Tuning intermolecular interactions of SiO2-TiO2-PBC Nanocomposite Membranes with Cation

Thivani Senathiraja Author

04/03/2021 Added

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Research Days Presentation 2021

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[00:00:01.210]Good morning.
[00:00:02.070]I'm Thivani Senathiraja, a graduate student
[00:00:04.140]from Chemical and Biomolecular Engineering at UNL.
[00:00:06.980]Today I'll be presenting my ongoing project
[00:00:09.350]which is Tuning the Intermolecular Interaction
[00:00:11.610]of Silicon and Titanium based PBC Nanocomposite Membrane
[00:00:15.610]with Cation.
[00:00:17.530]We know that fossil fuels have led to global warming
[00:00:19.960]and researchers are seeking for an alternative method
[00:00:22.270]to produce clean and efficient energy.
[00:00:25.170]Currently, one of the most promising technology
[00:00:27.250]is fuel cell.
[00:00:28.760]Fuel cell is a device which converts the chemical energy
[00:00:31.060]stored in the fuel to its electrical energy.
[00:00:33.920]The picture on the right
[00:00:34.760]shows the working mechanism of a fuel cell.
[00:00:37.530]As you can observe, it's very similar to that of batteries.
[00:00:41.420]One of the most important component of a fuel cell
[00:00:44.440]is the polymer electrolyte membrane
[00:00:46.470]which helps to conduct ions, in this case protons,
[00:00:49.700]from one electrode to the other.
[00:00:51.890]There are many types of polymer electrolyte membrane.
[00:00:55.190]However, the proton exchange membrane has many advantages.
[00:00:59.400]The car shown on the lower right is Toyota Mirai
[00:01:02.550]which is actually based on
[00:01:04.240]the proton exchange membrane fuel cell.
[00:01:07.450]For my study, I focused on a proton exchange membrane
[00:01:11.370]called Nexar or Pentablock Copolymer or simply PBC.
[00:01:16.110]The figure on the lower right shows the structure of PBC
[00:01:19.630]and as you see the Sulfonic acid group actually helps
[00:01:22.870]in the conduction of proton across the membrane.
[00:01:26.400]However, pure material alone cannot embody all
[00:01:29.250]the required properties needed for fuel cell application.
[00:01:32.960]Hence in this study, the PBC membranes were
[00:01:35.680]fabricated with Silicon and Titanium based nanocomposites.
[00:01:39.850]However, there are many other factors
[00:01:41.450]which affect the performance of a fuel cell.
[00:01:43.650]And one such factor is the effect of cations.
[00:01:48.270]The ion transport mainly depends
[00:01:50.100]on ionic interactions of cation and water.
[00:01:53.230]The figure on the right highlights this effect.
[00:01:56.530]Imagine the gray areas to be the polymer membrane domain
[00:01:59.880]with Sulfunic acid group indicated in orange as shown
[00:02:03.810]and the water molecules in blue circles.
[00:02:07.340]As you see the water molecules will form a network
[00:02:09.920]while ionic interaction with the Sulfonic acid group
[00:02:12.680]by displacing the cations.
[00:02:15.410]So why is this water channel formation important?
[00:02:19.720]Let's look at the picture here.
[00:02:21.360]You can imagine the water molecules
[00:02:23.100]as the human skeleton,
[00:02:24.890]which by forming this interconnected network
[00:02:27.840]help to transfer the ions indicated by the blue balls
[00:02:31.030]from one end of the membrane to the other.
[00:02:34.260]So far, the effect of different cation
[00:02:36.730]on the membrane have not been fully understood
[00:02:39.140]though they play a vital role.
[00:02:41.000]Thus the focus of the study is to investigate the effect
[00:02:44.930]of cation on the cell performance
[00:02:47.170]and durability of PBC membrane
[00:02:49.170]fabricated with the Silicon
[00:02:51.640]and Titanium based nanocomposites.
[00:02:54.490]So based on our motivation, we had three objectives.
[00:02:57.570]The first one is to design PBC membrane fabricated
[00:03:00.490]with Silicon and Titanium based nanocomposite
[00:03:02.730]with varying composition and weight percentage,
[00:03:05.710]and then modify this membrane with cations
[00:03:08.320]by exchanging ions with the respective salt solution.
[00:03:12.290]And finally investigate the effect of cation
[00:03:14.550]on the membrane.
[00:03:16.230]In this study, I'll be presenting the effect
[00:03:18.980]of cation on water uptake and thermal stability.
[00:03:23.390]Coming to the experimental method.
[00:03:25.350]The first step involves designing homogeneous
[00:03:27.994]PBC membrane based on different composition
[00:03:30.820]and weight percentage of Tetraethyl orthosilicate
[00:03:34.320]also known as TEOS and Titanium isopropoxide
[00:03:37.710]known as TIP
[00:03:39.080]where x and y indicates the ratios that are used.
[00:03:42.890]Basically TEOS and TIP give rise to the Silicon
[00:03:45.640]and the Titanium based nanocomposites.
[00:03:48.590]In all the scenario,
[00:03:49.820]creating homogeneous membrane is important.
[00:03:52.470]You can relate to this as a cup of coffee.
[00:03:55.520]Obviously we don't desire a cup
[00:03:57.560]with visible lumps of milk and sugar.
[00:03:59.850]We record a homogeneous blend of these ingredients.
[00:04:03.470]Now I'm looking at the method.
[00:04:05.090]We first create homogeneous mixture
[00:04:06.980]of TEOS and TIP in isopropanol,
[00:04:09.630]and slowly added to the required weight percentage
[00:04:13.400]to the solution of PBC in Tetrahydrofuran,
[00:04:16.290]which is the solvent.
[00:04:18.550]Then we stir it for three days
[00:04:20.440]at room temperature to create homogeneous mixture.
[00:04:23.400]The picture shows the vial containing different
[00:04:25.619]homogeneous mixture with different weight percentage
[00:04:28.840]and ratios of TEOS and TIP
[00:04:31.330]that we prepared in our lab.
[00:04:33.030]The color differences you observed is due
[00:04:35.090]to the different weight ratios and the weight percent.
[00:04:38.870]Then we cast this mixture on a Teflon mold
[00:04:42.200]and finally dry it in the vacuum oven.
[00:04:44.570]This picture shows the appearance
[00:04:46.260]of the membranes that we actually got after drying.
[00:04:49.540]Next we exchange the produced membranes with cation
[00:04:53.770]by first boiling it with sulfuric acid
[00:04:56.970]and then rinsing it thoroughly with water
[00:04:59.050]to remove any excess acid.
[00:05:00.560]Then again, boiling it with the required salt solution
[00:05:03.530]based on the cation you want to exchange,
[00:05:05.960]and then rinse it with the DI water
[00:05:09.030]and finally dry the membrane.
[00:05:12.150]Now let's look at the results and discussion.
[00:05:15.490]The first one is water uptake.
[00:05:17.530]Water uptake is measured by shown below.
[00:05:20.270]It's simply the difference between the wet
[00:05:22.030]and dry mass of the same polymeric membrane.
[00:05:25.989]As we discussed before,
[00:05:28.700]ideally we want the water uptake to be high.
[00:05:31.640]However, there's a upper limit to how high it can get
[00:05:35.680]because very high water uptake can lead to swelling
[00:05:39.340]which can lead to reduction in mechanical strength.
[00:05:42.250]The graph on the right shows the results obtained.
[00:05:45.580]As you see, when compared to the membranes exchange
[00:05:47.970]with sodium ions, the unmodified membrane exhibit
[00:05:51.270]significantly higher water uptake in all cases,
[00:05:55.600]and water uptake increases
[00:05:57.860]with increasing TEOS - TIP weight percentage
[00:06:01.270]except a 10 weight percentage
[00:06:03.700]TEOS-TIP three is to one ratio.
[00:06:06.140]These observation may be attributed
[00:06:07.830]to the morphological transition that occurred
[00:06:10.000]due to the change in ionic interaction.
[00:06:12.880]Second, we'll look at the thermal stability.
[00:06:15.570]This is important because higher operating
[00:06:17.920]temperature creates greater fuel cell efficiency.
[00:06:21.015]The thermal stability was measured using a instrument
[00:06:24.050]known as thermal gravimetric analysis.
[00:06:27.330]The figure below shows this instrument.
[00:06:30.330]If you look at the graph,
[00:06:31.840]you can observe that the decomposition temperature
[00:06:34.550]of all the sodium exchange membranes
[00:06:38.560]are significantly higher than that of unmodified membranes,
[00:06:41.660]which shows that thermal stability is enhanced with cation
[00:06:45.790]and maybe attribute it to the stronger ionic interactions.
[00:06:49.670]Also, it can be noted that introducing TIP
[00:06:52.360]reduces the decomposition temperature
[00:06:54.590]except five weight percent
[00:06:56.765]PBC-TEOS-TIP three is to one ratio.
[00:07:00.070]The reduction in the TIP,
[00:07:02.540]the reduction in the decomposition temperature with TIP
[00:07:05.530]maybe attributed to factor TIP
[00:07:07.850]which is a Lewis acid can act kind of
[00:07:10.810]as a catalyst,
[00:07:11.818]and increase the decomposition rate.
[00:07:16.670]Thus in our conclusion.
[00:07:18.490]We observed that incorporating Silicon
[00:07:20.750]and Titanium based nanocomposites improved the properties
[00:07:23.840]of PBC membrane as indicated by the previous studies
[00:07:27.620]and exchanging this membrane with cations
[00:07:30.190]significantly alters the properties
[00:07:32.530]such as thermal stability and water uptake.
[00:07:35.490]These changes can be attributed
[00:07:37.140]to the morphological transitions that occur
[00:07:39.320]due to the ionic interactions.
[00:07:41.520]Thus this highlights the importance
[00:07:43.240]of the role of cations on cell performance and durability.
[00:07:47.359]For future study,
[00:07:48.930]we'll be conducting a proton conductivity tests
[00:07:51.550]and morphological studies.
[00:07:54.030]And I would like to take this opportunity to thank
[00:07:57.300]the Nebraska Public Power District
[00:07:59.380]and Nebraska Center for Energy Science Research
[00:08:01.890]for funding this project.
[00:08:03.100]Thank you.

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Tuning intermolecular interactions of SiO2-TiO2-PBC Nanocomposite Membranes with Cation

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