Tutorial: Fuel Cells and… Telechelic Fluoropolymer Ionomers Suitable for Surface Grafting onto Mesoporous Solid Supports Stephen Creager , Jiyoung Park, Jung-Min Oh, Jamie Shetzline Clemson University, Clemson, SC Department of Energy National Science Foundation Steve Creager Electrochemistry & Carbon Fluoropolymers 2014, San Diego, CA. Oct 13-16 2014 Darryl DesMarteau Fluoropolymers Dennis Smith Polymers & Carbon Joe Thrasher Fluoropolymers
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Tutorial: Fuel Cells and…
Telechelic Fluoropolymer Ionomers Suitable for
Surface Grafting onto Mesoporous Solid Supports
Stephen Creager, Jiyoung Park, Jung-Min Oh, Jamie Shetzline
Clemson University, Clemson, SC
Department of
Energy
National Science
FoundationSteve Creager Electrochemistry & Carbon
Fluoropolymers 2014, San Diego, CA. Oct 13-16 2014
Darryl DesMarteau Fluoropolymers
Dennis Smith Polymers & Carbon
Joe ThrasherFluoropolymers
The Creager Research Group, Fall 2014
Four topics for today;
1. Fuel Cell Tutorial; History and fluoropolymer connections for PEM fuel cells
Separator; Transports ions between electrodes. Ion type is often protons but can vary depending upon fuel cell type. Must prevent fuel / oxidant from mixing
Anode CathodeElectron acceptor;
Chemical oxidant. Often oxygen gas but could also be:
From Hoogers, “Fuel Cell Technology Handbook”, Table 1.1
Apollo Mission Fuel CellsPratt & Whitney, circa 1965
Reproduced from Hoogers,
“Fuel Cell Technology
Handbook”, CRC Press,
2003.
Alkaline fuel cells;
Power = 460 - 1400 W
Lifetime = 400 hours
Note; A typical midsized SUV
uses about 200 kW of power.
The 1966 General Motors Electrovan; An alkaline- fuel-cell-powered electric vehicle
Reproduced from
Hoogers, “Fuel Cell
Technology
Handbook”, CRC
Press, 2003.
The Electrovan also had a range of 120 miles, which was not too shabby for 1966. Because of safety concerns, the Electrovan was only used on company property, where it had several mishaps along the way.”
From the web site “Hydrogen Cars Now”; http://www.hydrogencarsnow.com/gm-electrovan.htm accessed Oct 13 2014
“After the GM Electrovan was built, tested and shown off to journalists in 1966, the project was scrapped largely because it was cost-prohibitive. The platinum used in the fuel cell was enough to "buy a whole fleet of vans" and there was absolutely no supporting hydrogen infrastructure in place at that time.”
General Electric, 1960 Reproduced from Hoogers, “Fuel Cell Technology Handbook”, CRC Press, 2003.
Nafion; First synthesized at DuPont in the early 1960’s
Walther Grot, “Fluorinated Ionomers; History, Properties and Applications”. Chapter 12 in Introduction to Fluoropolymers: Materials, Technology and Applications, William Andrews Publishers, an imprint of Elsevier, Waltham MA 2013 ISBN 978-1-4557-7442-5
Ballard Fuel Cells; Power for Electric Vehicles, ~ 2003
Mark 5;
5 kW
Mark 513;
10 kW
Mark 700;
25 kW
Mark 800;
50 kW
Mark 900;
85 kW
Reproduced from Hoogers, “Fuel Cell Technology Handbook”, CRC Press, 2003.
FYI: 85 kW =
114 horsepower
DaimlerChrysler’s first three fuel-cell-powered vehicles: NeCar 1,
NeCar 2, and NeCar 3
Reproduced from
Hoogers, “Fuel Cell
Technology
Handbook”, CRC
Press, 2003.
Fuel-Cell-Powered Buses
Reproduced from
Hoogers, “Fuel Cell
Technology
Handbook”, CRC
Press, 2003.
Chicago
2008; Honda FCX Clarity Hydrogen Fuel-Cell Car
• Fitted with a 100 kW (138 hp) fuel-cell-powered engine and a 5000 psi
Perfluoroalkyl sulfonic acid ionomers (PFSAs, e.g. NafionTM)
• Often very high MW with few end groups. • No obvious way to attach to a solid surface.
Barricade – Control and Reaction Modules(H1-Rated Laboratory for TFE and Other Hazardous
Chemistry)
A telechelic perfluorocyclobutyl (PFCB) ionomer
Why do this???
1. Attach ionomer to a solid support2. Prevent ionomer dissolution into solvent (water) 3. Enable use of higher IEC / lower MW ionomers4. Allow for greater ionomer penetration into pores5. Create a nanoporous mixed electronic / ionic conductor
A cartoon:
A real polymer:
Jiyoung Park, Jung-Min Oh, Stephen E. Creager and Dennis W. Smith Jr. “Grafting of Chain-End-Functionalized Perfluorocyclobutyl (PFCB) Aryl Ether Ionomers onto Mesoporous Carbon Supports” Chemical Communications, 48, 8225-8227 (2012)
Electrolyte binding via embedded zirconia particles
1. Resorcinol / formaldehyde RF gel; add silica sol as pore-forming templating agent, then add zircona sol as anchoring sites for electrolyte attachment
2. Gel / Dry / Carbonize / Etch, carbon nanofoam with embedded zirconia!
1050oC Drying Na2CO3,
heat
RF Monomers Wet RF sol/gel
OH
OH H H
O 2 +
Dry RF gel Carbon aerogel/
Carbon xerogel
1050oC Drying Na2CO3,
heat
RF Monomers Wet RF sol/gel
OH
OH H H
O 2 +
Dry RF gel Carbon aerogel/
Carbon xerogel
1050oC Drying Na2CO3,
heat
RF Monomers Wet RF sol/gel
OH
OH H H
O 2 +
Dry RF gel Carbon aerogel/
Carbon xerogel
Jung-Min Oh, Amar S. Kumbhar, Olt Geiculescu, and Stephen E. Creager, “Nanoscale ZrO2 - embedded Mesoporous Carbon Composites: A Potential Route to Functionalized Mesoporous Carbon Composite Materials”, Langmuir, 28, 3259-3270 (2012)
+ SiO2 + ZrO2
Platinum deposition onto carbon nanofoams• Platinum nanoparticles were deposited from hexachloro-
platinic acid solution by the incipient wetness method with reduction by ethylene glycol / borohydride.
• Resulting materials are approximately 20 wt% Pt, with Pt particle sizes of 2.8 – 3.5 nm by TEM and XRD
Jung-Min Oh, Jiyoung Park, Amar Kumbhar, Dennis Smith Jr., and Stephen Creager “Electrochemical Oxygen Reduction at Platinum / Mesoporous Carbon / Zirconia / Ionomer Thin-Film Composite Electrodes” Electrochimica Acta 138, 276-287 (2014)
• Ionomer binds to Pt/ZCS in exactly the same way as it binds to ZCS.
• The resulting material is 18 wt% Pt, 13 wt% ionomer, and has an IEC of 0.46 mmol/g.
• No Pt is lost when the ionomer binds
Jung-Min Oh, Jiyoung Park, Amar Kumbhar, Dennis Smith Jr., and Stephen Creager “Electrochemical Oxygen Reduction at Platinum / Mesoporous Carbon / Zirconia / Ionomer Thin-Film Composite Electrodes” ElectrochimicaActa, submitted Feb 2014
Oxygen Reduction Reaction (ORR) Electrocatalysis
Pt/CS Pt/ZCS
Pt/ZCS/Ionomer
Pt/CS Pt/ZCS
Pt/ZCS/Ionomer
• Oxygen reduction was studied using rotating-disk electrode voltammetry with glassy carbon disks coated with thin films of Pt/carbon/zirconia/ionomer, bound with Nafion, in 0.1 H H2SO4
at ambient temperature.
• Kinetic currents for ORR were obtained at 0.90 V vs. NHE (+0.22 V vs. Hg/HgSO4) using a Koutecky-Levech analysis to account for possible limitations on the current from mass transfer
Jung-Min Oh, Jiyoung Park, Amar Kumbhar, Dennis Smith Jr., and Stephen Creager “Electrochemical Oxygen Reduction at Platinum / Mesoporous Carbon / Zirconia / Ionomer Thin-Film Composite Electrodes” Electrochimica Acta 138, 276-287 (2014)
Table 1 Critical parameters for platinum ORR catalysts on mesoporous carbon supports.
Sample
Pt
conten
t
Ptloading
onto
RDEb
Tafel
slopec
Ikat0.9
Vvs.
NHE
massORR
activityd
arealORR
activityd
weight
% μg
mV/de
cade μA mA/mgPt μA/cm2Pt
Pt/CS 20 467 108 358 77 124
Pt/ZCS 21 490 129 248 51 101
Pt/Ionomer-ZCSe 18 479 131 354 74 145
VulcanXC-72,0.05M
H2SO4,30Cf 20 70 105
VulcanXC-72,0.10M
HClO4,60Cg 20 130-160 200-230
a. From hydrogen adsorption / desorptionb. RDE area = 0.196 cm2
c. For data points 0.10 V and 0.25 V vs. MSE, or 0.78 V and 0.93 V vs. NHEd. Activity at +0.90 V vs. NHEe. Sample is 13 wt% ionomer and 87 wt% Pt/ZCS. f. Y. Garsany, O.A. Baturina, K.E. Swider-Lyons, S.S. Kocha, Experimental Methods for Quantifying the Activity of Platinum Electrocatalysts for
the Oxygen Reduction Reaction, Analytical Chemistry, 82 (2010) 6321-6328.g. H.A. Gasteiger, S.S. Kocha, B. Sompalli, F.T. Wagner, Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction
catalysts for PEMFCs, Applied Catalysis B: Environmental, 56 (2005) 9-35
Jung-Min Oh, Jiyoung Park, Amar Kumbhar, Dennis Smith Jr., and Stephen Creager “Electrochemical Oxygen Reduction at Platinum / Mesoporous Carbon / Zirconia / Ionomer Thin-Film Composite Electrodes” Electrochimica Acta, submitted Feb 2014
Mixed Ionic Electronic Conduction (MIEC)
GlassyCarbon
DC voltage
Dc current
Silver
Nafion-H+
DC voltage
Dc current
Nafion Ag+
Electronic Ionic
SampleSample
Cell Design
b)
c)
d)
e)
f)
g)
h)
a)
i)h)
h)
Mixed conduction in samples containing carbon black and Nafion
• Increasing relative humidity causes electronic conductivity to fall and ionic conductivity to rise.
• This finding probably reflects a combination of dimensional changes and intrinsic phase conductivity changes associated with water uptake as RH increases.
Jamie Shetzline and Stephen Creager “Quantifying electronic and ionic conductivity contributions in carbon/polyelectrolyte composite thin films” Journal of the Electrochemical Society, 161 (14), H917-H923 (2014)
20% carbon black
Conductivity values measured at 80 C.
10% carbon black
Blue = electronic conductionRed = ionic conduction
Summary
• Fuel cells are electrochemical energy conversion devices that utilize ionically-conductive materials in multiple ways
• Low-temperature fuel cells often use fluoropolymer ionomer electrolytes as ion conductors (usually proton conductors) in membrane separators and in electrodes.
• Mixed electronic / ionic conduction in electrodes is important in optimizing electrode activity
Thank you Scott for the invitation and ACS for logistical support!