Fuel Cell Electrode Materials with Durability and FlexibilityBy-product hydrogen, Reformed fossil...

Fuel Cell Electrode Materials Fuel Cell Electrode Materials with Durability and Flexibilitywith Durability and Flexibility

Kazunari SASAKI([email protected])

(http://www.mech.kyushu-u.ac.jp/lab/ki06/index.html)

Kyushu UniversityFaculty of Engineering & Hydrogen Technology Research Center

Presented at ETH-ZürichSeptember 5, 2008

KazuKazu. Sasaki c/o Prof. . Sasaki c/o Prof. GaucklerGauckler (1989(1989--95)95)

(Cited from the HP of ETHZ-NMW)

TOTO

Aqumentrics

Kyushu Electric

MHI(Nagasaki)

Hitachi

Kyocera (R&D)

MHI(Kobe)Tokyo Gas

Kansai Electric

Chubu Electric

MitsubishiMaterials

Toho Gas

Nipponsteel

Sumitomo

FukuokaMHI(Hiroshima)

MatsushitaSanyo

FujiNTT

Toyota

Honda

Nissan

Tokyo ElectricToshiba

Kyushu University Kyushu University ““Hydrogen CampusHydrogen Campus””：：Towards realizing clean energy society with FUEL CELLSTowards realizing clean energy society with FUEL CELLS

産総研水素材料先端科学研究センター

HYDROGENIUS

水素材料強度実験棟

水素材料曝露実験棟

水素利用技術研究センター

水素ステーション

風レンズ風車

家庭用燃料電池実証研究

家庭用燃料電池実証研究

燃料電池評価実験室

九大方式水素蓄圧器

水素材料疲労強度評価装置

水素物性評価装置

（学内食堂）

（飲食店）

Hydrogen Technology Research Center

AIST-Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS) Hydrogen station

Materials fatigue testing units for hydrogen-related materials

Wind power generator

SASAKI-LAB(Fuel cell research

laboratory)

Stationary PEFC

Stationary PEFC

High-pressure H2 Lab.

High-pressure H2 Lab.

H2 container developed

(for Restaurant)

Researchers: ca 200Lab-area: ca. 6000m2

Kyushu University,Kyushu University,Hydrogen Technology Research CenterHydrogen Technology Research Center

Fukuoka Hydrogen Strategy ConferenceFukuoka Hydrogen Strategy Conference(collaborating with (collaborating with ca. 330 private companies)ca. 330 private companies)

AISTAIST--HydrogeniusHydrogenius((Research Center for Hydrogen Research Center for Hydrogen Industrial Use and StorageIndustrial Use and Storage))

Kyushu Univ. ITOKyushu Univ. ITO--campuscampus

Kyushu University Kyushu University ““Hydrogen CampusHydrogen Campus””：：A CenterA Center--ofof--Excellence on Fuel Cells and Related Hydrogen TechnologiesExcellence on Fuel Cells and Related Hydrogen Technologies

Kyushu University,Kyushu University,INAMORIINAMORI Frontier Research CenterFrontier Research Center

Research topics: Fuel cells, Electrolysis, Sensors, Combustion, Safety etc

Research topics: Structural materials for high-pressure hydrogen energy systems, Tribology, Simulation techniques

Research topics: Energy, Environment, Electronics, Nanotechnologies

Maebaru-city

150 stationary PEFCswill be installed !

Fukuoka Fukuoka ““HydrogenHydrogen--TownTown”” and and ““HydrogenHydrogen--HighwayHighway””

““HydrogenHydrogen--TownTown”” ““HydrogenHydrogen--HighwayHighway””

Suitable for driving fuel cell vehicles

Fukuoka-prefecture (“Kanton”)

Fukuoka-prefecture (“Kanton”)

To be extended to Tokyo !

Hydrogen Station in Hydrogen Campus of Kyushu University

Hydrogen-town near the Hydrogen Campus of Kyushu University

FC

Public vehicles, Bus

Expected numbers of FCV

Type of vehicles

Expected numbers of hydrogen stations

Expected hydrogen supply

Expected consumption of hydrogen

General vehicles

5,000,00050,000

FCV

By-product hydrogen, Reformed fossil fuel, Electrolysis of water

500

Small cargos, Business use vehicles

Type ofstationary fuel cell

Polymer Electrolyte Fuel Cell (PEFC)

FC

10 million kW2 million kW

Fuel

cel

l veh

icle

(FC

V)

2010 20202005 2020 2030

FC-BUS

15,000,000

3,500 8,500

40,000 t 580,000 t 1,510,000 t

Biomass fermentation, Heat disassembly of water

Spread scale FC12.5 million kW

Sta

tiona

ry fu

el c

ell

High temperature cogeneration system (SOFC)

High temperature combined cycle system

Hydrogen Society Proposed by Japanese GovernmentHydrogen Society Proposed by Japanese Governmentfor Fuel Cell Commercializationfor Fuel Cell Commercialization

Hydrogen Energy based on Fuel Cell TechnologiesHydrogen Energy based on Fuel Cell Technologies

• DurabilityDurability• High performance• Low cost ⇒Alternative electrode materials are desired !

ElectrolyteElectrolyteAnodeAnode

CathodeCathode

Coal gasCoal gas

Digester gasDigester gas BiogasBiogasNatural gasNatural gas

PL gasPL gasHydrogenHydrogenKeroseneKerosene

GasolineGasoline

AlcoholsAlcohols

Reforming, Purification & Direct reformingReforming, Purification & Direct reforming

Power plants

Stationary applications

Mobile applications

Transportations

Various possible fuels !

DDurable highurable high--performance fuel cell electrodesperformance fuel cell electrodes

＜ Alternative Electrode Materials for PEFC/DMFC＞

• Pt/Semiconducting oxide support• Pt/Carbon nanofiber support• Pt alloy/Carbon black support

＜ Alternative Electrode Materials for SOFC＞

• Degradation mechanisms• Ni nanocomposite/Zirconia

Thermochemical stability is a key to ensure long-term durability of fuel cells !

FESEM-STEM observation

Colloidal impregnation

10nm 10nm

FESEM secondary-electron image STEM image

Nanostructure: Pt/CNanostructure: Pt/C(Carbon black, Vulcan)(Carbon black, Vulcan)

Electrocatalysts tolerant against voltage cycling are desired!

Driving＝

Low cell voltage

― ―― ――

Idling＝

High cell voltage

PEFC PEFC electrocatalystselectrocatalysts without catalyst support without catalyst support corrosion are desired!corrosion are desired!

PourbaixPourbaix diagram of Cdiagram of C--HH22O systems at 80O systems at 80ooCC

14121086420-2

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

C - H2O - System at 80.00 CEh (Volts)

H

C

CH4(g)+CH4(a)

CO2(g)+CO2(a)

CO3(-2a)HCO3(-a)

Carbon (graphite) is thermochemically not stableespecially under cathodic conditions!

pH

Anode condition

Cathode condition

strongly-acidic condition (PEFC electrolyte: Nafion)

Fig. Pourbaix diagram of the Sn-H2O system

SnO2-supported carbon-free electrocatalysts !?

pH-2 -1 0 1 2 3 4 5 6

Eh / V

-0.6

-0.4

-0.2

0.2

0.4

0.6

0.8

1.2

1.4

0.0

1.0

SnH4(g)

SnO2

Sn4+

Sn2+

SnStability limit of H2O

Stability limit of H2OCathode condition

Anode condition

PourbaixPourbaix diagram of Sndiagram of Sn--HH22O systems at 80O systems at 80ooCC

pH5

SnCl2H2O

Filtration-Washing-Drying

Calcination

NH4OH

SnO2 (ammonia)

SnO2 solEvaporation-to

-drynessSnO2 (sol)

Preparation of catalyst supports

Colloidal impregnation of electrocatalysts

Pt-colloid preparation

H2PtCl6・6H2ONaHSO3

SnO2

Reduction20wt% Pt/SnO2

H2O2 Filtration-Washing-Drying

Preparation procedures of Preparation procedures of PEFCPEFC electrocatalystselectrocatalysts

Calcination

SEM

micrograph

of Pt/SnO2

100nm

Pt nanoparticles of ca. 2-3 nmφ are supported on SnO2.Metal(Pt) / semiconductor(SnO2) junctions !?

CarbonCarbon--freefree Pt Pt electrocatalystselectrocatalysts successfully prepared !successfully prepared !

Current density / mA cm-2

0 200 400 600 800 1000

Cel

l vol

tage

/ V

0.0

0.2

0.4

0.6

0.8

1.0Pt/SnO2 (100oC)

Pt/SnO2 (200oC)Pt/C

Fig. I-V characterization of single cells with 20% Pt/SnO2(0.6 mg-Pt cm-2), and 20% Pt/C (0.6 mg-Pt cm-2), cathodes. Anode catalyst: 46% Pt/C (0.4 mg-Pt cm-2). The cell was operated with H2/Air at a rate of 150 ml min-1, Cell temperature at 80oC, atmospheric pressure, and humidification temperature at 80oC. Temperature in the figure indicates the calcinationtemperature of SnO2.

II--V of MEA using SnOV of MEA using SnO22--supported Pt supported Pt electrocatalystselectrocatalysts

Comparable performance of Pt/SnO2 with conventional Pt/C has been obtained.

Frequency / cycle0 2000 4000 6000 8000 10000

Pt sp

ecifi

c su

rfac

e ar

ea /

m22 g

-1

0

10

20

30

40 Pt/SnO2 (100)Pt/SnO2 (200) Pt/C

Fig. Change of ECSA

of Pt up to 10000 cycles.

(From 0.6 to 1.1 VRHE)

Durability of Pt/C and Pt/SnODurability of Pt/C and Pt/SnO22

Electrochemical surface area (ECSA) of Pt remained almost constant, while Pt/C lost ECSA with cycles.

Tubular Herringbone Platelet

Cross section Cross section Cross section

Structure of carbon Structure of carbon nanofibersnanofibers as catalyst supportsas catalyst supports

PEFCsPEFCs with Pt/CNF electrode catalystswith Pt/CNF electrode catalysts

Pt/CNF(VGCF) electrocatalyst layers

Fig.: FESEM micrograph of catalyst layer using CNF electrode supports

Pt/Platelet electrocatalyst after steam-activation

Pt particles are well impregnated “into” the surface.

Pt/CNF surface modified by activation proceduresPt/CNF surface modified by activation procedures

TiH2(s)

TiO2(s)Stability limit of H2O

353.15 K

Stability limit of H2O

TiO2-X(s)

Ti-H2O, 353.15 Km = 1e-6, '+' = 1.0 atm P(total) isobar

2004/06/08� �C:\KAZU\‹ã‘å“Š e˜ _•¶\“c’†ŒN ì•›ŒNPtTi˜ _•¶\Ti-H2O(80C)wmf.wmf

pH

E(vo

lts)

-2 0 2 4 6 8 10 12 14-2

-1.8-1.6-1.4-1.2

-1-.8-.6-.4-.2

0.2.4.6.81

1.21.41.61.8

2

Anode condition

Cathode condition

Ti is a stable element under PEFC conditions. Pt/Ti alloy electrocatalysts

strongly-acidic condition

Fig. pH-potential equilibrium diagram for system Ti-H2O

PourbaixPourbaix diagram of Tidiagram of Ti--HH22O systems at 80O systems at 80ooC C

Fig. STEM micrograph of PtTi/C electrocatalysts, showing nanocrystalline Pt-Ti alloy particles, where surface Ti may be oxidized.

4.3Pt1Ti3(900)

4.6Pt1Ti1(900)

4.2Pt3Ti1(900)

4.7Pt(700)

3.9Pt(450)

3.5Pt(200)

Particle size / nmCatalyst

Table: Particle size.

PtPt--Ti Ti electrocatalystselectrocatalysts are successfully prepared !are successfully prepared !

(Kawasoe et al., J. Electrochem. Soc.,154, B969 (2007))

Pt-Ti alloy or Pt-TiO2 nanocomposite?

Pt(200

)Pt(7

00)

Pt3Ti1(

900)

Pt1Ti1(

900)

Pt1Ti3(

900)

j k /

mA

cm

-2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.50.85 V0.80 V0.75 V Figure . Kinetic current

densities (jk) at 0.85, 0.80 and 0.75 V vs. RHE in 0.1 M HClO4 solution saturated with O2. Sweep rate: 10 mV/s, temperature: 25 ˚C. The current density was normalized to ECSA measured by CV.

CatalytiCatalytic activity of Ptc activity of Pt--Ti Ti electrocatalystselectrocatalysts

Comparable or even higher catalytic activity was obtained for Pt-Ti catalysts.But, Pt-Ti alloy or Pt-TiO2 nanocomposite?

(Kawasoe et al., J. Electrochem. Soc.,154, B969 (2007))

Importance of Importance of ““chemical degradationchemical degradation”” of of SOFCsSOFCs

Chemical degradationMajor origins:• Practical fuels • Ambient air• System components

Kerosene

Gasoline

Alcohol

H2

Biogas LP gas

Coal gasVarious energy resources

Natural gas

AnodeElectrolyte

Cathode

Minor constituents in practical SOFC fuelsSulfur-related impurities

(City gas, LP gas, Coal gas, Coke oven gas, Biogas, Petroleum-related fuels)

Halogen-gas (Cl2 gas in water, HCl in coal gas etc.)Ammonia (Biogas)Aromatic compounds (Petroleum-related fuels)

Internal or external reforming

CO

Minor constituents in ambient airSOx in contaminated airSalt-containing mist near seashoreHumidity in ambient air

Direct supply

Anode poisoning

Cathode poisoning

Kerosene

Gasoline

Alcohol

H2

Biogas LP gas

Coal gasVarious energy resources

Natural gas

AnodeElectrolyte

Cathode

Minor constituents in practical SOFC fuelsSulfur-related impurities

(City gas, LP gas, Coal gas, Coke oven gas, Biogas, Petroleum-related fuels)

Halogen-gas (Cl2 gas in water, HCl in coal gas etc.)Ammonia (Biogas)Aromatic compounds (Petroleum-related fuels)

Internal or external reforming

CO

Minor constituents in ambient airSOx in contaminated airSalt-containing mist near seashoreHumidity in ambient air

Direct supply

Anode poisoning

Cathode poisoning

Impurities from system componentsHeat insulation materialsStructural componentsElectric insulatorMaterials for heat exchanger

Fuel supply tubesAir supply tubesBonding materials

Evaporation

Practical Practical fuelsfuels

AmbientAmbientairair

System System componentscomponents

K. Sasaki and Y. Teraoka, J. Electrochem. Soc., 150 [7] A885 (2003).

O0 20 40 60 80 100

0

20

40

60

80

100

H

0

20

40

60

80

100

CH4

C2H6

C2H4

CH3OHC2H5OHC3H7OHH2O

1000oC800oC600oC400oC200oC100oC

C

1000o C

800o C

600o C CO2

H2O

CO

CH4

CnH2n

Carbondeposition

region

100o C

CC--HH--O ternary diagram: O ternary diagram: Carbon deposition regionCarbon deposition region

Equilibrium compositions can be specified by the C:H:O ratio.

CC--HH--O ternary diagram: O ternary diagram: Reactivity of Ni with SReactivity of Ni with S

Reactivity of Ni with minor impurities can be described in the C-H-O diagrams !

C-H-O-Ni-S diagram (600oC, PH2S=5ppm)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.10.20.30.40.50.60.70.80.9

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

C

H Omole fraction /(C+O+H)

Ni(s) + gas_ideal + C(s)

Ni3S

2(s2) + C(s) + Ni(s) + gas_ideal

Ni3S

2(s2) + gas_ideal + NiO(s) + Ni(s)

NiO(s) + NiSO4(s) + gas_ideal

Ni(s) + gas_ideal

H2O

CO2

CO

CH4 Humidification

Fuel comsumption

(Assuming C+H+O>>Ni>Impurity)

(K. Sasaki et al., Proc. 8th Europ. SOFC Forum, Schoenbein Medal 2008 awarded!)

Stable cell voltage up to 1000 hours is confirmed. Cell voltage drop is reversible.

Poisoning by HPoisoning by H22S up to 1000 hoursS up to 1000 hours

（K. Haga et al., Solid State Ionics, in press）

Cl2： sublimation&precipitation typeSiloxane： precipitation (deposition) typeP, B： eutectic-type, grain-growth-type

500 nm

NiK5ppm Cl5ppm Cl22

10μm

SiK

cross sectioncross section

surfacesurface30μm

surfacesurface 10μm

Cl2 Siloxane

P B

surfacesurface

Degradation mechanisms for each impuritiesDegradation mechanisms for each impurities

（K. Haga et al., Solid State Ionics& J. Electrochem. Soc., in press）

Poisoning / degradation mechanismsPoisoning / degradation mechanisms-- II

O2- O2-

Adsorption-type

X`ad

Anode(Ni)

X

X

X

X

X X

X

XX

Electrolyte

H2

Electrolyte

Sublimation-type Deposition-type

Ni- X`

Ni- X`X

O2-

X`

Electrolyte

XH2

Sulfur (low concentration)

Chlorine Siloxane

X: Impurity X: Impurity X: ImpurityAnode

(Ni)Anode

(Ni)


Poisoning / degradation mechanismsPoisoning / degradation mechanisms-- IIII

Reaction-type Grain-growth-type Eutectic-type

O2-

Electrolyte

NiX`Y(Solid)

O2-

Electrolyte

Ni(+X`)

O2-

Electrolyte

NiX`Y(Liquid)

H2 H2 H2

Sulfur(high conc., low temp.)

Boron PhosphorusSulfur

(high conc., high temp.)

X: Impurity X: Impurity X: ImpurityAnode(Ni) Anode

(Ni)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

1

2 BeO

3 MgO Al2O3

4 CaO Sc2O3 TiO2 V2O3 Cr2O3 MnO Fe Co Ni Cu Ga2O3

5 SrO Y2O3 ZrO2 NbO2 Mo Ru Rh Pd

6 BaO La2O3 HfO2 Ta2O5 W Ir Pt

7

CeO2 Pr2O3 Nd2O3 Sm2O3 Eu2O3 Gd2O3 Tb2O3 Dy2O3 Ho2O3 Er2O3 Tm2O3 Yb2O3 Lu2O3

ThO2 UO2 NpO2 PuO2

Lanthanides

Actinides

： Stable as an oxide in H2-3%H2O at 1000oC： Stable as a metal in H2-3%H2O at 1000oC

StableStable compounds in the SOFC anode atmospherecompounds in the SOFC anode atmosphere

P

Temperature：200oC

Air：50L/min

Starting solutions

Temp.：80oC

Powders prepared

Air：0.69MPa

Pump

Heater

Preparation of Preparation of anode materials via sprayanode materials via spray--mist dryermist dryer

⇒ Larger electrode reaction area

SpraySpray--mistmist--dryer for anode materials synthesisdryer for anode materials synthesis

(J. Yamamoto et al.)

NiO+ScSZ

Ni0.95Mn0.05O+ScSZ

In oxidizing atmosphere

In reducing atmosphere

NiMeOxNiNi Ni

Ni

Ni

Ni

MeOx

Pinning effect to keep larger electrode reaction areaagainst poisoning and to prevent Ni agglomeration!

MeOx

MeOx

Mn concentration / mol%

0 5 10 15 20

Volta

ge d

rop

/ mV

0

20

40

60

80

100

120

Time / hrs

0 1 2 3 4 5

Volta

ge /

V

0.70

0.75

0.80

0.85

0.90

NiO + ScSZNi0.99Mn0.01O + ScSZNi0.97Mn0.03O + ScSZNi0.95Mn0.05O + ScSZNi0.9Mn0.1O + ScSZNi0.8Mn0.2O + ScSZ

Impurity tolerant anode, NiImpurity tolerant anode, Ni--MnO/ZirconiaMnO/Zirconia, has been developed., has been developed.Cell voltage drop due to sulfur poisoning decreased considerably.

(J. Yamamoto et al.)

NiNi--MnOMnO/Zirconia/Zirconia nanocompositenanocomposite anodesanodes

SummarySummary

Various electrode materials have been developed for fuel cells with high durability and flexibility, based onthermochemical stability and nanostructuring:

＜PEFC/DMFC＞Carbon-free electrocatalysts have been developed using semiconducting oxide support.

Various nanostructured electrocatalysts have been developed with thermochemical and geometrical stability.

＜SOFC＞Degradation mechanisms by foreign species have been specified.

Sulfur-tolerant Ni-Mn based nanocomposite anode has been developed.

SasakiSasaki--Lab. in Kyushu UniversityLab. in Kyushu University

Fuel Cell Evaluation Systems (30 systems available)

Fuel Cell Laboratory

Contributing to various fuel cell applications via Contributing to various fuel cell applications via materials synthesis, cell preparation, electrochemical / materiamaterials synthesis, cell preparation, electrochemical / materials characterizations !ls characterizations !

○ Fuel cell materials preparation facilities (Apparatus for various wet-chemical procedures) ○ Fuel cell fabrication facilities (Automated spray-coating systems, Hot-press etc.)○ Fuel cell evaluation facilities (30 evaluation systems available for SOFC/PEFC/DMFC, 20 are full-automated.)○ Electrochemical experimental apparatus (4 impedance analyzers, 5 CV, RDE etc.)○ Microscopes (FESEM-STEM-EDX, AFM-STM) (Own STEM-EDX-EELS & FIB-MS will be installed in this year.)○ Materials analytical instruments (XRD, XPS, DTA-TG-MS etc.)○ Gas analytical instruments (GC-MS, automated GC etc.)○ Materials database

Fuel Cell Electrode Materials with Durability and FlexibilityBy-product hydrogen, Reformed fossil...

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