Technical Report
報文

Development of 1 kW Class PEFC Stack Systemwith Variable Gas Flow Channel
Shunsuke Mizutani*
Hideo Yasuda*

Shuji Hitomi*

Masanori Yamachi**

Abstract
The 1 kW class PEFC stack system with a new function of variable gas flow channel has been developed tokeep stable operation with high efficiency in a wide range of load. This stack system with the new function
was turned out to suppress a flooding phenomenon by switching the connection of the channel from parallel toseries flow to expel the remained water within the channels with increase of gas flow velocity at the low load
less than 100 mA cm-2. This system will be beneficial for the practical PEFC stack system as a power source
capable to use for the wide range of load.

1

Introduction

gas flow channels caused by the increase of amountof fed gas to meet its corresponding electrochemi-

Polymer electrolyte fuel cell (PEFC) is considered

cal reaction, resulting in the extra energy of aux-

to be a promising candidate of clean power source

iliary systems such as a gas feed pump and so on.

for electric vehicles or stationary systems because

We have proposed the variable gas flow channel ofof its high energy conversion efficiency. The stable

which function is to solve these problems by switch-and efficient operation of PEFC at various loads has

ing the connection of gas flow channels in series orbeen strongly required for the practical use. There

parallel. The beneficial function will be discussed inneeds, for example of electric vehicle, the minimum

more detail for the 1 kW class PEFC stack system.

power for idling step and the maximum for acceler-2

ating step, respectively. Two main problems wereExperimental

observed in such a wide load operation. One is aflooding phenomenon caused by insufficient gas flow

The 1 kW PEFC stack composed of 20 single cells

velocity enough to expel the remained water withinin series was designed with the function of variable

gas flow channels, resulting in the remarkable volt-gas flow channel. Each cell has gas flow plates andage drop under the low power operation when thegas diffusion backings on both sides of membrane

gas utilization is same as the case of high power.

1)electrode assembly (MEA). The MEA was prepared

The other is an increase of pressure loss throughby hot-pressing the catalyst layers on the both sidesof polymer electrolyte membranes (Nafion 115). The*Department-E, Corporate R & D Center

catalyst material was Pt/C (platinum supported on**Corporate R & D Centercarbon) for cathode and Pt-Ru/C (platinum-ruthe-© 2004 GS Yuasa Corporation, All rights reserved.

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GS Yuasa Technical Report

2004 年 12 月

nium supported on carbon) for anode. The value of

第 1巻

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Inlet (a)platinum loading level for the cathodes and anodes
was 0.8 mg cm-2 and 0.4 mg cm-2, respectively. The

Outletapparent surface areas of these electrodes were 230
cm2. Each cell was layered and then pressed withthe metal plates set on either end of the stack. The

Inlet

representative structure of gas flow plates of theOutletstack with variable gas flow channel is shown in

Inlet

(b)

Fig. 1. The two kinds of gas flow directions in series
and parallel within the plates are shown with arrow in Fig. 2. These connections of gas flow chan-

Fig. 2 Representative illustrations for the gas
ﬂow direction of series ﬂow (a) and parallel ﬂow (b)within gas ﬂow plate.

nels were switched by the operation of valves set on
the outside of stack.
The evaluation of stack was carried out selecting
the connection of the channels for both sides of an-with the same direction as the air flow in the selec-

odes and cathodes. Air and reformed gas or hydro-tion of the parallel flow condition. The difference of

gen were used as oxidant and fuel gas, respectively.

temperature between inlet and outlet of the coolant

The composition of reformed gas was 80% H2, 20%

was also controlled so as to maintain to be less thanCO2, and 10 ppm CO. These gases were humidified

2 oC. The change in average cell voltage of the stackat the temperature of 80 oC. The utilizations of oxi-

on short-term was measured at 50 mA cm-2 with se-dant and fuel gas were 40% and 80%, respectively.

ries and parallel flow under the condition of air and

The coolant flow channel was equipped in every cell

pure hydrogen. The pure hydrogen was only used

and the temperature of MEA was controlled by set-

for this measurement in order to avoid an affect ofting the temperature of 80 C at the position of cool-

voltage drop due to CO poisoning. The distribution

ant outlet. The coolant was supplied to the channelsof operation voltage of single cells within the stacko

was measured at constant current density of 50 mA
cm-2 using four types of combination flows in series
Gas flow channels
for oxidant gas(a)and parallel. The evaluation of voltage-stability test
after switching the connection of the channels for
only air was conducted at 300 mA cm-2. The evaluation of stability performances on continuous operation of the stack with suitable connection of the(b)

Manifolds foroxidant gas

channels was conducted at constant current density

Manifolds forfuel gasof 50 and 300 mA cm-2.

3

Results and Discussion
Polarization curves for 1 kW PEFC stack with gas

flow channel in series and parallel flow are shown

Gas flow channels
for fuel gas

in Fig. 3. The obvious drop in average cell voltage
is observed at lower current density than 50 mA

Fig. 1 The representative structure of gas ﬂow
plates for cathode (a) and anode (b) of the stackwith variable gas ﬂow channel.

cm-2 in the case of parallel flow. This voltage drop is
considered by the occurrence of shortage of reactant

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GS Yuasa Technical Report

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the higher current density over 100 mA cm-2. That

0.8

Average cell voltage / V

第1号

flow for both of air and reformed gas especially at

0.9

is, the former flow shows the larger pressure loss
than that of the latter flow. It is obviously due to

0.7

the longer length of gas-flow-pass for the former

0.6

one. Considering the above mentioned undesirable
phenomena observed in lower and higher current

0.5

density, it is natural that the stack with fixed con-0.4

nection of either series flow or parallel flow should
not be proper for the operation in wide range of cur-

0.3
0.2
0

第 1巻

rent density. Therefore, a new function of variable
100

200

300

400

500

gas flow channels was added to the PEFC stack

600

-2

system to be capable for the application in the wide

Current density / mA cm

range of load, especially for electric vehicle or stationary power sources.

Fig. 3 Polarization curves for 1 kW stack withseries ﬂow ( ○ ) and parallel ﬂow ( △ ) under thecondition of air and reformed gas at 80 OC.

The combined functions of prototype 1 kW PEFC
stack with variable gas flow channel were evaluated by selecting optimum condition of series flow lessgas caused by the flooding phenomenon within thethan or equal to the current density of 100 mA cm-2

gas flow channel. The change in pressure loss of air

and parallel flow beyond 100 mA cm-2 to show theand reformed gas flow channels in series and paral-

improvement of the combined flow direction system.

lel for the stack under various current densities is

The representative polarization curve and air pres-shown in Fig. 4. There observes the big difference

sure loss of gas flow channels are shown in Fig. 5.

in pressure loss between series flow and parallel

The function of variable gas flow channel is turned
out to provide stable average cell voltage and low
pressure loss for air and reformed gas at wide40

range of operating current density from 10 to 600
mA cm-2. The selection of series flow at the lower

35

current density below 100 mA cm-2 is considered to

Pressure loss / kPa

30

expel the remained water from its channel to outlet

25

by increasing of gas flow velocity, resulting in the20stable cell voltage. The switching of the connection

15

from series to parallel is also considered to reduce
the pressure loss of feed gas, resulting in the reduc-10tion of energy loss for auxiliary systems at highload operation. The change in average cell voltage

5
0

0

100

200

300

400

500

for the stack with series at the lower current densi-

600

ty during the continuous operation is shown in Fig.

Current density / mA cm-2

6 for the clear difference of the effect of variable gas

Fig. 4 Change in pressure loss of air and reformed
gas in gas ﬂow channel for 1 kW stack with inseries ﬂow ( ● , ■ ) and parallel ﬂow ( ▲ , ◆ ) undervarious current densities at 80 OC.
(a) Air; (b) Reformed gas.

flow channel. The average cell voltage with series
flow is confirmed to be stable compared with thecase of parallel flow in which the repetitious voltagechange with a momentary drop was observed by the57

2004 年 12 月

0.9

30

0.8

25

第1号

in Fig. 7. Uneven distribution of cell voltage is ob-

0.7

20

0.6

15

0.5
10

0.4

served in the combination of parallel flow for eachelectrode. This means that the large cell voltage
drop is occurred by the flooding phenomenon evenin the anode as well as cathode.
Inevitable backward flow is considered to be appeared after switching the gas flow channel becauseof the change of the stream of gas flow as indicatedby the change of the direction of arrow in Fig.2. The

5

0.3
0.2

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representative distribution of cell voltage is shown

Pressure loss / kPa

Average cell voltage / V

GS Yuasa Technical Report

0

100

200

300

400

500

600

representative behavior of average cell voltage of0

the stack after switching the connection of chan-

Current density / mA cm

nels for cathode is shown in Fig. 8. The operation

Fig. 5 Representative polarization curve andchange in pressure loss of cathode gas ﬂow channel
for the prototype 1 kW stack with optimum selectionof the variable gas ﬂow channel with series ﬂow ( ○ ,● ) and parallel ﬂow ( △ , ▲ ) at 80 OC under thecondition of air and reformed gas.

time was counted from the switching. The sudden-2

drop of average cell voltage is observed subsequent
to the gradual increase towards the stable voltage
in the case of the change from parallel to series as
expected. The reverse behavior is also observed in
the case of the change from series to parallel. Thesephenomena are derived from the temporary varia-

0.85

tion of gas utilization towards higher value, in oth-

0.80

0.85

0.75

0.80

0.70

0.65

0

50

100
150
Operation time / min.

Cell voltage / V

Average cell voltage / V

er words, shortage of oxygen gas by the increment

200

0.75

0.70

Fig. 6 Change in average cell voltage of 1 kW
stack on short-term operation at 50 mA cm-2 and80 OC under the condition of air and hydrogen withseries ﬂow ( ○ ) and parallel ﬂow( △ ).

0.65

0

5

10
15
Cell number / -20

Fig. 7 Cell voltage distributions for prototype 1 kW
stack operated at 50 mA cm-2 and 80 OC under thecondition of air and reformed gas.
○ Series ﬂow for both air and reformed gas; △ Parallel ﬂow for both air and reformed gas; □ Parallel
ﬂow for air and series ﬂow for reformed gas; and ◇Series ﬂow for air and parallel ﬂow for reformed gas.

flooding phenomenon caused of remained water.
The voltage distribution of each cells composedfor 1 kW PEFC stack was investigated to clear theeffect of different combination of series flow andparallel flow for each of cathode and anode. The

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1 kW PEFC stack with variable gas flow channels

0.80

is shown in Fig. 9. The average cell voltages areflow over 100 h at low and high current density.

0.70

0.9

0.65

0.60
-10

0

10
Operation time / s

20

Average cell voltage / V

Average cell voltage / V

turned out to be stabled in both series and parallel
0.75

30

Average cell voltage / V

0.80

0.8

0.7

0.6

0.75

0.5

0

20

0.70

0

10
Operation time / s

20

80

100

Fig. 9 Change in average cell voltage for prototype
1 kW stack operated at 80 OC under the condition of
air and reformed gas.
○ Series ﬂow at 50 mA cm-2;△ Parallel ﬂow at 300 mA cm-2.

0.65

0.60
-10

40
60
Operation time / h30Fig. 8 Representative change in average cellvoltage for prototype 1 kW stack after switchingconnection of gas ﬂow channels for air operated at
300 mA cm-2 and 80OC under the condition of air
and reformed gas.
(a) Switching of channels for air from parallel ﬂow( △ ) to series ﬂow ( ○ ); (b) Switching of channels
for air from series ﬂow ( ○ ) to parallel ﬂow ( △ ).

4

Conclusion
The 1 kW class PEFC stack system with a new

function of variable gas flow channel has been successfully developed to keep stable operation withhigh efficiency in the wide range of load. The PEFC
stack system with the new function was turned out
to be able to suppress a flooding phenomenon byof pressure loss in the former case and lower value,

switching the connection of the channel from paral-

excess of the gas by reduction of pressure loss inlel flow to series flow to expel the remained water

the latter case at the condition of constant current

within the channels with the increase of the veloc-

density operation (See Fig. 4 (a)). However, these

ity of gas flow at the low load of low current den-phenomena are limited to be observed only up to 15

sity less than 100 mA cm-2. This new system will beseconds.

beneficial for the practical PEFC stack system with

Finally, the representative change in average cell

the wide range of load use, especially for electric ve-

voltages on continuous operation of the prototype

hicles or stationary power sources.

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Acknowledgememt

Reference

This work was performed by financial support of1) P. Rodatz, F. Buchi, C. Onder and L. Guzzella, J.

Power Sources , 128, 208 (2004).

New Energy and Industrial Technology Development Organization (NEDO) of Japan.

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