This method extends the cycle life of soluble lead flow batteries by employing sodium acetate as an electrolyte additive, which is an economical and effective approach. In addition, the beaker cell design used in this method is convenient for studying the effects of the electrolyte additive on single flow redox flow batteries. Demonstrating the procedure will be Yong-Hong Lai, Ho-Wei Chan, and Kai-Rui Pan, two grad students and an undergraduate student from my laboratory.
To begin, in a fume hood, pour 274.6 grams of 70%methanesulfonic acid into a beaker, and start stirring it with a stir bar. Add 300 milliliters of deionized water, and continue stirring for one to two minutes to thoroughly mix the solution. Then, add 223.2 grams of 98%lead II oxide to the stirring solution in spatula tip-sized increments.
Wait for each portion to dissolve completely before adding the next one. Filter the resulting lead methanesulfonate solution three times. Dilute it to one liter with deionized water, and stir it for two to three hours to obtain a one-molar solution.
Next, combine in a beaker 20.595 grams of 70%MSA, 150 milliliters of one-molar lead methanesulfonate, and 1.23 grams of sodium acetate. Dilute the mixture to 300 milliliters with deionized water, and stir it for one to two minutes to make an electrolyte solution with sodium acetate as an additive. Next, polish a bare graphite electrode with P100-grit aluminous sandpaper until no impurities are visible.
Rinse the polished electrode with deionized water. Then, add 20.83 grams of 35%hydrochloric acid to 200 milliliters of deionized water, and stir well to obtain a one-molar solution of hydrochloric acid. Soak the graphite electrode in the solution for at least eight hours.
Thoroughly rinse the graphite electrode with deionized water, and dry it with a low-lint laboratory wipe. Polish a nickel electrode with P100-grit aluminous sandpaper, rinse it with deionized water, and dry it in the same way. Then, wrap polytetrafluoroethylene tape around one side of each electrode, leaving a portion exposed to be connected to the battery tester.
Dissolve 3.03 grams of potassium nitrate in 300 milliliters of deionized water. Immerse the exposed sides of both electrodes in this 0.1-molar potassium nitrate solution. Also, place a reference silver-silver chloride electrode in the solution.
Then, connect the electrodes to a potentiostat. The graphite working electrode will be the positive electrode, and the nickel counter electrode will be the negative electrode. Apply a potential of 1.80 volts versus silver-silver chloride to the positive electrode for five minutes.
Then, apply a potential of negative one volt versus silver-silver chloride to the positive electrode for two minutes to finish the pretreatment. Rinse and dry the electrodes afterwards. Then, connect the pretreated electrodes to a custom electrode positioning board.
Place the positioning board on a beaker equipped with a stir bar, and fill the beaker with electrolyte until the solution reaches the appropriate level. Place the beaker assembly on a stirring hot plate, and connect a battery tester to the electrodes. Cover the beaker cell with plastic wrap to prevent evaporation before performing the battery test.
Stir the mixture at about 200 rpm during the test. To start the throwing index measurement procedure, weigh two positive electrodes and record their masses. Place a negative electrode in the center position of a Haring-Blum cell apparatus.
Place one positive electrode in the assembly near the negative electrode. Place the other positive electrode at a distance several times greater than the distance between the first positive electrode and the negative electrode. Immerse the electrode in the electrolyte of interest, and connect them to a battery tester.
Start the test by charging the battery assembly with a constant current density of 20 milliamperes per square centimeter for 30 minutes. After performing the desired charge-discharge cycles, rinse the positive electrodes with deionized water and allow them to dry in ambient air overnight. Then, weigh the positive electrodes, and calculate the amount of metal plated on each electrode.
Repeat this process at various linear distance ratios, and generate a throwing index diagram. To prepare an electroplated graphite electrode for SEM, first rinse it with deionized water and allow it to dry at room temperature. Then, use a diamond saw to carefully slice the electrode into samples of the desired size.
Cold-mount an electrode sample, fix it in a polisher, and mechanically polish it with 14-eight-and three-millimeter silicon carbide sandpaper in sequence. Rinse the sample with deionized water, and dry it with nitrogen gas after each polishing. Then, polish the sample with a one-millimeter diamond suspension, followed by a slurry of 0.05-millimeter alumina in deionized water.
After that, deposit a layer of platinum on the polished sample, and attach it to the sample platform with copper tape. Acquire SEM images of the electroplated material. Adding sodium acetate to the SLFB electrode extended the charge-discharge cycle lifetime by about 50%Adding sodium acetate also improved the throwing characteristics at the positive electrodes, as indicated by the shallower slope in a throwing index diagram.
Sodium acetate had no significant effect on the plating behavior at the negative electrode. SEM images of positive electrodes electroplated with lead IV oxide in electrolyte with and without sodium acetate showed that the additive corresponded to a smoother lead IV oxide surface with fewer defects. Impurities are detrimental to the performance of SLFBs.
Make sure that lead oxide is completely dissolved in the MSA, and filter out all residual solids before using the electrolyte. Once the plated electrode sample is harvested, other material scalarization techniques such as EBSD, nanoindentation, or x-ray diffraction can be performed to gain insight into the additive's effect on electrodeposition. Remember to prepare the electrolyte in a fume hood because the gas released during this procedure can be hazardous.
