Ionic conductor membrane for oxygen separation

Ionic conductor membrane for oxygen separation

SolidgtmeI~ni~ 2g-~0 ( 198~) ~2~28 N~h-Holla~ Amst~am IONIC CONDUCTOR MEMBRANq~ FOR OXYGEN SEPARATION M. DUMI~LI~, G. NOWOGROCKI ~ d LC. BOIVIN Labom...

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SolidgtmeI~ni~ 2g-~0 ( 198~) ~2~28 N~h-Holla~ Amst~am

IONIC CONDUCTOR MEMBRANq~ FOR OXYGEN SEPARATION M. DUMI~LI~, G. NOWOGROCKI ~ d LC. BOIVIN Labomroi~ d~ Cr~mrl~mie et Physi~h~m~ du Snide, UACNRS #J2, Boule~ o n a f e S*~ri~ ~ ~teC h i ~

R ~ i v ~ 22 July1987 T ~ ~i~bility of a bismu~ ad m x d c l d . Bi0s,iPb~~tOi ~ , foro ~ n ~p~ra~on~1mod~tc t e m ~ t u ~ h~ been evallat~d.Mee~ni~l p~0mi~ ofehe solid9 ha~ beenenhancedby i n * ~ t i ~ g Zr~ into the ~mrfi~gmalr Severalmetalsando x i ~ ~ ~ as theeleOr~e ~ m d a l . ~ c ~ t i m i ~ memb~atis ablet o ~ cominuougYuPto 3~

1. lnn'mluction

2. Experimental

Usinga solid e]cc~lyte membranei n order to ~ lectivelysepa~le o x y g ~ is a well-known method which has already induced a lot o f ~ e a r c ~ ~ r k s . Ho,~ver, t he m i n t ~ m m o n materialswhicha ~ used to manufacto~t h ~ m e m b r ~ e s are zirconia-based ~mpounds. Unforomatelythe quite limited ~ n ductivityo f the zireonia el~trot~tes ~ m p e l s these systems w operate at ~ high tempe~tures ( typical 900-1000 r C) i n order to be able to reach rmsonahle ~ c n t d ~ s i t i ~ , We reported earlieron the existence i n the Bi20~PbO s~stem I 1 ] o f a highly~ d u c t l v e solid solution ~lleA ~. It exhibitsa a val~e elme to 1 n - cm-I at 600'C and a low actlvationenergy (0.A.-0.5 eV). Transport number measu~ments p e r f o r m by the EMF method and thr rical power invcsti8ations showed the It phasa to be a pure o x y g ~ ion ~nductor. H o ~ v e r , the p r i t h e e i n the ~ t e r l a l o f the quixe ~duelbleBP+ ~ t i o a d o ~ not make i t sultable for operatingat very low oxygen prcss~c. Taking into account its ex~ptionalvalue,we deC~dedto check the ability o f this matedal 1o be used ~ a membranefor oxy$~ ~pa{-ation at 600 ~C hx an oxidizingenvironment,

2.1. phase synthesis and m e m b r a ~ preparation

Starting mat~itds (PbO,Bi~O~,ZOD2 purity> 99.9~) ~ symemati~]lyh ~ t e d at 600"C for a few hou~ to eliminateany t r a ~ o f mrbonat~. The elev trolytewas p ~ p a ~ d by weightingthe p u ~ o x l d ~ i n the ~ q u i ~ d provortio~. The powde~ ~ then thoroughlymixed i n an agate m o r t ~ and heated for 24 h at 6lOOC in sinle~d alumina~ eibles. After grindin8 sad sifting,the purityo f the flnc groinpewd ~ was controlled by m ~ n $ o f X-ray diffraetinnu v lag a G u i n i ~ D e Wolf cameo. T ~ diffe~ntways were used to manufaetu~the memb~ues. In the f i ~ t ~ e , the powdered phase was introducedin a ~ b b ~ mould and compassed in an isostatic press The resultingcyIinder (about 25 m m diameter, 50 m m height) was then machined i n order to get the sample sha!~ ~ i n fig. I. After sin~ refine, e l ~ t r o d ~ ~ deposited on the ~mple. Gold electrodes were vacuum deposited, whileoxide el~trodes were paintedusinga cyclohe~nolsuspension o f the sel~ted oxide. The second typ~ o f mereb m n ~ w~e simplyp~sscd pellets (2O m m diam~ter and 4 m m thiek~ss); they were obtained by compressing the powdered materials bctw~n two gold grids. The rumples we~ then slntered at 610~C.

0 167-2735/88/$ 03.50 9 Elsevi~ Scien~ P u b l i s h ~ B.V. (North.HollandPhysics PublishingDivision)

2.2. Experimental enrichment ~l]

2.3. El~zrieal me~rements

526

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posited gold electrodes. Under t h e ~ ~ndifions, a n enrichment was o b s ~ e d at cu~eat densities in the ~ g e 50-2OO m A era-2. However, the perfo~ances rapidly deceased after a few vpenting h o n ~ E~. amimtlon o f lhe m e m b ~ n e di~]os~ lhe developmeat of numerous cracks running through the electrolyte a ~ m ~ a n l e d by a dramatic increase ~ f the fragility of the e~amie. The cricks r~ult from the f o ~ a t i o n in fine bulk of the rumples of an orieared raiea-like texau~. Several altempts ~ made

m

~

~g~ ~

to solve this problem. The best results w e ~ obtained by incorpo~fing a smaU ~ o u m of Zr02 ~itb the eleCtrOlyte. The ~ m p a r i ~ n of lhe two types of membrane emphaslze~ a highly ctVstalliggd ~exture of the p n ~ bismuth-leadoxideeleetmlyteandafinegraintextufe oblained when zrO~ is incorporated. In addilion, the m ~ h a n i ~ ] ~ s i s t a n ~ o f the samgl~ was greally improved. X.rays p ~ d e r diffraction shows that at least, for weight mtlo of ZrO~ ~ess than 4.~%,

the ~ m p l ~ are constitutedo f the Iow-temperatu~ f o ~ o f 13phase and PbZrO,, Conductivitymeas~ements we~ undertaken on the Za'O:-added electmtytes i n order to ~ m p a ~ their behaviourto the "parQ" pha~. Fig. 2 r e p ~ e n t s the A ~ h ~ i u s p l o tfor t w o ~ m p l e s ~ n t a i n J n g Z r O z ~ d the ~ e s p o n d l n g ~ for a B nn*~P~ss~2srt phase. In all ~ses, a d~slle increase o f o arises when entering the I] domain. The ~ l u e s o f ~ a b o ~ the transitiont e m p ~ a t u ~ a ~ very close to I f l - I em ' at 6~KI*Cin all cases, Oxygen transport number was also m ~ s u r e d as* ing aa EMF oxygen ~neentrationcalL Similarto the p ~ v l o ~ rewalts on 13b l s m u l h - I ~ d oxide, lhe I o ~ temlmmtu~ ~ g l o n (t<580~C) exhibits a mLxed ~nduetl,hty while in the high-tem~rature~gion, the matedal b e h a ~ as a p u ~ anionicconductor, Fig, 3a rep~sents the p e e r a g e o f o x y ~ enrlchmenlo f a 1600 em~ h ' l air f l ~ using a 1 cm~ membrane with the composition Bilz~Pbo,,Oz~z +0.187 g~o~. The intensitywas maintained ~ n slant duringthe experiment,However, the ~11 voltage continuouslyincreased and a f t ~ 3 to 4 h o f operation, the efficiencyo f the m e m b r ~ e started r~

d ~ . Electron microprobe examinationo f the surface showed that gold bad diffused~ d was ~gmgated at the grgin boundari~, The h e t ~ g ~ u s distribution~ s ac~mpanied by a large i n e ~ a ~ of the surfa~ ~sistivity. As a ~ n ~ q u e n ~ , we d~ided to investigate ~ the electrode a le~ diffilsible material. In o r d ~ to get a 8oo
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Fig 4 ~ m p a ~ n or~c v ~ r

cr evolul~n at 100mA r

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At~t%vol~a~

In e~der to o v ~ e lhie d i f f i ~ l t y ,we 1tied to find a mow compatible eleclrode material. At this point, ~ rea[ized that the bismuth-based elect~lytr snffia~ ~ u l d i t . l l mta[yze the oxygen ~ a c l i ~ . H ~ , owing to the insufficienteleetronie ~ n duvtlvityo~'the surface, it has b ~ n ne~ssaly to sdd a gold~Sid to act as ~ eleclroneolieet~ = d thus get an homogeneous ~ t line distribution.This was umdr ~ s i e r by usinga slntetxdpellet in~t~d o f the originalmorn ~ m p ] i ~ t ed ~ m p l e shRpe. Two tyl~s o f pellets ~ m ~ u f a e t u r e d . In the t i m type. the grids~ only appliedagainstthe eleet~[yteduring t ~ e x p e ~ e m w h i i e i n t ~ e S e ~ d o n e ,t h e g r i d s ~ m dkectly ~ p ~ s ~ e d ~ t h ~ c el~tmtyte before sinterlng F~. 4 ~ m p a ~ s the ~11 voltage under a 100 mA e m ` ~ e u ~ n t dens/ty, i n b o t h ~ses. It s l t ~ s that, with the e o - p ~ i grids, the operatingvoltage w~s lower and, m o ~ e r , perf ~ t i y ~ n s t ~ t .

the cu~e~ ~ d the membrane efficiencyr after a few minute~ This m a x l m ~ indicatesthat a poierieationelTect t~k~ pLaea:this is ceI~alnly due to a ldnttiG[intitation at the triple interface between the electrolyte, 1]~ atmosphere and the r col/ector. "Ihe pr~ent work deraonst rat~ that bismuth-lead mixed oxides are sintabJc materialsfor oxygen sepamtion up to 200-250 iliA em -2 c u ~ n t density. I m e n s i ~~ n t i n ~ op~ations i n thismrtgeha~e been made o*er periods o f l e ~ r a l days withoutany sig~ifi~ntloss of p e r f ~ a n ~ . Other p h ~ exMbiti~g the inCh-temperature smzetu~ have been imlated i n our tabomtory and a ~ e ~ e n t l y u~d~ examinationusing the s ~ e procedures.

Thee~]utionoftlm~tichmentwitha~p~s~d system is pr~ented in fig, 5 for ~ e ~ l e u ~ n t d ~ -

[ l ~F Ho~n~ j C B0ivi~.D.~om~s a ~ ~j. ~Vfies. Soilfl state [onies9/10(1983)921. [21 N. ~e~Mr, P. Conll~a~LC. Boivin,~. Ab~hamand D. Thews, J, Phy$C h ~ ~id~ g6 (1985)297. 3 D.E.CoxandKW.S~ ~ a Ae~C~,t n35(1979 L

sltles. A quantitative~ y g e n t ~ s p o n was o b s r up tO 200 mA em-~. For e u ~ n t d e ~ i t i ~ equal or g~l~rthaa300mAcm-~,a~ximumlspce~nt~

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