The Study of Monovalent and Multivalent Cations Exchanged with Sulfonated Ionomers: Water Uptake and Ion Transport

Aidan Larsen Author

04/04/2021 Added

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Research Days Presentation 2021

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[00:00:01.120]Hello, my name is Aidan Larsen.
[00:00:03.520]I'm a Chemical Engineering undergraduate student
[00:00:05.460]at the University of Nebraska-Lincoln
[00:00:07.140]in the Department of Chemical and Biomolecular Engineering.
[00:00:09.940]For my research, I did The Study of Monovalent
[00:00:12.090]and Multivalent Cations Exchanged with Sulfonated Ionomers,
[00:00:15.250]focusing on Water Uptake and Ion Transport.
[00:00:19.440]In the past 60 years, our CO2 levels have increased
[00:00:22.120]by hundred parts per million.
[00:00:23.630]This is mainly due to the fact that 80% of our energy
[00:00:25.780]comes from fossil fuels.
[00:00:27.910]A desirable energy alternative is fuel cells
[00:00:31.090]which are categorized by the electrolyte which they employ.
[00:00:35.420]Of the many different types,
[00:00:36.920]proton exchange membrane fuel cells have many advantages.
[00:00:40.520]They work by separating hydrogen at the catalyst,
[00:00:43.300]transferring that hydrogen proton along the membrane
[00:00:45.930]between the electrodes further reacting it with oxygen
[00:00:49.280]from the air to produce water and an electrical circuit.
[00:00:54.550]Proton exchange membrane fuel cells
[00:00:56.360]use an ionomer membrane as the electrolyte,
[00:00:58.930]which are ionically charged polymers
[00:01:01.220]containing an ionic functional group or moiety.
[00:01:04.900]Currently, the industry standards is Nafion
[00:01:07.290]but due to its fluorinated chemical makeup,
[00:01:09.950]it is expensive to produce and environmentally harmful
[00:01:13.360]when it breaks down into perfluorocarbons.
[00:01:16.410]A promising alternative is PBC 1.0.
[00:01:19.421]1.0, referring to the ion-exchange capacity
[00:01:21.780]of this membrane.
[00:01:23.310]It is cheaper to produce and less environmentally harmful
[00:01:26.300]to dispose off due to the fact that it is not fluorinated.
[00:01:29.340]In both cases, the functional group responsible
[00:01:32.290]for transporting the ions is the sulfuric acid group.
[00:01:38.320]To understand my motivation,
[00:01:39.470]you need to understand that the ion transport properties
[00:01:42.120]are correlated with the water and cation interaction.
[00:01:45.160]I have this displayed with my graphic on the right.
[00:01:47.270]You can see that the positive cation
[00:01:49.430]is interacting solely with the water molecules
[00:01:51.510]moving through the membrane.
[00:01:53.030]This is easily understood with my graphic on the bottom
[00:01:55.770]where you can imagine that the people
[00:01:57.890]are acting as the water, and that the ball
[00:02:00.340]is the cation moving along the line
[00:02:02.920]much like the cation moves through the membrane.
[00:02:05.810]The strength of this interaction can change
[00:02:08.450]with a different size or different charge of the cation
[00:02:11.350]that is being used.
[00:02:13.060]Further investigations with varying cations is necessary
[00:02:15.910]to fully understand their effect on cell performance.
[00:02:18.270]As thus far, the majority of studies has been done
[00:02:20.450]on H+ proton ion due to that being the principal ion
[00:02:24.450]used in the membrane.
[00:02:26.160]For my research, I'm focusing on investigating the effect
[00:02:29.010]on cations on water uptake and ion transport.
[00:02:33.790]For my first objective,
[00:02:34.930]I will need to exchange the hydrogen ions
[00:02:37.010]with the variety of metal ions.
[00:02:38.990]I will then use those to investigate the effect
[00:02:41.060]on ion transport and water uptake.
[00:02:45.220]To do this, first I only need to acidify the membrane
[00:02:48.190]To do this, I boiled it in sulfuric acid
[00:02:50.310]at 80 degrees Celsius.
[00:02:51.830]I then rinsed and boiled it in DI water
[00:02:54.010]at 80 degrees Celsius.
[00:02:55.510]Finally, to store it in DI water
[00:02:57.000]in a sealable container.
[00:02:58.750]To incorporate the metal ions,
[00:03:00.110]I boiled it in a salt solution at 80 degrees Celsius
[00:03:02.470]which contained the metal ions.
[00:03:04.300]I rinsed in DI water and boiled in DI water again
[00:03:06.750]at 80 degrees Celsius.
[00:03:08.190]And finally, to remove any remaining contaminants,
[00:03:10.650]we dried the membrane in a vacuum oven
[00:03:12.440]at 60 degrees Celsius.
[00:03:16.620]For my ion transport data, you can notice
[00:03:18.660]that the Y-axis is the average conductivity value
[00:03:21.280]measured in milliSiemens per centimeter.
[00:03:23.550]On the X-axis,
[00:03:24.470]I have the variety of cations that we employed.
[00:03:27.400]We also took measurements at three different temperatures
[00:03:29.680]being 30 degrees Celsius, 50 degrees Celsius,
[00:03:32.770]and 70 degrees Celsius.
[00:03:34.430]You may notice that despite a change in temperature
[00:03:36.610]all trends remained constant.
[00:03:39.380]We can also notice the monovalent cations
[00:03:41.400]are more conductive than divalent cations in all cases.
[00:03:45.140]Also, the H+ form is approximately
[00:03:47.800]10.6 times more conductive than all metal forms.
[00:03:53.420]When coming to our water uptake data,
[00:03:55.270]we define that as the wet mass
[00:03:57.170]subtracted by the dry mass,
[00:03:58.740]divided by the dry mass,
[00:04:00.120]multiplied by a hundred.
[00:04:01.950]That percentage I have displayed as the Y-axis.
[00:04:04.460]And then once again, on the X-axis,
[00:04:05.890]I have the cations that we used.
[00:04:09.140]From this graph, we can notice that monovalent cations
[00:04:11.620]had a greater increase in mass than all divalent cations.
[00:04:16.310]The greatest increase is being held by lithium ion
[00:04:19.050]which is associated with the changes in the
[00:04:20.740]interconnected sulfonated domains that it causes.
[00:04:25.660]The conclusion we can make from this data
[00:04:27.530]are that cell performance when pertaining to water uptake
[00:04:30.160]and ion transport of the PBC 1.0 membrane
[00:04:34.010]is significantly affected when exchanged with cations.
[00:04:38.340]Also, divalent cations have greater interactions
[00:04:41.640]than monovalent with the sulfonic acid moieties
[00:04:44.630]which prevents the greater water uptake.
[00:04:48.410]Furthermore, the increased interaction
[00:04:50.100]between the metal cations and the sulfonic acid moieties
[00:04:53.280]decreases the conductivity when compared to the H+ form.
[00:04:57.440]Future investigations would involve investigating the effect
[00:04:59.840]on mechanical and thermal stability,
[00:05:01.750]as well as the morphological transitions to gain a better
[00:05:04.380]perspective on the overall effect on fuel cell performance.
[00:05:10.410]I'd like to take a moment
[00:05:11.400]to thank the Nebraska Public Power District
[00:05:13.430]and the Nebraska Center for Energy Science Research
[00:05:15.720]for funding this project. Thank you.

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The Study of Monovalent and Multivalent Cations Exchanged with Sulfonated Ionomers: Water Uptake and Ion Transport

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