MEA & DM Characterization/Optimization for Low Pt Loadings ...

Chair of Technical Electrochemistry

Technical University of Munich, Germany

PEM fuel cell materials / structures

Pt reduction strategies:

- Pt needs for the HOR

- ORR catalyst status / limitations

- mass-tx loss phenomena

- MPL/DM design for high-i

- effect of catalyst morphology

Summary

MEA & DM Characterization/Optimization

for Low Pt Loadings and High Current Densities

page 1 11/15/2017 Hubert Gasteiger | Chair of Technical Electrochemistry | Technical University of Munich

G.S. Harzer, C. Simon, A. Orfanidi, P. Madkikar, H.A. El-Sayed, H.A. Gasteiger

Fuel Cell Electric Vehicle Challenges

since 2008: >300 mi. range 70 MPa H2 (4-6 kgH2 at 5%wt) with refuelling <5 mins.

catalyst cost & supply (100kW car):

current: 0.3-0.5 gPt/kW 30-50gPt/car

5-10x vs. automotive emission catalysts

long-term: <0.1gPt/kW <10gPt/car

large-scale commercial viability

H2 generation & distribution infrastructure...

approaches to get to <0.1 gPt/kW ?


Membrane Electrode Assembly

Diffusion Media (DM)

Diffusion Media (DM)

Bipolar Plate (BP)

Bipolar Plate (BP)

20-40 cm

1 mm

C-fiber paper

(7 mm fibres)

Mathias, Roth, Fleming,

Lehnert; in: Handbook of

Fuel Cells; Wiley, vol. 3

(2003) chapter 46

high electronic Rcontact

H2/Air Fuel Cell Components

O2

RO2-tx

Baker, Caulk, Neyerlin, Murphy;

J. Electrochem. Soc. 156

(2009) B991


membrane

H+

e-

O2

O2 + 4H+ + 4e- 2H2OPt

Diffusion

Medium

membrane

H+

e-

O2

O2 + 4H+ + 4e- 2H2OPt

O2 + 4H+ + 4e- 2H2OPt

O2 + 4H+ + 4e- 2H2OPt

Diffusion

Medium

PEFC Electrode Composition / Structure

dominated by carbon-black structure

40 nm

46% Pt/carbon

40 nm

46% Pt/carbon Pt/C & ionomer at 1 gionomer/gcarbon

60% void volume (dpore 50-100 nm)

from: Z.Y. Liu, B.K. Brady,

R.N. Carter, B. Litteer, M. Budinski,

JECS 155 (2008) B979

H+-tx resistance (RH+-tx) in electrodes*)

assumes homogenous ionomer distr.

*) Y. Liu, M.W. Murphy, D.R. Baker, W. Gu, C. Ji, J. Jorne,

H.A. Gasteiger; J. Electrochem. Soc. 156 (2009) B970


11/15/2017 Hubert Gasteiger | Chair of Technical Electrochemistry | Technical University of Munich








Summary

high transport-limited current 80 A/cm2 at 100 kPaabs H2

HOR/HER Kinetics via PEM H2-Pump

2 mgmetal/cm2 0.4 mgPt/cm2

working electrode counter & reference

electrode m

em

bra

ne

DM DM

determination of transport-resistance-free HOR/HER kinetics

( K.C. Neyerlin, W. Gu, J. Jorne, H.A. Gasteiger, J. Electrochem. Soc. 154 (2007) B631)

H2-pump: minimized ohmic /transport losses & maximized kinetic resistance

- thin membrane (20mm) and electrode (2mm)

minimize ohmic losses

- ultra-low Pt loading on working electrode

increase kinetic resistance


HOR Kinetics on Pt/C

HOR kinetics on Pt/C (100 kPaa H2, 100%RH)

for h>100 mV: Tafel-reaction limited

(itx-limit > 50 A/cm2geo)

for h<50 mV: Tafel/Volmer(rds)

5% Pt/Vu

APt = 100 m2/gPt

LPt = 2 mgPt/cm2geo

gas-phase H2 dissociation rate const.1) :

kH2/D2 = 2.4 cm/s at 295 K

≡ ”Tafel” reaction: H2 2 Had

with iTafel 0.5 A/cm2Pt

1) Vogel, Lundquist, Ross, Stonehart,

Electrochim. Acta 20 (1975) 79

on Pt/C at 353 K2) : - i0 ≈ 0.3 A/cm2

Pt

- αa = αc = 0.5 ≡ 140 mV/dec.

a cF F

R T R T0i i rf e e

h h

fit to:

Had H+ + e-


from: Durst, Simon, Hasché, Gasteiger, J. Electrochem. Soc. 162 (2015) F190

HOR Kinetic Losses on Pt/C in PEMFC

predicted hHOR/HER at igeo = 3 A/cm2geo & 0.05 mgPt/cm2 (80C and 100 kPaabs H2) ?

for typical Pt/C catalyst:

APt = 80 m2

Pt/gPt 800 cm2Pt/mgPt

rf = 40 cm2Pt/cm2

geo

required kinetic current:

ik = igeo / rf = 0.7510-2 A/cm2

Pt

hHOR <10 mV at 0.05 mgPt/cm2 even at very low Pt anode loadings


H2 Oxidation Reaction (HOR) Kinetics on Pt/C

H2 2 H+ + 2 e

- kinetics via rotating disk electrode (RDE) in liquid electrolytes

but, slow H2-transport

fast transport in liquid electrolytes:

- Floating VCF Pt/C Electrode3)

- Scanning Electrochemical

Microscopy (SECM) on Ptpc4)

- Ultra Micro Electrode (UME)5)

1) J. Durst, C. Simon, F. Hasché, H. A. Gasteiger, J. Electrochem. Soc. 162 (2015) F190 2) J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz, H. A. Gasteiger, Energy Environ. Sci. 7 (2014) 2255

i0 (RDE) 102-fold too low

fast HOR/HER kinetics

very fast transport in PEM setup:

H2-pump measurements1,2)

3) C.M. Zalitis, D. Kramer, A.R. Kucernak, Phys. Chem. Chem. Phys. 15 (2013) 4329 4) J. Zhou, Y. Zu, A.J. Bard, J. Electroanal. Chem. 491 (2000) 22 5) V. Bagotzky, N. Osetrova, J. Electroanal. Chem. 43 (1973) 233









Summary


H2/Air PEMFC Performance Model

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.0 0.3 0.6 0.9 1.2 1.5 [A/cm2]

Vo

ltag

e (

V)

Ecell

hHFR=90 mV (hmem=30 mV)

ST19-S0559 (Nano-x coating) RC FCPM op-line

MEA: Gore 5720 (18 mm, 0.2/0.3 mgPt/cm2, I/C=1.2)

DM/MPL: Pre-compressed SGL 25BC

htx,O2(dry)=26 mV

hORR=410 mV

htx,H+ =18 mV

htx,O2(wet)=18 mV

Pt

2

PtMEA

2

MEA

mg0.45

gcm0.5

W kW0.9

cm

at 1.5 A/cm2:

H2/air (s=1.5/2), 150kPaabs, <50% RHinlet

25mm membrane and 0.05/0.40 mgPt/cm2MEA

( 60 mV Rcontact)

from: W. Gu, D.R. Baker, Y. Liu, H.A. Gasteiger, in:

Handbook of Fuel Cells, Wiley (2009): vol. 6, pp. 631.

( hHOR < 5 mV*) )

need 10x better ORR catalysts to reach 0.05/0.04 mgPt/cm2MEA 0.1 gPt/kW

O2 + 4 H+ + 4 e

- 2 H2O


Fuel Cell Cathode Catalyst Options

options envisaged in 2009: ultra-high activity Pt-based or Pt-free

TOF at 0.8V RHE 4) (80°C, 100kPa O2)

from: H.A. Gasteiger & N.M. Marković; Science 324 (2009) 48


de-alloyed Pt-alloys1): leaching of Ni-rich Pt-Ni alloys

proven in fuel cell stacks: 0.4-0.6 A/mgPt

shape-controlled Pt-alloys2):

2) C.Chen, Y. Kang, Z. Huo, Z. Zhu, W. Huang, H.L. Xin, J.D. Snyder, D. Li, J.A. Herron,

M. Mavrikakis, M. Chi, K.L. More, Y. Li, N.M. Markovic, G.A. Somorjai, P. Yang, V.R. Stamenkovic; Science 343 (2014) 1339

Pt3Ni octahedra Pt3Ni nanoframes

highest activity for C-supported catalysts so far

O2 Reduction Reaction (ORR) Catalysts

1) B. Han, C.E. Carlton, A. Kongkanand, R.S. Kukreja, B.R. Theobald, L. Gan, R. O’Malley, P. Strasser, F.T. Wagner, Y. Shao-Horn; Energy Environ. Sci. 8 (2015) 258


FC Cathode Catalyst Roadmap (2015)

from: O. Gröger, H.A. Gasteiger,

P.-J. Suchsland, J. Electrochem.

Soc. 162 (2015) A2605

likely ORR catalyst candidates for applications (green) & new concepts (white)

3-4x catalysts (0.4-0.6 A/mgPt) feasible for next gen. FCEVs

sufficient for reaching <0.1 gPt/kW target ?










Summary

Best-Case High-i Performance Limit

projected performance without ‘film resistance’: - im = 0.4 A/mgPt (Pt-alloy)

- Lan/ca = 0.05/0.05 mgPt/cm2

- tmembrane = 10 mm (0.1 S/cm)

- Rcontact = 15 mWcm2

- rH+,cath. = 50 Wcm (10 mm thick)

- RO2-tx = 0.5 s/cm (for DM only)

- hHOR negligible (<10mV)

0.06 gPt/kW at 0.60 V

would meet DOE target, if

low-Pt cathodes can be made

low Rcontact & low RO2-tx req.

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0 1 2 3 i [A/cm2]

E [

V]

H2/air (150kPaabs), 80ºC, 100%RHmembrane


Low-Pt Cathode – Surface Film Resistance

additional O2 transport resistance

found for low-loaded Pt cathodes

from: J.P. Owejan, J.E. Owejan, W. Gu;

J. Electrochem. Soc. 160 (2013) F824

htx-film for >0.02 A/cm2Pt at 150 kPaa H2/air

ascribed to interfacial resistance from: A. Kongkanand, M.F. Mathias;

J. Phys. Chem. Lett. 7 (2016) 1127


htx-film

H2/air (150kPaabs)80ºC/100%RH

H2/air at 100 kPaa

and 80C/100% RH

0.05 mgPt/cm2cathode

Low-Pt Cathode – Pt/Support Morphology

effect of catalyst morphology on Pt mass activity and H2/air performance

poor high-i performance of burried Pt lower ORR poisoning by burried Pt

from: Y.-C. Park, H. Tokiwa, K. Kakinuma, M. Watanabe, M. Uchida, J. Power Sources 315 (2016) 179


controlled by

carbon morphology*)

carbon-support vs. Pt deposition method ?









Summary

Micro-Porous-Layer (MPL) Design

Denka carbon black Li100 Li400

Primary particle size (spec.) [nm] 35 48

BET – surface powder [m2/g] 64 37

DBP absorption [ml/100g] 175 140

- MPLs with 20 wt.% PTFE

& different carbon blacks

- coated on commercial

Freudenberg GDL substrate

perfo

ratio

n o

f MP

Ls

perforation of MPLs via a thermally

decomposable pore forming polymer:

dmean = 30 µm (order of dMPL)

10 20 30 40 50 60 70 800

5

10

15

20

25

30

qvo

l. [

%]

dparticle

[µm]


ε = 79%

dpore = 67 nm

ε = 68%

dpore = 328 nm

dpore = 64 nm

Commercial

Freudenberg Commercial

Freudenberg

Li100 Li100

Li400 Li400

MPL Morphology

change MPL structure (t30mm) by: - carbon black (Li100 & Li400) smooth layers

- perforation large pores/cracks

effect on oxygen and water transport ?


from: Simon, Kartouzian, Müller, Wilhelm, Gasteiger, J. Electrochem. Soc., in press

H2/Air Performance – MPL Structure Effect

differential-flow H2/air performance with 0.1/0.4mgPt/cm2 (an/ca) Gore MEA (18mm)

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]

no MPL commercial MPL Li100 Li100 perforated Li400 Li400 perforated

0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s

cm

-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06H

FR

[W

cm

²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s

cm

-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s c

m-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s

cm

-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s

cm

-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s

cm

-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

at 50C / 300kPaa (wet cond.):

Li400 w. larger 2ndary pores

better than Li100 (Hg poros.)

MPLs with cracks superior

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s c

m-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s c

m-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Tcell

= 50 °C

pabs

= 300 kPa

RH = 120%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 100%

Tcell

= 80 °C

pabs

= 170 kPa

RH = 70%

Ec

ell [

V]

0.02

0.04

0.06

HF

R [

W c

m²]


0.02

0.04

0.06

b) c)

0.02

0.04

0.06

0 1 2 3 40.0

0.5

1.0

RT

,O2

[s c

m-1]

i(lim)

[A cm-2]

0 1 2 3 40.0

0.5

1.0

i(lim)

[A cm-2]

0 1 2 3 41.5

2.0

2.5

3.0

i(lim)

[A cm-2]

at 80C / 170kPaa (std. cond.):

minor differences

suggests tx of H2Oliquid via cracks and O2 via fine pores

MPL design relevant at potential FC operating conditions ?

Ca

tho

de

Su

bstr

ate

MP

L

O2



0.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4 5 60.0

0.5

1.0

1.5

0.02

0.04

0.06

Ecell [

V]

GDL substrate with

commercial MPL (H14C10)

Li400 MPL

Li400 perforated MPL

RT

,O2

[s

cm

-1]

i(lim)

[A cm-2]

HF

R [

W c

m2]

H2/Air Performance at High Pressure

differential-flow H2/air performance with 0.1/0.4mgPt/cm2 (an/ca) Gore MEA (18mm)

P = 300 kPaa

80°C / 100%RH

optimized MPL shows improved performance

1.5-fold (from 1.3 to 1.9 W/cm2)




H2/air at 100 kPaa

and 80C/100% RH

0.05 mgPt/cm2cathode

effect of catalyst morphology on Pt mass activity and H2/air performance

poor high-i performance of burried Pt lower ORR poisoning by burried Pt

from: Y.-C. Park, H. Tokiwa, K. Kakinuma, M. Watanabe, M. Uchida, J. Power Sources 315 (2016) 179

controlled by

carbon morphology*)

carbon-support vs. Pt deposition method ?








Summary


slides removed (unpublished data)

Summary

<0.1 gPt/kW target can be met by improved catalysts & design for high-i

catalyst morphology is critical

MPL/GDL-substrate design critical for high-i performance

h unaccounted affected by H2Oliquid saturation

Technical Electrochemistry Group !

Thanks to the


MEA & DM Characterization/Optimization for Low Pt Loadings ...

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