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Electrochimica Acta 53 (2008) 4096–4103

An inorganic/organic self-humidifying composite membranesfor proton exchange membrane fuel cell application

Yu Zhang a,b, Huamin Zhang a,∗, Cheng Bi a,b, Xiaobing Zhu a,b

a Lab of PEMFC Key Materials and Technologies, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,457 Zhongshan Road, Dalian 116023, China

b Graduate School of Chinese Academy of Sciences, Beijing 100039, China

Received 30 September 2007; received in revised form 19 November 2007; accepted 4 December 2007Available online 25 December 2007

bstract

With an aim to operate the proton exchange membrane fuel cells (PEMFCs) with dry reactants, an inorganic/organic self-humidifying membraneased on sulfonated polyether ether ketone (SPEEK) hybrid with Cs2.5H0.5PW12O40 supported Pt catalyst (Pt-Cs2.5 catalyst) has been investigated.he Pt-Cs2.5 catalysts incorporated in the SPEEK matrix provide the site for catalytic recombination of permeable H2 and O2 to form water, andeanwhile avoid short circuit through the whole membrane due to the insulated property of Cs2.5H0.5PW12O40 support. Furthermore, the Pt-Cs2.5

atalyst can adsorb the water and transfer proton inside the membrane for its hygroscopic and proton-conductive properties. The structure of thePEEK/Pt-Cs2.5 composite membrane was characterized by XRD, FT-IR, SEM and EDS. Comparison of the physicochemical and electrochemicalroperties, such as ion exchange capacity (IEC), water uptake and proton conductivity between the plain SPEEK and SPEEK/Pt-Cs2.5 composite

embrane were investigated. Additive stability measurements indicated that the Pt-Cs2.5 catalyst showed improved stability in the SPEEK matrix

ompared to the PTA particle in the SPEEK matrix. Single cell tests employing the SPEEK/Pt-Cs2.5 self-humidifying membrane and the plainPEEK membrane under wet or dry operation conditions and primary 100 h fuel cell stability measurement were also conducted in the presenttudy.

2007 Elsevier Ltd. All rights reserved.

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eywords: PEMFC; Self-humidifying membrane; Pt-Cs2.5 catalyst; SPEEK; P

. Introduction

During the past several decades, much attention has beenocused on the research and development of proton exchangeembrane fuel cells (PEMFCs) due to their advantages of high

ower density, simplicity of operation, high energy conversionfficiency and low harmful emissions [1–3]. However, the cost,urability and operation flexibility of PEMFCs still remain theurdles to its commercialization and should be greatly improved.urrently, the proton exchange membranes (PEMs), such asafion or sulfonated poly (ether ether ketone) (SPEEK), requireater to maintain their proton conductivity. Thus, to prevent

rying out of the membrane and keep the membrane at most con-uctive state, the reactant gases are usually humidified throughn external humidification system before entering the fuel cells.

∗ Corresponding author. Tel.: +86 411 84379072; fax: +86 411 84665057.E-mail address: zhanghm@dicp.ac.cn (H. Zhang).

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013-4686/$ – see front matter © 2007 Elsevier Ltd. All rights reserved.oi:10.1016/j.electacta.2007.12.045

conductivity

owever, this method increases the weight and complexity ofhe fuel cell system, and makes PEMFCs unsuitable for portablepplication.

In order to realize the operation of PEMFCs withoutxternal humidification, many composite membranes withelf-humidifying ability have been developed. Currently, theesearchers developed self-humidifying membranes mainlyocusing on the following directions: (1) incorporating Pt ort/C catalysts in the membrane to combine the permeable oxy-en and hydrogen to produce water and humidify the membrane4–6]; (2) incorporating hygroscopic metal oxides, such as SiO2,r TiO2 to adsorb water and accordingly improve the protononductivity [4,7,8]; (3) incorporating some proton-conductivearticles, such as ZrP, HPA, ZrO2/SO4

−2or Cs2.5H0.5 PW12O40o improve the proton conductivity of the membrane under dry

peration condition [9–12]. For the first method, how to avoidhe electron short circuit through the membrane after incor-orating the Pt or Pt/C particles is an important issue. Manyesearchers developed two-layered or three-layered membrane

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tructures to resolve this problem [13–15]. However, these mem-ranes fabrication processes are too complex to spread widely.ecently, many Pt-based supported catalysts with the supportf nonelectron-conducting as well as hygroscopic propertiesSiO2, zeolite) were synthesized and incorporated in the poly-er matrix to fabricate the self-humidifying membranes [16,17].hese electron-insulated catalysts can avoid electron circuit in

he whole membrane, and keep good membrane hydration forn situ adsorbing water produced at Pt particles on the surfacef hygroscopic supports. However, the supports of these cata-ysts were not proton-conductive materials and thus limited theurther enhancement of cell performance.

To enhance the proton conductivity of the membrane operatedt low humidity conditions, inorganic/organic composite mem-ranes based on Heteropolyacids as the additive were widelytudied [18–21]. Among them, 12-Phosphotungstic acid (PTA)f Keggin structure was the most widely used due to its highcid strength. However, the extreme high water solubility ofTA is a potential problem for its detrimental effect to theembrane structure. Cs2.5H0.5PW12O40, which was insoluble

or less exothermic of hydration enthalpy, was synthesized asn additive used in PEMFCs in the recent reports [10,22]. Fur-hermore, it was reported that the acidity per unit acid site ofs2.5H0.5PW12O40 was superior to Nafion-H as well as homo-eneous acids, e.g., H2SO4, H3PW12O40, and p-toluenesulfoniccid [23]. Recently, Pt-Cs2.5H0.5PW12O40 catalyst as a sup-orted catalyst was widely studied for the application of skeletalsomerization of n-butane [24,25]. So far, no research of Pt-Cs2.5atalyst was investigated as an additive in self-humidifying com-osite membrane.

Currently, perfluorosulfonic acid (PFSA) membranes, in par-icular Nafion®, are a favorable option and are commonly usedn fuel cell stacks, but they are difficult to synthesize, and theirapital cost still remains high. In recent researches, SPEEK isonsidered as a promising candidate of PEMs because it possessood thermal stability, mechanical property, proton conductiv-ty and low cost. Several studies have been reported on SPEEKsed as a PEM material in both hydrogen and direct methanoluel cells [26–28].

In the present study, the SPEEK/Pt-Cs2.5H0.5PW12O40SPEEK/Pt-Cs2.5) self-humidifying membrane was fabricatedo improve the fuel cell performance using dry reactantas. The structure of SPEEK/Pt-Cs2.5 self-humidifying mem-rane was characterized by X-ray power diffraction (XRD),ourier transform infrared (FT-IR) spectroscopy, scanninglectron microscopy (SEM) and energy dispersive X-rayetector (EDS). Furthermore, the physicochemical and elec-rochemical properties of the membranes, e.g., ion exchangeapacity (IEC) value, water uptake and proton conductivityere also investigated. The results of single cell evaluation

howed that the SPEEK/Pt-Cs2.5 self-humidifying mem-rane exhibited better performance than the plain SPEEKembrane under both wet and dry conditions. Electrochem-

cal impedance spectroscopy (EIS) measurements were alsoarried out on the plain SPEEK and SPEEK/Pt-Cs2.5 mem-rane under dry operation condition to further corroboratehe better cell performance of SPEEK/Pt-Cs2.5 membrane.

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cta 53 (2008) 4096–4103 4097

urthermore, additive stability and primary 100 h fuel celltability measurements were also conducted in the presentork.

. Experimental

.1. Preparation of the Pt-Cs2.5H0.5PW12O40 catalyst andhe membranes

Pt-Cs2.5H0.5PW12O40 catalyst (Pt-Cs2.5) was synthesizedy a titration method [29]. An aqueous solution of H2PtCl60.03 mol dm−3) was added to an aqueous solution of

3PW12O40 (0.08 mol dm−3) at room temperature to obtainyellow solution. Then an aqueous solution of Cs2CO3

0.12 mol dm−3) was added dropwise to the mixture withigorous stirring at room temperature. The resulting milkyolution was evaporated at 50 ◦C to solid and then reducedy H2 at 200 ◦C for 3 h. The designing loading of Pt ons2.5H0.5PW12O40 was 3 wt.%.

SPEEK polymers were prepared following the pro-edure reported in the literature [30]. The SPEEK/Pt-s2.5H0.5PW12O40(SPEEK/Pt-Cs2.5) membrane was preparedy solution cast method. First, the SPEEK was dissolved in N,Nimethylacetamide (DMAc) at room temperature to prepare a0 wt% solution. Then required quantity of 15.0 wt.% Pt-Cs2.5atalyst was added to the polymer solution and stirred with aagnetic stirrer for 4 h. The resulting solution was cast ontoclean flat glass and then removed at 60 ◦C for 12 h followed

y further drying at 120 ◦C under vacuum. The loading of thelatinum in the membranes was 1.2 × 10−2 mg/cm2. The thick-ess of the composite membrane was controlled to 24 �m. Foromparison, the plain SPEEK membrane was fabricated withhe same method and the thickness was also 24 �m.

.2. Membrane characterizations

.2.1. XRD measurement of the Pt-Cs2.5 catalystThe X-ray power diffraction (XRD) analysis on the

s2.5H0.5PW12O40 particles and Pt-Cs2.5 catalysts was per-ormed using a Panalytical X’pert PRO diffractmeter (Philps’pert PRO) with Cu K� radiation source. The X-ray diffrac-

ogram was obtained for 2θ varying between 20 and 90◦.

.2.2. SEM-EDS measurement of the self-humidifyingembraneThe morphology of the cross-sectional SPEEK/Pt-Cs2.5

elf-humidifying membrane was investigated by SEM (JEOL360LV, Japan) measurement. To determine the Pt-Cs2.5 cat-lyst distribution along the membrane cross-section, the Cs/Slemental profiles across the sample thicknesses was carried outy EDS (Oxford Instruments Microanalysis 1350).

.2.3. FT-IR measurement of the membranes

FTIR spectrums of the Pt-Cs2.5 catalyst, plain SPEEK mem-

rane and SPEEK/Pt-Cs2.5 self-humidifying membrane wereecorded on a JASCO FT-IR 4100 spectrometer. The KBr pelletethod was used to measure the spectrum of Pt-Cs2.5 catalyst.

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dasSalyst in the membrane, SEM attachment of EDS was conductedand the results were shown in Fig. 2. From Fig. 2(a) it can be seenthat the cross-sectional SPEEK/Pt-Cs2.5 membrane appeareddense and clean, with no agglomerates of Pt-Cs2.5 particles in

098 Y. Zhang et al. / Electrochim

he Pt-Cs2.5 powder was mixed with KBr at ratio of 1 wt% andhe IR spectrum was measured. For the membranes measure-

ent, the samples were dried at 100 ◦C for 4 h and subsequentlyeasured using ATR mode.

.2.4. Additive stability measurementTo determine the stability of Pt-Cs2.5 catalyst in the SPEEK

atrix, the samples were immersed in water and H2SO40.5 mol/L) at 60 ◦C for 100 h, respectively. During this period,he samples were taken out several times and dried to constanteight and subsequently weighed. Thus, the weight changesf the membranes as a function of the immersion time wereecorded. The SPEEK/PTA and SPEEK/Pt-Cs2.5 compositeembranes were measured in this test.

.2.5. Ion exchange capacity (IEC) of the membranesThe IEC values of plain the SPEEK membrane and

PEEK/Pt-Cs2.5 self-humidifying membrane were determinedy titration method: 2–3 g of the samples was placed in 1 Mqueous NaOH and kept for 24 h. The solution was then backitrated with 0.1 M HCl using phenolphthalein as an indicator.

.2.6. Water uptake of the membranesThe water uptake of the membranes was calculated from Eq.

1), W1 is the weights of the wet membrane after immersing inater at 60 ◦C for 6 h and W2 is the weight of the membraneried under vacuum at 100 ◦C for 12 h.

W(wt.%) = (W1 − W2)

W2× 100% (1)

.2.7. Proton conductivity and areal resistance measuredy EIS

Proton conductivity of the membranes was determined fromembrane resistance measured by electrochemical impedance

pectroscopy (EIS) over a frequency range of 100 mHz to00 kHz. The membrane samples were humidified by vaporater at 60 ◦C in a sealed vessel described in the literature [31].frequency response daetector (EG&G model 1025, Princetonpplied Institute) and a potentiostat/galvanostat (EG&G model73A, Princeton Applied Institute) were employed for the mea-urements. Moreover, areal resistances of the cells operated athe current density of 100 mAcm−2 under dry or wet conditionsere also measured by EIS.

.3. The membrane electrode assemblies (MEAs)reparation

The MEAs with active area of 5 cm2 were fabricated by hot-ressing method at 160 ◦C and 10 MPa for 2 min. The anode and

he cathode were prefabricated using SGL carbon paper as theubstrate and the 46.6 wt.% Pt/C (TKK, Japan) as the catalyst.he respective loadings of Pt and Nafion in the electrode were.4 mg/cm2.

cta 53 (2008) 4096–4103

.4. Single cell evaluation

Firstly, the single cells were operated at 60 ◦C with fullyumidified H2/O2. The operation pressure was set at 0.20 MPand the gas utilizations were fixed at 90% for H2 and 50% for2 (40% when air was used). After stable performances werebtained, the cells were then operated with dry gases. Beforeperation with dry reactants, the cells were dried overnighty flowing dry N2. The fuel cell stability test was performedy an intermittent process. The single cell was operated at00 mA/cm2 with dry H2/O2 during the day and left off duringhe night.

. Results and discussion

.1. XRD measurement of the Pt-Cs2.5 catalyst

Fig. 1 showed the results of XRD measurement employinghe Cs2.5 particle and Pt-Cs2.5 catalyst. The power XRD pat-ern of Cs2.5 presented the characteristic peaks corresponding tohe H3PW12O40 cubic phase and was consistent with the resultseported by other literatures [32,33]. For the Pt-Cs2.5 catalyst,wo obvious peaks corresponding to the Pt (1 1 1) and Pt (2 0 0)ere observed besides the peaks of pure Cs2.5 particle. Accord-

ng the Debye–Scherrer formula, the particle size of the Cs2.5nd Pt were about 12 and 4 nm, respectively.

.2. SEM-EDS images of the self-humidifying membrane

It is desirable that the inorganic additive is high-uniformlyispersed so as to increase the interface between the additivend the polymer matrix and thus increase the possibility of theirynergism. To examine the morphology of the cross-sectionalPEEK/Pt-Cs2.5 membrane and the distribution of Pt-Cs2.5 cat-

Fig. 1. XRD patterns of the Cs2.5 particle and Pt-Cs2.5 catalyst.

Y. Zhang et al. / Electrochimica Acta 53 (2008) 4096–4103 4099

ional SPEEK/Pt-Cs2.5 self-humidifying membrane.

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he whole membrane cross-section. This implied that Pt-Cs2.5articles were not recrystallized into large particles after incor-orating with SPEEK, but was highly dispersed throughout theolymer matrix. Fig. 2(b) showed that the Cs element distributedniformly in the whole membrane cross-section. Furthermore,s can be seen in Fig. 3, the Cs/S ratios were almost the same inhe whole membrane cross-section, indicating the good disper-ive quality of Pt-Cs2.5 particles in SPEEK matrix. The uniformistribution of additive is good for the membrane structure andembrane performance.

.3. FT-IR spectrum of the self-humidifying membrane

To obtain the structure information of the Pt-Cs2.5 cata-yst, plain SPEEK membrane and SPEEK/Pt-Cs2.5 membrane,T-IR measurements were conducted and showed in Fig. 4.he characteristic peaks of Pt-Cs2.5 catalyst were attributed

he peaks of Cs2.5H0.5PW12O40 particles. From Fig. 4 typi-

al characteristic peaks at 1080 cm−1 for υas(P–O), 890 cm−1

or υ(W–Oc–W) and 798 cm−1 for υ(W–Oe–W), which weressigned to the Keggin’s structure of H3PW12O40, werebserved in Pt-Cs2.5 spectrum, and the whole spectrum showed

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Fig. 4. FT-IR spectrums of the Pt-Cs2.5 catalyst, plain SPEEK

ig. 3. Relative intensity of Cs/S across the SPEEK/Pt-Cs2.5 self-humidifyingembrane.

o be a good accordance with those previous reported [34]. How-ver, the typical vibration of υ(W = O) at 983 cm−1 splits intowo components at 992 and 984 cm−1 in the Pt-Cs2.5 spec-rum. This splitting can be assigned as W = O associated with

membrane and SPEEK/Pt-Cs2.5 composite membrane.

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ig. 5. Weight changes of SPEEK/PTA and SPEEK/Pt-Cs2.5 composite mem-ranes during the additive stability measurement.

+(H2O)n species (984 cm−1), and W = O interacting with Cs+ons (992 cm−1) [35]. For the plain SPEEK membrane, the peakst 1080, 1020 and 1257 cm−1 were assigned to the sulfonic acidroup in SPEEK [36]. In the case of the SPEEK/Pt-Cs2.5 self-umidifying membrane, both characteristic peaks of Pt-Cs2.5atalyst and plain SPEEK membrane were clearly found.

.4. Additive stability measurement

For the heteropolyacids-based composite membranes, theater stability of the heteropolyacids particles in the polymeratrix was important for its close correlation to the membrane

tructure stability. Fig. 5 showed the quantified weight changesf the SPEEK/PTA and SPEEK/Pt-Cs2.5 composite membraness a function of immersion time. It can be seen that the weightf the SPEEK/PTA composite membrane obviously decreaseduring the 100 h immersion in water with the remaining weightf 85.3%, which indicated the most of PTA particles leached outrom the SPEEK matrix during the measurement (original PTAontent in the membrane was 15 wt.%). In contrast, the weightf the SPEEK/Pt-Cs2.5 membrane immersed in water slightlyecreased during the beginning 70 h with the weight loss of%, and was stable during the last 30 h immersion. The smalleight loss was attributed the leaching out of fine Cs2.5 parti-

le [23]. Furthermore, the weight loss of the SPEEK/Pt-Cs2.5embrane immersed in H2SO4 (0.5 M) was almost the sameith that immersed in water, which indicated that the Cs+ did

ot ion-exchanged by H+ during the immersion period. The goodtability of Pt-Cs2.5 catalyst in the SPEEK matrix is beneficialo membrane structure stability. s

able 1omparison of IEC, water uptake and proton conductivity between the plain SPEEK

embrane Thickness (�m) IEC (mmolg−1)

PEEK 24 1.81PEEK/Pt-Cs2.5 24 1.94

cta 53 (2008) 4096–4103

.5. IEC value measurement

The IEC values of the plain SPEEK and SPEEK/Pt-Cs2.5embrane were listed in Table 1. It can be seen the SPEEK/Pt-s2.5 composite membrane has the higher IEC value relative to

he plain SPEEK membrane, indicating more acid property thanhe plain SPEEK membrane. This is attributed to the incorpora-ion of high acidity Pt-Cs2.5 catalyst. The higher acid propertyf the SPEEK/Pt-Cs2.5 membrane was beneficial to improveater adsorbing and proton conducting abilities.

.6. Water uptake measurement

For the PEMs, water uptake is an important property for itsirect relation to the proton conductivity. Table 1 showed thathe water uptake of SPEEK/Pt-Cs2.5 membrane was higher thanhat of the plain SPEEK membrane, with the value of 30.6%nd 21.2% at 60 ◦C, respectively. The similar trend of increas-ng water uptake after incorporation of Cs2.5H0.5PW12O40 waseported by Li et al. [10] and the reason was the hydrophilic prop-rty of Cs2.5H0.5PW12O40 for its strong interaction with water.hen the membrane absorbs higher amount of water, the num-

er of exchange sites available per cluster increases, this resultsn the increase of the proton conductivity of the membrane.hus, compared to the plain SPEEK membrane, the propertyf higher water uptake for SPEEK/Pt-Cs2.5 self-humidifyingembrane is expected to possess higher proton conductivity

nder dry operation condition.

.7. Proton conductivity of the membranes

Proton conductivity is the foremost requirement for PEMs,igher proton conductivity resulting in higher cell performance.ere, the membrane proton conductivity was determined byeasuring the membrane resistance at 60 ◦C at fully hydrated

tate by ac impedance. From Table 1, it indicated that the pro-on conductivity of the SPEEK/Pt-Cs2.5 membrane was higherhan that of the plain SPEEK membrane. The incorporation oft-Cs2.5 catalyst increased the acidity and the water uptake of

he membrane from above experiments and thus increased theroton conductivity. Furthermore, the addition of HPAs-basedarticles in the polymer matrix may decrease the activationnergy for proton hopping by bridging proton conducting path-ay between shrunken clusters, and thus increase the proton

onductivity according to the V.Ramani et al. [37].

To verify the self-humidification effect of SPEEK/Pt-Cs2.5elf-humidifying membrane, the single cell performances of the

and SPEEK/Pt-Cs2.5 membranes

Water uptake (%,60 ◦C) Proton conductivity (S/cm, 60 ◦C)

21.2 0.04230.6 0.053

Y. Zhang et al. / Electrochimica Acta 53 (2008) 4096–4103 4101

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Fig. 7. IR-corrected I–V curves of single cells employing the plain SPEEK,SPEEK/Pt-Cs2.5 membranes with wet and dry H2/O2 at 60 ◦C.

Table 3OCV values of single cells employing different membranes under dry and wetoperation

Membrane Open circuit voltage (V)

Wet operation Dry operation

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The cell performances of a SPEEK/Pt-Cs2.5 self-humidifying membrane at different operating temperaturesunder dry operation conditions were presented in Fig. 8. It wasobserved from Fig. 8 that the best performance was obtained

ig. 6. Performance comparison of single cell employing the plain SPEEK,PEEK/Pt-Cs2.5 membranes with wet and dry H2/O2 at 60 ◦C.

lain SPEEK membrane and SPEEK/Pt-Cs2.5 self-humidifyingembrane with dry H2/O2 at Tcell = 60 ◦C and with fully humid-

fied H2/O2 at TH2 = Tcell = TO2 = 60 ◦C were evaluated, ashown in Fig. 6. The single cell employing the SPEEK/Pt-s2.5 self-humidifying membrane outperformed that of thelain SPEEK membrane under fully humidified operation con-itions, with the peak power density of 1.43 and 1.24 W cm−2,espectively. This was consistent with their proton conductivityesults listed in Table 1. At dry operation condition, the plainPEEK membrane exhibited very poor output performance. Ashown in Table 2, the areal ohmic resistance of the cell employ-ng the plain SPEEK membrane was large with the value of.145 � cm2 at 100 mA/cm2. Furthermore, in the IR-corrected–V curves shown in Fig. 7, the large polarization at both thenode and the cathode, which was due to the low electrocat-lyst utilization at dry condition, was also a reason leading tohe poor performance. In contrast, the SPEEK/Pt-Cs2.5 self-umidifying membrane showed much better performance thanhe plain SPEEK membrane. The areal ohmic resistance ofPEEK/Pt-Cs2.5 self-humidifying membrane was 0.107 � cm2

t 100 mA/cm2, which was close to that of the fully humidi-ed plain SPEEK membrane (0.103 � cm2). The existence oft-Cs2.5 catalyst can in situ adsorb the water produced on Ptarticles by chemical catalytic reaction of permeable H2 and O2o hydrate the membrane, and meanwhile provide the new acidites for proton transport, thus leading to the small resistance.urthermore, the polarization at both electrodes was reduced by

sing the self-humidifying membrane.

The open circuit voltage (OCV) is a good measurementf hydrogen or oxygen crossover through the PEMs dur-ng the operating fuel cell. The cell with less hydrogen and

able 2hmic resistances of single cells operated at 0.1 A/cm2 under dry and wetperation

embrane Ohmic resistance (�cm2)

Wet operation Dry operation

PEEK 0.103 0.145PEEK/Pt-Cs2.5 0.094 0.107 F

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PEEK 1.01 0.96PEEK/Pt-Cs2.5 1.01 0.99

xygen crossover will lead to a higher OCV value. Table 3howed the OCV values of the plain SPEEK membrane andPEEK/Pt-Cs2.5 self-humidifying membrane under dry and wetperation conditions. It was obvious that the single cells with thePEEK/Pt-Cs2.5 self-humidifying membrane exhibited higherCV values than those of the plain SPEEK membrane bothnder dry or wet conditions. The Pt-Cs2.5 catalyst inside theelf-humidifying membrane could catalyze the permeable H2nd O2 and thus result in the higher OCV values.

ig. 8. Single cell performances employing the SPEEK/Pt-Cs2.5 membraneith dry H2/O2 at different operation temperatures.

4102 Y. Zhang et al. / Electrochimica A

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t 60 ◦C. Increasing cell temperature bring two reverse effectsn the cell performance change, improved kinetics of theell reaction and better proton transport leading to increasederformance, and more water loss due to vaporization leadingo decreased performance.

Fig. 9 showed the single cell performance of the self-umidifying membrane with dry H2/Air at 60 ◦C. Theerformance of the plain SPEEK membrane was too unstable toe recorded at this condition. However, it can be seen from Fig. 9hat the SPEEK/Pt-Cs2.5 self-humidifying membrane still haveeak power density of 0.54 W cm−2, indicating that the Pt-Cs2.5s a very effective additive for membrane self-humidification.

To determine the stability of fuel cell performance employ-ng the SPEEK/Pt-Cs2.5 self-humidifying membrane, primary00 h fuel cell operation test with dry H2/O2 was conducted andhe results were shown in Fig. 10. It was observed that the per-ormance with the SPEEK/Pt-Cs2.5 membrane does not exhibit

2

bvious drop on both OCV and the voltage at 800 mA/cm after00 h operation at 60 ◦C with dry reactants. However, the long-erm operation of fuel cell with SPEEK/Pt-Cs2.5 membraneould be investigated in the future work.

ig. 10. Single cell stability measurement employing the SPEEK/Pt-Cs2.5embrane at 60 ◦C with dry H2/O2.

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cta 53 (2008) 4096–4103

. Conclusion

An inorganic/organic self-humidifying membrane SPEEK/t-Cs2.5 was developed to improve the single cell performanceperating with dry H2 and O2. The addition of supported catalystt-Cs2.5 can avoid the short circuit through the whole mem-rane due to the insulated property of the support. The XRD,TIR and SEM coupled EDS measurements were conducted toharacterize the catalyst property and the membrane structure.he IEC, water uptake and proton conductivity measurement

ndicated that the SPEEK/Pt-Cs2.5 self-humidifying membraneas higher water adsorbing, acid and proton-conductive prop-rties relative to the plain SPEEK membrane due to the highlyygroscopic and acidy properties of Pt-Cs2.5 catalyst. The sin-le cell employing the SPEEK/Pt-Cs2.5 membrane exhibitedigher cell OCV values and cell performances than those of plainPEEK membrane under dry or wet conditions. Furthermore, thePEEK/Pt-Cs2.5 membrane showed good water stability anderformance stability. Therefore, this self-humidifying mem-rane is very promising for application in PEM fuel cells.

cknowledgement

This work was supported by National Natural Scienceoundation of China (Grant No. 20476104) and (Grant No.0236010)

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