Calibrating the Liquid Cell
Over the weekend Allison and I prepared our first solution which was a 1:10 LiTFSI:C4mPyrrTFSI. The solution appears to have completely dissolved. I also took the time that weekend to prepared two solution of 1.0M KCl for calibrating both liquid cell 1 & 2 and attempted to cleaning liquid cell 2 after the damaged caused to it from last week. A solution of 6:1 hexanes to ethyl acetate seemed to help a bit in comparison to methanol and acetone, but the damaged area is still visible. I managed to run the 1.0M KCl solution for LC2 on Sunday, but it appears to have been outside the window of conductivity and therefore plateaued for a bit, but then fell dramatically to a far lower conductivity at high frequency, so the data gained from that cannot be used to calibrate the liquid cell. Some salt also precipitated onto the O-rings which is probably not a good sign. I lost the 1.0M KCl solution for LC 1, since I filled it before replacing the spacers after the short compensation. On Tuesday I prepared 20mL of a 0.1M KCl solution and am now currently running a test on LC2 and shortly on LC1. Hopefully this allows us to fully calibrate both liquid cells in reference to the CRC. In order to avoid contamination from the thermal fluid we will/have been running these standardizing tests outside of the thermal bath. Luckily the room temperature today has been consistently 20 degree Celsius in the lab so we should be able to use the CRC value without too much error. Based on the several other KCl solutions I have run with LC2 it looks as if LC2 is consistently reporting +20% above the literature values, so a calibration is definitely needed.
We ran the 0.1M KCl solutions at RT outside the of the thermal bath in order to avoid additional damage to the liquids cell, and tests were successful and I was able to calibrate them to a 20C 0.1M KCl conductivity value from the CRC. Both calibration values (k) were about 0.017 1/cm compared to the original theoretical value for k which was 0.018, calculated by k = d/A where d is the distance between the parallel plates and A is the area of the electrode, this would indicate that both LCs are not significantly damaged.
With these results we hoped to verify these calibrations by running the liquid cells with a 0.1M KCl solution at a temperature regime of 5-85C, but liquid cell 1, which was run first, was visible contaminated with thermal fluid. In order to avoid this contamination, we have decided to replace the Teflon cap of the liquid cells and lower the level to which the thermal fluid reaches on the liquid cell. We implemented these changes for a similar run for liquid cell 2, but still found there was significant contamination. Given that liquid cell 2 has been showing more signs of corrosion and contamination in general compared to liquid cell 2 we decided to run liquid cell 1 with these changes to see if there was still contamination of the solution by the thermal fluid. We ran this test with DI water and found that no thermal fluid was present in the sample. We will now continue with a KCl standardization for liquid cell 1.
Atmospheric H2O concerns
We have been recently concerned that if thermal fluid can enter the liquid cells that atmospheric water can also contaminate our samples, at Lawrence, Allison has assumed that the LCs were air tight and therefore conductivity test could be run outside of the glovebox. I am going to verify this by performing a conductivity measurement using a 0.2M LiTf Cyclohexanone solution. I have purified the cyclohexanone by doing several distillation (1st distilling off the cyclohexanone leaving the oxidized contaminate, hexanedioic acid, and the 2nd distilling off the H2O), then I used MgSO4 to remove excess water from the cyclohexanone, and verified that there was no H2O present via IR analysis (no 3000 1/cm peak present). I also did this IR verification with our original cyclohexanone (which had a prominent H2O peak) and the LiTf ( which also had a prominent H2O peak). Given that our LiTf has significant amount of water in it, I will have to dry it in the vacuum oven tonight and hopefully prepare the solution tomorrow. The goal is that if there is atmospheric H2O leaking into the liquid cell the lithium will readily absorb it, and we can run another IR to confirm either our samples contamination or purity.
In other news, Allison believes that maybe the electrodes on LC 2 need to be replaced given the significant amount of damage sustained and the fact that it continues to leak despite our best efforts. She has told me to inquiry into the cost of replacing the electrode.