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Effect of alumina additions on the anodeelectrolyte interface in solid oxide fuel cells

Effect of alumina additions on the anodeelectrolyte interface in solid oxide fuel cells
Effect of alumina additions on the anodeelectrolyte interface in solid oxide fuel cells

Available online at https://www.doczj.com/doc/fe18872351.html, Journal of Power Sources179(2008)

511–519

Effect of alumina additions on the anode|electrolyte

interface in solid oxide fuel cells

R.Knibbe a,J.Drennan a,?,A.Dicks a,J.Love b

a Centre for Microscopy and Microanalysis,The University of Queensland,St Lucia Queensland4072,Australia

b Cerami

c Fuel Cells Limited,170Browns Road,Noble Park,Victoria3174,Australia

Received6September2007;received in revised form14September2007;accepted21December2007

Available online11January2008

Abstract

The longevity of a solid oxide fuel cell(SOFC)stack is curtailed by the fragility of its ceramic components.At Ceramic Fuel Cells Limited (CFCL),15wt.%alumina is added to the commonly used10mol%Y2O3–ZrO2(YSZ)electrolyte to improve both the fracture toughness and grain-boundary conductivity of the electrolyte.This study investigates the effect of such addition of alumina on the anode|electrolyte interface; more speci?cally,which reactions occur with the Al2O3at the interface and how these reactions in?uence fuel cell performance.X-ray diffraction (XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)are used to characterize the formation of NiAl2O4in the alumina regions in the electrolyte.The NiAl2O4is observed to grow into the adjacent grain boundaries to form an interconnected NiAl2O4 network up to4?m deep into the electrolyte.Impedance spectroscopy shows that the formation of NiAl2O4does not affect the grain bulk ionic conductivity.The grain-boundary conductivity is markedly reduced at low temperatures.However,at the high SOFC operating temperature at CFCL(850?C)the contribution of the grain-boundary conductivity to the total conductivity is diminished,and the NiAl2O4is found not to have an effect on the total electrolyte conductivity and is deemed not to be a detrimental reaction.

Crown Copyright?2008Published by Elsevier B.V.All rights reserved.

Keywords:Solid oxide fuel cell;Nickel aluminate;Interface;Yttria-stabilized zirconia;Ionic conductivity;Transmission electron microscopy

1.Introduction

The high operating temperature(typically750–1000?C)of electrolyte-supported solid oxide fuel cells(SOFCs)is dictated by the oxide ion conductivity of the electrolyte.Bene?cially, the high operating temperature increases the electrode kinetics and also allows for internal reforming of hydrocarbon fuels.On the other hand,the high manufacturing and operating tempera-tures that are demanded by ceramic fuel cell materials promote material interaction and degradation,and thus limit the mate-rial choices.Furthermore,the thermal stresses induced by the high operating temperatures encourage interfacial stress and delamination of contiguous fuel cell components.

Despite extensive investigations into alternative electrolytes, yttria-stabilized zirconia(YSZ)still remains the most popular electrolyte material due to its stability,strength and low cost.In

?Corresponding author.

E-mail address:j.drennan@https://www.doczj.com/doc/fe18872351.html,.au(J.Drennan).an attempt to reduce the sintering temperature of cubic zirco-nia,Radford and Bratton[1,2]added various oxides,including alumina,to YSZ.Although alumina only decreased the sinter-ing temperature of YSZ by~100?C,it was found that such an addition improved the YSZ grain-boundary conductivity[3,4]. This discovery resulted in a plethora of studies on the effect of alumina additions on the conductivity of zirconia[5–12].

It is argued that alumina acts as a‘getter’of the silicon impu-rities,which are ubiquitous in zirconia from processing[11]. The mechanism suggests that the siliceous grain-boundary phase preferentially associates with the alumina grains—ultimately ‘cleaning’the YSZ grain boundaries.This increases the grain-to-grain connectivity and results in an increased grain-boundary conductivity.The main trade-off with alumina is that it decreases the bulk conductivity of the electrolyte as it is an ionic insulator and exists as a second phase.

The other major bene?t of alumina additions is that alu-mina increases the fracture toughness and Young’s modulus of YSZ and therefore decreases the probability of fracture. Tekeli[12]reported an increase in fracture toughness from

0378-7753/$–see front matter.Crown Copyright?2008Published by Elsevier B.V.All rights reserved. doi:10.1016/j.jpowsour.2007.12.111

512R.Knibbe et al./Journal of Power Sources179(2008)511–519

1.5to

2.41MPa √

m when10wt.%Al2O3was added to8YSZ

(16mol%Y2O3ZrO2).At Ceramic Fuel Cells Limited(CFCL), 15wt.%Al2O3is added to a10YSZ(20mol%Y2O3–ZrO2) electrolyte to improve both the grain-boundary conductivity and strength.

The present study looks at the reaction between the anode and the electrolyte during fuel cell synthesis and at the sub-sequent anode reduction and fuel cell operation.The work was stimulated by observations at CFCL that an uncharacter-istic blue phase was forming on the surface of the typically white electrolyte during anode sintering.As nickel aluminate (NiAl2O4)is known to form a bright blue phase when NiO is reacted with Al2O3,it was therefore anticipated that this blue phase was indeed NiAl2O4.Nickel aluminate has been shown to reduce to nickel and alumina in a suf?ciently reducing atmosphere[13],therefore the stability of the nickel aluminate during anode reduction and fuel cell operation is of interest. In addition,the location and morphology of the nickel alumi-nate is of great importance as NiAl2O4has a very low oxygen diffusivity[14]and would severely inhibit the oxide ion con-ductivity of the electrolyte if an interconnected layer was to form.

During both anode reduction and fuel cell operation,the NiAl2O4would experience a reducing atmosphere.Various authors have reported the partial reduction of NiAl2O4to Ni and Al2O3and that this is accompanied by an18%volume decrease [15,16].The NiAl2O4cannot easily accommodate such a vol-ume reduction and therefore microcracks form at the interface between the unreduced and reduced spinel[16].The formation of microcracks in the NiAl2O4would be detrimental as the struc-tural integrity of YSZ would be reduced.After anode reduction, when all of the NiO has reduced to Ni,the formation of NiAl2O4 is no longer feasible.

The anode oxygen partial pressure P O

2-anode would be the

lowest during anode reduction,i.e.,when the cells were at an open-circuit voltage(OCV).For an anode environment of

60%H2/40%H2O at850?C,the P O

2-anode is calculated to be

3.6×10?13Pa.From the NiO–Al2O3thermodynamic stability

diagram,the spinel(NiAl2O4)stability limit is4.9×10?9Pa at

940?C[13],but the lower operating temperature(850?C)of the

fuel cell would therefore require a lower oxygen partial pressure

to reduce the NiAl2O4.As the calculated values of P O

2-anode during anode reduction are signi?cantly lower than the spinel

stability limit,NiAl2O4reduction is anticipated.

Investigations have been conducted on the anode|electrolyte

interface with YSZ as the electrolyte(Linderoth et al.[17]

and Liu and Jiao[18]),but to date no work has been reported

on the effect of alumina additions to the electrolyte on the

interface.

The aim of the present research is to examine the

anode|electrolyte interfaces after fuel cell production,anode

reduction and prolonged fuel cell operation using X-ray

diffraction(XRD),scanning electron microscopy(SEM)and

transmission electron microscopy(TEM).Subsequently,the

in?uence of anode|electrolyte interactions on the electrical

performance is investigated using impedance spectroscopy.

This study is performed on samples based on the electrolyte-supported fuel cell design employed by CFCL.The electrolyte is a composite of15wt.%Al2O3in10YSZ;the anode is the typical Ni-YSZ cermet manufactured from NiO and YSZ.

2.Experimental methods

2.1.Material synthesis

The following fuel cell manufacturing process is used at CFCL.15wt.%Al2O3(Alcoa)is mechanically mixed with 10YSZ(Mel Chemicals).The mixture is tape cast,dried and laser cut into the desired circular shape with a diameter of 13.2cm.The electrolyte is?red at1600?C for1h.Once the electrolyte is?red,an8-cm diameter concentric,10?m thick circular functional anode layer is printed on to the electrolyte sur-face.The anode consists of a50:50mixture of NiO and10YSZ. The second layer(overlayer)contains CeO2and is printed on to the functional anode layer.The two anode layers and the gas-diffusion layer(GDL)are co-?red at1300?C for6h.To complete fuel cell production,the cathode and GDL layer are ?red at1150?C for2h.

2.2.Physical material characterization

Three different types of samples were examined for mate-rials characterization—after fuel cell production(unreduced), after anode reduction(reduced)and after500h of fuel cell oper-ation(operated).The anode sample was reduced at850?C in a ?owing(65ml H2min?1)atmosphere for2h and fuel cell oper-ation was carried out at850?C in a60%H2/40%H2O?owing atmosphere for500h.Physical materials characterization was performed using XRD,SEM and TEM.

2.2.1.X-ray diffraction(XRD)

To analyze interfacial reactions at the anode|electrolyte inter-face,the samples were prepared by grinding off the bulk of the anode layers using SiC paper.X-ray diffraction was per-formed on the remaining solid electrolyte which also contained the anode|electrolyte interface and some of the remnant anode. The analysis was performed with a Bruker D8Advance X-ray diffractometer with parallel beam geometry and a graphite monochromator using Cu K?radiation.Measurements were car-ried out from2θ=2?to90?using a step size of0.02?at a speed of1?per https://www.doczj.com/doc/fe18872351.html,pounds were identi?ed using peak search Diffrac Plus V9.0software.

2.2.2.Scanning electron microscopy(SEM)

The samples were mounted in epoxy resin and were vacuum embedded.The samples were ground using SiC paper,polished using6,3and1?m diamond paste,and then carbon-coated to eliminate surface charging.

The morphology of the samples was observed with a JEOL6460LA SEM equipped with a tungsten?lament and JEOL JED2300Energy Dispersive X-ray Spectrometry(EDS) detector in secondary and backscattered electron(BSE)mode using an accelerating voltage of15keV.X-ray mapping was

R.Knibbe et al./Journal of Power Sources179(2008)511–519513

performed using the aforementioned SEM in conjunction with JEOL Analysis Station Software.

2.3.Transmission electron microscopy(TEM)

The samples were prepared for TEM investigations using the tripod polishing method and a focused ion beam(FIB).For the tripod samples,4mm×5mm sections were cut from the samples using a Gatan ultrasonic rectangular cutter.Four sec-tions were thinly coated with an epoxy resin and placed in a Te?on mould.The stack was cured for30min at120?C.Once cured,the stack was cut into1.5mm slices by means of a Struers Accutom50?tted with a diamond cut-off https://www.doczj.com/doc/fe18872351.html,ing a tripod polisher,a wedge sample was made using30,15,6,3,1,0.5and 0.1?m diamond?lm.The samples were then thinned to elec-tron transparency with a Gatan Precision Ion Polishing System (PIPS).

Samples of the unreduced and the reduced anode|electrolyte interface were examined with an XT Nova Nanolab200dual beam FIB,operated with a30-keV Ga+ion beam.

Samples were investigated with a Phillips Technai F20scan-ning transmission electron microscope(STEM).The F20was operated at200keV and was equipped with a?eld emission zirconia-coated tungsten?lament and an EDAX Ltd.thin-window EDS detector.

2.4.Impedance spectroscopy

Two types of samples were investigated using impedance spectroscopy,namely,a15-wt.%Al2O3-YSZ electrolyte (15A10YSZ)and a NiO reacted15A10YSZ sample(15A10YSZ NiAl2O4).

A set of15A10YSZ samples were reacted with NiO to form NiAl2O4on the electrolyte surface.The sintering technique and pro?le used were employed to mimic the sintering of the anode on to the electrolyte during typical fuel cell production at CFCL. The major difference is that the NiAl2O4reaction is occurring on both sides of the electrolyte to create a~8-?m thick reac-tion layer in total.The electrolyte samples were placed in a bed of NiO in a platinum crucible with a lid to prevent pos-sible furnace contamination of the sample.The samples were ?red at1300?C for6h with a heating and cooling ramp rate of3?C per min.After?ring,the samples were placed in a beaker with dilute HCl and slightly heated to remove any excess NiO.

Platinum electrodes were painted on to the samples using No.6082Englehard platinum paste and then?red in air at 850?C for1h with a heating and cooling rate of3?C per min. Two-terminal a.c.impedance measurements were carried out in air from230to800?C using a Solartron1260impedance analyser operated with a100-mV root mean square(RMS) amplitude and ZPlot/View software.At temperatures below 230?C,the impedance of the sample exceeds1M ,which is beyond the probing capabilities of the Solartron1260Impedance Analyser.

The data was geometry corrected by using a A/l multiplier in the Nyquist plots,where A is the surface area of the sample and l is the sample thickness.To determine the bulk,grain-boundary and total conductivity,the Nyquist plots were?tted using an equivalent circuit model of a resistor in series with two RC couples.

3.Results

3.1.X-ray diffraction

Representative XRD scans are shown in Fig.1.Cubic YSZ phase is seen in all of the scans as it is the main component of the electrolyte and a signi?cant component of the anode.Similarly, weak Al2O3peaks(from the electrolyte)are observed in all of the XRD scans.

Strong NiO peaks(from the anode)are found in the unre-duced sample.These NiO peaks are fully replaced by Ni peaks in the reduced and operated samples,showing a reduction of NiO to Ni.As cubic NiO has a lattice parameter of4.177?A and cubic Ni has a lattice parameter3.524?A,the Ni peaks are shifted to higher2θrelative to the NiO peaks.The stronger inten-sity of the Ni peaks indicates a higher nickel content in the operated sample,which is merely due to less anode bulk being removed during XRD sample preparation,which was dif?cult to control.

Several additional peaks are observed in the unreduced XRD pattern at~31.7?,45.5?and68.8?and these peaks are attributed to NiAl2O4.The other major NiAl2O4peaks are overlapped by the NiO and YSZ peaks,which dominate due to their higher con-centrations.The most signi?cant is the strongest NiAl2O4peak of the{113}planes,which is overlapped by the NiO{111} peak at~37.8?.

The reduction of NiO to Ni allows the strongest NiAl2O4 {113}peak to be seen at~37?in the reduced and operated samples.The presence of the NiAl2O4peaks indicates that after anode reduction the NiAl2O4phase is not fully reduced.The reduction of NiAl2O4would form Ni and alumina,as these are both already present in the sample,X-ray diffraction analysis provides no information on the partial reduction of NiAl2O4

.

Fig.1.XRD scans of unreduced,reduced and operated anode|electrolyte sam-ples.YSZ:*;NiO: ;Ni: ;Al2O3: ;NiAl2O4:?.

514R.Knibbe et al./Journal of Power Sources179(2008)

511–519

Fig.2.SEM backscattered micrograph of typical anode|electrolyte interface after anode sintering,with corresponding Al(b)and Ni(c)elemental maps. Ni map shows migration of nickel from anode region into electrolyte grain boundaries and alumina grains.Circled areas are NiAl2O4grains.

3.2.Electron microscopy

3.2.1.Unreduced sample

Fig.2(a)shows a backscattered electron(BSE)image of the unreduced fuel cell interface.The difference in grey scale in the image re?ects a chemical composition difference—the dark grains have a lower average atomic number,whereas the light grains have a higher average atomic number.The average atomic number of Al2O3,YSZ and NiO is10.0,18.7and18.0,respec-tively.Therefore,the Al2O3grains appear the darkest and the YSZ grain the lightest.The small difference in average atomic number,between NiO and YSZ results in only a slight difference in grey scale contrast between the NiO grains and YSZ grains in the anode.The darkest regions in the anode are open pores ?lled with epoxy with a low atomic number of6.

At the interface,there is a light grey phase which is seen to grow~4?m into the electrolyte region and has replaced the dark alumina grains.Elemental maps(Fig.2(b)and(c))show that this area is rich in both aluminium and nickel.This suggests that NiAl2O4formation as expected from XRD phase analysis. NiAl2O4has an average atomic number of~12.3and should appear darker than alumina,but lighter than both YSZ and NiO, which is consistent with the grey scale contrast observed.

TEM selected area diffraction(SAD)(Fig.3)provides further irrefutable evidence that the grains forming in the electrolyte are NiAl2O4.

On closer inspection of the SEM nickel map(Fig.2(c)),it is observed that the nickel is not only present in the alumina grains, but also in the surrounding grain boundaries.There are two rea-sons for the presence of the nickel in the grain boundaries of the electrolyte,namely:(i)the formation of NiAl2O4is associated with a7%volume expansion of the original NiO and Al2O3;(ii) the grain boundaries provide a fast diffusion path for the nickel to the alumina grains.

Further evidence for the expansion of the NiAl2O4can be obtained when comparing the spherical morphology of the Al2O3grains deep in the electrolyte with the NiAl2O4grains at the anode|electrolyte interface,which are invariably associ-ated with thin regions that taper off into the adjoining grain boundaries(circled areas in Fig.2(a)).

As the nickel diffusion through the alumina and the grain boundaries produce a very even migration front,it is postu-lated that NiO is supplied to the electrolyte in both a solid and vapour form.Several authors,including de Roos et al.[19],have reported NiO vapourisation starting at1100?

C.

Fig.3.TEM micrograph of NiAl2O4grain(marked with arrow)prior to anode reduction,with 011 selected area diffraction inset.

R.Knibbe et al./Journal of Power Sources 179(2008)511–519515

The presence of the nickel in the electrolyte grain bound-aries in the form of both diffusing nickel and expanded NiAl 2O 4is of major signi?cance to the ionic conductivity of the elec-trolyte.YSZ grain boundaries pose a signi?cant barrier to the migration of oxide ions during the operation of fuel cells.In the current study,the electrolyte grain boundaries are signi?cantly contaminated with nickel to a depth of 4?m.3.3.Reduced sample

After anode reduction,NiAl 2O 4is still observed at the anode |electrolyte interface and the NiAl 2O 4microstructure at the interface is unaltered.Nickel and aluminium elemental maps (Fig.4)of the FIB TEM sample clearly show the pres-ence of nickel in the alumina grains in the electrolyte.The micrograph also shows grains that have clearly grown out into the adjacent grain boundaries,i.e.,similar to what is seen in Figs.2and 3.

A typical NiAl 2O 4grain taken in dark-?eld mode using TEM SAD is shown in Fig.5.The micrograph highlights the ‘squeezed’morphology of the grain.The additional re?ections observed in the SAD are from an adjacent YSZ grain.The partial reduction of NiAl 2O 4would result in the presence of additional re?ections in the SAD pattern from either alumina or nickel,or microcracks between the reduced and unreduced NiAl 2O 4should be observed in the micrographs.As none of these are found in the NiAl 2O 4at the anode |electrolyte interface,it is concluded that the NiAl 2O 4is neither fully nor partially reduced during anode reduction.3.4.Operated sample

Even after 500h of fuel cell operation,NiAl 2O 4is still found (Fig.6(a))within the ?rst several microns of the electrolyte.The aluminium and nickel elemental maps (Fig.6(b)and (c))appear similar to those observed for both the unreduced and reduced samples.Furthermore,the lack of additional re?ections in the TEM SAD pattern (Fig.7)and the homogeneity of the NiAl 2O 4grain con?rms that the NiAl 2O 4is still stable after 500h of fuel cell operation.

Full or partial reduction of NiAl 2O 4is expected as the oxy-gen partial pressure of 3.6×10?13Pa is signi?cantly lower than the previously reported spinel stability limit of 4.9×10?9Pa at 940?C.The lack of NiAl 2O 4reduction could be due to a num-ber of factors such as:(i)the oxygen partial pressure calculated is the most severe and would only occur at the fuel inlet dur-ing OCV and therefore the actual oxygen partial pressure at the anode |electrolyte interface would be much higher;(ii)850?C is an insuf?cient temperature to initiate the NiAl 2O 4reduction;(iii)the oxygen supply from the electrolyte could increase the oxygen activity and stave off NiAl 2O 4reduction.

Due to the stability and interconnected nature of the NiAl 2O 4phase in the electrolyte,it is of paramount importance to under-stand the effect that NiAl 2O 4has on fuel cell performance.From a mechanical standpoint,the stability of the interface is of inter-est as the formation of microcracks would impair the mechanical

integrity.

Fig.4.STEM micrograph of anode |electrolyte interface after anode reduction,with corresponding Al (b)and Ni (c)elemental maps.From nickel elemental map,nickel aluminate is still found in electrolyte and appears unaltered after anode reduction.

3.5.Impedance spectroscopy

In order to evaluate the effect of NiAl 2O 4formation on the ionic conductivity of the 15A10YSZ electrolyte,a.c.impedance spectroscopy was performed on two sets of samples,namely,unreacted 15A10YSZ samples and reacted 15A10YSZ samples (15A10YSZ/NiAl 2O 4).

A series of Nyquist plots for four temperatures,378,400,423and 449?C,is given in Fig.8.The ?rst arc represents the grain bulk impedance and the second arc represents the grain-

516R.Knibbe et al./Journal of Power Sources179(2008)

511–519

Fig.5.Dark-?eld TEM micrograph of NiAl2O4grain after anode reduction, in YSZ matrix with 011 selected area diffraction pattern inset.Additional re?ections in pattern,indicated by arrows,are attributed to YSZ from adjacent grain.NiAl2O4grows out into surrounding grain boundaries.

boundary impedance,followed by an electrochemical response. The frequency of the point at the maxima of each arc is referred to as the point of equivalenceω0.The shape of the curve remains unaltered at the various temperatures,but as the temperature increases the resistance of the electrolyte samples decreases.The lower resistance at higher temperatures consequently decreases the relaxation time(τ)and increases the point of equivalence (ω0)in accordance with

τ=1

=RC(1)

where R is the resistance,C is the capacitance,τis the relaxation time(or time constant),andω0is the angular frequency at the point of equivalence.

At suf?ciently high temperatures,the point of equivalence is shifted to frequencies higher than the maximum1MHz probing frequency of the Solartron1260.Consequently,the detail in the Nyquist plots is lost and,as fewer data points are being modelled, inaccuracies are introduced in curve?tting.At378?C(Fig.8), most of the bulk and grain-boundary impedance curves can be seen,but as the temperature increases to449?C,the equivalence point of the bulk is at too high a frequency to be measured and hence modelled,and only the full grain-boundary impedance response is seen.

Fig.9shows Nyquist plots for15A10YSZ and15A10YSZ NiAl2O4taken at378?C.The bulk conductivity(σbulk) does not vary within experimental error between the two samples withσbulk calculated as 2.36±0.06×10?5and 2.39±0.06×10?5S cm?1for15A10YSZ and15A10YSZ NiAl2O4,respectively.The grain-boundary conductivity(σgb)is ~26%higher in the unreacted15A10YSZ sample withσgb

cal-Fig.6.SEM micrographs of anode electrolyte interface after500h of fuel cell operation,with corresponding Al(b)and nickel(c)maps.Maps still show presence of nickel in electrolyte grain boundaries and alumina grains. culated as2.32±0.06×10?5and2.91±0.07×10?5S cm?1 for15A10YSZ and15A10YSZ NiAl2O4,respectively.Similar trends are observed at all temperatures.

The best way to present this data is by?tting the model and plotting the Arrhenius relationship

σT=Aσexp

?Eσ

R.Knibbe et al./Journal of Power Sources 179(2008)511–519

517

Fig.7.STEM images of anode |electrolyte interface after 500h of fuel cell operation,with 011 selected area diffraction pattern

inset.

Fig.8.Nyquist plots of 15A10YSZ electrolyte at various temperatures,geome-try and density corrected.At higher temperatures,point of equivalence exceeds maximum probing frequency of Solartron 1260and therefore bulk impedance is

lost.

Fig.9.Nyquist plots of 15A10YSZ and 15A10YSZ NiAl 2O 4at 378?C.High-frequency grain bulk impedance appears identical between two samples,but low-frequency grain-boundary impedance is markedly higher in 15A10YSZ NiAl 2O 4

.

Fig.10.Arrhenius plot of bulk conductivity of 15A10YSZ and 15A10YSZ NiAl 2O 4samples.

where σis the conductivity,T is the temperature,A ?is the pre-exponential constant,and E ?is the activation energy for conduction.

The Arrhenius plot of the bulk conductivity (Fig.10)shows that the NiAl 2O 4reaction has no effect on the bulk conductivity of the 15A10YSZ electrolyte.Additionally,any nickel diffu-sion through the YSZ grains in the 15A10YSZ/NiAl 2O 4sample has a negligible effect on the bulk conductivity.The grain bulk activation energies of 15A10YSZ and 15A10YSZ/NiAl 2O 4are 1.16±0.03and 1.17±0.03eV ,respectively,which are simi-lar to the activation energies reported by Feighery et al.[5].The activation energy of 15A10YSZ/NiAl 2O 4is only 1%higher than that of 15A10YSZ,and is within experimental error.This ?nd-ing indicates a similar transport mechanism in the grain bulk of the two samples.

A signi?cant decrease in the grain-boundary conductivity (Fig.11)is observed in the reacted 15A10YSZ/NiAl 2O 4sample.At 231?C,the conductivity of the 15A10YSZ grain-boundary (7.76±0.19×10?8S cm ?1)is 38%higher than that of the 15A10YSZ/NiAl 2O 4(5.61±0.14×10?8S cm ?1).The

large

Fig.11.Arrhenius plot of grain-boundary and total conductivity of 15A10YSZ and 15A10YSZ NiAl 2O 4.

518R.Knibbe et al./Journal of Power Sources179(2008)511–519

Table1

A?and E?for15A10YSZ and15A10YSZ/NiAl2O4in low-temperature(300–500?C)and high-temperature(600–800?C)regions

Low temperature(300–500?C)High temperature(600–800?C)

A?E?(eV)A?E?(eV) 15A10YSZ9.88×106 1.17 1.62×106 1.04

15A10YSZ/NiAl2O410.99×106 1.18 2.16×106 1.07

difference in grain-boundary conductivities indicates that the

diffusion of the nickel into the YSZ grain boundaries and the

growth of the NiAl2O4into the grain boundaries impede the

conduction of oxide ions through the grain boundaries.At

400?C,the grain-boundary conductivity is still16%lower in

the reacted15A10YSZ/NiAl2O4sample than in the unreacted

sample.

The grain-boundary activation energies of the15A10YSZ

and15A10YSZ/NiAl2O4samples are 1.19±0.03and

1.20±0.03eV,respectively,which are similar to the grain-

boundary activation energies reported by Rizea et al.[9].The

activation energies of15A10YSZ and15A10YSZ/NiAl2O4

are the same within experimental error.This suggests a similar

transport mechanism in the grain boundaries of the two

samples.

Although there is a signi?cant difference in the grain-

boundary conductivity at low temperatures,the total con-

ductivity of the electrolyte is of higher importance to fuel

cell performance(Fig.11).The Arrhenius plot of the total

conductivity shows that at231?C the conductivity of the

15A10YSZ/NiAl2O4sample(3.06±0.08×10?8S cm?1)is ~22%lower than that of the unreacted15A10YSZ sam-ple(3.74±0.09×10?8S cm?1).When the temperature is

increased,the conductivities begin to converge and at570?C

the conductivity of the15A10YSZ/NiAl2O4sample is only6%

lower than that of the15A10YSZ sample.At700?C,there is no

difference in the total conductivities.

Previous authors[9,20,21]have reported that the bulk

activation energy of YSZ is characterised by two regions,

viz.,a low-temperature(300–500?C)and a high-temperature

(600–800?C)region.At high temperature,the bulk acti-

vation energy decreases,but the grain-boundary activation

energy remains unaffected.From the Arrhenius plot of the

total conductivity(Fig.11),A?and E?were determined for

the abovementioned two regions;the results are given in

Table1.

The total conductivity at850?C of the15A10YSZ sample is

0.0310±0.001S cm?1,which is the same as the conductivity

for15A10YSZ/NiAl2O4.This is consistent with previous in-

house tests at CFCL,in which the conductivity of the15A10YSZ

electrolyte was measured to be0.033S cm?1at850?C[22].

The trend indicates that at the high temperatures of fuel

cell operation,the NiAl2O4has little effect on the total con-

ductivity of the electrolyte.Due to the higher activation of

the grain boundaries,at high temperatures the grain-boundary

conductivity increases faster than the bulk conductivity,which

has a lower activation energy at high temperature(≥600?C)

[9,20,21].Therefore,at high operating temperatures,the grain-

boundary contribution to the total resistivity diminishes.4.Conclusions

This study sought to examine the effect of alumina addi-tions to the YSZ electrolyte on the anode|electrolyte interface in SOFCs at CFCL.From investigations with XRD,SEM, TEM and impedance spectroscopy,the following conclusions are drawn.

?During anode sintering on to the YSZ-Al2O3electrolyte, NiAl2O4forms in the electrolyte and replaces the alumina grains up to a depth of4?m.

?The NiAl2O4tapered morphology is created by the7%expan-sion required to accommodate the reaction and this forces the NiAl2O4reactant into the grain boundaries.

?Grain boundaries up to a depth of4?m into the electrolyte are also?lled with diffusing Ni.

?No signs of NiAl2O4reduction,in the form of microcracks or additional re?ections in the TEM SAD,are found in the reduced or operated fuel cells.Due to the stability of NiAl2O4, it is not considered detrimental to the mechanical integrity of the interface.

?NiAl2O4formation decreases the conductivity of the grain boundaries in the electrolyte,but does not affect the bulk/grain conductivity.At low temperatures,therefore,the total con-ductivity is impeded by the formation of NiAl2O4but at the present SOFC operating temperature of850?C NiAl2O4does not affect the total conductivity of the electrolyte and is there-fore concluded not to be of detrimental to the performance of the fuel cell.

The addition of alumina is an effective way to increase the fracture toughness of the YSZ electrolyte.Despite the forma-tion of NiAl2O4,this does not have an adverse effect on the conductivity of the electrolyte.If the operating temperature of the SOFC was to be lowered,however,this study indicates that the NiAl2O4would begin to impede the oxide ion conductivity of the electrolyte.

References

[1]K.C.Radford,R.J.Bratton,J.Mater.Sci.14(1979)59–65.

[2]K.C.Radford,R.J.Bratton,J.Mater.Sci.14(1979)66–69.

[3]M.Miyayama,H.Yanagida,A.Asada,Am.Ceram.Soc.Bull.65(1986)

660–664.

[4]M.J.Verkerk,A.J.A.Winnubst,A.J.Burggraaf,J.Mater.Sci.17(1982)

3113–3122.

[5]A.J.Feighery,J.T.S.Irvine,Solid State Ionics121(1999)209–216.

[6]X.Guo,R.Z.Yuan,J.Mater.Sci.30(1995)923–931.

[7]M.Mori,T.Abe,H.Itoh,O.Yamamoto,Y.Takeda,T.Kawahara,J.Am.

Ceram.Soc.77(1994)2217–2219.

R.Knibbe et al./Journal of Power Sources179(2008)511–519519

[8]S.Rajendran,J.Drennan,S.P.S.Badwal,J.Mater.Sci.Lett.6(1987)

1431–1434.

[9]A.Rizea,D.Chirlesan,C.Petot,G.Petot-Ervas,Solid State Ionics146

(2002)341–353.

[10]A.Yuzaki,A.Kishimoto,Solid State Ionics116(1999)47–51.

[11]E.P.Butler,J.Drennan,J.Am.Ceram.Soc.65(1982)474–478.

[12]S.Tekeli,Compos.Sci.Technol.65(2005)967–972.

[13]F.A.Elrefaie,W.W.Smeltzer,J.Electrochem.Soc.128(1981)2237–2242.

[14]L.Kou,J.R.Selman,J.Appl.Electrochem.30(2000)1433–1437.

[15]I.Halevy,D.Dragoi1,https://www.doczj.com/doc/fe18872351.html,tundag,A.F.Yue1,E.H.Arredondo,J.Hu,

M.S.Somayazulu,J.Phys.-Condens.Mat.14(2002)10511–10516.[16]https://www.doczj.com/doc/fe18872351.html,tundag,P.Ret,R.Subramanian,R.Dieckmann,S.L.Sass,Mater.Sci.

Eng.A-Struct.195(1995)39–50.

[17]S.Linderoth,N.Bonanos,K.V.Jensen,J.B.Bilde-S?rensen,J.Am.Ceram.

Soc.84(2001)2652–2656.

[18]Y.L.Liu,C.G.Jiao,Solid State Ionics176(2005)435–442.

[19]G.de Roos,J.M.Fluit,J.H.W.Dewit,J.W.Geus,Surf.Interface Anal.3

(1981)229–234.

[20]S.P.S.Badwal,Solid State Ionics52(1992)23–32.

[21]I.R.Gibson,J.T.S.Irvine,J.Mater.Chem.6(1996)895–898.

[22]S.Amarasinghe,P.Ammala,S.Aruliah,O.Bellon,R.Knibbe,J.Love,R.

Ratnaraj,X.Zheng,Solid Oxide Fuel Cells IX(2005)1037.

on the contrary的解析

On the contrary Onthecontrary, I have not yet begun. 正好相反,我还没有开始。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, the instructions have been damaged. 反之,则说明已经损坏。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, I understand all too well. 恰恰相反,我很清楚 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, I think this is good. ⑴我反而觉得这是好事。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, I have tons of things to do 正相反,我有一大堆事要做 Provided by jukuu Is likely onthecontrary I in works for you 反倒像是我在为你们工作 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, or to buy the first good. 反之还是先买的好。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, it is typically american. 相反,这正是典型的美国风格。 222.35.143.196 Onthecontrary, very exciting.

恰恰相反,非常刺激。 https://www.doczj.com/doc/fe18872351.html, But onthecontrary, lazy. 却恰恰相反,懒洋洋的。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, I hate it! 恰恰相反,我不喜欢! https://www.doczj.com/doc/fe18872351.html, Onthecontrary, the club gathers every month. 相反,俱乐部每个月都聚会。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, I'm going to work harder. 我反而将更努力工作。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, his demeanor is easy and nonchalant. 相反,他的举止轻松而无动于衷。 https://www.doczj.com/doc/fe18872351.html, Too much nutrition onthecontrary can not be absorbed through skin. 太过营养了反而皮肤吸收不了. https://www.doczj.com/doc/fe18872351.html, Onthecontrary, I would wish for it no other way. 正相反,我正希望这样 Provided by jukuu Onthecontrary most likely pathological. 反之很有可能是病理性的。 https://www.doczj.com/doc/fe18872351.html, Onthecontrary, it will appear clumsy. 反之,就会显得粗笨。 https://www.doczj.com/doc/fe18872351.html,

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base on的例句

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英语造句大全

英语造句大全English sentence 在句子中,更好的记忆单词! 1、(1)、able adj. 能 句子:We are able to live under the sea in the future. (2)、ability n. 能力 句子:Most school care for children of different abilities. (3)、enable v. 使。。。能句子:This pass enables me to travel half-price on trains. 2、(1)、accurate adj. 精确的句子:We must have the accurate calculation. (2)、accurately adv. 精确地 句子:His calculation is accurately. 3、(1)、act v. 扮演 句子:He act the interesting character. (2)、actor n. 演员 句子:He was a famous actor. (3)、actress n. 女演员 句子:She was a famous actress. (4)、active adj. 积极的 句子:He is an active boy. 4、add v. 加 句子:He adds a little sugar in the milk. 5、advantage n. 优势 句子:His advantage is fight. 6、age 年龄n. 句子:His age is 15. 7、amusing 娱人的adj. 句子:This story is amusing. 8、angry 生气的adj. 句子:He is angry. 9、America 美国n.

(完整版)主谓造句

主语+谓语 1. 理解主谓结构 1) The students arrived. The students arrived at the park. 2) They are listening. They are listening to the music. 3) The disaster happened. 2.体会状语的位置 1) Tom always works hard. 2) Sometimes I go to the park at weekends.. 3) The girl cries very often. 4) We seldom come here. The disaster happened to the poor family. 3. 多个状语的排列次序 1) He works. 2) He works hard. 3) He always works hard. 4) He always works hard in the company. 5) He always works hard in the company recently. 6) He always works hard in the company recently because he wants to get promoted. 4. 写作常用不及物动词 1. ache My head aches. I’m aching all over. 2. agree agree with sb. about sth. agree to do sth. 3. apologize to sb. for sth. 4. appear (at the meeting, on the screen) 5. arrive at / in 6. belong to 7. chat with sb. about sth. 8. come (to …) 9. cry 10. dance 11. depend on /upon 12. die 13. fall 14. go to … 15. graduate from 16. … happen 17. laugh 18. listen to... 19. live 20. rise 21. sit 22. smile 23. swim 24. stay (at home / in a hotel) 25. work 26. wait for 汉译英: 1.昨天我去了电影院。 2.我能用英语跟外国人自由交谈。 3.晚上7点我们到达了机场。 4.暑假就要到了。 5.现在很多老人独自居住。 6.老师同意了。 7.刚才发生了一场车祸。 8.课上我们应该认真听讲。9. 我们的态度很重要。 10. 能否成功取决于你的态度。 11. 能取得多大进步取决于你付出多少努力。 12. 这个木桶能盛多少水取决于最短的一块板子的长度。

初中英语造句

【it's time to和it's time for】 ——————这其实是一个句型,只不过后面要跟不同的东西. ——————It's time to跟的是不定式(to do).也就是说,要跟一个动词,意思是“到做某事的时候了”.如: It's time to go home. It's time to tell him the truth. ——————It's time for 跟的是名词.也就是说,不能跟动词.如: It's time for lunch.(没必要说It's time to have lunch) It's time for class.(没必要说It's time to begin the class.) They can't wait to see you Please ask liming to study tonight. Please ask liming not to play computer games tonight. Don’t make/let me to smoke I can hear/see you dance at the stage You had better go to bed early. You had better not watch tv It’s better to go to bed early It’s best to run in the morning I am enjoy running with music. With 表伴随听音乐 I already finish studying You should keep working. You should keep on studying English Keep calm and carry on 保持冷静继续前行二战开始前英国皇家政府制造的海报名字 I have to go on studying I feel like I am flying I have to stop playing computer games and stop to go home now I forget/remember to finish my homework. I forget/remember cleaning the classroom We keep/percent/stop him from eating more chips I prefer orange to apple I prefer to walk rather than run I used to sing when I was young What’s wrong with you There have nothing to do with you I am so busy studying You are too young to na?ve I am so tired that I have to go to bed early

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《The Kite Runner》追风筝的人--------------------------------美句摘抄 1.I can still see Hassan up on that tree, sunlight flickering through the leaves on his almost perfectly round face, a face like a Chinese doll chiseled from hardwood: his flat, broad nose and slanting, narrow eyes like bamboo leaves, eyes that looked, depending on the light, gold, green even sapphire 翻译:我依然能记得哈桑坐在树上的样子,阳光穿过叶子,照着他那浑圆的脸庞。他的脸很像木头刻成的中国娃娃,鼻子大而扁平,双眼眯斜如同竹叶,在不同光线下会显现出金色、绿色,甚至是宝石蓝。 E.g.: A shadow of disquiet flickering over his face. 2.Never told that the mirror, like shooting walnuts at the neighbor's dog, was always my idea. 翻译:从来不提镜子、用胡桃射狗其实都是我的鬼主意。E.g.:His secret died with him, for he never told anyone. 3.We would sit across from each other on a pair of high

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改写句子练习2标准答案

The effective sentences:(improve the sentences!) 1.She hopes to spend this holiday either in Shanghai or in Suzhou. 2.Showing/to show sincerity and to keep/keeping promises are the basic requirements of a real friend. 3.I want to know the space of this house and when it was built. I want to know how big this house is and when it was built. I want to know the space of this house and the building time of the house. 4.In the past ten years,Mr.Smith has been a waiter,a tour guide,and taught English. In the past ten years,Mr.Smith has been a waiter,a tour guide,and an English teacher. 5.They are sweeping the floor wearing masks. They are sweeping the floor by wearing masks. wearing masks,They are sweeping the floor. 6.the drivers are told to drive carefully on the radio. the drivers are told on the radio to drive carefully 7.I almost spent two hours on this exercises. I spent almost two hours on this exercises. 8.Checking carefully,a serious mistake was found in the design. Checking carefully,I found a serious mistake in the design.

用以下短语造句

M1 U1 一. 把下列短语填入每个句子的空白处(注意所填短语的形式变化): add up (to) be concerned about go through set down a series of on purpose in order to according to get along with fall in love (with) join in have got to hide away face to face 1 We’ve chatted online for some time but we have never met ___________. 2 It is nearly 11 o’clock yet he is not back. His mother ____________ him. 3 The Lius ___________ hard times before liberation. 4 ____________ get a good mark I worked very hard before the exam. 5 I think the window was broken ___________ by someone. 6 You should ___________ the language points on the blackboard. They are useful. 7 They met at Tom’s party and later on ____________ with each other. 8 You can find ____________ English reading materials in the school library. 9 I am easy to be with and _____________my classmates pretty well. 10 They __________ in a small village so that they might not be found. 11 Which of the following statements is not right ____________ the above passage? 12 It’s getting dark. I ___________ be off now. 13 More than 1,000 workers ___________ the general strike last week. 14 All her earnings _____________ about 3,000 yuan per month. 二.用以下短语造句: 1.go through 2. no longer/ not… any longer 3. on purpose 4. calm… down 5. happen to 6. set down 7. wonder if 三. 翻译: 1.曾经有段时间,我对学习丧失了兴趣。(there was a time when…) 2. 这是我第一次和她交流。(It is/was the first time that …注意时态) 3.他昨天公园里遇到的是他的一个老朋友。(强调句) 4. 他是在知道真相之后才意识到错怪女儿了。(强调句) M 1 U 2 一. 把下列短语填入每个句子的空白处(注意所填短语的形式变化): play a …role (in) because of come up such as even if play a …part (in) 1 Dujiangyan(都江堰) is still ___________in irrigation(灌溉) today. 2 That question ___________ at yesterday’s meeting. 3 Karl Marx could speak a few foreign languages, _________Russian and English. 4 You must ask for leave first __________ you have something very important. 5 The media _________ major ________ in influencing people’s opinion s. 6 _________ years of hard work she looked like a woman in her fifties. 二.用以下短语造句: 1.make (good/full) use of 2. play a(n) important role in 3. even if 4. believe it or not 5. such as 6. because of

英语造句

English sentence 1、(1)、able adj. 能 句子:We are able to live under the sea in the future. (2)、ability n. 能力 句子:Most school care for children of different abilities. (3)、enable v. 使。。。能 句子:This pass enables me to travel half-price on trains. 2、(1)、accurate adj. 精确的 句子:We must have the accurate calculation. (2)、accurately adv. 精确地 句子:His calculation is accurately. 3、(1)、act v. 扮演 句子:He act the interesting character.(2)、actor n. 演员 句子:He was a famous actor. (3)、actress n. 女演员 句子:She was a famous actress. (4)、active adj. 积极的 句子:He is an active boy. 4、add v. 加 句子:He adds a little sugar in the milk. 5、advantage n. 优势 句子:His advantage is fight. 6、age 年龄n. 句子:His age is 15. 7、amusing 娱人的adj. 句子:This story is amusing. 8、angry 生气的adj. 句子:He is angry. 9、America 美国n. 句子:He is in America. 10、appear 出现v. He appears in this place. 11. artist 艺术家n. He is an artist. 12. attract 吸引 He attracts the dog. 13. Australia 澳大利亚 He is in Australia. 14.base 基地 She is in the base now. 15.basket 篮子 His basket is nice. 16.beautiful 美丽的 She is very beautiful. 17.begin 开始 He begins writing. 18.black 黑色的 He is black. 19.bright 明亮的 His eyes are bright. 20.good 好的 He is good at basketball. 21.British 英国人 He is British. 22.building 建造物 The building is highest in this city 23.busy 忙的 He is busy now. 24.calculate 计算 He calculates this test well. 25.Canada 加拿大 He borns in Canada. 26.care 照顾 He cared she yesterday. 27.certain 无疑的 They are certain to succeed. 28.change 改变 He changes the system. 29.chemical 化学药品

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