@2013 SAFCell, Inc. @2013 SAFCell, Inc. 1 · Chicago, IL. June 7th 2013. @2013 SAFCell, Inc. 3. Contents ... (SeO 4) 2 (NH 4) 3 H(SO 4) 2 Cs 2 (HSO 4)(H 2 PO 4) CsHSeO 4 CsHSO 4 log

1@2013 SAFCell, Inc.

@2013 SAFCell, Inc.

Solid Acid Fuel Cells: Overview and Opportunities

ARPA-E Workshop

Chicago, IL

June 7th 2013


Contents

Solid Acid Electrolytes

Cesium Dihydrogen Phosphate

Solid Acid Fuel Cells

SAFC Fuel Flexibility

Cost Reduction Opportunities

Summary




Intermediate salts and acids

1Cs3

PO4

+ 2H3

PO4

3CsH2

PO4

General Formula: Mx

Hy

(XO4

)z

M = Cs, Rb, K, NH4

, Tl

X = S, Se, P, As

Properties (Low Temperature)

Slow proton conductor

Brittle/Gas permeable

Water soluble

Properties (High Temperature)

Fast proton conductor

solid state

Plastic-like/Gas impermeable

Water (steam) insoluble

50 100 150 200 250 3001E-8

1E-6

1E-4

0.01

1

Con

duct

ivity

(1/c

m)

Temperature (C)

Polymer (Nafion)

Solid Acid (CsH2PO4)

Solid Acid Conductivity

superprotonic

normal phase transition

Haile, Nature, 2001; Boysen, Science, 2004


Cs+

SO4–2

H+

“Superprotonic” Solid Acids

Structural solid-solid phase transition (order-disorder)

Heat 100

-1000 fold increase in proton conductivity

Superprotonic (σ

~ 10-2

Ω-1cm-1)

Oxy-anions “freely”

rotate

OrderedNormal Structure

DisorderedSuperprotonic

heat


1. Oxy-anion Reorientation

2. Proton Transfer

Proton Transport Mechanism

H

OS

109 Hz

1012 Hz

Grotthus Mechanism

Cesium Dihydrogen Phosphate


0 2 4 6 8 10 12

90

92

94

96

98

100

CsHSO4

Cs2SO4

Cs2(HSO4)(H2PO4)

(NH4)3H(SeO4)2

Rb3H(SeO4)2

Mas

s (w

t%)

Time (hours)

(NH4)3H(SO4)2

2.0 2.5 3.0 3.5

-7

-6

-5

-4

-3

-2

-1250 200 150 100 50

Rb3H(SeO4)2

(NH4)3H(SO4)2

Cs2(HSO4)(H2PO4)

CsHSeO4

CsHSO4

log

/

-1cm

-1)

1000/T (K-1 )

CsH2PO4

Temperature (C)

Cesium Dihydrogen Phosphate What about other solid acids?

Proton Conductivity Thermal Gravimetric Analysis in Hydrogen

Sulfates and selenates are not stable in hydrogen only phosphates and arsenates usable in fuel cells

Sulfates and selenates are not stable in hydrogen only phosphates and arsenates usable in fuel cells

superprotonic

Merle, Energy & Fuels, 2003


Cesium Dihydrogen Phosphate Thermodynamic stability

No evolution of phosphate species from CsH2 PO4 (Pt) in either hydrogen and oxygen atmospheres

92

94

96

98

100

100 150 200 250 300 350 400

10-13

10-12

10-11

10-10

10-9

10-8

92

94

96

98

100

100 150 200 250 300 350 400

10-13

10-12

10-11

10-10

10-9

10-8

285C

Hea

t flo

w DSC

5C min-1

238C285C

endo

M

ass

(w

t%)

TG/DTG 223C

T (C)

Ion

curr

ent

(mA

)

T (C)

Mass Spec

ArH2

H2O

O2

P/P2/PO2/P2H4PO/PH3

285C

DSC238C

285C

5C min-1

en

do

TG/DTG

285C

223C

-6.3 wt%

-6.3 wt%

H2O

O2

Ar

Mass Spec

P

PH3/P2/P2H4/PO2H2/PO

285C

H2 Atmosphere O2 Atmosphere


Cesium Dihydrogen Phosphate Electrical properties

1.9 2.0 2.1 2.2 2.3

-4

-3

-2

-1

0

1

log(T

/-1cm

-1K

)

1/T10-3 (K-1)

270 240 210 180 150

T (C)

Superprotonic phase transition

TSP

= 231°C

Proton conductivity jump

< 8.5 x 10-6 Ω-1cm-1 at 223°C

> 1.8 x 10-2

Ω-1cm-1

at 233°C

Hysteresis

Upon cooling 5-30 °C

Superprotonic conductivity

Typical conductivity

~ 2.5 x 10-2

Ω-1cm-1 at 250°C

Temperature range

232-280°C*

* Dependant on PH2O

Haile et al, Faraday Discussions, 2007

Arrhenius Plot of Conductivity

Ea

= 0.42 eV

CsH2

PO4


Cesium Dihydrogen Phosphate Thermal properties

Long debated in literature

Stability proven under water partial pressure (PH2O

)

How much PH2O

to stabilize superprotonic CsH2

PO4

?

CsH2

PO4

CsPO3

+ H2

O

Dehydration temperature (Td

) is almost commensurate with superprotonic phase transition temperature (TSP

) at ambient humidity levels

Td

TSP

(PH2O

< 0.1 bar)

Dehydration temperature (Td

) is almost commensurate with superprotonic phase transition temperature (TSP

) at ambient humidity levels

Td

TSP

(PH2O

< 0.1 bar)


220 240 260 280 3000.0

0.1

0.2

0.3

0.4

CsH 2(1-x)PO 4-x

(l)<-->

CsPO 3

+ (1-x)

H 2O(g)

liquiddehydrant

solid dehydrant

superprotonic

CsH 2(1-x)

PO (4-x)

(l )

CsPO3(s)

CsH2PO4(s)

Wat

er p

artia

l pre

ssur

e, P

H2O

/ ba

r

Temperature, T / C

CsH2PO4(s)

paraelectric

CsH2PO4 Stability-Phase Diagram

CsH 2PO 4

<--> CsPO 3 + H 2

O(g)

CsH 2

PO4 <

--> C

sH2(

1-x)

PO4-

x (l

) + x

H 2O

(g)

Cesium Dihydrogen Phosphate Humidity-temperature stability-phase diagram

Region of “safe” fuel cell

operation

Region of “safe” fuel cell

operation

Can easily avoid electrolyte dehydration with slight humidification (Tdew > 65 °C)

Can easily avoid electrolyte dehydration with slight humidification (Tdew > 65 °C)

*Taninouchi, J. Mater. Chem., 2007; Taninouchi, Solid State Ionics, 2007;

Ikeda, Solid State Ionics, 2012


0 100 200 300 400 5000

2

4

6

8

10

12

Pure CDP 10 wt% SiO2

250C, 1.44105 Pa

stra

in,

1

03 / (

l/lo)

time, t / min

Cesium Dihydrogen Phosphate Mechanical properties

Thermal Mechanical Analysis

Superprotonic = Superplastic

Ferroelastic

paraelastic

phase transition

Plastic deformation under load

Creep mechanism through dynamic disorder

Physically similar to clay or plasticine

Tailored mechanical properties

Silica “binder”

decreases plasticity

Grain boundary pinning


Cesium Dihydrogen Phosphate Properties pertinent to fuel cell operation

Water solubility

Must keep humidity below dew point of water

PH2O

< PH2O

(Tdew

)

Superprotonic transition temperature

No fuel cell operation until T > 231°C

Requires independent system for heating upon start-up

Dehydration temperature

Both fuel and air streams must be hydrated

Maximum operating temperature Tdehyd

~ 280°C

No condensation, no dehydration, no problem

Tdew < T < Tdehyd

No condensation, no dehydration, no problem

Tdew < T < Tdehyd

Solid Acid Fuel Cells


Solid Acid Fuel Cells Membrane electrode assembly

Membrane Electrode Assembly (1) Nickel foam, 98% porous

(2) PTFE sub-gasket

(3) Pt/C/CDP cathode catalyst

(4) CDP electrolyte

(5) Pt/C/CDP anode catalyst

(6) C/CDP/pore-former microporous

layer

(7) SS sinter mesh gas diffusion layer


Solid Acid Fuel Cells Bipolar plate and stack design

End Plate (304SS)

Gasket (SiO2-PTFE)

MEA

Bipolar Plate (Ni-coated 6061Al)


Solid Acid Fuel Cells Performance, scaling the cell

Performance scales with cell area. Performance scales with cell area.

0 100 200 300 400 500400

500

600

700

800

900

1000

3/4" D = 1.5 cm2 active area 2" D = 15 cm2 active area 5" D = 110 cm2 active area

Cel

l Vol

tage

[mV]

Current Density [mA/cm2]


Solid Acid Fuel Cells Performance, 5” MEA stacks

Stack performance scales linearly with number of cells.

Stack performance scales linearly with number of cells.

2”

MEA

Stack

5”

MEA

Stack

0 100 200 300 400 500400

500

600

700

800

900

1000

T = 240OCpH2O = 0.3 atmH2 stoich = 1.2Air stoich = 2

Aver

age

Cel

l Vol

tage

[mV

]

Current Density [mA/cm2]

Cells in Stack 1 = 25 W 5 = 125 W 30 = 750 W 60 = 1400 W


Solid Acid Fuel Cells Long-term performance, 10-cell stack (5” MEA)

Stack Voltage

5.6 V

Stack Current

20 A

~ 200mA/cm2

Stack Power

112 W @ 5.6 V

Degradation rate

-136 μV/h

-0.24% over 100 h 20 40 60 80 100 1200

2

4

6

8

10

60

80

100

120

140

160

180

200

Sta

ck P

ower

(W)

Stac

k V

olta

ge (V

)

Time (h)

Voltage

T = 240OCpH2O = 0.3 atmH2 stoich = 1.2Air stoich = 2

Stack Power

SAFC Fuel Flexibility

23@2013 SAFCell, Inc.H2 L

iquid

H2 Gas

[70M

Pa]LP

G prop

ane

LPG bu

tane

Gasoli

neDies

el

JP-8/

keros

ene

Biodies

elButa

nol

Ethano

l Meth

anol

0

5

10

15

20

25

30

35

40 V

olum

etric

ene

rgy

dens

ity (M

J/L)

Solid Acid Fuel Cells Why Fuel Flexibility?

Hydrocarbon-based fuels have 3-7 times the volumetric energy density of compressed hydrogen fuel Hydrocarbon-based fuels have 3-7 times the volumetric energy density of compressed hydrogen fuel


Solid Acid Fuel Cells Fuel flexibility, fuel reforming

Fossil fuel reforming (e.g. diesel, propane, natural gas)

Approaches: steam, auto-thermal, partial oxidative

High temperature gas shift reaction (500-700 °C)

Low temperature gas shift reaction (250-350 °C)

High measured impurity tolerances:

> 20% CO

> 250 ppm

H2

S

> 100 ppm

NH3

> 5% CH4

> 1% NO


Solid Acid Fuel Cells Performance on Commercial Propane Reformate

0.0 0.5 1.0 1.5 2.0 2.5 3.00

4

8

12

16

20

0.0

6.2

12.4

18.6

24.8

31.0

37.2

Hydrogen Commercial propane reformate (0 h) Commercial propane reformate (4 h)

Stac

k Vo

ltage

[V]

Current [A]

Sta

ck P

ower

[W]

Minimal effect of reformate on 20 cell stack performance

Mostly H2

dilution effect

Gas flow/compositions

Cathode

6.4 LPM air + 0.3 bar H2

O

Anode

Hydrogen: 1.0 LPM H2

+ 0.3 bar H2

O

Reformate: 5.8 LPM commercial* propane reformate + 0.3 bar H2

Ocommercial propane reformate:

41.1%H2

,

34.6%N2

10.6%CO

9.84%CO2

0.24%CH4

0.005%C3

H8

0.5ppmH2

S

*From Home Depot


Solid Acid Fuel Cells Performance on Commercial Diesel Reformate

Minimal effect of reformate on 20 cell stack performance

Mostly H2

dilution effect

Gas flow/compositions

Cathode

19 LPM air + 0.3 bar H2

O

Anode

33% Hydrogen: 8.0 LPM H2

+ 16 LPM N2

+ 0.3 bar H2

O

Reformate: 30 LPM commercial* diesel reformate + 0.3 bar H2

Ocommercial diesel reformate:

30%H2

,

38%N2

12%CO

19%CO2

1%CH4

0.1%heavy hydrocarbons

10 ppmH2 S

Testing at Nordic Power Systems

*From STATOIL Fuel Station

0 5 10 15 200

2

4

6

8

10

12

14

16

18

20

0

50

100

150

200

Sta

ck P

ower

[W]

Stac

k V

olta

ge [V

]

Current [A]

33% Hydrogen Reformate

Cost Reduction Opportunities: Next Generation Electrodes


Solid Acid Fuel Cells Performance increase via electrode fabrication

Electrode activity ~ electrolyte SA

TPB ~ SA1/4 (thanks Anil)

SAFC: effect of decreasing APS/ increasing electrolyte SA

2.5x increase CD/@0.8V

Low electrolyte SA limiting electrode performance

Active SA = 0.5 m2/g-Pt

Need for “nano-particle”

electrolyte

Try to match Pt SA (100 m2/g-Pt)

Chisholm, Interface, 2009


Solid Acid Fuel Cells Performance increase via electrode fabrication

Electrode activity ~ electrolyte SA

SA1/4 (thanks Anil)

Low electrolyte SA limiting electrode performance

Active SA = 0.5 m2/g-Pt

Need for “nano-particle”

electrolyte

Try to match Pt SA (100 m2/g-Pt)

Example: Electrospray process

Aron Varga—Caltech*

Ordered structures

3-D printing

*Varga, PhD Thesis, 2013


Solid Acid Fuel Cells Performance increase with Pt-alloys

Pt Tafel slope: 210-240 mV/dec

SAFC: Pt-Pd system*

Tafel slope 60 mV/dec

3x increase in performance

> 70% effective Pt reduction

System unstable

PAFC comparison

PtV, PtCr, PtCoCr, etc.

> 2.5x increase in mA/mg Pt

PEM comparison

Pt3Co, PtCu, etc.

Pt-M core shell

Nanostructured

Pt film

*Chisholm, Interface 2009



*Papandrew, J. Electrochem. Soc. 2013

Pt Tafel slope: 210-240 mV/dec

SAFC: Pt-Pd system*

Tafel slope 60 mV/dec



System unstable

PAFC comparison



PEM comparison

Pt3Co, PtCu, etc.

Pt-M core shell

Nanostructured

Pt film



SAFC: Pt-Pd system

Tafel

slope 60 mV/dec



System unstable

PAFC comparison*



PEM comparison

Pt3Co, PtCu, etc.

Pt-M core shell

Nanostructured

Pt film

*Jalan, J. Electrochem. Soc. 1983



SAFC: Pt-Pd system

Tafel

slope 60 mV/dec



System unstable

PAFC comparison



PEM comparison*

Pt3Co, PtCu, etc.

Pt-M core shell

Nanostructured Pt film

*Gasteiger, Science 2009


Solid Acid Fuel Cells Cost reduction with non-Pt catalysts

SAFC: Chalcogenides

Initial results show promise

OCV > 800mV

Stable performance

Metal oxides, carbides, nitrides, oxynitrides, carbonitrides

M-Nx/C materials

Non-pyrolized

& pyrolized

M = Co, Fe, Ni, etc.

Electrically conductive support materials

Non-carbon based fast carbon oxidation


Solid Acid Fuel Cells System simplification with internal reforming

SAFC: methanol

Performance ≈

hydrogen

Perfect thermal match between stack operating/reforming temp.

Increase efficiency

Stack cooling

Simplest possible system

0 100 200 300 400 500 600 7000

100

200

300

400

500

600

700

800

900

1000

0

50

100

150

200

250

Pow

er d

ensi

ty [m

W/c

m-2]

Elec

tric

pote

ntia

l [m

V]

Current density [mA/cm-2]

H2:N2 2:1 (vol) MeOH:H2O 1:1 (vol)

Fuel cell

Reformer

Cathode

Anode

Uda, Electrochem. & Solid St., 2006


Solid Acid Fuel Cells Performance on Internally Reformed Methanol

Fuel cell

Reformer

Cathode

Anode0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

0

2

4

6

8

10

0

5

10

15

20

25

Hydrogen (0 h) Internally reformed methanol (0 h) Internally reformed methanol (140 h)

Sta

ck V

olta

ge [V

]

Current [A]

Sta

ck P

ower

[W]

SAFC: methanol

Performance ≈

hydrogen

Perfect thermal match between stack operating/reforming temp.

Increase efficiency

Stack cooling




SAFC: methanol

Performance ≈

hydrogen


Cheapest system

Most durable

1kW RMFC unit



SAFC: methanol

Performance ≈

hydrogen


Cheapest system

1kW RMFC unit 1 kW Diesel APU

SAFC: diesel

Not simplest possible system

Not cheapest system

Summary


Technology Comparison Optimal temperature for fuel cell operation

cold hot

minimum conductivityfor fuel application

optimal operating

temperature

< 150 C cold -

expensive/complex system

> 650 C hot -

expensive stack & system components

200-400 C just right! -

inexpensive/simple stack & system

0 100 200 300 400 500 600 700 800 900 10001E-3

0.01

0.1

1

C

ondu

ctiv

ity /

c

m-1

Temperature / C

Solid Oxide(YSZ, (ZrO2)0.9(Y2O3)0.1)

Polymer (Na fion )

Solid Acid (CsH2PO4)


Summary Solid Acid Fuel Cells

Solid acid electrolytes

Solid state proton conducting membranes -

CsH2

PO4

Operate at favorable temperatures -

230-280°C

Fuel flexibility

Hydrogen, methanol, ethanol, reformed fossil fuels

Optimal temperature for low T gas shift

High tolerance to CO (100%), H2

S(100ppm), & NH3 (100ppm),

Rugged/Low cost system

Mechanically robust cells

Metal and polymer stacks parts

Commercially available system components

Simple reforming/heating-cooling/water management sub-systems

LOTS of room for improvement!


Further Information

Calum Chisholm, Ph.D.

CEO & President

(626) 795-0029 x101

[email protected]

SAFCell, Inc.

36 South Chester Ave.

Pasadena, CA 91106

www.safcell.com

mailto:[email protected]

http://www.safcell.com/

Documents

@2013 SAFCell, Inc. @2013 SAFCell, Inc. 1 · Chicago, IL. June 7th 2013. @2013 SAFCell, Inc. 3. Contents ... (SeO 4) 2 (NH 4) 3 H(SO 4) 2 Cs 2 (HSO 4)(H 2 PO 4) CsHSeO 4 CsHSO 4 log