Plasma Processing for Fuel Cell Technology - ANUPlasma Processing for Fuel Cell Technology GDL...

Plasma Processing for Fuel Cell TechnologyPlasma Processing for Fuel Cell Technology

GDL coated by platinum nanoparticles (100µg Pt /cm²)

A.Caillarda, D. Ramduttb , P. Braulta, C. Charlesb, R. Boswellb,a Groupe de Recherche sur l’Energétique des Milieux Ionisés, UMR 6606 Université d’Orléans – CNRS Polytech’Orléans BP6744, F-45067 Orleans Cedex 2, France

B Space Plasma, Power and Propulsion, Research School of Physical Science and Engineering Australian National University, Canberra ACT 0200, Australia

Plasma processing for fuel cell electrode deposition

Proton Exchange Membrane Fuel Cell

A PEMFC is an electrochemical cell that is fed hydrogen, whichis oxidized at the anode, and oxygen, which is reduced at thecathode. The protons released during the oxidation areconducted through the PEM to the cathode while the electronstravel along an external circuit and are available to do work.

There are three critical transport processes, (a) protons fromthe membrane to the catalyst, (b) electrons from the currentcollector to the catalyst through the GDL and (c) reactant toand catalyst layer from the gas channel. Part of theoptimisation of the electrode design is to correctly distribute thecatalyst layer throughout the transport media for each of thethree phases (electrons, protons and gases) to reducetransports losses.

Bipolar plate

Proton Exchange

Membrane

Anode Cathode

H2 O2

O2 + H2OH2

5x1011 1x1012c m-3 Ne and Ni

15 23 VPlasma potential

2 3.5 eVElectron temperature

1016 ions/s/cm2Ar+ flux on Pt

5 50 µbarDeposition pressure

-300 -100 VTarget bias

0 1000 WRF Generator Power

TEM image showing carbon particles surroundedby Pt nano-particles

50 nm

T. C

acci

ague

rra (C

RM

D, O

rléan

s,Fr

ance

)

Nafion MembraneCarbon ParticleCarbon Cloth

Nafion FilamentsActive CatalystInactive Catalyst

Half fuel cell

H+

H+

H+

e-

H2

The Membrane Electrode Assembly (MEA) of PEM fuel cells (two electrodes and an ion membrane) is usually produced by wet chemicalprocesses and assembled by hot pressing. During the last few years, some laboratories have developed low power micro-PEM fuel cell byplasma deposition processes. These PEM fuel cell, powered in general by methanol, are not yet optimised for industrial manufacture. Throughour expertise in plasma physics, our aim is to build an optimised nano-structured PEMFC by plasma depositing ultra thin films of platinum andplasma polymerisation of new membranes which allow proton diffusion while reducing poisoning and degradation of the PEM from methylgroups.

Toward a plasma PEM fuel cell

Styrene HC-CH2 +H2

Triflic acid (CF3-SO3H)+ H2

Argon

40 kHz ~50 W

+

Output

Precursor

Film growth

+

++

+

++

++

(b)

Plasma membrane deposition on catalysed GDL

Plasma membraneis deposited 6 µm

into the GDL

plasma membrane deposited on an E-Tek GDL

1 - High electrochemical activity due to the high electrodeactive volume.

Porous substrate(GDL)

Target (Catalyst)

Vb < 0

++

+

+

++

++

+

+

+

++

++

++

++

+

Helicon antennaArgon in

Argon out

13.56 MHz(0-100 Gauss)

(0-100 Gauss)

PIGLET (SP3, Canberra,Australia)

Institut Européen des Mem

branes (FR)

~ 250 nm/minDeposition rate

~ 50 WGenerator power

0,5 mbarTotal pressure (Ar + H2 + styrene + acid)

* 50 times less than the Nafion 117 whose the wet depth is 185 µm** 6 times less than the Nafion 117

3.10- 4 mol.cm²/s**Methanol permeability

10-4 σ/cm*Conductivity

2 - Plasma membrane is dense (high permeability) andthin (high conductivity).

Carbon paper05MEA8

Carbon cloth05MEA4

Carbon cloth-405MEA3

Carbon cloth020MEA2

Cathodic BackingGDL bias (V)Pressure (µbar)Parameters

Fuel cell I-V characteristics (70°C, 4 bar, chemical anode – 0.35 mgPt/cm^2)

Results on H2 fuel cell tests:

1 - Better proton conductivity at high deposition pressuredue to the porous catalyst layer (SEM and TEM)

2 - Better active surface area at low deposition pressuredue to smaller catalyst nano-particles (SEM and TEM)

3 - Voltage drop at high current density due to catalystabsence in the GDL : catalyst diffusion length is around200 nm (FC electrode model)

Platinum and carbon nano-structures must bemixed / deposited together in around a 1 µm

thickness.

Proton polymerCatalyst +Carbon

Catalyst + carbon 200 nm

Carbon

Carbon

Proton polymer

Catalyst +Carbon

Catalyst +carbon

20 µm

Standard chemical PEM fuel cell New “plasma” PEM fuel cell

Bipolar plateElectrodeMembraneAssembly

O2 + H2O

O2 +H2O

H2 +H2O

H2 + H2O

Gasket

FC testing station

FC stacks

1 - Platinum catalyst deposition on GDL by plasma sputtering 2 - Carbon nano-fibres (CNF) deposition by PECVD

SEM of GDL coated by Pt nano-particles

CNF deposition on a carbonpaper

Pt nano-particles deposition onCNFs (2)

Nano-sheets(PECVD)

Nano-horns (laserablation)

Nano-particles(Dusty plasma)

Ro

tar

y pu mp

Con

vec

tor

gaug e

DC Su bst

rat e bia s

Ni

tar

get

bia

sPt tar

get

bia

s

Ni

tar

get

Pt tar

get

Cu

rre nt ge ner

ato

r (he

ate

r)

Inp

ut ga s (Ar

– CH

4 )

ICP

ante

nna po

we

red

by a

RF

gene

rato

r& m

atc

hing

box

Car

bon clot

h

1) GDL (CNT/CNF) growing : Ni catalyst clusters deposition by sputtering then CH4 / N2 PECVD2) Pt nano-particles deposition by plasma sputtering

Ion and neutral beam modification of Nafion

π Matching Network

Nafion® membrane in mount Membrane mounted in diffusionchamber of plasma reactor

Water droplet on treated membrane surface

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

Current Density (mA/cm^2)

Pote

ntial (V

)

E-Tek (0.35 mgPt/cm^2)

MEA2 (0.1 mgPt/cm^2 - Cathode)

MEA3 (0.1 mgPt/cm^2 - Cathode)

MEA4 (0.1 mgPt/cm^2 - Cathode)

MEA8 (0.1 mgPt/cm^2 - Cathode)