PLASMA PROCESSING FOR FUEL CELL - RSPhys - ANU · Nowadays, fuel cells are being developed to power...

PLASMA PROCESSINGPLASMA PROCESSINGFOR FUEL CELLFOR FUEL CELL

A. Caillard, C. Charles, D. Ramdutt,R. W. BoswellSP3 - PRL – RSPhysSE – ANU Canberra,

Australia

P. BraultGREMI - CNRS, Université d’Orléans, France

J. Durand, S. RoualdesIEMM CNRS- Université de Montpellier II,

France

C. Coutanceau, C. LamyLACCO CNRS – Université de Poitiers, France

The greenhouse effects of current CO2 emissions have resulted in extensiveinternational research on the use of hydrogen as an energy carrier for a loweremissions society.

From 1960, NASA has been using fuel cells in space and military operations (GEMINI)Nowadays, fuel cells are being developed to power cars, homes (stationaryapplication) and mobile electronic devices.

Fuel cell Technologies

Fujitsu Laboratories Ltd(26 jan 2004)

NTT DoCoMo (30sep 2004)

FC classe A (june 2004)

Fuel cell Membrane depositionCatalyst Sputtering Gas diffusion layer

1 kW electricmodule (GEMINI)

Proton Exchange Membrane Fuel cell (PEM)

Fuel cell

PEMFC

Proton Exchange

Membrane FC

PAFC

Phosphoric acid

FC

MCFC

Melted carbonate

FC

SOFC

Solid Oxide FC

Electrolyte Proton exchange

membrane Phosphoric acid Melted carbonate Solid Oxide

Temperature 70 - 100°C 150 -210°C 650 -1000°C 800 -1000°C

Transport Ion H+ H+ CO3- O2-

Combustible H2 & Methanol H2 H2 H2 & CH4


Anode Cathode

e-

Cathodic fuelAnodic fuel

Electrolyte

Transportion

Electrodes Requirements :-High ionic and electronic conductivities-High fuel diffusion coefficient-High chemical and thermal stabilities-High and selective reactivity of theanode and cathode chemical reactions

Electrolyte Requirements :-High ionic conductivities-Low electronic conductivities-High chemical and thermal stabilities-Low fuel permeability

Protonic solution

2H+ + 1/2 O2 + 2e- H2O

Catalyst

cathode

H2 2H+ + 2e-

anode

CxHxO CO2 + 2H+ + 2e-Catalyst

Chemical PEM Fuel cell : structure

Electrodes(Gas diffusion layer and

catalyst layer )

H2O / O2

H2 O2

Membrane ElectrodeAssembly(MEA)

Bipolar plate(gas feeding channel )

Proton exchangemembrane

H2

Active catalyst

Inactive catalyst

Protonic Membrane

Carbon particleBacking support

e- e-

H+

e-

O2

O2

O2

O2

O2

H+

H+


Chemical PEM Fuel cell : structure

1 – Backing (carbon cloth)

2 - Electrode mixture : a) Carbon particles (50-150 nm) (50 µm) b) Nafion polymer (50 µm) c) Catalyst nano-particles (50 µm)

3 - Nafion membrane (150/250 µm)A

1

1

2

23

100 µm

H+


SEMSEM

Chemical PEM Fuel cell : ProcessingCarbon support (nano-particles,nanofibers, …) + Catalyst salt

Catalyst supported on carbon

Colloidal, carbonyl methods

Proton solution

Ink ( Catalyst supported on carbon,proton solution, alcohol)

Isopropanol

Electrode supported on abacking

Spraying, painting methods

Auto-supported ProtonExchange Membrane

Membrane Electrode Assembly (MEA)

Hot pressing methods


Catalyst

Protonpolymer

Catalyst

Catalyst

Protonpolymer

Catalyst

Plasma PEM Fuel cell

Platinum price dramatically increases


Only 10% of the platinum load is active in a chemical fuel cell. To decrease platinumload (increase platinum activity), the electrode structure must be optimized :

Three separate layers (MEA)with hot press assembly

US$/carUS$/gg/car

7503025

Platinum for a 50 kW car (6 persons) :

Three progressive layerscontinuously deposited by plasma

processing (in situ assembly) :

30

20

US$/g

2000 2002 2004

Catalyst, carbon and polymer deposition

1 - Catalyst clusters deposition onuncatalysed chemical electrode (≈GDL)by plasma sputtering

2 - Carbon nanostructure deposition onbacking by plasma enhanced chemicalvapor deposition and by plasma sputtering

Catalyst clusters deposition on this newgas diffusion layer

3 – Polymer deposition by PECVD and plasmasputtering

4 – Proton Polymer deposition by PECVD

Plasma processing for PEM Fuel cell

Carbon particles (Vulcan CX72, 40 nm)surronded by platinum no-particles

Electrode

Electrolyte

Carbon Nonofibre (CNF) deposited on a carbon paper (FCbacking) + platinum deposition by a chemical method

Proton membrane deposited on achemical electrode


Platinum catalyst

Carbon

Polymer

CATAPULP (GREMI, Orleans, France)

-

+

Pump

+

Catalyst GDL

TCP Antenna

Argon in

++

+ +

+

+

Vc

BA (L)

13.56 MHz(0/20gauss)

Z (mm)

0

170

PIGLET (PRL, Canberra, Australia)

GDL

Catalyst

Vc < 0

++

+

+

+

+

++

+

+

+

++

+

+

++

++

+

Double saddle antennaArgon in

BA (π)

13.56 MHz(0/40 gauss)

(0/200 gauss)

Z (mm)

0

Catalyst deposition by plasma sputteringFuel cell Membrane depositionCatalyst Sputtering Gas diffusion layer

After Pt deposition

(0.08 mg/cm²) – 20 µbar

Before Pt deposition

Pt : 0.08 mg/cm² : clusters size φPt< 10 nm

GDL (80% Carbone + 20% PTFE – porosity ~ 50 %)

Catalyst Sputtering on (into) GDLPt deposition morphology, MEB

J. Durand, IEM, Montpellier


Proton polymerCatalyst + Carbon

Catalyst + carbon

?Carbon

Carbon

Proton polymer

Carbon

Carbon

T. Cacciagerra, CRMD Orléans

5 µbar 5 µbar

50 µbar 50 µbar

<∅Pt> = 2,5 nm , σ(∅Pt) = 1 nm 10 nm

10 nm 10 nm

<∅Pt> = 7 nm , σ(∅Pt) = 4 nm Porous Pt deposit

Dense and smooth Pt deposit

Catalyst Sputtering on (into) GDLPt deposition morphology, TEM


0 500 1000 1500 20000

2000

4000

6000

8000

Energie (keV)

Counts

Experience

Simulation

PtProgram principle :

(1) Build a virtual target(mathematical Pt profil)whose RBS spectrum isclosest to theexperimental spectrum

(2) Minimize error betweenexperimental andsimulated RBS spectrum

Ei = f(MPt,z)

T. Sauvage, CERI, Orléans

GDL + Pt(MPt)

Eo He(α)

Experimental principle

C

0 1000 2000 30000

0.2

0.4

0.6

0.8

1

Depth (nm)

Pt (µg/cm?/nm)

Pt:stretched exp

C :Heveaside

F :Heveaside

Pt Concentration gradient :solution of porous media

equation

Catalyst Sputtering on (into) GDLPt depth density, RBS


Asymmetric Pt peak Pt deposition into

the GDL

0 200 4000

0.2

0.4

0.6

Depth (nm)

Pt (µg/cm

2/nm)

5 µbar 10 µbar20 µbar

T. Sauvage, CERI, Orléans

Catalyst Sputtering on GDLPt depth density, RBS

0 100 2000

0.2

0.4

0.6

0.8

Depth (nm)

Pt (µg/cm

2/nm)

Pt = 7 µg/cm_Pt = 14 µg/cm_Pt = 33 µg/cm_Pt = 66 µg/cm_Pt = 109 µg/cm_Pt = 138 µg/cm_Pt = 159 µg/cm_

1

1

2

2

3

3

4

4

5

6

7

5

6

7

Platinum diffusion into porous GDLduring deposition process :

1 – When the deposition pressure decreases,diffusion depth of platinum atoms in GDLincreases.

2 – When the deposition pressure increases, aporous platinum layer forms on the GDL surface.

3 – When the platinum load increases, diffusioninto the GDL is limited deposition on thesurface of a low active area layer


Maximum diffusion length is around200 nm

Proton polymerCatalyst

Catalyst200 nm

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 300 600 900 1200 1500 1800

Densité de courant (mA/cm_)

Pote

ntiel (V

)

E-Tek (0,35 mgPt/cm_)MEA2MEA3MEA4MEA8

Carbon paper05MEA8

Carbon cloth05MEA4

Carbon cloth-405MEA3

Carbon cloth020MEA2

CathodicBacking

GDLbias(V)

Pressure(µbar)Parameters

C. COUTANCEAU, LACCO, Poitiers

Catalyst Sputtering on cathode GDLElectrochemical efficiency for oxygen reduction

Fuel cell I-V characteristics (70°C, 4 bars, chemical anode)

Results on H2 fuel cell tests:1 - Better proton conductivity at high depositionpressure due to the porous catalyst layer (SEMand TEM)2 Better active surface area at low depositionpressure due to smaller catalyst nano-particles(SEM and TEM)3 Voltage drop at high current density due tocatalyst absence in the GDL : catalyst diffusionlength is around 200 nm (FC electrode model)


Platinum and carbon nanostructuresmust be mixed / deposited together

in around a 1 µm thickness.

Proton polymerCatalyst + Carbon

Catalyst + carbon 200 nm 1 µm

Carbon

Carbon

Requirements : High surface area, chemical and thermal stability and high electronic conductivity

Gas diffusion layerCarbon nanostructures deposition on carbon paper

Carbon graphitic (amorphous) nanostructures

CNT/CNF ((PECVD)Nano-horns (laser ablation)

Nanosheets (PECVD)Nanocoils (PECVD)

Nano-particles(Dusty plasma)

Nano-particles (carbonsputtering in Tokamak )

a-C layer (plasma sputtering)


Gas diffusion layerCNT / CNF


Methods of synthesis :- laser vaporization,- arc discharge,- catalytic-CVD,- catalytic-PECVD

High quality CNT/CNF in large quantity, uncontrolled spatialarrangement, high temperature.

High quality CNT/CNF in quite small quantity, controlled spatialarrangement in particular with a C – PECVD, quite lowtemperature.

Helicon - PECVD for CNT/CNF growing :- Ni catalyst clusters : Ar sputtering- CNT/CNF : CH4 / (N2 or Ar) PECVD- Pt nano-particules : Ar sputtering

π13.56 MHz

PumpGas input(CH4 / Ar )

Target(Ni)

Target(Pt)

Heating and bias hold – substrate(200 < T < 400 °C, - 300 V < V < 0 V)

Carbonpaper

ArgonH2 +

Styrene HC-CH2

Triflic acid(CF3-SO3H)

+ H2

40 kHz ~50 W

+

Pump

Precursor

+++

+ +

Circular gasinput

+ +

3.10-4 mol/cm²/sMethanol permeability

0,2 10-2 σ/mProton Membrane Conductivity

~ 250 nm/minDeposition rate

~ 50 WPower

- 10 VSubstrate bias

0,5 mbarTotal pressure

~ 0,1 mbarH2 / Triflic acid partialpressure

~ 0,025 mbarH2 / Styrene partial pressure

Membrane deposition by PECVDS. ROUALDES, IEM, Montpellier, France

(IEM, Montpellier, France)

Requirements :- High proton conductivity,- Chemical and thermal stability,- Low methanol / gas permeability,- Low cost and long Life

Reference membrane Nafion (DuPont) :- Perfluorated membrane with fix acid groups SO3-

- Conductivity = 0.2 S/m ( T, hydration )- T > 90°C : water evaporation conductivity

decreases


Membrane deposition by PECVD

Plasma membraneMembrane Nafion® 117

100 µm

2 µm

⇒ Plasma membrane is dense

3 10-4

2 10-3

MeOH Flux(mol.m-2.s-1)

Up to 120°0,6Plasma membrane (1µm)

Up to 90°0,5Nafion® 117

Thermal StabilityResistivity (mΩ)

Plasma membranes are adapted for micro fuel cell andhave a good chemical and thermal stability.

S. ROUALDES, IEM, Montpellier, France


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