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論文誌テンプレート Ver.2002.10.02
Progress in Fuel Cell Technologies
Yasuzo Tanaka＊Member
Abstract Progress in fuel cell technologies is reviewed for this special issue. In the diversified society, the fuel cell technology
is a significant and most promising field. The fuel cell technologies provide many variations for our uses and possibilities for ourlives. Especially, some technological battles in the PEFC, SOFC and DMFC are excitedly interested us.
Keywords: energy conservation, CO2 exhaust gas reduction, electricity generation, fuel cell, AFC, PAFC, MCFC, SOFC, PEFC, DMFC

1839. This fuel cell did not enable commercially to compete withthe existing technology because there is the lack of appropriatematerials or manufacturing routs.
(2) AFC-generation
The alkaline fuel cell, AFC, waspractically applied to Apollo Spaceshipand Space Shuttle. This fuel cell has many
merits of low operation temperaturearound 80oC, low material cost and highpower density at a range of 10 kW.
However the fuel cell has some demeritsof carbon dioxide poisoning and low life.
(3) First-generation
The phosphoric acid fuel cell, PAFC, has recorded aninstallation of 142 stacks in 2003 as a MW-class power-generation
plant in the ordinary thermal power plant. Furthermore, anadvanced type PAFC of 100kW capacity with higher reliability hasbeen installed by 2006. The new one has recorded a long operationof total 40,000
hours for 7 stacks of 20 stacks, reported by
Fuji Electric Advanced Technology.
(4) Second-generation
The molten carbonate fuel cell,
MCFC,operating
athighertemperatures such 650oC has theadvantage that both CO and H2 canbe electrochemically oxidized at theanode. So MCFCs have been applied also for
the MW-class ordinary thermal power plant, where exhausted heatfrom the MCFC has been used for the combined generation with acarbon dioxide recycle process.
(5) Third-generation
The solid-oxide fuel cell, SOFC, can in principle, be designed tooperate within a wide temperature range of 800-1000oC and toadapt oxide ions or protons as a conduction member. The SOFC is
to be useful for an integration system with a gas micro-turbine, asteam reformation of fuel such as diesel, petrol and propane toproduce H2 and CO gases for the anode, and a co-generation
system with a small capacity for a residential use.
(6) Residential and Mobile-generation
In our residential use andtransportation vehicle use, thediversification in our energy uses,
especially electricity and the energy
saving efforts move onward steeply.
Figure 2 shows an energy
consumption rate of an average
domestic in 2002 from the Mainichi.

1. Introduction
The Kyoto Protocol was adapted at COP3, the Third Conferenceof Parties to the UN Convention on Climate Change, in Kyoto,
Japan, on 11 December, 1997. After the Kyoto Protocol, thecomplexity of the negotiations has been overcome, and the Kyoto
Protocol has been validated on 16 February, 2005. Consequently,
for Japan a total cut in greenhouse-gas emissions of at least 6%
from 1990 levels should be obligatory in the commitment period
2008-2012.
To overcome this environmental issue, we should make every
effort to develop the following items:(1) To use in higher efficiency of the fossil fuels.
(2) To promote an introduction of petroleum-substitute energies
such as natural gasses or coal.
(3) To lower the CO2 exhaust and environmental pollution matters.
On the other hand, we understand that the electricity is
indispensable for our lives and industries. Furthermore, we know
an electrify rate of 41 %, which is the electricity energy to the total
primary energy, and an electricity generation dependency of the
primary energy sources as shown in Figure 1.
As the most promising technology to solve the above mentioned
items, we recognize to introduce the fuel cells in the electricitypredominant society, and to be necessary to develop the fuel cell
technologies more and more.
N uclar pow er
C oal
N aturalgas
O ilW ater pow rO thers

Figure 1 Electricity generation dependency of the primaryenergy sources in the fiscal year 2005, Japan from the Yomiuri
August 10, 2006

2. Generation Changes in Fuel Cell Technology(1) Creation-generation
The first primitive fuel cell, which converts chemical energy
into electrical energy, was successfully demonstrated by Grove in* International Superconductivity Technology Center
34-3, Shimbashi 5-chome, Minato-ku, Tokyo, 105-0004
E−mail:tc90tanaka@istec.or.jp

電学論 A，127 巻 1 号，2007 年

1Kogyochosakai Pub. Co., Ltd.
(1)To increase in three-phase interface area
In principle, the electrode reaction of the dissociation reaction,oxidation reaction and reduction reaction on the air electrode andthe fuel electrode takes place at the three-phase interface amongvapor phase, electrode and electrolyte as shown in Figure 3.
Therefore, it is most important factor to increase in the interface
area for effective electrode reactions. For the purpose, more efforts
of developing fine or porous electrode structures, efficientelectro-catalysts and electrolytes with high-ion mobility are carriedout steadily.

Hot-water supply

H eating

lighting, Residensial
electrical appliancesand Others

Figure 2 Energy consumption rate of the average residential use
The polymer electrolyte fuel cell, PEFC, has appeared in thelate 1980’s as a power source for the hybrid-cars or electric motorvehicles. The PEFC for the residential
uses orthe small dispersed power sources has
highersystem efficiency, tried to popularize
widely.
On the other hand, the direct
methanol fuel cell, DMFC, can inprinciple, design to exclude the reformer from the hydrocarbon to
the pure H2 fuel, and to compact a stack shape and a light weightfor mobile or portable uses. Especially, the DMFC will expand for
portable electric instruments such the note personal computer, PC,or the mobile phone as a micro-fuel cell. Forinstance, NEC Corporation has alreadydemonstrated the DMFC with a methanol
cartridge for the PC supported by the New
EnergyandIndustrial
Technology
Development Organization, NEDO.

3.

Vapor phase
Electrode(2)To reduce the carbon monoxide poisoning
The reformed hydrogen from methanol or natural gas contains
generally small amount of carbon monoxide, CO, which isabsorbed at below 100oC on the Pt based electro-catalyst to leadthe cell voltage drop. In PEFC for the carbon monoxide poisoning,
the effort for developing CO-tolerant Pt-alloys such as Pt-Ru
against the poisoning, and the installation of CO clean-up unit areinevitable to be below 10ppm of CO content.
(3)To suppress the crossover
In DMFC the fuel gas and the air penetrate through polymer
electrolyte to increase in over-voltage level as shown in Figure 4,
to drop cell voltage and to decrease in fuel efficiency. Thesephenomena are called by the crossover. Some schemes ofincreasing an operation temperature or decreasing the fuelconcentration are carried out.
Air electrode carried catalyst
O2 AirH2O

Table 1 shows a summary of typical fuel cells. In these cells themost important materials are construction materials for cell frames,
electrode plates, catalysts and electrolytes, depending on the fuelgases, the oxygen sources and operating temperatures.
Table 1 Summary of typical fuel cells
PAFC

MCFC

PEPC

DMFC

Electrolyte

H3PO4
dense
solution

Li2CO3K2CO3/
Na2CO3

ZrO2(Y2O3, CaO)

Ion
exchangefilm

Methanolsolution

H+

CO32-

O2-

H+H+

Electrode
substrate

Porouscarbonplate

Poroussintered
Ni-Cr,
porousoxide NiplateNiplate,
La-Ni
oxide

Porouscarbonplate

Carbonnanohorns

Electro-catalyst

Pt based−−Pt based

Pt

Fuel

H2
including
CO2H2, COH2,COH2including
CO2Methanol

150-200

600-700

8001,000

70-10070-120

32-42

-45

40-50

30-40

−

-2,000-1,500-3,500-5,000700-1,000

Conduction ion

Operation
temperature, oC
Generation
efficiency, %Power density,
W/m2

SOFC

Electrolyte

Figure 3 Schematic view of three-phase interface

Requirements for Cell Component

Type of fuelcell

Three-phaseinterface

MEA

O2

H+Fuel gas

e-CO2
Fuel gas
PolymerFuel electrode carried catalyst
Electrolyte
Figure 4 Principle of DMFC with polymer electrolyte(4)To eliminate the cation impurity
Polymer film has a function of cation exchange in PEFC tointroduce some cations such metallic ions into the fuel cell system.
It needs to purify using water, to use the filtered air or to clean-up
transfer tubes.
(5)To suppress the carbon deposition
Reformed gas used in the fuel cell is called by the water gas
consisting hydrogen, carbon monoxide, carbon dioxide and water,
and is in the Boudouard equilibrium above 500oC.

Every fuel cell in the table is developing or demonstrating forthe present. To popularize the fuel cells dramatically, it needs torespond the following requirements up the practical demands.
Some requirements have been suggested by textbooks such “abig-cyclopedia of the new energies”, 2002, edited by the2T. IEE Japan, Vol. 127-A, No.1, 2007

TITLE
H2 + CO2 ⇔ H2O + CO
But CO also deposits easily carbon at 500-700oC on a metallic
surface.
2CO ⇔ CO2 + C
Since in MCFC and SOFC this carbon deposition phenomenon
happen frequently, some amount of water are used to adding to theinlet fuel gas to suppress the carbon deposition.
(6)To prevent the nickel dissolution and deposition
In MCFC the air electrode of NiO contacted with carbonate
electrolyte solutes slightly to diffuse in the electrolyte, and the
diffused nickel ion reduces on the fuel electrode to deposit a
metallic nickel. This phenomenon prevents to keep a desired CO2
partial pressure during the operation.
(7) To relieve in the thermal stress
It is a significant factor to shorten starting time up by theoperation temperature. Therefore, in SOFC, which operates thetemperature range of 800-1000oC, the thermal stress due to thethermal expansion differences among constituting materials haveto be relieved to keep them safety. Because PEFC, which consistsof water or liquid solutions, operates around room temperature,these constituting materials transform into the different phases
under atmospheric temperatures below the frozen temperature.
(8) To achieve a quick start
On the other hand, the starting time generally requires forlowering more and more in the practical fuel cell. Because the fuelcell is based on the electrochemical principle, the starting time isconsiderably long. In the case of SOFC, the starting time up by theoperation temperature of 900oC needs about few hours.
In a recent report, a quick start of 30 seconds in a new SOFC
has been achieved by the Ritsumeikan Universiry group,announced by the Nikkan Buisiness & Technology, 2006. In thisannouncement, the SOFC using a gas-transmission type solid
electrolyte, some radical oxygen and a flame burning instrument
achieved the quick starting time of 30 seconds.
(9) To perform higher power density
The DMFC as the micro fuel cell is developing against thelithium-ion battery for installing it on the PCs or the portableelectric instruments. There are significant problems in the DMFCof low power density as shown in Table 1, and large cost share of
25% in the membrane electrode assembly, MEC as shown inFigure 4.
As a solution for the problems, a new type of micro fuel cell has
been proposed by NTTDOCOMO group, announced by the Nikkei
Business Daily, 2006. The new micro fuel cell can be operated byan aluminum hydride with water, instead of the methanol fuel inthe DMFC. The aluminum hydride can produce from somealuminum scraps with a super fine grinding method as shown in
Figure 5.

4.

Today’s fuel cell market may divide into three fields of 100 kW
or more class for the power generation plant, 1 kW class forresidential use or automobile, and the micro-fuel cell for mobile
electric instruments.
The 100 kW or more class fuel cells such PAFC or MCFC havea long experience in demonstration, and a steady advancement intheir technologies.
The 1 kW class fuel cells such PEFC or SOFC are in a dramaticcompetition as shown in Table 2, announced by the Nikkei
Business Daily. 2006. The PEFC and the SOFC are developing for
applying to the residential use and the automobile use.
Table 2 Relative performance in the fuel cell market
Typical fuel cell

PEFCSOFCMCFC

Generation efficiency inpractical installation, %

33.9

49

<45

Starting time
Compatibility withco-generation
Cost characteristics

Market targets

Short

Long to short

Residential use
with hot-watersupplyExpensive Pt
forelectro-catalyst

1 kW,
residential use
for 2,000hrs
Using
expensive rareearth materials

Residential use
Automobile

Residential use
AutomobileMiddle
Low cost inmaterials
Fixed
installationin plants

On the other hand, the micro-fuel cells are in creating
technologies for practical demands already issued in section 4 (9)against the current advanced battery technologies.

5.

Conclusion

As a promising candidate to overcome the environment issues
related to the Kyoto Protocol, we propose intensely the fuel celltechnologies.
The fuel cell technologies intend to play an important part in
total energy conservation and CO2 exhaust gas reduction. In thediversified society, the fuel cell technologies have many variationsand possibilities. In addition of R&D for each fuel cell
technologies, many energy systems installed the fuel cells should
be significant. Because the generation efficiency of the fuel cell
itself may stay around 30-45%, some combinations suchmicro-turbine or heating instruments increase up to 70% or morein the total generation efficiency.
Finally, we are looking forward to discussing with you in themeeting of the fuel cell promoted by the Metal and Ceramics
Technological Committee.
(Manuscript received September 04, 2006)

Aluminum scraps from an automobile plant
Aluminum chips with water

Yasuzo Tanaka (Member) was born on December 12, 1940.
He works in the International Superconductivity
Technology Center (ISTEC). He has been
engaged in the chairman of Metal and Ceramics
Technical Committee of A sector in the IEEJ.

Grinding chips to few micrometers in diameter
Forming aluminum hydride in 10-nanometer cracks
Freeze-drying the aluminum hydride
Aluminum hydride powder

Figure 5 Procedure of the aluminum hydride
電学論 A，127 巻 1 号，2007 年

Prospect of Fuel Cell Market3