i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 0 1 2 9e1 0 1 3 5

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Preparation of dense composite membrane with Ba-cerateconducting oxide and rapidly solidified Zr-based alloy

Jin-Ho Kima,**, Yong-Mook Kang b,*, Byoung-Goan Kim c, Sang-Hoon Lee c,Kwang-Taek Hwang a

a Icheon Branch, Korea Institute of Ceramic Engineering & Technology (KICET), Icheon-si, Gyeonggi-do, Republic of KoreabDivision of Advanced Materials Engineering, Kongju National University, 275 Budae-dong, Cheonan, Chungnam 330-717, Republic of KoreacKorea Energy Materials Co.Ltd., 409 Daegu Technopark, 1-11 Hosan-Dong, Dalse-Gu 704-230, Republic of Korea

a r t i c l e i n f o

Article history:

Received 9 January 2011

Received in revised form

21 February 2011

Accepted 28 February 2011

Available online 6 July 2011

Keywords:

Ba cerate perovskite oxide

Rapidly solidified Zr-based hydride

Hydrogen separation

Aerosol deposition

Dense BCYO/RSZ alloy composite

composite membrane

* Corresponding author.** Corresponding author. Tel.: þ82 31 645 143

E-mail addresses: jino.kim@kicet.re.kr (J.0360-3199/$ e see front matter Copyright ªdoi:10.1016/j.ijhydene.2011.02.145

a b s t r a c t

Hydrogen separationwith dense ceramicmembranes is non-galvanic, i.e. it does not require

any electrode or an external power supply to drive the separation, and the hydrogen selec-

tivity is almost 100% because the membrane contains no interconnected porosity. In this

study, amixedproton-electron conducting perovskitemade fromBaCe0.9Y0.1O3-d (BCYO)was

prepared using a solidestate reaction, whereas a rapidly solidified Zr-based alloy (RSZ) was

obtained via a melt-spinning process at a specified cooling rate. Finally, the BCYO/RSZ

composite membrane was successfully fabricated by aerosol deposition (AD) at room

temperature. The powders and composite membranes were characterized by

high-temperature X-ray diffraction (HTXRD), particle size analysis (PSA), scanning electron

microscopy (SEM), and X-ray elemental mapping (XRM). The hydrogen permeability of the

dense BCYO/RSZ composite membrane was measured with the change of temperature.

Under a pure hydrogen atmosphere at 773 Ke1073 K, the BCYO/RSZ composite membrane

exhibited higher permeability compared with the sole BCYO membrane over the entire

investigated temperature range.

Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction BaCe1-xYxO3-d (BCYO), show the highest proton conductivity

In recent years, the development of dense ceramicmembranes

withmixedprotonic andelectronic conductivitieshas received

considerable attention due to their possible applications in

hydrogen-based energy, petrochemical processes, fuel cells,

separating membranes, and other technologies [1,2]. In

particular, proton transport in multivalent cation-substituted

Ba cerate and Sr cerate (BaCe1-xMxO3-d, SrCe1-xMxO3-d, M: Y,

Yb, Tm, Eu) has been widely studied for high temperature

hydrogen separation [3e14]. Y-doped Ba cerate materials,

2; fax: þ82 31 645 1488.-H. Kim), dake1234@kong2011, Hydrogen Energy P

among the multivalent cation-substituted cerates. However,

despite its fast proton conduction, BCYO has not yet been

successfully applied for use in a gas separationmembrane due

to its long-term chemical instability and poor hydrogen

permeability under atmosphere containing carbon dioxide or

water content [5e8].

In addition, the abovementioned candidate materials for

hydrogen separation membranes require thin metal layers on

both sides of the membrane or well-distributed metals

throughout the whole membrane [15e17]. These metals can

ju.ac.kr (Y.-M. Kang).ublications, LLC. Published by Elsevier Ltd. All rights reserved.

Fig. 1 e SEM images of (a) VIM-melted ingot and (b) melt-

spun ribbons of Zr-based alloy.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 0 1 2 9e1 0 1 3 510130

promote the dissociation and recombination of

H2 4 2Hþ þ 2e� as a catalyst in the membrane, resulting in

a larger flux of permeated hydrogen through the ceramic

membrane. The intrinsic surface activity of the melt-spun Zr-

based nanocrystalline alloy is very important for its potential

application in areas such as hydrogen storage materials or

hydrogenation catalysts [18e20]. In addition, it is well known

that rapidly solidified Zr-based alloys are more homogenous

in composition and enhanced physical and chemical proper-

ties of high strength and low corrosion resistance under toxic

atmosphere [21e23]. Adams et al. reported that themelt-spun

Zr-based alloys not only exhibit a superior steady-state

hydrogen permeation rate but also a high elastic toughness

and excellent resistance to hydrogen embrittlement [16].

Hydrogen separation of dense ceramic membranes is

significantly dependent on membrane characteristics such as

thickness, particle size, roughness, and adhesion with porous

support [24]. Several methods are available for the fabrication

of ceramicfilms including sol-gel [9,10], sputtering [11], e-beam

evaporation [25],metal organic chemical vapor deposition [26],

and aerosol deposition [27e33]. Among these methods, the

aerosol deposition (AD) method is a novel technique that

enables the fabrication of ceramic films at room temperature

with a high deposition rate as well as a strong adhesion to the

substrate. It is based on the impact adhesion of sub- or micron

particles to a substrate. The oxide particles accelerated by gas

up to a subsonic velocity impinge on the substrate, resulting in

the formation of a dense ceramic layer. Operation of the

aerosol deposition at room temperature enables the fabrica-

tion of the ceramic membrane without any phase change.

In this study, a cost-effective technique for fabricating

BCYO/Rapidly solidified Zr-based alloy (RSZ) composite

membranes at room temperature is proposed. A BCYO/Rapidly

solidified Zr-based alloy (RSZ) composite membrane with

a uniform thickness and composition was successfully fabri-

cated frommicron-sized powder using the ADmethod at room

temperature. In order to clarify the membrane performance of

the BCYO/RSZ composite, the hydrogen fluxmeasurementwas

conducted for the BCYO/RSZ composite membrane fabricated

by aerosol depositionmethod.

2. Experimental

Polycrystalline BCYO, BaCe0.9Y0.1O3-d, powders were prepared

using conventional, solidestate reaction methods. High-

purity oxide powders of BaCO3 (99.9%, Aldrich Co.), CeO2

(99.9%, Aldirich Co.), and Y2O3 (99.9%, Aldrich Co.) weremixed,

ground in a ball mill with ethanol, and calcined at 1473 K for

2 h in ambient air. The calcined powders were then crushed

and sieved into powders below 20 mm. Rapidly soldified Zr-

based alloys (RSZ) were fabricated from an ingot of

(ZreTi)(VeMneCr)2.0 prepared by vacuum induction melting

(VIM). RSZ ribbons with a 300 mm thickness were prepared

using the melt-spinning method where its cooling rate was

approximately 4 � 10e5 Ks�1. The rapidly solidified Zr-based

alloy (RSZ) ribbons were mechanically ground into powders

below 50 mm. Then, the calcined BCYO and RSZ powders were

mixed with a weight ratio of 80 to 20 by ball milling using ZrO2

balls in ethanol. Fig. 1 shows photographic images of (a) an

ingot of Zr-based alloy prepared by VIM and (b) the melt-spun

Zr-based ribbons.

Fig. 2(a) shows the schematic diagram of the aerosol

deposition apparatus, which consists of three parts: the

aerosol generator, the mass-flow controller, and the deposi-

tion chamber. The aerosol formed in the aerosol generator

was transported with a carrier gas into the deposition

chamber, which was evacuated by a rotary pump with

a mechanical buster, and accelerated through the nozzle to

collide with the substrate. The deposition conditions of the

BCYO/RSZ composite films are given in Table 1. Yttrium-

stabilized zirconia powders (TZ-8Y, Tosho Co.) were used as

a porous substrate, pressed into pellets, and finally sintered at

1533 K for 1 h in ambient air to afford disks with a porosity of

28%. The radius and thickness of the ZrO2 porous substrate are

20 mm and 2 mm, respectively. Rockwell-A indentation tests

were conducted to access adhesion of the BCYO/RSZ

composite membrane on ZrO2 substrate by a Hoyton inden-

tation instrument.

The H2 permeation experiments were performed on lab-

made high temperature permeation cells as shown in Fig. 2(b).

Fig. 2 e Schematic illustration of (a) aerosol deposition

apparatus and (b) set-up used to measure hydrogen flux

through dense ceramic membrane.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 0 1 2 9e1 0 1 3 5 10131

In order to measure the H2 permeation rate (i.e. H2 flux), an

alumina tube was inserted into the furnace with a sealed

membrane and the associated gas flow tubes. Amixture of 10%

H2: 90% N2 was used as the feed gas, while 0.5 ml$min�1 inner

standard Ar was used as the sweep gas on the permeation side.

The effluent on the permeation side was analyzed using an

Table 1 e Deposition conditions of hydrogen separationmembrane by AD method.

Raw powder BCYO& Melt-spun Zr-based powders

Substrate ZrO2 Porous disc (dia. 20 mm, th.

22 mm)

Carrier gas He

Size of nozzle orifice 20 � 0.4 mm2

Working pressure <10 Torr

Consumption of carrier

gas

8e10 L/min

Deposition area 10 � 10 mm2

online gas chromatography (DS 6200model). Leakage of neutral

gas through pores in the sample or through an incomplete seal

wascheckedbymeasuringtheHetracercontentof thepermeate

stream. No discernible was detected.

The particle size distribution of the Ba cerate oxides was

measured using a laser diffraction particle size analyzer

(HORIBA LA-950V2 model). D50 is defined as the particle size

corresponding to 50%accumulation volume in the particle size

distribution curve. High temperature X-ray diffraction

(HTXRD) was conducted in a q/2q geometry using a Rikaku

instrumentwithCuKa radiationat 40kVand100mAinair. The

morphology and alloying element distribution of the aerosol-

deposited film were observed via scanning electron micros-

copyandenergydispersiveX-ray spectroscopy includingX-ray

dot mapping (SEM, HITACHI S-4800 model).

3. Results and discussion

Fig. 3 shows the (a) X-ray diffraction (XRD) spectra and the (b)

particle size distribution (PSD) of the BaCe0.9Y0.1O3-d (BCYO)

powders calcined at 1473 K for 2 h. As shown in Fig. 3(a)), the

XRD spectrum confirms a single-phase perovskite with an

orthorhombic structure. To further analyze the size

Fig. 3 e (a) XRD pattern and (b) Particle size distribution of

BCYO.

Fig. 5 e The multiple plots of powder XRD patterns of the

melt-spun Zr-based alloy scanned in air at various

temperatures from 373 K to 1073 K at 100 K intervals (Scan

rate:10 K/min, Holding time:1 h).

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 0 1 2 9e1 0 1 3 510132

distribution of the calcined BCYO powders, a laser diffraction

particle size analysis was used and it has a high accuracy of

�0.6% over discrete size ranges, as shown in Fig. 3(b). Based on

this method, the geometric mean diameter, D50, of the BCYO

particles had an average value of 6.5 mm, with the values

ranging from 2 mm to 11 mm.

Fig. 4 shows the XRD patterns of the (a) as-cast and (b)melt-

spun Zr-based alloys. Herein, it is clear that the as-cast alloy is

composed of C14 and C15 Laves phases. The peak intensity of

the melt-spun alloy is much weaker than that in the as-cast

alloy. However, it is not amorphous and all diffraction peaks

can be reasonably attributed to the C14 Laves phase. As is well

known, the microstructure of the melt-spun alloy is deter-

mined by its composition, melting temperature, and cooling

rate. Luet al. reported that the rapidly solidifiedZr-basedalloys

are mostly composed of micro-crystalline C14 and C15 Laves

phases, and the increase of the cooling rate tends to exclude

the C15 Laves phase [20]. Due to its fine grain and lamellar

structure of the thin plates, there are many interfaces in the

C14 Laves phase, which may cause a large anisotropic stress

and strain in the melt spun alloy [19]. Many interfaces,

including the grain boundaries and the interfaces between the

thin plates, in the C14 Laves phase provide local stress relax-

ation to delay the pulverizing of the C14 phase powders.

In this study, the hydrogen permeation of the aerosol-

deposited BCYO/RSZ composite membrane was measured at

a high temperature conclusively showing that the RSZ alloy is

more likely tobecrystallized.Topredict thisoccurrence, in-situ

HTXRD measurements of the melt-spun Zr-based alloy were

conducted from373Kto1073K inambientairas showninFig. 5.

TheXRDprofilesof theRSZalloyatdifferent temperatureswith

100 K intervals shows that there is no marked change in both

phase andpeak intensity, indicating that themicrostructure of

the C14 Laves single phase is retained up to 1073 K.

Fig. 6 shows SEM images of the aerosol-deposited BCYO/RSZ

composite film (membrane) on ZrO2 porous support. In Fig. 6(a),

a dense filmwithoutmicro cracks or poreswas observed, which

maintainedgoodadhesionwith theZrO2porous supportwithan

adhesive strength of up to 30 MPa. The high-resolution SEM

image of the aerosol-deposited film in Fig. 6(b) shows that

Fig. 4 e XRD patterns of (a) VIM-melted and (b) melt-spun

ribbon of melt-spun Zr-based alloy.

Fig. 6 e SEM images of top view of the aerosol-deposited

BCYO/RSZ composite film (a) low magnitude and (b) high

magnitude.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 0 1 2 9e1 0 1 3 5 10133

submicron particles were uniformly deposited on the ZrO2

support, indicating that the fragmentation of the BCYO/RSZ

composite powders occurred during aerosol depositionmethod.

TheSEMimageandX-raymapping for thepolishedcross section

of the aerosol deposition composite filmonZrO2 porous support

are given in Fig. 7. The film thickness was approximately 10 mm

and it appears to be firmlydeposited on the support. In addition,

the X-raymapping in Fig. 7(b) shows that various elements such

as Ba, Ce, Y, O, Zr, Ti, Cr, V andMn,which originated from the Ba

cerate oxides and rapidly solidified Zr-based alloy, were

uniformly dispersed without any elemental segregation. This

means that themixturecomposedofBaCe0.9Y0.1O3-dandRSZcan

be well deposited on ZrO2 porous supports using the aerosol

deposition method, satisfying the thickness and uniformity for

the H2 separationmembrane.

The H2 fluxes through the aerosol-deposited BCYO and

BCYO/RSZ compositemembranesweremeasured as a function

of the temperature under dry hydrogen ambient, as shown in

Fig. 8. At 1073 K, the H2 fluxes of the BCYO and BZYO/RSZ

composite membranes reached the 0.113 and 0.170 ml$min-

1$cm-2, respectively. In Fig. 8, the hydrogen fluxes increase with

the temperature for both systems, and theBCYO/RSZ composite

Fig. 7 e X-ray mapping of elemental constituents within the cro

composite membrane.

membrane exhibited higher permeability when compared with

the BCYO membrane over the investigated temperature range

under dry conditions. The superiority of the BCYO/RSZ

composite to BCYO in thehydrogen flux can be explainedby the

excellent catalytic activity of themelt-spun Zr-based alloy upon

hydrogen dissociation. Generally, the hydrogen permeation

through the dense membrane includes the following stages: (1)

absorption of H2 molecules, (2) dissociation of H2 molecules, (3)

dissolution and diffusion of proton and electron, and (4)

recombinationanddesorptionofH2molecules [15,24].Thelarger

fluxpermeatedhydrogenthroughthedensemembranecouldbe

resulted in improvement of the dissociation and recombination

of H2 4 2H. According to previous literatures, amorphous or

nanocrystallineZr-basedalloy formedbymelt-spinningmethod

showed an enhanced electrocatalytic activity and hydrogen

permeability [34e37]. The rapidly solidified Zr-based nano-

crystalline alloy tends to show good hydrogenation properties

due to its fine grain size and uniformly distributed composition

[19,20]. However, it was difficult to investigate the hydrogen

permeability of amorphous alloys having high Zr content due to

severe hydrogen embrittlement during the measurement.

Therefore, it appears that the enhanced hydrogen permeability

ss section of BCYO/Rapidly solidified Zr-based alloy (RSZ)

Fig. 8 e H2 permeation flux of aerosol-deposited BCYO/

Rapidly solidifiedZr-basedalloy (RSZ) compositemembrane

as a function of temperature under dry H2 condition.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 3 6 ( 2 0 1 1 ) 1 0 1 2 9e1 0 1 3 510134

to the BCYO/RSZ composite membrane can be attributed to not

only better electrocatalytic activity by the additionmelt-spunZr

based alloy but also suppression of the embrittlement by the

existence of Ba-cerate oxide alloy.

4. Conclusion

Amixed proton-electron conducting perovskite fabricated from

BaCe0.9Y0.1O3-d (BCYO) and rapidly solidified Zr-basedalloy (RSZ)

were prepared using solidestate reaction and melt-spinning

processing, respectively. A nano-sized, dense BCYO/RSZ

compositemembranewas successfully fabricated frommicron-

sized raw powders via aerosol deposition at room temperature.

An extremely rough and dense composite membrane with

a 10 mm thickness was obtained without heat treatment. The X-

raymapping indicates thatvariouselements suchasBa,Ce,Y,O,

Zr,Ti,Cr,VandMn,wereuniformlydispersedwithoutelemental

segregation. This indicates that the mixture composed of

BaCe0.9Y0.1O3-d and RSZ powders can be deposited well on ZrO2

porous support using the AD method, satisfying the thickness

and uniformity for H2 separation membranes. Its hydrogen

permeability was studied by measuring the gas permeation as

a function of the temperature. The H2 fluxes increasedwith the

temperature for both systems, and the BCYO/RSZ composite

membrane exhibited higher permeability when compared with

the BCYO membrane over the entire investigated temperature

range under dry conditions. The enhanced hydrogen perme-

ability to the BCYO/RSZ compositemembrane can be attributed

to not only better electrocatalytic activity by the addition melt-

spun Zr based alloy but also suppression of the embrittlement

by the existence of Ba-cerate oxide alloy.

Acknowledgement

This work was supported by Energy & Resource Technology

Development Program (2008-C-CD11-P-10-0-0000) under the

Ministry of Knowledge Economy, Republic of Korea. This

research was performed for the Hydrogen Energy R&D Center,

one of the 21st Century Frontier R&D Program, funded by the

Ministry of Education, Science and Technology of Korea.

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