Fabrication and Performance ofTubular, Electrode-SupportedBaCe0.2Zr0.7Y0.1O3–d Fuel Cells�

S. Robinson1, A. Manerbino2,3, W. Grover Coors3, N. P. Sullivan1*1 Department of Mechanical Engineering, Colorado Fuel Cell Center, Colorado School of Mines, Golden, Colorado 80401, USA2 Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado 80401, USA3 CoorsTek, Inc., Golden, Colorado 80403, USA

Received October 07, 2012; accepted April 09, 2013; published online April 30, 2013

1 Introduction

In this work, we report on the fabrication and performanceof the first tubular, electrode-supported protonic ceramic fuelcells based on the BaCe0.2Zr0.7Y0.1O3–d (BCZY27) electrolytematerial. Rare-earth doped perovskites such as BCZY arebeing developed as proton-conducting membranes for fuel-cell and membrane-reactor applications [1–3]. The stability ofthese materials under reducing atmospheres and their highprotonic conductivity at intermediate temperatures makethem attractive for these applications. Doped barium ceratesare well known for high protonic conductivity, but can bechemically unstable in high-CO2 environments [4–7]. Dopedbarium zirconates are chemically stable but exhibit lower pro-tonic conductivity. Solid solutions of barium cerate and bar-

ium zirconate, such as BaCe0.2Zr0.7Y0.1O3–d (BCZY27), havebeen shown to exhibit high protonic conductivity and long-term stability [8–11].

Charge transport across the BCZY27 membrane is a com-plex process, with multiple charge defects introduced at thegas-solid interfaces (using Kröger–Vink notation):

12

H2 � O ×O � OH�

O � e′

12

O2 � V��O � O ×

O � 2 h�

H2O � V��O � O ×

O � 2OH�

null � e′ � h�

AbstractIn this report, we describe fabrication and electrochemical-performance testing of tubular, anode-supported fuel cellsbased on the protonic ceramic BaCe0.2Zr0.7Y0.1O3–d

(BCZY27). These devices are comprised of a 20-lm-thickBCZY27 electrolyte spray-coated and co-fired onto anextruded, tubular 9.8-mm-diameter, 1.25-mm-thick 65 wt.%NiO/35 wt.% BCZY27 anode support. Reactive sinteringwith NiO forms the BCZY27 material from parent oxides.An La0.6Sr0.4 Co0.2Fe0.8O3–d (LSCF) cathode is applied follow-ing co-sintering. While anode supports can be extruded to 3-m lengths, the active area of the cells tested here is 7.5 cm2.Performance is quantified through polarization measure-ments across a range of temperatures with hydrogen-airreactants. Peak power ranges from 78 to 189 mW cm–2 over

the 700–850 °C temperature range. Open-circuit voltagedecreases with increasing operating temperature due to theco-diffusion of the multiple charge carriers present. Theionic transference number is determined over a range oper-ating temperatures and anode-gas compositions, and isfound to range from 0.77 to 0.88. Finally, an external powersupply is used to drive hydrogen across the BCZY27 mem-brane. At an applied current density of 1 A cm–2 and 700 °Coperating temperature, hydrogen flux is measured at7.5 smL min–1 cm–2 active area.

Keywords: Fuel Cell, Hydrogen Separation, MembraneReactor, Proton Conducting Ceramic, Proton Transport,Tubular

–� Paper presented at the 10th European SOFC Forum 2012,

June 26–29, 2012 held in Lucerne, Switzerland. Organized bythe European Fuel Cell Forum – www.efcf.com

–[*] Corresponding author, nsulliva@mines.edu

584 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim FUEL CELLS 13, 2013, No. 4, 584–591

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DOI: 10.1002/fuce.201200191

Robinson et al.: Fabrication and Performance of Tubular, Electrode-Supported BaCe0.2Zr0.7Y0.1O3–d Fuel Cells

In this series of reactions, the defects are OH�O (protons),

V��O (vacancies), e′ (electrons), and h� (holes), with oxygen

sites O ×O [12]. Reduction of ceria in the BCZY may potentially

create additional vacancies:

2Ce ×Ce � O ×

O � 2Ce′Ce � V��O � 1

2O2

with ceria sites Ce ×Ce reduced to Ce′Ce [13]. Electronic conduc-

tivity due to electrons has not been measured previously inBCZY, though it is well known that hole conductivity plays arole in the performance of protonic ceramics [1, 8, 14–16]. Themobilities of the numerous charge carriers (protons, oxygenvacancies, holes, electrons) are generally unknown, andhighly dependent on gas composition and temperature[15, 17].

In fuel-cell applications, there is great asymmetry in thegas environments to which the BCZY27 membrane isexposed. The reducing conditions at the anode result in ahigh concentration of protonic defects and (potentially)vacancies from the ceria reduction. The highly oxidizing con-ditions at the cathode result in a large concentration of holeson the cathode-side of the membrane and consumption ofvacancies. The counterdiffusion of these charge carriersthrough the thin membrane enables charge transport in theabsence of an external circuit [18], and open-circuit measure-ments that are below the theoretical Nernst potential [12].The magnitude of this internal short could be considerableacross thin membranes like those described here. This effectcan be deleterious for fuel-cell applications, but beneficial formembrane-reactor applications. Regardless, the permeabilityand transport of these multiple charge carriers, and theirdependence on operating conditions, are unknown and war-rant further investigation.

As discussed by Bentzer et al. [19] and Sutija et al. [20], theratio of the measured open-circuit potential to the theoreticalNernst potential can provide insight on the magnitude of theionic transference numbers:

ti ��

tk

� �OCVEN

where ti is the ionic transference number, tk is the ionic trans-ference number of each charge carrier, OCV is the measuredopen-circuit potential, and EN is the theoretical Nernst poten-tial. Such a straightforward measurement can provide insightinto the roles of the different charge carriers in BCZY, and

serve as a useful experimental data set for validation of com-putational models [12, 21, 22]. However, the result is limitedto quantification of an integrated transference number, that isthe sum of the transference numbers of the multiple chargecarriers.

Performance of protonic-ceramic fuel cells has steadilyimproved as new materials and fabrication methods havebeen developed (Table 1 [23–31]). Previous work on protonicceramics has been almost-exclusively on button-cell devices.Low-cost, high-throughput fabrication of meter-scale devicesutilizing thin BCZY27 membranes on thick NiO-BCZY27 tu-bular supports has been established at CoorsTek, Inc.(Golden, Colorado, USA). This work outlines fabrication andperformance characterization of these devices. Performance ischaracterized through measurement of open-circuit potentialand power density over a range of operating conditions.Hydrogen pumping across the membrane is also explored.The data set generated through this series of experiments canbe valuable in characterizing the performance of these uniquedevices, and in development of theory on the charge-trans-port processes in mixed ionic conductors.

2 Experimental

2.1 Cell Fabrication

Dense unfired “green” tubes of 65 wt.% NiO/35 wt.%BCZY27 are prepared by extrusion; these tubes form the me-chanical support for the BCZY27 membrane coating. TheBCZY27 material contained in both the anode and electrolyteis formed by “reactive sintering” during cell fabrication [32–34]. During reactive sintering, the presence of NiO leads toaccelerated sintering of materials and formation of single-phase BCZY27 from the parent materials during high-temper-ature co-sintering. By combining the formation of single-phase BCZY with cell fabrication, reactive sintering has thepotential to significantly reduce cell-fabrication costs [35].Reactive sintering has also been demonstrated with yttria-sta-bilized zirconia for solid-oxide fuel cell applications [36, 37].

The anode-support fabrication process is described byCoors and Manerbino [32], and is summarized here. Stoichio-metric amounts of industrial-grade reactant powders BaSO4

(Solvay, Italy), CeO2 (AMR, China), ZrO2 (Zirchem 2005,AMR, China) and Y2O3 (Ultra Fine, 99.99+ purity, HJD, Intl.,

Table 1 Materials and power densities of protonic ceramic button-cells found in literature.

Electrolyte Anode Cathode Peak power at 700 °C (mW cm–2) Ref.

BaZr0.80Y0.16Zn0.04O3–d spin coated – 20 lm 60 wt.% NiO/40 wt.% BZY Pt 90 [15]BaCe0.9Y0.1O3–d PLD 7 lm 60 wt.% NiO/40 wt.% BCY10 Sm0.5Sr0.5CoO3 295 [16]BaZr0.1Ce0.7Y0.2O3–d drop coated – 20 lm 60 wt-% NiO/40 wt.% BZCY27 PrBaCo2O5+d 545 [17]BaCe0.8Y0.2O3–d PLD 0.7 lm Pd membrane N/A 1,400 at 600 °C [18]BaCe0.9Y0.1O3–d pressed 60 wt.% NiO/40 wt.% BCY10 La0.8Sr0.2Co0.8Fe0.2O3–d/BaCe0.9Yb0.1O3–d 63 [19]BaZr0.1Ce0.7Y0.2O3–d co-pressed 25 lm 50 wt.% NiO/50 wt.% BZCY27 BaCe0.5Fe0.5O3–d 395 [20]Ba(Zr0.1Ce0.7Y0.2)O3–d co-pressed 60 lm NiO/BZCY slurry BaZr0.1Ce0.7Co0.2O3–d 370 [21]BaZr0.1Ce0.7Y0.2O3–d drop coated 20 lm 60 wt.% NiO/40 wt.% BZCY27 60 wt-% Ba0.5Sr0.5Fe0.8Cu0.2O3–d/40 wt-%

BZCY27430 [22]

BaCe0.9Y0.1O3–d co-pressed 20 lm 60 wt.% NiO/40 wt.%BCY10 Ba0.5Sr0.5Co0.8Fe0.2O3–d 550 [23]

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USA) are mixed with 65 wt.% NiO (Inco F-grade, Novamet,USA), and the mixture is ball-milled for 16 h. The resultingpowder is then sieved through a 40-mesh screen. Water and amixture of organic binders are blended into the powder usinga mixer (Lancaster K-Lab) producing a green-body materialthat is suitable for extrusion. Green tubes are extruded on a40-ton extrusion press (Loomis) through an encapsulated dieset (0520-0424). This yields final green tubes with dimensionsof 13.8 mm outside diameter and a wall thickness of 1.8 mm.The tubes are produced in approximately 3.0-meter lengths,and laid on Plaster-of-Paris V-groove trays for slow drying inair for several days. After drying, shorter sections of the tubeare cut and prepared for membrane coatings.

The membrane is coated onto the unfired anode-supporttubes by spraying. A BCZY27 spray mixture is formulatedfrom the same reactant powders and oxide loadings used inthe anode-support slurry (BaSO4, CeO2, ZrO2, and Y2O3), butin the absence of NiO. The spray mix is prepared by adding a50 wt.% solids loading of stoichiometric ratios of reactantoxide and sulfate powders to a vehicle made from an acrylicbinder in a solvent system. It is important to note the spraymix does not have the addition of NiO. Reactive sinteringand densification of the membrane occurs through diffusionof NiO present in the extruded support tube into the thinmembrane.

The membrane coating is applied to the dense extrudedtubes through a semi-automated spray system composed offour main independent components: an air-supply system,spray head, liquid delivery, and substrate conveyor. Coatedtubes are fired at 1,600 °C for 6 h. The fired shrinkage is30.9% ± 1.5%, yielding dimensions of 9.98-mm outside diam-eter and 1.25-mm wall thickness. Membrane thickness isapproximately 20 lm. As shown in Ref. [32], XRD analysis ofthe reactive-sintering membrane confirms formation of sin-gle-phase BCZY under these conditions.

The anode-supported BCZY membrane is painted with athin La0.6Sr0.4 Co0.2Fe0.8O3–d (LSCF) cathode ink (Electro-science, Inc., 4421) and sintered at 1,000 °C in air for 30 min.This cathode material has shown good performance in proto-nic-ceramic applications [27, 38–42]. An SEM image of thedevice described is shown in Figure 1.

2.2 Electrochemical Performance Testing

A tube-in-shell test apparatus is used to characterize cellperformance, as detailed in Robinson [43]. An illustration ofthis test configuration is shown in Figure 2, with a process-flow diagram shown in Figure 3. This configuration enablescontrol of both anode (tube) and cathode (shell) gas composi-tions, and downstream gas analysis of reactor-exhauststreams. Both the anode and cathode gas compositions arecontrolled using mass flow controllers (Alicat Scientific) andsteam-injection humidification systems. The tubular cell isbonded and hermetically sealed to Al2O3 tubes using glasspaste (Schott G018-345) and a ceramic cement (CotronixResbond FS-989). These alumina tubes serve as anode-gas

feed and exhaust, and are connected to anode-gas manifold-ing using compression fittings (Swagelok UltraTorr). Thistube assembly is captured within an outer quartz shell that isalso connected to cathode-gas manifolding via compressionfittings. The assembly is placed within a furnace (AppliedTest Systems) so that the stainless steel tubing and compres-sions seals are located outside of the hot zone. Both the tubeand shell gases are fed to a mass spectrometer (MS) (SRSRGA 200) for measurement of exhaust-gas composition andleak detection. This arrangement enables control of reactantpartial pressures on both sides of the BCZY27 membrane,and quantification of hydrogen flux through the membrane.

For each gas feed, water vapor is generated by using a lL-flow pump (Global FIA milliGAT) to inject deionized waterin coannual flow with anode or cathode fed into a heatedcylinder. Heat rope is applied to all stainless-steel tubingdownstream of the steam-addition units to prevent water

Fig. 1 SEM image of a fracture cross section of the protonic-ceramic fuel cell.

Fig. 2 Illustration of the tube-in-shell test configuration.

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condensation. A gas-dryer line (Nafion Perma Pure MD Ser-ies) is used to remove moisture from the exhaust gases priorto sampling by the mass spectrometer.

Electrochemical performance of tubular cells is accom-plished using four-point DC-conductivity electrical connec-tions. As shown in Figure 4a, the anode current collector isformed by wrapping two grades of nickel mesh around a3.175-mm-dia nickel rod (Ed Fagan, Inc.). The anode voltage-sense connection is made by interlaying a flattened 1-mm di-ameter silver wire between the Ni mesh makes. The nickelmesh is lightly coated with NiO paste (Electroscience 4410)and inserted into the inside diameter of the cell. Cathode cur-rent collection is shown in Figure 4b. A thin coating of plati-num ink (Electroscience 5542) is painted over the cathode,wrapped with Pt gauze (Alpha Aesar 10283), and securedwith a 1-mm-diameter Pt current collector wire (Alpha Aesar43276). A second 0.5-mm-dia Pt wire (Alfa Aesar 43288)secures the cathode electrode components in place and serves

as the cathode voltage-sense wire. The cathode voltage sensewire is also insulated using a small alumina tube, completingthe membrane electrode assembly. The active area is∼7.5 cm2.

Cathode electrical connections are fed into the shell cham-ber through a vacuum feed-through (Kurt J. Lesker). A Type-K thermocouple (Omega) is placed near the cell for continu-

Fig. 3 Process flow diagram for the tube-in-shell test apparatus.

Fig. 4 Current-collection and voltage-sensing hardware: (a) anode; and(b) cathode.

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ous temperature measurement during performance testing.After installation into the test stand, wiring is connected to aDC electronic load cell (Chroma 6130).

After assembly and installation into the test stand, the fur-nace is heated to 850 °C at 60 °C/h with 25-sccm of He andAr are fed to the tube and shell, respectively. Shell exhaust-gas composition is continuously monitored with the massspectrometer. When sealing is confirmed, the tube and shellflow rates are slowly increased to 100 sccm. Water vapor isgradually added to 4% mole fraction in the shell gas feed,and the H2 composition in the tube flow channel is graduallyincreased to 2% (balance He) to reduce the NiO in the anodesupport to Ni. The porosity of the anode support after thereduction process is approximately 27%. After 24 h, the cath-ode gas composition is gradually changed to humidified syn-thetic air (78% Ar, 20% O2, 2% H2O).

The tube-in-shell test apparatus is used to characterize theperformance of the tubular BCZY fuel cells. Polarization mea-surements are conducted over a temperature range between700 and 850 °C in steps of 50 °C. The anode and cathode gascomposition are held constant at 80% H2, 19% He, 1% H2O,and 78% Ar, 20% O2, 2% H2O, respectively. In order to pro-vide a measure of cell degradation, an identical series of po-larization measurements are taken over a period of 6 weeksof cell operation.

The presence of multiple charge carriers and resultinginternal short across the thin BCZY membrane is alsoexplored over a range of operating temperatures and anode-gas compositions as shown in Table 2. For this series ofexperiments, the anode-gas composition is varied such thatconcentration of one reactant is held fixed, while the concen-tration of the second reactant is varied as shown in Table 2.For example, as the H2 concentration is varied, the H2O con-centration is held fixed by compensating the total withhelium. This approach can be useful in providing data onspecies-dependent reaction orders [44]. The cathode-side gascomposition is held constant at 70% argon, 20% oxygen, 10%water vapor. Operating temperature is varied from 600 to

850 °C in steps of 50 °C. Total anode- and cathode-gas flowrates are kept high (300 sccm) to minimize effects of concen-tration variations along the length of the cell. Two series ofexperiments are conducted, one for 20–80% hydrogen molefraction, and a second for 1–20% water-vapor mole fraction,as seen in Table 2. The magnitude of the internal short isquantified through the ionic transference number, ti.

In the final series of experiments, an external power sup-ply is connected to the tubular BCZY membrane-electrodeassembly and used to drive H2 the across the membrane fromthe tube into the shell gas stream. The inlet compositions ofthe anode (tube) and cathode (shell) gas streams are held con-stant at 47.5% H2/47.5% He/5% H2O, and 94% Ar/1% O2/5% H2O, respectively. The small amount of O2 contained inthe cathode gas prevents deleterious reduction of the LSCFcathode materials. Both flow rates are fixed at 300 sccm;experiments are conducted at 700 °C. Shell exhaust gas com-positions are measured using the mass spectrometer.

3 Results and Discussion

3.1 Polarization Measurements

Electrochemical performance of the tubular BCZY mem-brane-electrode can be observed in the polarization measure-ments shown in Figure 5. These curves are generated over aperiod of 6 weeks, and provide insight into the power-gener-ating capacity and degradation of these devices.

Peak power at 850 °C reaches 189 mW cm–2, but decreases25% over the 6-week testing period (Figure 5b). Nearly negli-gible degradation is observed at 700 °C, where peak powerreaches ∼78 mW cm–2 (Figure 5a). In comparison to the

Table 2 Ionic transference number test matrix.

Experiment

[0,2-5]Fixed H2O, varied H2 [0,3-6]Fixed H2, varied H2O

1 2 3 4 5 6 7 8

XH280% 60% 40% 20% 80% 80% 80% 80%

XH2 O 10% 10% 10% 10% 1% 5% 15% 20%Xhe 10% 30% 50% 70% 19% 15% 5% 0%

Fig. 5 Polarization characteristics of tubular BCZY27 membrane electrode assembly over 6 weeks of operation: (a) 700 and 750 °C; and (b) 800 and850 °C.

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power densities of some protonic-ceramic fuel cells shown inTable 1, this performance is lower than that found in pre-vious studies utilizing thin electrolytes. However, all pre-vious studies utilize a planar architecture at “button-cell”dimensions. The tubular architecture examined here has anactive area that is an order-of-magnitude greater than thoseof previous works, with significantly larger sizes possible.

The cause of the performance degradation is unclear. SEMimaging of a fracture cross section of this cell at the BCZY-electrolyte/LSCF-cathode interface is shown in Figure 6. Theelectrolyte has a non-uniform appearance at the interface.EDS analysis of the interface shows slight migration oflanthanum from the LSCF cathode into the BCZY electrolyte.This migration could play a role in the observed degradation.Higher power density and improved long-term performancemay be possible with more-advanced cathode materials andarchitectures [42].

The open-circuit voltage is consistently observed to be sig-nificantly lower than the theoretical Nernst potential, both inthe results shown in Figure 5, and in other performance testsconducted in our laboratory. This is attributed to the activityof the multiple charge carriers within the BCZY electrolytemembrane. Our mass-spectrometer measurements confirmthat gas leakage due to pinholes or inadequate sealing is neg-ligible. This small-but-measureable internal short appears tobe dependent upon temperature and gas composition. Thismotivates the experiments presented in the next section.

3.2 Effects of Operating Conditions on Ionic TransferenceNumber

The small internal short that arises from ambipolar diffu-sion across the BCZY membrane causes reduced efficiency infuel-cell applications, but may be desirable in membrane-reactor applications. In order to explore the effects of anode-gas composition and operating temperature on the magni-tude of this internal short, the test matrix shown in Table 2 isexecuted.

Results for the variable H2 and variable H2O cases arecompared in Figure 7a and b, respectively. Throughout theseexperiments, the oxygen partial pressure in the cathode(shell) is held constant at pO2

� 0�21. In Figure 7a, pH2O � 0�10for both the anode (tube) and cathodegas streams, while pH2

varies from 0.2 to0.8. The ionic transference number spans0.77 < ti < 0.88 over the range of condi-tions tested. Only modest variability isobserved at or below operating tempera-tures of 700 °C, but ti decreases signifi-cantly at higher temperatures as the mo-bility of minority charge carriersincreases. For the conditions tested, theionic transference number shows a mod-est-but-steady increase with increasingH2 mole fraction (Figure 7a), rising from0.77 to 0.80 as the hydrogen mole fraction

is increased from 20 to 80% at 850 °C. This result implies thatthe relative role of hole conduction is decreased under highlyreducing conditions at the anode. The thin electrolyte used inthese cells appears to result in an internal short that is greaterthan observed by past researchers, yielding an overall lowerionic transference number [23, 24].

Under varying water-vapor conditions, the peak in ti isfound at the low-water-vapor condition (Figure 7b). A mini-mum value is observed at the 10% water-vapor mole fraction,when the cathode- and anode-side H2O concentrations arebalanced. As the water vapor content in the anode increases,the ionic transference number decreases, implying a greaterrole for vacancy transport. These results are indicative of theeffects of the multiple charge carriers in the BCZY27 material,and how the mobilities of these charge carriers change withtemperature and hydrogen mole fraction.

3.3 Hydrogen Pumping

The protonic ceramic devices reported here can be used totransport hydrogen across two gas streams at high tempera-ture. In the experiments described in this section, an externalpower supply is connected to the membrane-electrode assem-bly and used to drive H2 from the tube into the shell gasstream. Figure 8 shows that the flux rate of hydrogen reaches7.2 mL min–1 cm–2 active area at a current density of

Fig. 6 SEM image of a fracture cross section of the protonic-ceramic fuelcell at the electrolyte-cathode interface after 6 weeks of performance test-ing.

Fig. 7 Effect of temperature and anode-gas composition on ionic transference number: (a) hydro-gen mole fraction; and (b) water-vapor mole fraction from 600 to 850 °C.

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1 A cm–2. Flux is nearly linear with current density, and fol-lows the theoretical Faradaic hydrogen flux rate, �nF:

�nF � inF

where i is the current, n is the number of electrons transferredper mole of hydrogen, and F is Faraday’s constant. The short-circuit current density under these conditions is estimated at0.086 A cm–2. Though the inlet cathode composition includes1 mol.% O2, no oxygen is detected in the shell exhaust gasstream, as the H2 transported from the anode side combustswith the O2 present on the cathode side, forming H2O. Thesehigh H2-flux rates require polarization to –2.5 V.

4 Conclusion

This paper presents fabrication and electrochemical perfor-mance characterization of tubular protonic-ceramic fuel cells.These devices are comprised of a thin, dense BaCe0.2Z-r0.7Y0.1O3–d (BCZY27) electrolyte that is spray-coated and co-sintered onto an extruded Ni-BCZY anode support, followedby application of an LSCF cathode layer. The BCZY27 mate-rial is formed from parent oxide powders during cell fabrica-tion through the process of reactive sintering with NiO. Whilethese tubular membrane-electrode assemblies can reach40 cm in length, a comparatively small active area of 7.5 cm2

is used in the experiments report here.The tubular protonic-ceramic fuel cells are sealed within a

tube-in-shell reactor for electrochemical characterization.Peak power density reaches 189 W cm–2 at 850 °C, thoughsignificant performance degradation is observed at this tem-perature over 6 weeks of testing. Cell performance is moremoderate at 700 °C (peak power of ∼78 W cm–2), but perfor-mance remains stable over a 6-week testing period.

The open-circuit voltage is observed to be significantlybelow the theoretical Nernst potential. This reflects the rolesof the multiple charge carriers that are present in this mate-rial, and the resulting internal short that may be magnified inthin membranes like those examined here. This internal short,quantified through the ionic transference number, is shownto more-than-double in magnitude when increasing the oper-ating temperature from 600 to 850 °C. The ionic transferencenumber is also found to be moderately dependent on water-vapor and hydrogen concentration in the anode gas stream.

When driven by an external power supply, hydrogen fluxacross the thin BCZY27 membrane reaches7.5 mL min–1 cm–2 active area. The data set generatedthrough this series of experiments can be valuable in develop-ment of theory on the charge-transport processes, and forproviding insight on the mobilities of the multiple charge car-riers through the BCZY27 membrane.

Acknowledgements

This work is supported by the U.S. Department of Energy,Office of Energy Efficiency and Renewable Energy throughGrant DE-EE0000260. Additional support is providedthrough the National Science Foundation Bridge-to-DoctorateProgram, and through a generous gift to the Colorado Schoolof Mines Foundation by Protonic Capital, LLC. The authorsalso wish to thank Dr. Christian Kjølseth, Department ofChemistry at the University of Oslo Center for Materials andNanotechnology for acquisition of the SEM images, and Dr.Sandrine Ricote at the Colorado School of Mines, Departmentof Mechanical Engineering, Colorado Fuel Cell Center for as-sistance in manuscript development.

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Fig. 8 Hydrogen flux rate across the BCZY27 membrane at 700 °C whendriving the tubular MEA with an external power supply.

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