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

2. Fluoropolymer Ionomers; TFE / TFVE copolymers, perfluoro-cyclobutyl (PFCB) aryl ether ionomers including telechelic ionomers

3. Electrochemistry of platinum at mesoporous carbon with surface-attached fluoropolymer ionomers

4. Mixed electronic / ionic conduction in carbon / fluoropolymer ionomer composites

The fuel cell; an energy conversion device

Electron donor;

Chemical fuel. Often hydrogen gas but could also be:

•Methanol• Ethanol•Carbon monoxide•Ammonia• Formic acid•Hydrocarbons•Glucose•Carbohydrates

Load

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:

•Hydrogen peroxide•Nitric oxide •Nitrous oxide • Sulfate •Nitrate

Exhaust. Often nothing, but sometimes CO2.

Exhaust. Often water, H2O

electrons

Some early fuel cell history

1842, Grove;

The gaseous

voltaic battery

1889, Mond & Langer;

Gas Battery with

Membrane Separator

1922, Rideal

and Evans; First

use of the term

“fuel cell”

1889, Wright &

Thompson; Double

Aeration Plate Cell

1937, Baur,

Solid-oxide

fuel cell

1967, Pratt & Whitney

Aircraft, Phosphoric

acid fuel cell

1954, Bacon,

Alkaline FC

1960, General Electric,

Polymer Electrolyte

Membrane (PEM) Fuel

Cell

1965, NASA, Alkaline

fuel cells used in Apollo

missions

1962, NASA, PEM fuel

cells used in Gemini

missions

1972, DuPont, first

use of Nafion

fluorinated

separators in PEM

fuel cell

1840 19751900 1950

1960,

Westinghouse,

Cylindrical

ceramic SOFC

1897, J. J. Thompson

discovers the electron

The Gaseous Voltaic BatteryWilliam R. Grove, Swansea, Wales, 1842

Reproduced from

Hoogers, “Fuel

Cell Technology

Handbook”, CRC

Press, 2003.

Gas Battery with SeparatorMond and Langer, 1889

Reproduced from Hoogers, “Fuel Cell Technology Handbook”, CRC Press, 2003.

Double Aeration Plate Cells

Reproduced from Hoogers, “Fuel Cell Technology Handbook”, CRC Press, 2003.

Wright and Thompson, 1889

Some common fuel cell types

Fuel cell

type

Electrolyte Charge

carrier

Operatin

g temp

(oC)

Fuel(s) Electric

efficiency

(system)

Typical

power

range

Proton

exchange

membrane

(PEM)

Proton-

conducting

polymer (e.g.

Nafion)

H+ 50 – 130 H2 with some

CO and/or

CO2 also,

Methanol

35-45% 5 – 250

kW

Alkaline KOH / H2O OH- 60 – 120 Pure H2 35-55% <5 kW

Phos-

phoric acid

Phosphoric

acid

H+ 200 – 220 H2 with some

CO and/or

CO2

40% 200 kW

Molten

Carbonate

Li2CO3 and

K2CO3

CO32- 650 H2, CO, CH4,

hydrocarbons

>50% 200 kW –

several

MW

Solid

Oxide

Solid oxide

electrolyte

(e.g. Yttria)

O2- 800 –

1000

H2, CO, CH4,

hydrocarbons

>50% 2 kW –

several

MW

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.”

Solid-Polymer-Electrolyte / PEM fuel cell

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

hydrogen storage tank. Fuel cell itself weighs 148 lbs.

• Hydrogen for refueling will be produced in a HOME ENERGY STATION by

steam reforming of natural gas

• Slated for limited release in California in summer 2008.

• Will lease for $600 / month for three years... but only 200 vehicles!

http://www.gizmag.com/honda-fuel-cell-fcx/8394/3/ accessed 10/15/08

A “mass-produced” hydrogen-fuel-cell-powered car for 2015; The Hyundai Tucson Fuel Cell

A similar car, the Tucson ix35 Hydrogen Fuel-Cell Electric vehicle, is already available in Europe.

From the Hyundai web site, https://www.hyundaiusa.com/tucsonfuelcell/ accessed 10/13/2014

“Mass produced” means they are manufactured on the same production line as the non-FC vehicles.

Hyundai says they will produce at least 1000 of these vehicles by 2016.

So far they are available in the US only in Southern California, and only for lease.

Hydrogen fueling

stations in southern California

http://www.cafcp.org/stationmap accessed Oct 12 2014

Materials in a PEM fuel cell The Membrane-electrode assembly (MEA)

Electrode; Carbon + catalyst + electrolyte

Membrane; Fluoropolymer electrolyte

TFE copolymer ionomers

25

Bis((perfluoroalkyl)-sulfonyl)imide acid ionomers (PFSIs)

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

R-PO3H2 =

carbon

zirconiaR-PO3H2

catalyst

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

NaOH

etchin

g

Mesoporous carbon nanofoamcontaining embedded zirconia

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 deposition onto carbon/zirconia/platinum proceeds

cleanly

Before ionomer modification

After ionomer modification

• 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!