投稿論文

Paper

Application of Sulfonated Carbon Ionomer toCatalyst Layers of Polymer Electrolyte Fuel Cells
Tomoya Oyama, Kazuki Matsumoto, Tetsuo Take
Department of Chemistry and Energy Engineering, Faculty of Engineering, Tokyo City University

Abstract：We have developed a sulfonated carbon ionomer and applied it to the anode and cathode catalyst layers（CLs）of polymer electrolyte fuel cells（PEFCs). The above ionomer can be prepared by the thiol group oxidation
method, while its ion exchange capacity（IEC）can be controlled by changing the proportions of carbon black,3 -mercaptopropyltrimethoxysilane, and H２O２ used in the synthesis. The sulfonated carbon ionomer can be usedin both anode and cathode CLs of PEFCs, leading to their decreased performance, as compared with that of PEFCs
utilizing the perfluorinated sulfonic acid（PFSA）ionomer at 80  ℃ and a relative humidity（RH）of 100 %. The
performance of PEFCs employing the sulfonated carbon ionomer hardly depends on its IEC and decreases withdecreasing RH at 80  ℃. These performance decreases are larger than those observed for the PFSA ionomer. On
the other hand, PEFCs using the sulfonated carbon ionomer are superior to those based on the PFSA ionomer attemperatures above 100  ℃ and RHs below 100 %.

Key Words ：Polymer electrolyte fuel cell, Sulfonated carbon ionomer, Catalyst layer, Gas diffusion electrode,
Operation at temperatures above 100  ℃ and RHs below 100 %１．Introductionof PEFC systems. The electrochemical kinetics of bothelectrode reactions are also enhanced by increasing thePolymer electrolyte fuel cells（PEFCs）are considered

PEFC operation temperature. In particular, the rate ofa promising technology for clean and efficient power

the oxygen reduction reaction is significantly increased,

generation and are becoming

increasingly important

improving the performance of PEFCs as a whole. Theseas alternative power sources for stationary, transporta-

factors result in increased efficiency and simplification oftion, or portable applications, in particular for residential

PEFC systems.  

co-generation systems or electric vehicles, due to their

The perfluorinated sulfonic acid（PFSA）ionomer has

high efficiency, rapid start-up, and low emission profile.

been commonly used as both a polymer electrolyte mem-

The operation of PEFCs above 100  ℃ provides numer-

brane（PEM）and proton conductor in anode and cath-ous advantages, like reducing the affinity of the Pt cata-

ode catalyst layers（CLs）of state-of-the-art PEFCs due

lyst to carbon monoxide, which is a by-product of theto its high proton conductivity and high chemical andreforming process, and thus increasing CO tolerance.

mechanical stability. However, this ionomer is not ap-

As a result, the operation of PEFCs above 100  ℃ allows

plicable to PEFCs operating above 100  ℃, since it leads

using impure fuel streams and simplifies fuel process-to loses of proton conductivity and mechanical strength,

ing. High-temperature operation also increases the heatalso causing considerable permeation（crossover）of fuel,transfer rate because of a lager temperature gradienthydrogen, and oxidants, air or oxygen, above its glass

between the fuel cells and external environment, sup-transition temperature（〜110  ℃). Alternative ionomers

plying waste heat that can be easily utilized by otherbased on non-fluorinated materials, showing stability

processes（e.g., co-generation of heat and power or on-

above 100  ℃, processability, environmental adaptability,board reforming). Therefore, the heat management sys-and low production cost, in addition to chemical andtem is simplified, increasing the weight- and volume-

electrochemical stability, are in high demand.  Intensive

specific energy densities and the overall energy density

research efforts have been devoted to developing alter-

82

燃料電池 Vol.18 No.2 2018

native dual-use ionomers（as both PEMs and proton
conductors in catalyst layers）for the PEFCs. Recently,
a sulfonated silane ionomer1） and non-fluorinated hydrocarbon ionomers, such as sulfonated polyether（SPE）2),
sulfonated polyether ether ketone（SPEEK)3）− 7）, sulfonated polyether ketone ketone（SPEKK）8）, sulfonatedpolyarylene ether（SPAE)9），10）, and sulfonated polysulufone（SPS) 11） have been developed for cost reduction,
elevation of the operating temperature, and avoiding
environmental pollution by fluoride after disposal. However, the application of hydrocarbon ionomers as catalyst

Fig. １layer（CL）ionomers often decreases the performance utline of surface sulfonation procedure by SH
O
oxidation method.

of PEFCs. In general, the proton conductivity of hydrocarbon ionomers is high under high humidity conditions

sulfonic acid groups（SO3H）to the carbon black. First,

but decreases steeply with decreasing humidity, leading

the carbon black was refluxed in 3 -mercaptopropyltri-

to low catalyst utilization in the gas diffusion electrodes

methoxysilane（3 -MPTMS, KBM- 802 , 98 . 9 %, Shin-Etsu（GDEs）of PEFCs.

Chemical Co., Ltd., Japan）solution at 110  ℃ for 24 h to

In this work, we have prepared a sulfonated carbon

attach SH precursor groups, with acetone（99. 0 %, Showa

ionomer and applied it to both anode and cathode CLs

Chemical Co., Ltd., Japan）used as solvent. The weightof PEFCs, supposing that this ionomer with high proton

ratio of acetone to carbon black was set at 15 : 1 . Second,

conductivity exhibits no harmful effects on the perfor-

the SH groups on the carbon black were converted tomance and stability of PEFCs above 100  ℃, because car-

SO3H groups by oxidation with 10 wt% H2O2 aqueous

bon material is usually used as a Pt catalyst support insolution（30 wt% H2O2 aqueous solution, Showa Chemi-

CLs of phosphoric acid fuel cells at 200  ℃ and possesses

cal Industry Co., Ltd., Japan）at 70  ℃ for 2 h. The weighthigh heat durability. We have evaluated the effects of us-

ratios of 3 -MPTMS and H2O2 to the carbon black were

ing the sulfonated carbon ionomer in the anode and/or

varied to change the IEC of the prepared sulfonated car-cathode CLs of PEFCs, its ion exchange capacity（IEC),

bon ionomer. The weight ratio of 3 -MPTMS to carbon

and the relative humidity（RH）of the reactant gases onblack was set at 0 . 5 and 1 , and the ratio of H2O2 to the

PEFC performance by conducting the single PEFC tests

carbon black was set at 2 and 3 .

at 80  ℃ and RH of 100 %. Subsequently, we have also
RHs below 100 % on the performance of PEFCs utiliz-

Characterization of the sulfonatedcarbon ionomer

ing the sulfonated carbon ionomer by conducting single

Fourier transform infrared（FTIR）spectroscopy wasevaluated the effects of temperatures above 100  ℃ and２．２

performed using the FTIR Spectrum One® spectrometer

PEFC tests.

and the Universal ATR Accessory®（PerkinElmer Inc.,

２．ExperimentalUSA）to verify presence of SO3H moieties on the pre-２．１

Preparation of the sulfonated carbon
ionomerfate used as a detector. The IEC of the prepared ionomer

The sulfonated carbon ionomer was prepared by us-

SO3H groups. The sulfonated carbon ionomer samples

ing the thiol group（SH）oxidation method used bywere dried at 120  ℃ for 30 min in air. The samples were

Munakata et al. for the surface sulfonation of a porous

immersed in 20 cm 3 of a saturated NaCl aqueous solution

silica membrane 12 ). The surface sulfonation of carbon（NaCl, 99 . 5 %, Showa Chemicals Co., Ltd., Japan）andpared sulfonated carbon ionomer1), with triglycine sul-®

was also measured to estimate the amount of formed

black（Aqua-Black 162 , Tokai Carbon Co., Ltd., Japan）

shaken for 24 h with a shaker to exchange the protons

was conducted as shown in Fig. 1 , covalently attachingof SO3H units for sodium ions. The solution was filtered,

燃料電池 Vol.18 No.2 2018

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投稿論文

Paper

and the filtrate was titrated against 0 . 01 M NaOH aque-

The anode and cathode CLs were deposited over theous solution（NaOH, 93 . 0 %, Showa Chemicals Co., Ltd.,GDL surface. To prepare the catalyst paste, 500 mg ofJapan）using a potentiometric titrator（AT- 510 , Kyoto

Pt-loaded carbon black catalyst powder（Pt/C catalyst;

Electronics Industry Co., Ltd., Japan）to quantify the

46 . 7 wt% Pt supported on high-specific-surface-areaamount of protons. Based on the obtained result and thecarbon black, TEC 10 E 50 E, Tanaka Kikinzoku Kogyo

weight of the sulfonated carbon ionomer sample, the IEC

K.K., Japan）were mechanically mixed with 2451 mg ofwas estimated using Eq.（1)IEC =（V × C) / Wdry

13）

ultrapure water and 549 mg of 1-propanol（99. 5%, Wako:  （1）   

Pure Chemical Industries, Ltd., Japan）in a planetary ball

] is the ion exchange

mill for 1 h using zirconia balls. The prepared sulfonatedcapacity, V [L] is the volume of the NaOH solution usedcarbon ionomer or the commercial PFSA ionomer（5for titration, C [mmol L

wt% Nafion® solution; D- 521 , E. I. du Pont de Nemours

where IEC [mmol g−１= meq g−１

−１

] is the concentration of theabove NaOH solution, and W dry [g] is the dry weight ofand Company, USA）were added into the mixture, which

the sulfonated carbon ionomer.

was mechanically homogenized in the planetary ball millfor 1 h using zirconia balls. The weight ratio of the dry

２．３

Preparation of GDEs and membraneelectrode assemblies

to Pt in the catalyst paste was set to 1 . The prepared

GDEs with a three-layer structure, i.e., CL/micropo-

catalyst paste was four times spread onto the GDLs withrous layer（MPL）/wet-proofed carbon paper, werea surface area of 27 cm2. The obtained catalyst-coatedprepared for each single PEFC as follows. Carbon paper

GDLs were dried at 2  ℃ in air for 1 h. The amount of（360 µm thick, TGP-H- 090 , Toray Industry Inc., Japan）

loaded Pt was adjusted to 0 . 45 ± 0 . 02 mg cm−2 in thewas immersed in an aqueous dispersion of polytetra-

anode CL and 0 . 30 ± 0 . 02 mg cm−2 in the cathode CL.

sulfonated carbon ionomer or the dry Nafion® ionomer

fluoroethylene（PTFE, 31 -JR, 60 wt%, Du Pont-Mitsui

The membrane-electrode assemblies（MEAs）wereFluorochemicals Co., Ltd., Japan）for 2 min, dried at 60  ℃

fabricated by hot-pressing the PEM sandwiched be-for 30 min in air, and then sintered at 350  ℃ for 1 min.

tween two GDEs（anode and cathode）using the hot-This wet-proofing procedure was repeated until a PTFE

pressing apparatus at 120  ℃ under 1 MPa for 1 min. The

loading of 5 wt% was reached. The MPL was formed

commercially available PFSA membrane, Nafion®NRE 212

on the wet-proofed carbon paper as follows. Ultrapure（50 µm thick, E. I. du Pont de Nemours and Company,

water, methanol, and the PTFE dispersion were mixedUSA), and a poly（styrene sulfonic acid)-grafted poly-with carbon black（Vulcan XC- 72 R, Cabot Corporation,

ether ether ketone （ssPEEK） membrane 14）（30 µm

USA). The weight ratio of ultrapure water/methanol/

thick）were used as PEMs. The ssPEEK membrane wascarbon black/PTFE was controlled at 10 / 10 / 1 . 0 / 0 . 84 .

donated by IHI Corporation, Japan. The geometrical sur-

The components were mixed under ultrasonic agitation

face areas of all electrodes were 25 cm2. The MEA was（SU- 9 TH ultrasonic cleaner, Shibata Scientific Technol-

assembled into a single PEFC unit, using carbon separa-

ogy Ltd., Japan）until a uniform paste was obtained. The

tors with serpentine gas-channels.

resulting paste was repeatedly coated onto one face of
the wet-proofed carbon paper followed by drying at

２．
４

Fuel cell operation

ambient temperature until reaching a loading of 10 − 15

All of single PEFCs were operated under atmospheric

wt%. The paste-coated wet-proofed carbon paper waspressure, with the setup of the experimental system®

then hot-pressed with a mini TEST PRESS - 10 hot-used in this study shown in Fig. 2 . Humidified H2 andpressing apparatus（Toyo Seiki Seisaku-sho, Ltd., Japan）

air were supplied to the anode and cathode, respectively,

at 120  ℃ under 1 MPa for 1 min and heated at 350  ℃ in

as reactant gases. The flow rates of H2 and air were

air for 1 h to form the MPL on the wet-proofed carbon

controlled at 500 and 2000 sccm（standard cubic centi-

paper. The gas diffusion layer（GDL）of the GDE wasmeter per minute, 20  ℃), respectively, using two mass-composed of the MPL and the wet-proofed carbon pa-

flow controllers. These flow rates corresponded to O2

per.

and H2 utilization of 21 . 0 and 34 . 8 % at a current density

84

燃料電池 Vol.18 No.2 2018

Fig. ２

Experimental setup.

of 1 A cm−2 . At 80  ℃, each reactant gas was humidified

larization defined in Eq.（2）:by bubbling through a humidifier prior to being fed toηa = b log（ I / I 0 . 90）
（2）the single PEFC. The RHs of reactant gases were set towhere ηa[V] is the overall activation polarization, b isequal values, controlled by changing the humidifier tem-the Tafel slope, I 0 . 90 [A cm−2] is the current density atperature.  For temperatures above 100  ℃, each reactant

0 . 90 V and I [A cm−2] is the measured current density.

gas was mixed with vaporized water（steam）using a va-

The Tafel slope was estimated by applying the leastporizer prior to being fed to the single PEFC. The RHs

squares method to the current densities at IR -free cellof reactant gases were set to equal values, controlled byvoltages between 0 . 82 and 0 . 92 V.

changing the amounts of water supplied to the vaporizer
by a pump. By controlling the cathode water supply at
1. 19 g min−1 and the anode water supply at 0. 30 g min−1,
the RHs of H2 supplied to the anode and air supplied to

３．Results and discussion
３．１

the cathode were set to 100 , 72 , and 53 % at 100 , 110 ,and 120  ℃, respectively.

Characterization of the prepared sulfonated carbon ionomer

The FTIR spectrum of the prepared sulfonated carbon

Current−voltage（ I −V ）and IR drop characteristics

ionomer is shown in Fig. 3 , the corresponding IEC be-of single PEFCs were measured using a fuel-cell evaluation system（TFC- 2000 G, Tsukasa Sokken Co., Ltd.,
Japan）under steady-state operation conditions. The IR
drop characteristics were measured by applying 100 µs current-off pulses to single PEFCs and recording
the resulting potential responses. The overall resistancepolarization was calculated using the measured IR -drop
characteristics. The current was normalized based on
the electrode geometrical surface area of 25 cm2. The IR
drop data was included in the I −V characteristics reported herein.

I −V characteristics were analyzed to evaluate thesources of polarization 15 ), with the overall activation po-

Fig. ３FTIR spectrum of prepared sulfonated-carbon ionomer.

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投稿論文
Table １Paper ysthetic condition and IEC of sulufonated carbon
S
ionomer.

SampleWeight ratio
Aqua-Black Ⓡ 162 3 -MPTMS

IEC
H2 O2

（meq g−１）

A

1

0.5

2

0 . 98

B

1

0.5

3

2 . 67C

1

1

3

4 . 37can be controlled by changing the weight ratio of  carbon
black/ 3 -MPTMS/H2O2.

３．
２

Application of the sulfonated carbon
ionomer in CLs

I −V and IR drop characteristics of single PEFCs were
measured at 80  ℃ and an RH of 100 %. Nafion®NRE 212
was used as the PEM and the prepared sulfonated car-

. The presence of sulfonic groups on

bon and Nafion® ionomers were used in the CLs. The IEC

the sulfonated carbon ionomer was confirmed by peaksof the used the sulfonated carbon ionommer was 0 . 98

ing 0 . 98 meq g−1

at 767 , 1012 , and 1257 cm−1

corresponding to the SO3H

meq g−1. Figure 4（a）shows the I −V characteristics ofbond. However, these peaks were not observed fora single PEFC with（i）the sulfonated carbon ionomer in

Aqua-Black® 162 . This qualitative study suggests thatboth anode and cathode CLs;（ii）sulfonated carbon iono-

the sulfonated carbon ionomer can be successfully pre-mer in the cathode CL and the Nafion® ionomer in the an-pared by the SH oxidation method.

ode CL; and（iii）the Nafion® ionomer in the cathode CL

Table 1 shows the synthetic condition and the IEC ofand the sulfonated carbon ionomer in the anode CL. For

the sulfonated carbon ionomer. The weight ratio of Aqua-

comparison, the I −V characteristics of a single PEFC®

black 162 / 3 -MPTMS/H2O2 was controlled. The IEC

with the Nafion® ionomer in both anode and cathode CLs

equaled to 0. 98 meq g−1 at a weight ratio of 1/ 0. 5/ 2, 2. 67

are also shown in Fig. 4（a). The PEFC with the sulfo-−1−1

nated carbon ionomer in the anode and/or cathode CLs

at a weight ratio of 1 / 1 / 3 , respectively. Increasing theshowed decreased performance, as compared with thatweight ratio of H2O2 from 2 to 3 promoted the oxidation

with the Nafion® ionomer in both anode and cathode CLs.

of SH groups to SO3H moieties, increasing the IEC from

Figure 4（b）shows the activation polarization character-meq g

at a weight ratio of 1 / 0 . 5 / 3 , and 4 . 37 meq g, respectively. Increasing the weightistics of the single PEFCs derived from the I −V charac-

ratio of 3 -MPTMS from 0 . 5 to 1 promoted the formation

teristics shown in Fig. 4（a). The activation polarization®

of the single PEFC with the sulfonated carbon ionomer, respectively. These resultsin the anode and/or cathode CLs increased in comparison

indicate that the IEC of the sulfonated carbon ionomerwith the value displayed by the PEFC with the Nafion®

−1

0 . 98 to 2 . 67 meq gof SH groups on Aqua-black 162 , and the IEC increased−1from 2 . 67 to 4 . 37 meq g

Fig. ４86

 ffect of application of sulfonated carbon ionomer (SC) to anode and/or cathode CLs on I−V and activation polarization
E
characteristics of single PEFC at 80  ℃ and RH of 100%: (a) I−V characteristics, (b) activation polarization characteristics.

燃料電池 Vol.18 No.2 2018

ionomer in both anode and cathode CLs. The resistancecharacteristics of single PEFC employing sulfonatedpolarization of the single PEFC with the sulfonated car-carbon ionomers with different IECs. The PEFC perfor-

bon ionomer in the anode and/or cathode CLs slightly

mance obtained for the sulfonated carbon ionomer de-increased compared with that of the PEFC with the Na-

creased in comparison with that obtained for the Nafion®

fion® ionomer in both anode and cathode CLs. In single

ionomer and the former slightly increased with increasing

PEFC with the sulfonated carbon ionomer in the anodethe IEC of the sulfonated carbon ionomer. Figure 5（b）

and/or cathode CLs, no large increases of resistance po-shows the activation polarization characteristics of thelarization due to the increased interfacial resistance oc-

single PEFC using sulfonate carbon ionomers with differ-curred, despite the ionomer different from the PEM.  

ent IECs, derived from the I −V characteristics shown in

These results indicate that the sulfonated carbon

Fig. 5（a). The activation polarization of the single PEFC

ionomer can be used for both anode and cathode CLs ofwith the sulfonated carbon ionomer increased compared

PEFCs and that the performance of PEFCs with the sul-with that of the PEFC with the Nafion® ionomer and thefonated carbon ionomer in the anode and/or cathode CLs

former slightly decreased with increasing the ionomer

decreases due to the increase of activation polarization,

IEC. The resistance polarization of the single PEFC with®

the sulfonated carbon ionomer hardly depended on theionomer in both cathode and anode CLs at 80  ℃ and anionomer IEC and was similar to the values obtained for

RH of 100 %. The decrease of the activation polarization

the Nafion® ionomer.

as compared with that of the PEFC with the Nafion

is required to improve the performance of the PEFCs
with the sulfonated carbon ionomer.

These results suggest that the proton conduction between the SO3H groups of the sulfonated carbon ionomer and the Pt particles of the Pt/C catalyst is inferior

３．３ Effect of the IEC of the sulfonated carbon ionomer

to that between the SO3H groups of the Nafion® ionomer

I −V and IR drop characteristics of single PEFCs were

the proton conduction is caused by the contact between

measured at 80  ℃ and an RH of 100 %. Nafion®NRE 212

the ionomer and Pt particles. The Nafion® ionomer is

was used as the PEM, and the sulfonated carbon iono-

composed of the PFSA polymer and uniformly contacts

mers were used in both anode and cathode CLs. The IECs

the Pt particles. On the other hand, the sulfonated car-of the employed sulfonated carbon ionomers were 0 . 98 ,bon ionomer is composed of the carbon black particles. Figure 5（a）shows the I −V

and does not uniformly contact the Pt particles. Thus,

2 . 67 , and 4 . 37 meq g

Fig. ５−1

and the Pt particles. We presume that this deference ofEffect of IEC of sulfonated carbon ionomer (SC) in both anode and cathode CLs on I−V and activation polarization
characteristics of single PEFC at 80  ℃ and RH of 100%: (a) I−V characteristics, (b) activation polarization characteristics.

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Paper

the proton conduction between the SO3H groups of the

75 , and 80 ℃ , respectively. Figure 6（a）shows the I −V

sulfonated carbon ionomer and the Pt particles is morecharacteristics of single PEFCs with the sulfonated car-preventable than that between the SO3H groups of thebon and Nafion® ionomers. The performance of the PEF-

Nafion® ionomer and the Pt particles. These results also

Cs with both sulfonated carbon and Nafion® ionomers

suggest that increasing the IEC of the sulfonated carbon

decreased with decreasing RH, however, the decreases

ionomer hardly improves the PEFC performance.    

for the former was larger than that for the latter. Figure6（b）shows the activation polarization characteristics of

３．４

Effect of the RH of reactant gases

the single PEFCs derived from the I −V characteristics

I −V and IR drop characteristics of single PEFCs

shown in Fig. 6（a). The activation polarization of the®

were measured at 80  ℃. Nafion NRE 212 was used as the®

single PEFC with the sulfonated carbon ionomer was

PEM and the sulfonated carbon and Nafion ionomers

larger than that of the PEFC with the Nafion® ionomer.

were used in both cathode and anode CLs. The IEC of

The values for both PEFCs increased with decreasing

the used sulfonated carbon ionomer was 0 . 98 meq g−1.

RH, the increases of the former being larger than that of

The RH of the reactant gases was set to 40 , 60 , 80 , andthe latter. This indicates that the proton conduction of

100 % by adjusting the humidifier temperature to 59 , 68 ,the sulfonated carbon ionomer highly depends on the RH

Fig. ６88

Effect of RH of reactant gases on I−V and polarization characteristics of single PEFC with sulfonated carbon ionomer (SC)in both anode and cathode CLs at 80  ℃ : (a) I−V characteristics, (b) activation polarization characteristics, (c) resistancepolarization characteristics.

燃料電池 Vol.18 No.2 2018

of the reactant gases, and that the water reserve charac®

sulfonated carbon ionomer is superior to that of PEFCs

teristics of the Nafion ionomer are superior to those ofwith the Nafion® ionomer above 100  ℃. Both the single

the sulfonated carbon ionomer.

PEFC with the sulfonated carbon ionomer and that with

Figure 6（c）shows the resistance polarization charac-

the Nafion® ionomer could not generate power at 120  ℃

teristics of the single PEFCs. The resistance polarization

and an RH of 52 %, which was attributed to the lowof the single PEFC with the sulfonated carbon ionomer

water-reserve characteristics of the ssPEEK membrane®

was similar to that of the PEFC with the Nafion ionomer at an RH of 100 %. The values for both PEFCs in-used under this condition.
Figure 7（b）shows the activation polarizationchar-creased with decreasing RH, the increases of the former

acteristics of the single PEFCs derived from the I −V

being larger than that of the latter. The larger increasecharacteristics shown in Fig. 7（a). The activation po-of the PEFCs with the sulfonated carbon ionomer is at-larization of the single PEFC with the sulfonated carbon

tributed to the characteristics of water transportationionomer decreased at 100 and 110  ℃ compared with thatfrom the cathode CL to the PEM. In the single PEFCsof the PEFC with the Nafion® ionomer. Thus, the ap-

with the Nafion® ionomer, an extensive water transporta-

plication of the sulfonated carbon ionomer to both anodetion network is present in the PEM and the above iono-

and cathode CLs can presumably decrease the activation

mer, since they consist of the same material. Therefore,

polarization above 100  ℃. This indicates that the proton

water produced in the cathode CL during the cathodeconductivity of the sulfonated carbon ionomer is superior

reaction is easily transferred to the PEM through theto that of the Nafion® ionomer above 100  ℃.

Nafion® ionomer, and the PEM drying at low RHs canFigure 7（c）shows the resistance polarization charac-

be suppressed. Conversely, in the single PEFC with theteristics of the single PEFCs. The resistance polarization

sulfonated carbon ionomer, the water transportationof the single PEFC with the sulfonated carbon ionomer

network in the PEM and sulfonated carbon ionomer is

was nearly equal to that of the PEFC with the Nafion®

not extensive, because the PEM and ionomer in the CLs

ionomer at 100  ℃ and an RH of 100 %. On the other hand,consist of different materials. The water produced in thethe resistance polarization of the PEFC with the sulfo-

cathode CL, therefore, is not easily transferred to thenated carbon ionomer decreased compared with that of

PEM through the sulfonated carbon ionomer, and thethe PEFC with the Nafion® ionomer at 110  ℃ and an RH

PEM drying at low RHs cannot be suppressed.

of 73 %. Thus, the application of the sulfonated carbon
ionomer to both anode and cathode CLs presumably sup-３．５ Effect of PEFC operation above 100 ℃

presses water discharge from the PEM at temperatures

I −V and IR drop characteristics of single PEFCs

above 100  ℃ and RHs below 100 %, which contrasts thewere measured at 100 , 110 and 120  ℃. The ssPEEK

experimental results described above. At 80  ℃, the resis-

membrane was used as the PEM, and the sulfonated car-tance polarization of the PEFC with the Nafion®NRE 212

bon and Nafion® ionomers were used in both anode andand the sulfonated carbon ionomer increased with de-cathode CLs. The IEC of the sulfonated carbon ionomer

creasing RH. This indicates that the sulfonated carbon. Figure 7（a）shows the I −V charac-ionomer suppresses water discharge from the PEM atteristics of the single PEFC with the sulfonated carbon

temperatures above 100  ℃ and RHs below 100 %. We

ionomer at temperatures of 100 , 110 , and 120  ℃ and RHs

presume that a larger amount of formed water is pre-of 100 , 73 and 52 %, respectively. The RHs at 110 andserved in the sulfonated carbon ionomer compared to the120  ℃ were set to keep the steam amounts constant at

Nafion® ionomer, preventing the PEM from drying under

the saturated steam amount at 100  ℃, supposing PEFC

these conditions and suppressing the increase of the re-operation under atmospheric pressure. The PEFC withsistance polarization.

was 0 . 98 meq g−１

the sulfonated carbon ionomer performed better than®

We used the SH oxidation method for the prepara-that with the Nafion ionomer at temperatures of 100

tion of the sulfonated carbon ionomers. This method wasand 110  ℃ and RHs of 100 and 73 %, respectively. These

used for the sulfonation of the porous silica membrane

results indicate that the performance of PEFCs with theand a hydrothermal treatment was conducted at 170  ℃

燃料電池 Vol.18 No.2 2018

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投稿論文

Fig. ７PaperEffect of operation above 100  ℃ on I−V and polarization characteristics of single PEFC with sulfonated carbon ionomer (SC)in both cathode and anode CLs: (a) I−V characteristics, (b) activation polarization characteristics, (c) resistance polarization
characteristics.

in order to increase silanol groups on the silica surface 12 ).

We suppose that the performance of the sulfonated

The FT-IR spectra of the porous silica membranes

carbon ionomer must be improved further by studying

before and after the hydrothermal treatment at 170  ℃

surface treatment of carbon, alternative carbon material,

showed that the peak intensity of silanol groups was in-and so on.  

creased with increasing duration for hydrothermal treatment. We, therefore, presume that the sulfonated carbon
ionomer is stable at 170  ℃.

４．Conclusion

We have showed that sulfonated carbon ionomer is

The sulfonated carbon ionomer can be prepared byavailable to PEFCs as proton conductor of anode andusing the SH oxidation method, and its IEC can be con-cathode CLs in this paper. The sulfonated carbon iono-

trolled by changing the weight ratio of carbon-black/ 3 -mer increases PEFC performance over 100  ℃ compared

MPTMS/H2O2. The sulfonated carbon ionomer can bewith the PFSA ionomer. The performance of the PEFC

used for both anode and cathode CLs of PEFCs. The

with the sulfonated carbon ionomer over 100  ℃, how-

performance of PEFCs with the sulfonated carbon iono-

ever, is lower than that with the PESA ionomer at 80  ℃.

mer decreases in comparison to that of PEFCs with the90

燃料電池 Vol.18 No.2 2018PFSA ionomer at 80  ℃ and an RH of 100  %, and hardly

ether ketone）as the electrode ionomer for poly-depends on the IEC of the sulfonated carbon ionomer.

mer electrolyte fuel cells, Electrochim. Acta , 54,

The performance of the PEFCs with both sulfonated3446−3452（2009）carbon and PFSA ionomers at 80  ℃ decreased with de-7）J. Peron, D. Edwards, A. Besson, Z. Shi, S. Hold-creasing RH, however, the decreases for the former wascroft : Microstructure-performance relationships

larger than that for the latter. On the other hand, theof sPEEK-based catalyst layer, J. Electrochem.

performance of PEFCs with the sulfonated carbon iono-

Soc ., 157, B1230−B1236（2010）

mer is superior to that of PEFCs with the PFSA ionomer8）V. Ramani, S. Swier, M. T. Shaw, R. A. Weis, H. R.

at temperatures above 100  ℃ and RHs below 100 %. We

Kunz, J. M. Fenton : Membranes and MEAs based

conclude that PEFCs with the sulfonated carbon ionomeron sulfonated poly（ether ketone ketone）and het-

can generate power and achieve higher performanceeropolyacids for polymer electrolyte fuel cells, J.

compared with that of the PFSA ionomer at tempera-

Electrochem. Soc ., 155, B532−B537（2008）9）T. Yoda, T. Shimura, B. Bae, K. Miyatake, M. Uchi-tures above 100  ℃ and RHs below 100 %.

da, H. Uchida, M. Watanabe : Gas diffusion electrodes containing sulfonated poly（arylene ether）

Acknowledgement
The authors thank IHI Corporation, Japan, for the do-ionomer for PEFCs  Part 1. Effect of humidity on

nation of the ssPEEK membrane and also thank Ms. Emi

the cathode performance, Electrochim. Acta , 54,

Sindou of Nanotechnology Research Center, Tokyo City

4328−4333（2009）

University for her help in FTIR measurements.

10）T. Yoda, T. Shimura, B. Bae, K. Miyatake, M. Uchida, H. Uchida, M. Watanabe : Gas diffusion elec-

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