Sedimentary Type All Lead Redox Flow Battery In Fluoroboric Acid Electrolyte

Redox flow battery, which is an important research direction of chemicalpower supply systems, is suitable for large scale energy storage. All lead redoxflow battery based on the electrode reactions of soluble lead（II） in fluoroboricacid electrolyte are proposed in the paper. The performance of the flow batteryand its materials is tested by using cyclic voltammetry （CV）, galvanostatictechnique, XRD and SEM measurements.First of all, the performance of the current collect electrodes is studied.The electrolyte of this battery for both negative electrode and positiveelectrode is high concentration solutions of Pb （BF4）2in aqueous fluoroboricacid, i.e.0.1,0.5,1.0and1.5mol L^-1Pb （BF4）₂in1.0mol L^-1HBF₄. Theproperties of graphite and glassy carbon electrodes for both positive andnegative electrodes as current collectors are compared by using cyclicvoltammetry. It is found that the graphite substrate is better than the glassycarbon for both negative electrode and positive electrode. All lead redox flowbattery is constructed using graphite substrates as both positive and negativeelectrodes. The performance of the batteries is carried out by using constantcurrent charge/discharge technique. Typically, when the charge capacity is limited at7mAh cm^-2, average coulombic efficiency of above87%and theaverage energy efficiency of about70%are obtained. An average coulombicefficiency of about97%and an energy efficiency of above74%can beachieved with an electrolyte containing1.0mol L^-1or1.5mol L^-1lead（Ⅱ） atcurrent density of10and20mA cm-2. When the charge capacity setting is15,30, or45mAh cm^-2, the battery can offer an average coulombic efficiency ofabout88%⁹8%and an average energy efficiency of about64%⁸2%atdifferent current densities and different electrolyte concentrations. Typically,the battery, in which1.5mol L^-1of Pb（BF4）2in1.0mol L-1of HBF4aqueoussolution is adopted as electrolyte, can offer an average coulombic efficiency ofabove97.8%, an average energy efficiency of above83.0%and an averagevoltage efficiency above84.8%at the current density of10mA-cm^-2.In order to improve the performance of the batteries, different electrodematerials for current collect electrodes are explored. We found that tantalumcarbide （TaC） and stainless steel can be used as electrodes for the all-leadredox flow battery in the intermixture of Pb（BF4）2and HBF4aqueouselectrolyte. This battery provides an average coulombic efficiency of above96%at different electrolyte concentration and charge/discharge currentdensities. When1.5mol L^-1of Pb（BF4）₂in1.0mol L^-1of HBF4aqueoussolution is adopted as electrolyte, the battery can offer an average energyefficiency of above80%at a charge/discharge current density of10mA cm^-2,but the TaC electrode used here are fragile. And then the preparation processes of the TaC electrode materials are improved by adjusting the amount of thecarbons to control the carbonization degree and the toughness of Ta foil. Theelectrochemical performance is superior while the carbon source quality（mainly for phenolic resin） is5grams. The battery can offer an averagecoulombic efficiency of above95%，an average energy efficiency of above70%and an average voltage efficiency of above70%in the different currentdensity. While the current density is10mA cm^-2, electrolyte adopted is1.5mol L^-1of Pb（BF14）2in1.0mol L-of HBF4, the battery can offer an averagecoulombic efficiency of95.2%, an average energy efficiency of76.19%, andthe average voltage efficiency of80.1%. XRD tests of the active materialsdeposited on the surface of the electrodes are carried out with the chargingcapacity of7mAh cm^-2and the electrolyte of1.0mol L^-1Pb（BF₄）₂^+1.0mol L^-1HBF4in order to analyze the process of electrochemical reaction. Byanalysising the results of the XRD tests, there were both alpha and beta crystalof PbO2on the surface of the electrodes whether in the initial charge/discharge cycles or after hundreds of cycles. But the dominating deposits arebeta PbO₂and the energy efficiency of the battery remains higher.All lead deposition/dissolution redox flow battery in fluoroboric acidelectrolyte is proposed in the paper. The performance of the new battery wasimproved and the cost was reduced in contrast to the battery in methyl sulfonicacid electrolyte.