Jun MaruyamaEnvironmental Technology Research DivisionOsaka Municipal Technical Research Institute

Topics

1. Importance of cathode catalyst forpolymer electrolyte fuel cell (PEFC)

2. Demand for noble-metal-free catalysts3. Development of carbon-based catalysts

Turkish-Japanese Joint Carbon SymposiumIstanbul Technical University, Istanbul, Turkey2010.3.19

Development of CarbonDevelopment of Carbon--BasedBasedNobleNoble--MetalMetal--Free Fuel Cell CatalystFree Fuel Cell Catalyst

Osaka Municipal Technical Research Institute

Founded in 1916Research mainly on chemistryOrganic chemistryInorganic chemistryBiochemistryMaterial chemistryEnvironmental technology

Operative at 80 ºC ・・・easy start-up, high power output⇒power source of electric vehicles and cogenerationsystems for domestic electricity and heating

Enabled by catalyst

H2

Proton-exchangemembrane

O2H+

Load

Anode

H 2H + 2e2 →+ _

Cathode

1/2O + 2H + 2e H O2 2

+ _→

Cell reactionH + H O2 2→1/2O2

＋－

Carbon paper

Mixed Nafion

Pt supported on carbon

Fig. Schematic representation of a proton-exchange membrane fuel cell and themembrane/electrode interface for gas diffusion electrodes.

3/3７

Importance of catalyst for PEFC

Conventional catalyst:Nanoparticles of Pt or Pt alloys supported on electron-conductive carbon black

Demand for noble-metal-free catalyst

Limitation of Pt reserves and supply⇒Demand for noble-metal-free catalystto realize widespread use of PEFC

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Current density/A cm-2

Pote

ntial/V

Anode activation

OhmicElectrodes

Membrane

Cathode activation overpotential

Cell potential

Open-circuit potential

Fig. Model calculations of the contributions to fuel-cell potential losses as a function of operatingcurrent density. Operating conditions: Cell temperature, 80ºC; O2 stoichiometric flow, 3; H2

stoichiometric flow, 1.3; Air-side pressure, 5 atm; Fuel-side pressure, 3 atm. [D. M. Bernardi andM. W. Verbrugge, J. Electrochem. Soc., 139, 2477 (1992).]

Large activation potential at cathode---requirement of large amount of Pt⇒Demand for noble-metal-free catalyst

particularly for cathode

Enzyme: Cytochrome c oxidaseProton movement→generation of membrane potential in mitochondria

・・・resembling fuel cells

Fig. The three-dimensional structure of cytochrome c oxidase.[S. Iwata, C. Ostermeier, B. Ludwig, H. Michel, Nature 376 (1995) 660.]

NN

NN

COOHHOOC

OHC

Fe

HO

H3

Active site: Heme a

Oxygen reaction in organisms

N N

NN

N

N

N

N

M

N N

NN

N

N

N

N

M

Phthalocyanine Naphthocyanine

N N

NN

M

N N

NN

CH3O

OCH3

OCH3

OCH3

M

Tetraphenylporphyr in Tet ramethox yphenylporph yr in

N N

NN

M

CH2CH3

CH3CH2

CH3CH2

CH2CH3 CH2CH3

CH2CH3

CH2CH3

CH2CH3

NN

N N

M

Octaethylporph yrin Bibenzote traazanulene

Loading onto carbon materials⇒O2 reduction catalyst[R. Jasinski, Nature 201 (1964) 1212.]

Heat treatment⇒Improvement of

activity and durability[V. R. Bagotzky, M. R. Tarasevich, K. A.Radyushkina, O. A. Levina and S. I. Andrusyova,J. Power Sources 2 (1977) 233.]

➣Many studiesfuel cell testreaction mechanismactive site structure

➣When center metal is Fe,the produced catalyst is associated with

living cells and advantageous in regard toresource and cost.

Macrocyclic compounds

M. E.Lai, A. Bergel, J. Electroanal. Chem. 494, 30, (2000).Catalase on GC have the activity for O2 reduction.Catalase: four equal subunits (molecular weight: 57000) containing Fe(III) porphyrin.

Problem: hydrolysis of the enzyme in the polymer electrolyte.

Carbonization of catalasea stable and active catalyst for O2 reduction with the active site homogeneouslydispersed in a carbon matrix, due to inherent inclusion of the Fe(III) porphyrin.(It has been reported that iron porphyrins adsorbed on carbon materials are active foroxygen reduction, stabilized and activated by heat-treatment.)

25/3７

Development of catalyst from catalaseJ. Maruyama et al. Chem. Mater. 16 (2005) 4660

Fig. Molecular structure of catalase.[cited from The Protein Data Bank (DOI:10.2210/pdb4blc/pdb)].

Carbonization of catalase

Carbonization conditionsAtmosphere: Ar, 0.1 dm3 min–1

Heat-raising speed: 5 ºC min–1

Temperature: 700, 750, 800, 850, 900, 1000 ºC

SampleHeat-treatment

temperature (°C)

Yield

(%)

Specific

surface area

(m2 g–1)

Pore volume

(mm3 g–1)

Mean pore

diameter

(nm)

CC700 700 24.6 290 148 2.04

CC750 750 19.6 449 229 2.04

CC800 800 14.2 790 439 2.22

CC850 850 4.33 975 861 3.53

CC900 900 4.60

CC1000 1000 3.13

Table. Yield and parameters of pore structure determined by N2

adsorption isotherm on carbonized catalase.

as large as surface area ofcommercial activated carbon

27/3７

Tafel plot

Fig. Relationships between electrode potential and log(–IK/A) for oxygen reductionat catalyst layers in O2-saturated 0.1 mol dm–3 HClO4. Concentration of CF3SO3Ksolution used for its adsorption onto CC800 was 0.5 mol dm–3. K+ was substitutedby H+ before the measurement. –IK was determined by

where I is the oxygen reduction current.

0

0.2

0.4

0.6

0.8

-6 -5 -4 -3 -2

log(–I K/A)

Po

ten

tial/V

vs.

RH

E

CC700 CC750 CC800

CF3SO3H-adsorbed

CC800

Carbon black

Pt/C

2/16/13/2K 620.0

111

cnFADII

IK: Current free of influenceof mass transfer in solution

Increase in heat-treatment temperature

Increase in activity

CF3SO3H adsorption

Enhancement of mass-transfer in the pores

28/3７

Fuel cell tests

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.1 0.2 0.3 0.4 0.5

Current density/A cm–2

Volta

ge/V

CF3SO3H-adsorbed

CC800

Pt/C

Fig. Relationships between cell voltage andcurrents generated by fuel cells formedfrom CF3SO3H-adsorbed CC800 (solidline) and Pt/C (dotted line).

[Anode]10 wt.% Pt/C(Pt, 0.1 mg/cm2; Nafion, 0.5 mg/cm2)[Cathode](a) CF3SO3H-adsorbed CC800(CC800, 10 mg/cm2; Nafion, 5mg/cm2; carbon black, 1 mg/cm2)(b) 10 wt.% Pt/C(Pt, 0.1 mg/cm2; Nafion, 0.5 mg/cm2)[Membrane]Nafion 112[Hot press]150 ºC; 2.5 MPa; 10 min[Operation conditions]Cell, 80 ºCH2, O2, 100 ml min–1, humidified at80 ºC

29/3７

Continuous operation

0.00

0.01

0.02

0.03

0.04

0 12 24 36 48

Time/h

Curr

ent

densi

ty/A

cm–

2

Fig. Current change at a fuel cell formed from CF3SO3H-adsorbed CC800 during a continuous operation at 0.5 V.Cell temperature was 80 ºC. Hydrogen and oxygen werehumidified at 80 ºC and passed into the cell apparatusunder atmospheric pressure at 100 cm3 min–1.

Improvement of theactivity and durability

Modification of thecarbonizing conditions

atmosphereheat-raising speed

23/3330/3７

HemoglobinConsisting of two pairs of subunits,represented as a1a2b1b2, containing the Fe(III) porphyrin(total molecular weight: 57000) Hemoglobin could be abundantly obtained (about 2 million tons per year),

especially from the meat industry producing more than 200 million tons ofmeat per year around the world and discarding the blood containinghemoglobin as waste.

Abundance and inexpensiveness of hemoglobin are advantageous for thewidespread use of the PEFC.

24/3331/3７

Development of catalyst from hemoglobinJ. Maruyama et al. Chem. Mater. 18 (2006) 1303

Fig. Molecular structure of hemoglobin.[cited from The Protein Data Bank (DOI:10.2210/pdb2dn2/pdb)].

Carbonization of hemoglobin

Carbonization conditionsAtmosphere: Ar, 0.1 dm3 min–1

Heat-raising speed: 5 ºC min–1

Temperature: 750, 775, 800, 825, 850 ºC

Table. Yield and parameters of pore structure determined by N2

adsorption isotherm on carbonized hemoglobin.

SampleHeat-treatment

temperature (°C)

Yield

(%)

Specific

surface area

(m2 g–1)

Pore volume

(mm3 g–1)

Mean pore

diameter

(nm)

CHb750 750 22.2 517 224 1.73

CHb775 775 20.3 597 256 1.71

CHb800 800 14.2 816 363 1.78

CHb825 825 11.50 1005 481 1.92

CHb850 850 1.89 Higher specific surface area

25 ºC-Difference --- large difference in pore strucutre32/3７

Tafel plot

Fig. Relationships between electrode potential andlog(–IK/A) for oxygen reduction at catalyst layers inO2-saturated 0.1 mol dm–3 HClO4.

Temperature increase

Surface area increase

Acitve site exposure

Activity increase

0

0.2

0.4

0.6

0.8

-6 -5 -4 -3 -2

log(–I K/A)

Pote

ntia

l/V

vs.

RH

E

CHb750

CHb775 CHb800Carbon black

CHb825

25 ºC-difference--- large activity difference

33/3７

Activity enhancement of carbonized hemoglobinJ. Maruyama et al. J. Phys Chem. 111 (2007) 6597

0.0

0.2

0.4

0.6

0.8

1.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6

Current density/A cm–2

Vo

ltag

e/V

[A][B]

+ –

H2

O2

H2O

H+

e–

Polymer electrolyte fuel cellCarbonized hemoglobin

Fe valence state change

Hemoglobin

700 705 710 715 720 725 730 735 740

Binding energy/eV

Inte

nsi

ty

[B]

[A]

0.02 kcps

Fe(III)Fe(II)

Change in heat treatment condition

Increase in Fe(II)

Activity enhancement

Catalyst formation from hemoglobin pyropolymerJ. Maruyama et al. J. Phys Chem. 112 (2008) 2784

Fig. Photographs, relative weights (yields, ), and elementalcompositions of hemoglobin and samples obtained by heat treatment ofhemoglobin. The TG/DTA data obtained at 5 ºC min–1 in flowing Ar arealso shown.

0.0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500 600Heat treatment temperature/°C

Re

lative

we

igh

t

Exo

the

rmic

En

do

the

rmic

H

C

N

O

Hemoglobin 150 ºC 200 ºC 250 ºC 350 ºC 500 ºC

Fuel cell test

Fig. Relationships between current density and cell voltage(white symbols) and relationships between current densityand power density (black symbols) for PEFC formed using10 mg cm–2 of CHb200900 in the cathode and 1 mg cm–2

of carbon black loaded with Pt (10 wt %) in the anode. Theelectrode area: 5 cm2. H2 and O2 were supplied at 100 cm3

min–1 under backpressures of 200 (circle) and 0 kPa(triangle). H2 and air were also supplied withoutbackpressure at 100 and 500 cm3 min–1, respectively(square). The partial pressures of O2 under backpressure at200 (O2), 0 (O2), and 0 (air) kPa were 254, 54, and 11 kPa,respectively.

[Anode]10 wt.% Pt/C(Pt, 0.1 mg/cm2; Nafion, 0.5mg/cm2)[Cathode]CHb200900(Catalyst, 10 mg/cm2; Nafion, 5mg/cm2; carbon black, 1 mg/cm2)[Membrane]Nafion 112[Hot press]150 ºC; 81 kPa; 10 min[Operation conditions]Cell, 80 ºCH2, O2 (Air), 100 (500) cm3 min–1,humidified at 80 ºC

10/11

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.2 0.4 0.6 0.8 1.0

Current density/A cm–2

Volta

ge/V

0.20

0.15

0.10

0.05

0.00

Po

we

rd

en

sity/Wcm

–2

0.25

0.30

O2 (254 kPa)

O2 (54 kPa)

Air

Durability

0.00

0.20

0.40

0.60

0.80

1.00

0 50 100 150 200

I 0.5

V/I

0.5

V,t

=0

Time/h

CHb200900

CHb350900C

0 1 2 3 4 5 6

Fourier

transfo

rmed

am

plit

ude

(a.u

.)

Radial coordination/Å

CHb200900

CHb350900C

Hematin

Fig. Change in the ratio of the current at 0.5 V (I0.5

V) to the current at the start of the operation (I0.5

V,t=0) during continuous operation at 0.5 V in thePEFCs formed using CHb200900 (thick line) andCHb350900C (thin line). Cell temperature: 80°C.Gas humidification temperature: 80°C. Hydrogenand air were supplied at atmospheric pressure and50 and 250 cm3 min−1, respectively, for the PEFCformed using CHb200900. Hydrogen and oxygenwere supplied at atmospheric pressure and 50 cm3

min−1 for the PEFC formed using CHb350900C.

Fig. Pseudo-radial distribution functionscalculated by Fourier transformation of extendedX-ray adsorption fine spectra at the Fe K-edgefor CHb200900, CHb350900C, and hematin.

Development of catalyst from amino acidJ. Maruyama et al. J. Electrochem. Soc. 154 (2007) B297

H NCH COOH2 2

Fe[CH CH(OH)COO]3 2

O

OHHO

HO

OH

OH

1) 150 ºC in Air2) 1000 ºC in Ar flow

FeNN

N N

Fig. Schematic representation of the generation of heme-like active site fromnitrogen atoms of glycine and iron during pyrolysis with glucose.

Durability

0 1 2 3 4 5 6

Fou

rier

tra

nsfo

rme

da

mp

litud

e(a

.u.)

Radial coordination/Å

GGI1000Fe foil (× 1/10)

G3GI1000

G4GI1000

Fig. Pseudo-radial distribution functionscalculated by Fourier transformation ofextended X-ray adsorption fine spectra atthe Fe K-edge for Fe foil, GGI1000,G3GI1000, and G4GI1000.

Fig. Change in the ratio of the current (I0.5 V) to the currentat the start of operation (I0.5 V, t = 0) during continuousoperation at 0.5 V in the fuel cells whose cathodes wereformed from GGI1000, G3GI1000, and G4GI1000. Celltemperature: 80 ºC. Hydrogen and oxygen were humidifiedat 80 ºC and passed into the cell apparatus at 50 cm3 min–1

and atmospheric pressure. The partial pressures of hydrogenand oxygen were 54 kPa.

Structure control in carbon-based catalystJ. Maruyama et al. Chem. Commun. 2879 (2007)

+ –

H2

O2

H2O

H+

e–

Polymer electrolyte fuel cell

Bended

graphene layer

Porous and

amorphous carbon

Intermediate

structure

Cu only

Fe only

Fe+Cu

0.00

0.05

0.10

0.15

0.20

0.25

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Current density/A cm–2

Po

we

rd

ensity/W

cm

–2

54 kPa

254 kPa

454 kPa

54 kPa(after 100 h)

Carbon source: glucoseNitrogen source: AdenineFe source: Fe gluconateCu gluconate addition in starting mixture⇒ Structure control of carbon matrix + Change in Fe oxidation state⇒ Increase in active sites

For future studies

Further improvement of activity and durability

Efficient generation of the Fe‒Nx active sitewith ordered structureSearch for appropriate carbon sourceSearch for appropriate nitrogen sourceExamination of heat treatment condition