Nanoscale Mechanical and Ion Conduction Properties of Fuel Cell Ionomers

Jackson Goddard Author

08/04/2020 Added

14 Plays

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Poster presentation of my 2020 NCESR internship.

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[00:00:00.110]Hello, my name is Jackson Goddard
[00:00:02.315]I am going into my junior year as a
[00:00:04.333]double major in chemical engineering
[00:00:06.033]and mathematics.
[00:00:07.216]This summer I worked with Dr. Dishari
[00:00:08.985]on a study of the nanoscale mechanical and
[00:00:10.986]ion conduction properties of fuel
[00:00:12.543]cell ionomers
[00:00:13.837]A little bit of background
[00:00:15.681]about this project, our current source of
[00:00:17.890]energy from fossil fuels is having a
[00:00:19.929]very large, negative impact on our
[00:00:21.280]environment
[00:00:22.363]So one of the ways to solve this problem
[00:00:23.877]is to improve our energy sustainability
[00:00:26.163]by implementing clean energy technologies
[00:00:28.862]An example is the proton exchange membrane
[00:00:31.059]fuel cell
[00:00:32.489]or hydrogen fuel cell
[00:00:34.164]the way that these cells work
[00:00:36.013]is that you have an anode and a cathode
[00:00:37.562]and also have some catalysts
[00:00:39.462]and a membrane to bind
[00:00:41.362]the catalyst to the substrate
[00:00:42.967]some of these membranes they are called
[00:00:47.134]ionomers they are the ion version
[00:00:49.567]of a polymer
[00:00:51.666]they can be very bad for the environment
[00:00:53.799]to produce and/or dispose of
[00:00:55.601]but they are also very expensive
[00:00:57.534]one of the options
[00:00:59.284]we have is you cut the membrane very thin
[00:01:00.917]so instead of having a few microns thick
[00:01:05.251]you only have a few nanometers thick
[00:01:06.734]when you do that you find that the
[00:01:08.084]mechanical properties and the
[00:01:09.384]ion conduction change dramatically
[00:01:10.785]the focus of this project
[00:01:12.469]was to develop a better understanding
[00:01:15.266]of the nanoscale characteristics as
[00:01:17.216]functions of film thickness and
[00:01:18.650]relative humidity
[00:01:20.933]So the materials used in this project
[00:01:23.201]are nafion which is the industry standard
[00:01:25.964]is has been produced for many years
[00:01:28.868]and is a perfluorosulfonic acid ionomer
[00:01:31.350]and we also used PFIA which is an
[00:01:33.135]alternative and is a perfluoroimide acid
[00:01:35.318]ionomer
[00:01:36.451]you can tell by looking at them that
[00:01:38.273]PFIA has a much longer sidechain
[00:01:39.957]and they also have different chemical
[00:01:42.139]backbones which obviously change their
[00:01:44.723]behavior in different ways
[00:01:47.138]So the methods we have to produce these
[00:01:49.928]samples we have some ionomer solutions
[00:01:52.719]of 1, 2, 5, 7, and 10 weight percent
[00:01:55.386]and they are sonicated and mixed then
[00:01:58.137]spin coated onto silicon oxide wafers
[00:02:00.705]and they are dried at 42 C for 3 hours
[00:02:04.107]then at 100 C for 7 hours
[00:02:06.493]before being cooled down to room
[00:02:08.991]temperature for about 12 hours
[00:02:10.775]and you do that to anneal them which
[00:02:13.463]makes them much tougher and harder
[00:02:17.042]to damage them so you can do more
[00:02:18.675]with them
[00:02:20.664]and the methods of measurement we have
[00:02:22.141]are contact resonance force microscopy
[00:02:25.126]which you take a cantilever a couple
[00:02:28.387]microns long and put it onto the surface
[00:02:30.404]of the film and send a current through it
[00:02:33.751]and it will vibrate and some data is
[00:02:38.569]put out that is entered to some equations
[00:02:40.923]to derive some properties
[00:02:42.473]we also use electrochemical
[00:02:44.207]impedance spectroscopy or EIS
[00:02:45.740]and it works by taking a special wafer
[00:02:50.173]called an interdigitated electrode array
[00:02:56.735]called an IDE and you put a current
[00:02:59.314]through that to measure the impedance
[00:03:04.419]going onto the results section
[00:03:07.053]we can look at the series of graphs from
[00:03:08.435]PFIA and nafion those graphs together show
[00:03:11.569]what we call the viscoelastic modulus
[00:03:14.569]which is the data we obtain from the CRFM
[00:03:17.126]so we have the storage modulus which you
[00:03:19.618]can think of as the stiffness of the film
[00:03:23.148]versus the loss modulus which is
[00:03:26.045]how much the film will stretch
[00:03:29.759]it is very clear that PFIA has higher
[00:03:32.998]storage and loss modulus than nafion
[00:03:36.754]but for both films as film thickness
[00:03:39.818]decreases the moduli increase
[00:03:44.122]the loss tangent is the ratio between
[00:03:46.759]the two
[00:03:49.227]the significant difference in the
[00:03:52.292]viscoelastic modulus of these two ionomers
[00:03:55.374]indicates that the bisulfonyl imide group
[00:03:58.610]of the PFIA is having a different impact
[00:04:01.710]than that of nafion or
[00:04:04.094]the differences in the relative humidity
[00:04:05.975]of the two films
[00:04:07.360]nafion was measured at about 30 percent
[00:04:09.662]and PFIA was measured at about 48 percent
[00:04:13.227]we'll talk about that later
[00:04:14.277]going onto the conductivity data only
[00:04:17.145]for nafion we had some issues with the EIS
[00:04:19.791]but that is resolved now so we can
[00:04:21.366]measure more later
[00:04:22.662]the film resistance is proportional to
[00:04:27.149]the diameter of the semi-circle on the
[00:04:29.498]impedance curve
[00:04:30.847]so looking at the curve now
[00:04:32.632]we can see that the thickest film of
[00:04:35.033]168 nanometers is almost a straight line
[00:04:37.200]while the curve for the 21 nanometer film
[00:04:41.649]the purple line has a large semicircle
[00:04:43.449]so film resistance is inversely related to
[00:04:47.769]conductivity so the 21 nanometer film
[00:04:50.169]has large resistance and therefore
[00:04:53.384]low conductivity while the thicker film
[00:04:55.851]has very low resistance and therefore very
[00:05:01.147]high conductivity films with low
[00:05:04.464]resistance and higher conductivity are
[00:05:06.530]more desirable for PEMFCs
[00:05:10.983]this is a technical detail the IDEs
[00:05:13.739]that were used had 110 gold teeth that
[00:05:17.307]were 10 microns wide 100 microns apart
[00:05:20.650]and an overlap of 8 millimeters
[00:05:22.551]depending on the IDE it will change
[00:05:24.635]the equations and yield slightly different
[00:05:26.569]results so it is important you report
[00:05:29.883]what kind of IDE you are using
[00:05:32.751]so in terms of relative humidity
[00:05:35.285]it is very important to manage this
[00:05:38.003]because it will have a drastic impact on
[00:05:42.233]your results so for PFIA which was
[00:05:45.934]measured in June while nafion was
[00:05:47.866]measured in January
[00:05:49.500]being in Nebraska you will have a large
[00:05:51.666]swing of humidity between those
[00:05:54.067]two seasons and so one thing I
[00:05:56.884]wanted to do was for the CRFM chamber
[00:05:59.034]was we wanted to control the relative
[00:06:00.733]humidity of it
[00:06:01.698]we started with the EIS which was a
[00:06:04.266]smaller volume and we found that if
[00:06:06.066]you use different salt solutions you
[00:06:07.866]produce different relative humidities
[00:06:10.233]so we scaled it up to the CRFM and that
[00:06:12.001]is ongoing but we hope to implement that
[00:06:14.176]before the end of the month
[00:06:15.948]going to the conclusions and future work
[00:06:19.518]talking about the film properties and
[00:06:22.468]the thickness effect
[00:06:24.648]as the film decreases below 100 nanometers
[00:06:26.415]you are going to see a much larger
[00:06:28.951]increase of the viscoelastic modulus
[00:06:30.501]this is mainly due to confinement
[00:06:33.466]which entire papers have written about
[00:06:35.417]this phenomenon but essentially you have
[00:06:37.266]films become thinner there is less room
[00:06:41.315]for them to move around I guess you
[00:06:43.984]can think of so therefore they will
[00:06:46.050]have different characteristics
[00:06:47.867]in this study the sizeable difference
[00:06:50.767]between to the two ionomers
[00:06:53.615]can be attributed to either the relative
[00:06:55.634]humidity or the side chains
[00:06:57.700]as we mentioned before PFIA has a much
[00:07:00.185]longer side chain than nafion therefore
[00:07:02.165]they are going to behave differently
[00:07:04.417]Also when you get to thinner films
[00:07:07.267]they may display non uniformity
[00:07:09.382]which basically because of the side chains
[00:07:12.214]if you measure a certain part of the film
[00:07:14.534]it is going to behave differently than
[00:07:16.899]another part of the film
[00:07:18.872]So we are going to include a larger
[00:07:20.651]array of area of measurement on these
[00:07:23.125]films hopefully we will figure out if
[00:07:25.322]that is the cause of if it is something
[00:07:26.936]else
[00:07:27.652]going on to relative humidity it is clear
[00:07:29.080]that humidity will change the property
[00:07:31.912]of the film
[00:07:34.030]one idea is that water creates strong
[00:07:35.779]intermolecular forces
[00:07:37.544]due to the highly polar side chains thus
[00:07:39.605]forming hydrogen bonds
[00:07:41.827]we are going to try to combat that
[00:07:45.633]by again modifying the CRFM machine
[00:07:48.266]to control the relative humidity and then
[00:07:50.716]also need to fix both of these devices
[00:07:53.482]so this project can continue
[00:07:56.464]I am hoping to present my upcoming
[00:07:59.000]findings in the spring
[00:08:00.799]I would like to thank the
[00:08:03.365]Nebraska Center for Energy Sciences
[00:08:05.216]Research NCESR for funding this project
[00:08:08.000]for me and also Dr. Dishari
[00:08:09.665]for being such a great mentor and such a
[00:08:11.766]great resource throughout all aspects
[00:08:13.783]of this project and in addition
[00:08:15.867]I would like to thank Tyler Johnson who
[00:08:18.082]is a grad student that mentored me
[00:08:19.816]throughout a large portion of this project
[00:08:21.698]he just graduated so congratulations to
[00:08:24.382]him and everybody involved in Dishari's
[00:08:26.731]lab has been phenomenal and I am
[00:08:28.783]very thankful for being able to
[00:08:29.661]work with them
[00:08:30.853]thank you and have a good rest
[00:08:31.611]of your day

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Nanoscale Mechanical and Ion Conduction Properties of Fuel Cell Ionomers

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