all vanadium flow batteries are the most mature system,accounting for over 90% of the flow battery market.However,due to the rise in global vanadium prices,the cost of using vanadium batteries has greatly increased.Therefore,it is necessary to increase the operating current and energy efficiency of batteries under the same conditions to achieve the goal of reducing the unit cost of battery use.However,as the current increases,the polarization of vanadium batteries increases,and the conversion efficiency of the battery is limited by poor vanadium negative electrode reaction kinetics and heavily polarized carbon felt electrodes.Therefore,this article improves the electrochemical activity of carbon felt electrodes in liquid flow batteries by doping them with heteroatoms and modifying them with loading additives,reducing battery polarization,and enhancing the operating current and energy efficiency of the battery.Firstly,this article selects sulfur element doping to treat the electrode,and the experiment proves the positive improvement effect of acid bubble heat treatment on the electrode.Verify through electrochemical testing that the hydrogen evolution trend,reaction reversibility,and reaction kinetics of the treated electrode are better than those of the original felt.The sample prepared with 3M sulfuric acid showed the best electrochemical performance.Later,characterization tests such as XRD,XPS,and SEM were used to demonstrate the effect of acid bubble heat treatment on carbon felt fibers,demonstrating that heteroatom doping treatment changed the carbon structure of the fibers,increased sulfur functional groups,and caused uniform defects on the carbon felt fibers.Finally,the rate performance of the electrodes was tested through a full cell experiment,proving that the polarization of the battery with the treated electrode sample decreased and the energy efficiency increased.The energy efficiency increased by 7% at 300 current density,demonstrating that the sulfur doping method can effectively improve the polarization problem of the battery.However,the complexity of the heat treatment process and the non-linear nature of the electrode parameters make it difficult to apply in engineering.Therefore,this article selects a treatment method that loads bismuth metal on the carbon felt electrode to improve its electrochemical performance.Firstly,the feasibility of bismuth oxide reduction to bismuth in the system was calculated by thermodynamics.The CV and EIS experiments proved that the optimal additive loading and the optimal reduction potential of electrode treatment were optimal;secondly,various characterization tests have demonstrated the successful loading of elemental bismuth on carbon felt fibers;first principles calculations have demonstrated the promoting effect of bismuth in the electrochemical reaction process;finally,a full cell experiment was conducted to demonstrate that the polarization of the treated electrode was much smaller than that of the original felt electrode,and the energy efficiency of the battery was significantly improved by 8% at 400 current density;the long-term cycling experiment verified the long-term stability of the treated electrode,and the treated electrode can cycle for 450 cycles without significant energy efficiency degradation.The above experiments have demonstrated the effectiveness and feasibility of loading bismuth additives.