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Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells
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Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells Jie-Yuan Lin a,1, Lin Shao a,b,1, Feng-Zhan Si a, Xian-Zhu Fu a,*, Jing-Li Luo a,c,** a
College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China c Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada b
article info
abstract
Article history:
Proton-conducting perovskite oxides such as doped barium cerate and barium zirconate
Received 29 June 2018
are promising electrolytes for solid oxide fuel cells (SOFCs). Multiple-doped barium cerate
Received in revised form
perovskite oxide proton conductors of BaCe0$7Zr0$1Y0.2-xNdxO3d (0 x 0.1) are prepared
21 August 2018
by solid state reaction and the properties of the fabricated material are characterized by
Accepted 29 August 2018
various technologies. Nd doping improves the sinterability and Zr doping enhances the
Available online xxx
chemical stability in CO2 atmosphere. The electrical conductivity order of the as-prepared electrolytes at elevated temperature in hydrogen atmosphere is: BaCe0$7Y0$17Zr0.1
Keywords:
Nd0.03O3d > BaCe0$7Y0$2Zr0$1O3d > BaCe0$7Y0$1Zr0.1Nd0.1O3d. Ethane is selectively dehy-
Solid oxide fuel cell
drogenated to ethylene with cogeneration of electrical power in the SOFC operated at 650
Doped barium cerate
e700 C. The maximum power density of the SOFC is 123 mW cm2 for ethane fuel and
Proton conducting electrolyte
138 mW cm2 for hydrogen fuel at the 700 C. These unique features make the multiple-
Membrane reactor
doped barium cerate perovskite oxide a promising electrolyte for chemical-energy cogen-
Conversion of ethane to ethylene
eration in SOFCs.
© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Nowadays, human society is encountering severe environmental and energy crisis due to the excessive consumption of fossil fuels. Hydrogen is regarded as the most ideal fuel due to its high energy conversion efficiency and clean exhaust comprising only water. Unfortunately, hydrogen does not
exist naturally as gas on the earth, and it is manufactured primarily using steam reforming of hydrocarbon fossil resources [1,2]. There is considerable CO2 emission and energy loss during the steam reforming manufacture process [3,4]. Solid oxide fuel cells (SOFCs) are considered as one of the cleanest technologies that can directly convert chemical energy to electrical energy with higher energy conversion efficiency and lower environment [5,6]. However, conventional
* Corresponding author. ** Corresponding author. College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China E-mail addresses: [email protected] (X.-Z. Fu), [email protected] (J.-L. Luo). 1 Lin Shao and Jie-Yuan Lin contributed equally to this work. https://doi.org/10.1016/j.ijhydene.2018.08.204 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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oxide ionic conducting SOFCs can use directly readily available hydrocarbon fuels, there still emit large amounts of CO2 [7]. Hydrocarbons are also important raw materials for production of petrochemicals. In addition, no value-added chemicals are produced as the hydrocarbon fuels are completely oxidized. Chemicals energy co-generation in SOFCs based on proton conducting electrolytes have been developed to utilize hydrocarbon fossil resources in more efficient and environmentally friendly processes [8e11]. “Hydrogen energy” in the hydrocarbons can be directly utilized to produce electrical energy without CO2 emission since the proton conducting ceramic electrolyte membrane insulates oxygen to hydrocarbons and only protons dehydrogenated from hydrocarbons in the anode migrate through solid electrolyte to react with oxygen in the cathode to form very clean exhaust of water [12]. For example, ethane is dehydrogenated to cogenerate valueadded ethylene with high selectivity and electrical power simultaneously in proton conducting SOFC membrane reactors, while producing almost zero CO2 emissions [13e15]. Proton conducting oxides have potentially higher ionic conductivity at intermediate or low temperatures relative to oxide ion conducting electrolytes since protons have lower activity energy of transportation than oxide ions [5,16e18]. Ydoped BaCeO3d perovskite exhibits high proton conductivity among conductive oxides [19]. However, Y-doped BaCeO3d is unstable in CO2 containing atmospheres, thus limiting its practical applications as electrolyte material in SOFCs [20,21]. While Zr doping may improve the stability of Y-doped barium cerate in CO2 atmospheres, there is a concomitant decrease in conductivity with the level of doping [22,23]; the level of doping in BaCe0$7Y0$2Zr0$1O3d provides good balance of chemical stability and conductivity among the BaeCeeZreY perovskite oxide family [24]. Small cations (Sc and In) led to the formation of relatively large and uniform average grains size; these cerate showed moderate proton conductivity [25,26]. In contrast, doping with larger cations (Y, Yb, Tu, Ni) led to the formation of grains with nonuniform and overall smaller average grain sizes showing comparatively higher protonic conductivity [27e30]. Herein, we report a proton conducting electrolyte, Zr, Y and Nd co-doped barium cerate perovskite oxide with the excellent sinterability, and good chemical stability toward CO2containing atmospheres at high temperature. And its utility in a hydrocarbon SOFC membrane reactor for conversion of ethane selectively to ethylene and power are evaluated.
reaction of mixtures. After a single perovskite phase was obtained, the powders were ball-milled again for 24 h, pressed at 5 ton to form discs, and sintered at 1500 C in air for 10 h. Then the sintered electrolyte pellets were polish to about 1.5 mm thickness. Gold paste was screen printed onto each side of polished pellets, then calcined at 900 C for 30 min to obtain membrane electrode assemblies (MEA) for conductivity measurements. Platinum paste was used to prepare porous electrodes on proton conducting electrolyte membranes to prepare MEA for SOFC membrane reactor performance tests, as Pt is an active catalyst for both conversion of ethane to ethylene and reduction of oxygen at the respective electrodes.
Characterization of multiple-doped barium cerate electrolytes The phase structure of doped barium cerate proton conductor was determined at room temperature using a Rigaku Rotaflex powder X-ray diffractometer (XRD) with Cu Ka radiation. The scanning electron microscope (Hitachi, S-2700) was carried out to characterize the morphology. The proton conductivity of doped barium cerate proton conductor was measured in humid 5% hydrogen (balanced Ar) atmosphere. The chemical stability of the electrolytes was evaluated using a TA SDT Q600 thermal gravity analysis (TGA) in CO2 atmosphere in the range of 30e1200 C with a heating rate of 10 C$min1.
Fabrication and testing of hydrocarbon fuel cell membrane reactors SOFC membrane reactor was fabricated by placing the Pt/ electrolyte/Pt MEA between concentric pairs of alumina tubes in a vertical Thermolyne F79300 tubular furnace. After the SOFC membrane reactor reached the prescribed operating temperature, 150 mL min1 pure dry ethane (99.9%) and oxygen (99.9%) were supplied as anode and cathode feed gas, respectively. The schematic of proton conducting SOFC membrane reactors was showed in Fig. 1. The current-voltage performance were carried out using an electrochemical analysis instrumentation (Solartron 1287 and 1255B). The gas chromatograph (Agilent, HP5890) was analyzed the effluent from the anode chamber. The ethane conversion and ethylene selectivity were calculated according to the previously reported method [9].
Experimental Preparation of multiple-doped barium cerate electrolytes
Results and discussion
Multiple-doped barium cerate proton conductors of BaCe0$7Y0$2Zr0$1O3d, BaCe0$7Y0.17Zr0.1Nd0.03O3d, BaCe0$7Y0$15 Zr0.1Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d powders were prepared using a solid state reaction method. Starting materials BaCO3, CeO2, ZrO2, Y2O3, and Nd2O3 were ball-milled in stoichiometric ratio for 24 h. The pressed mixtures of precursor for BaCe0$7Y0.2-xZr0.1NdxO3d then were calcined at temperatures in the range of 1100e1400 C in air for 10 h to determine the optimum perovskite phase formation temperature. Then the temperature was used for the solid state
Preparation of multiple-doped barium cerate electrolytes Solid state reaction reactions provide straightforward, proven means to prepare perovskite oxides. To determine the temperature required for formation of the perovskite phase of the doped barium cerate, separate pressed stoichiometric mixtures of BaCO3, CeO2, ZrO2, Y2O3, and Nd2O3 each were heated at 1100 C, 1200 C, 1300 C and 1400 C for 10 h in air. XRD patterns in Fig. 2 showed that the main phase is perovskite when sam ples were sintered at 1100 C or 1200 C, however these XRD
Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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Fig. 1 e Schematic of proton conducting SOFC membrane reactors for co-generation of ethylene and power from ethane.
Fig. 2 e XRD patterns for BaCe0.7Zr0.1Y0.15Nd0.05O3¡d precursor mixtures calcined at different temperatures for 10 h in air.
patterns also showed small diffraction peaks for ZrO2. When the sintered temperature was 1300 C or 1400 C, the XRD showed only perovskite phase diffraction peaks. Thus, it was necessary to heat samples at least 1300 C in air to convert the mixtures of BaCO3, CeO2, ZrO2, Y2O3, and Nd2O3 precursors to pure Nd, Zr, Y doped barium cerate perovskite oxide.
Properties of multiple-doped barium cerate electrolytes Barium cerate based conductors are hard to sinter, which is an obstacle to their application. We used SEM to evaluate the
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sinterability of electrolyte membranes. Fig. 3 showed surface SEM images of BaCe0$7Y0$2Zr0$1O3d, BaCe0$7Y0$17Zr0.1Nd0.03 O3d, BaCe0$7Y0$15Zr0.1Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d discs after sintering at 1500 C for 10 h in air. There were a few holes on the surface of the BaCe0$7Y0$2Zr0$1O3d discs without Nd doping, resulting from incomplete sintering of BaCe0$7Y0$2Zr0$1O3d powders. While there were no holes on the surface of BaCe0$7Y0$17Zr0.1Nd0.03O3d, BaCe0$7Y0.15Zr0.1 Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d membranes, which were very dense membrane. Furthermore, the grain sizes of BaCe0$7Y0$17Zr0.1Nd0.03O3d, BaCe0$7Y0$15Zr0.1Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d were much larger than that of BaCe0$7Y0$2Zr0$1O3d. The relative density of the sintered samples is shown in Fig. 4, suggesting that the relative density of BaCe0$7Zr0$1Y0.2-xNdxO3d (0 x 0.1) sintered membranes increased from 95.2% to 99.3% as the Nd doped amount of X increased from 0 to 0.1. It is consistent with the SEM results, which also indicating that Nd doping improved the sinterability of doped barium cerate perovskite oxide. All the conductivities increased with temperature for the BaCe0$7Y0$2Zr0$1O3d, BaCe0$7Y0$17Zr0.1Nd0.03O3d, BaCe0$7Y0$15 Zr0.1Nd0.05O3d, and BaCe0$7Y0$1Zr0.1Nd0.1O3d electrolyte membranes in 2.7% H2O humidified hydrogen atmosphere (Fig. 5). At the same test temperature, the conductivity of BaCe0$7Y0$17Zr0.1Nd0.03O3d was slightly higher than that of BaCe0$7Y0$2Zr0$1O3d, but the conductivity decreased as the Nd doping amount increased for the other Nd doped samples whose conductivity was lower than that of BaCe0$7 Y0$2Zr0$1O3d. The enhancement of conductivity by a small amount of Nd doping might be resulted from the enhancement of sinterability of barium cerate ceramic membrane. For the same electrolyte materials, better sintering density results higher electrical conductivity [31]. The lowering of conductivity by higher Nd doping which substituted Y than 0.05 might be due to the fact that the Nd-doped barium cerate has lower conductivity than Y-doped barium cerate [32]. Fig. 5 also shows that the electrical conductivity of BaCe0$7Zr0. lNd0.2O3d was lower than that of BaCe0$7Zr0. lY0.2O3d. Fig. 6 compares TGA curves for BaCe0$85Y0$15O3d (BCY) and multiple-doped barium cerate in the about 2% CO2 balance with He flow. When the temperature was above 500 C there was large weight uptake to a maximum of 10.1% for BaCe0$85Y0$15O3d due to formation of BaCO3. In contrast, there was negligible weight uptake when BaCe0$7Y0$17Zr0.1Nd0.03 O3d and BaCe0$7Y0$15Zr0.1Nd0.05O3d was heated in CO2, resulting from that Zr doping improved the chemical stability of barium cerate at high temperature. There is report that only 10% Zr doped barium cerate is unstable in 100% CO2 atmosphere [33]. However, the concentration of CO2 is very low as trace of amount in the hydrocarbon proton conducting SOFC membrane reactors0 condition [10]. Thus the BaCe0$7Zr0$1Y0.2-x NdxO3d proton conductors have enough chemical stability for application in the hydrocarbon SOFC membrane reactors.
Performance of the hydrocarbon fuel cell membrane reactor A hydrocarbon fuel cell membrane reactor was assembled using BaCe0$7Y0$17Zr0.1Nd0.03O3d proton conducting electrolyte membrane and Pt electrodes since BaCe0$7Y0$15Zr0.1 Nd0.05O3d displayed the highest conductivity among the as-
Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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Fig. 3 e Surface SEM images of discs sintered at 1500 C for 10 h in air: (a) BaCe0.7Zr0.1Y0.2O3¡d, (b) BaCe0.7Zr0.1Y0.17Nd0.03O3¡d, (c) BaCe0.7Zr0.1Y0.15Nd0.05O3¡d, and (d) BaCe0.7Zr0.1Y0.1Nd0.1O3¡d.
Fig. 4 e Relative density of BaCe0.7Zr0.1Y0.2-xNdxO3¡d discs after sintering at 1500 C for 10 h in air.
prepared proton conductors. A cross-sectional SEM image (Fig. 7a) showed that BaCe0$7Y0$17Zr0.1Nd0.03O3d electrolyte was very dense similar to the surface shown in Fig. 2. The Pt anode adhered very well to the electrolyte throughout fuel cell reactor tests (Fig. 7a). The surface SEM of Pt electrode (Fig. 7b) demonstrated that it was very porous which enabled good mass transport and an extensive reactive area. Ethane conversion increased from 3% to 23% while the ethylene selectivity decreased from 99.5% to 91% in the fuel cell reactor as the operating temperature increased from 600 C to 700 C (Fig. 8). The fueled anode gas was dry pure
Fig. 5 e Conductivity of BaCe0.7Zr0.1Y0.2-xNdxO3¡d in humid (2.7% H2O) hydrogen atmosphere: (a) x ¼ 0.03, (b) x ¼ 0, (c) x ¼ 0.05, and (d) x ¼ 0.1.
ethane with 150 mL min1. The ethane conversion decreased comparing to that in the fuel cell membrane reactor with the ethane flow rate of 100 mL min1 [9]. It might be attributed to the lower contact time of ethane in the fuel cell anode with higher flow rate. Dehydrogenation of ethane to ethylene was the major reaction over Pt porous catalyst in the anode chamber. BaCe0.7Y0.17Zr0.1Nd0.03O3d electrolyte predominantly is a proton conductor which separates anode feed and products from cathode feed. Thus, there should be essentially no oxide ion transport from cathode to anode, in contrast to
Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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Fig. 6 e Chemical stability of sintered (a) BaCe0.85Y0.15O3¡d, (b) BaCe0.7Zr0.1Y0.2O3¡d, (c) BaCe0.7Zr0.1Y0.17Nd0.03O3¡d, (d) BaCe0.7Zr0.1Y0.15Nd0.05O3¡d determined using TGA in dilute CO2 atmosphere. conventional oxide ion conducting SOFCs. Thus, the protonic SOFC avoided deep oxidization of ethane or ethylene to CO2 and ensured high ethylene selectivity. Water was the only exhaust product at the cathode, formation of which provided the thermodynamic driving force for the electrochemical
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oxidative dehydrogenation; as the anode and cathode reactions were separated, there was no equilibrium limitation of the dehydrogenation reaction. Nevertheless, trace amounts of carbon oxides were detected in the anode effluent when the SOFC membrane reactor operated at higher temperature which was possibly attributed to reaction with the very small oxide ion transport number in doped barium cerate electrolyte at higher temperature or, less probably, diffusion of oxygen through the sealant [9,34]. Although the dehydrogenation of ethane rate increased with temperature, formation of methane by-product increased more quickly. Methane formation was attributable to thermal cracking of the carbonecarbon bond of ethane, in competition with ethane dehydrogenation at higher temperature. Nevertheless, ethylene selectivity was much higher when compared with conventional oxidative dehydrogenation of ethane [35,36]. In addition, there was no detectable amount of acetylene in the anode effluent. Acetylene is usually produced as a by-product during ethylene manufacture using conventional steam cracking processes, and acetylene is a major poison for catalysts used in polymerization of ethylene [37]. Dehydrogenated of ethane to ethylene concurrently generated electrical power, derived from the energy from the partial oxidation reaction of C2H6 to C2H4 and H2O. The maximum power density of the fuel cell membrane reactor at 650 C was 82 mW cm2 (Fig. 9). When the operating
Fig. 7 e SEM images of (a) cross-section of BaCe0.7Zr0.1Y0.17Nd0.03O3¡d proton conducting electrolyte membrane supporting porous Pt anode, and (b) surface of Pt electrode after fuel cell membrane reactor test.
Fig. 8 e (a) Dependence on temperature of ethane conversion and ethylene selectivity in the ethane/oxygen SOFC membrane reactor with BaCe0.7Zr0.1Y0.17Nd0.03O3¡d proton conducting electrolyte; (b) change of ethane conversion and ethylene selectivity at different current densities in proton ceramic fuel cell reactors at 700 C. Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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from 650 C to 700 C compared to the electrochemical oxidation of hydrogen in the proton conducting fuel cells. Although both the ethane and hydrogen fuel cells demonstrated relatively low power density due to the thick electrolyte membrane used herein, the comparable power density at 700 C suggests that the “hydrogen energy” in ethane was efficiently utilized in the proton conducting SOFC membrane reactor at elevated temperature.
Conclusions
Fig. 9 e Current density-voltage and power density curves of the ethane/oxygen SOFC membrane reactor.
Fig. 10 e Current density-voltage and power density curves of the hydrogen/oxygen SOFC.
temperature was increased to 700 C, the maximum power density of the reactor increased to 123 mW cm2. Advantages of this energy production process using hydrocarbon electrochemical oxidative dehydrogenation in a proton conducting SOFC membrane reactor include: (1) chemical energy is converted more efficiently to high grade electricity than processes utilizing heat energy in chemical oxidative dehydrogenation reactions; and (2) as hydrogen atom (proton) is the only content of ethane feed consumed to produce electrical energy there is clean water as the cathode exhaust. Thus “hydrogen energy” in the hydrocarbon fuels is converted directly to electricity with co-production of value-added alkenes from hydrocarbon feed in the proton conducting fuel cell membrane reactor. For comparison, the electrochemical performance of the same proton conducting fuel cell while using hydrogen as fuel is shown in Fig. 10. The maximum power densities were 112 mW cm2 and 138 mW cm2 at 650 C and 700 C, respectively. The open circuit voltage of the hydrogen fuel cell was about 0.15 V higher than that of the ethane fuel cell. The maximum power density of the ethane fuel cell reactor was slightly smaller than that of the hydrogen fuel cell at 700 C while it was significantly lower at 650 C. This effect is attributed to enhanced electrochemical oxidative dehydrogenation of ethane to power as the temperature increased
Pure multiple-doped barium cerate of BaCe0$7Y0.2-xZr0.1NdxO3d perovskite proton conductors were synthesized by solid state reaction at least 1300 C. The BaCe0$7Y0$17Zr0.1Nd0.03O3d electrolyte has a combination of the highest conductivity, excellent sinterability, and good chemical stability toward CO2-containing atmospheres at high temperature. An intermediate temperature SOFC membrane reactor with BaCe0$7Y0$17Zr0.1Nd0.03O3d as proton conducting electrolyte and porous Pt electrodes exhibited excellent performance for conversion of ethane selectively to ethylene with cogeneration of electrical power. When the operating temperature increased from 600 C. to 700 C, ethane conversion increased from 3% to 23% while the ethylene selectivity decreased from 99.5% to 91% in the SOFC membrane reactor. The main by-product is methane and there is no detected acetylene in anode exhaust. The power density of BaCe0$7Y0$17Zr0.1Nd0.03O3d thick membrane electrolyte SOFC membrane reactor fueled by ethane is 123 mW cm2, compared to 138 mW cm2 generated the same SOFC fueled by hydrogen at 700 C. This suggests that barium cerate based proton conductors are not suitable for direct application under most hydrocarbon fuels. This suggests that BaCe0$7Y0$17Zr0.1Nd0.03O3d is an interesting candidate for electrolytes in SOFC membrane reactor for conversion of ethane to ethylene.
Acknowledgements This work was supported by National Natural Science Foundation of China (No.21203236), Natural Sciences and Engineering Research Council of Canada/NOVA Chemicals CRD Grant, Alberta Innovates Energy and Environment Solutions, and Micro Systems Technology Research Institute.
Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.ijhydene.2018.08.204.
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[20] Tao SW, Irvine JTS. A stable, easily sintered protonconducting oxide electrolyte for moderate-temperature fuel cells and electrolyzers. Adv Mater 2006;18:1581e4. [21] Katahira K, Kohchi Y, Shimura T, Iwahara H. Protonic conduction in Zr-substituted BaCeO3. Solid State Ionics 2000;138:91e8. [22] Bae K, Jang DY, Choi HJ, Kim D, Hong J, Kim B-K, et al. Demonstrating the potential of yttrium-doped barium zirconate electrolyte for high-performance fuel cells. Nat Commun 2017;8:14553. [23] Tseng C-J, Chang J-K, Hung IM, Lee K-R, Lee S-W. BaZr0.2Ce0.8-x YxO3d solid oxide fuel cell electrolyte synthesized by solegel combined with composition-exchange method. Int J Hydrogen Energy 2014;39:14434e40. [24] Zuo C, Zha S, Liu M, Hatano M, Uchiyama M. Ba(Zr0.1Ce0.7Y0.2) O3d as an electrolyte for low-temperature solid-oxide fuel cells. Adv Mater 2006;18:3318e20. [25] Ling Y, Chen H, Niu J, Wang F, Zhao L, Ou X, et al. Bismuth and indium co-doping strategy for developing stable and efficient barium zirconate-based proton conductors for highperformance H-SOFCs. J Eur Ceram Soc 2016;36:3423e31. [26] Danilov N, Vdovin G, Reznitskikh O, Medvedev D, Demin A, Tsiakaras P. Physicо-chemical characterization and transport features of proton-conducting Sr-doped LaYO3 electrolyte ceramics. J Eur Ceram Soc 2016;36:2795e800. [27] Zhu Z, Guo E, Wei Z, Wang H. Tailoring Ba3Ca1.18Nb1.82O9d with NiO as electrolyte for proton-conducting solid oxide fuel cells. J Power Sources 2018;373:132e8. [28] Su F, Xia C, Peng R. Novel fluoride-doped barium cerate applied as stable electrolyte in proton conducting solid oxide fuel cells. J Eur Ceram Soc 2015;35:3553e8. [29] Hakim M, Joo JH, Yoo C-Y, Kim B-K, Yu JH. Enhanced chemical stability and sinterability of refined protonconducting perovskite: case study of BaCe0.5Zr0.3Y0.2O3d. J Eur Ceram Soc 2015;35:1855e63. [30] Kim D, Lee D, Joo JH. Effect of Y-doping on the phase relation and electrical properties of Fe-doped BaZrO3. J Eur Ceram Soc 2018;38:535e42. [31] Guan L, Le S, Rooney D, Zhang N, Zhu X, Sun K. Understanding the sintering temperature effect on oxygen ion conductivity in doped ceria electrolytes. Ionics 2016;22:1699e708. [32] Chen F, Wang P, Sorensen OT, Meng G, Peng D. Preparation of Nd-doped BaCeO3 proton-conducting ceramics by homogeneous oxalate coprecipitation. J Mater Chem 1997;7:1533e9. [33] Fabbri E, Bi L, Tanaka H, Pergolesi D, Traversa E. Chemically stable Pr and Y Co-doped barium zirconate electrolytes with high proton conductivity for intermediate-temperature solid oxide fuel cells. Adv Funct Mater 2011;21:158e66. [34] Hibino T, Hashimoto A, Suzuki M, Sano M. A solid oxide fuel cell using Y-doped BaCeO3 with Pd-loaded FeO anode and Ba0.5Pr0.5CoO3 cathode at low temperatures. J Electrochem Soc 2002;149:A1503e8. [35] Bodke AS, Olschki DA, Schmidt LD, Ranzi E. High selectivities to ethylene by partial oxidation of ethane. Science 1999;285:712e5. [36] Flick DW, Huff MC. Oxidative dehydrogenation of ethane over a Pt-coated monolith versus Pt-loaded pellets: surface area and thermal effects. J Catal 1998;178:315e27. [37] Azizi Y, Petit C, Pitchon V. Formation of polymer-grade ethylene by selective hydrogenation of acetylene over Au/ CeO2 catalyst. J Catal 2008;256:338e44.
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Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells Jie-Yuan Lin a,1, Lin Shao a,b,1, Feng-Zhan Si a, Xian-Zhu Fu a,*, Jing-Li Luo a,c,** a
College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China c Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2G6, Canada b
article info
abstract
Article history:
Proton-conducting perovskite oxides such as doped barium cerate and barium zirconate
Received 29 June 2018
are promising electrolytes for solid oxide fuel cells (SOFCs). Multiple-doped barium cerate
Received in revised form
perovskite oxide proton conductors of BaCe0$7Zr0$1Y0.2-xNdxO3d (0 x 0.1) are prepared
21 August 2018
by solid state reaction and the properties of the fabricated material are characterized by
Accepted 29 August 2018
various technologies. Nd doping improves the sinterability and Zr doping enhances the
Available online xxx
chemical stability in CO2 atmosphere. The electrical conductivity order of the as-prepared electrolytes at elevated temperature in hydrogen atmosphere is: BaCe0$7Y0$17Zr0.1
Keywords:
Nd0.03O3d > BaCe0$7Y0$2Zr0$1O3d > BaCe0$7Y0$1Zr0.1Nd0.1O3d. Ethane is selectively dehy-
Solid oxide fuel cell
drogenated to ethylene with cogeneration of electrical power in the SOFC operated at 650
Doped barium cerate
e700 C. The maximum power density of the SOFC is 123 mW cm2 for ethane fuel and
Proton conducting electrolyte
138 mW cm2 for hydrogen fuel at the 700 C. These unique features make the multiple-
Membrane reactor
doped barium cerate perovskite oxide a promising electrolyte for chemical-energy cogen-
Conversion of ethane to ethylene
eration in SOFCs.
© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Nowadays, human society is encountering severe environmental and energy crisis due to the excessive consumption of fossil fuels. Hydrogen is regarded as the most ideal fuel due to its high energy conversion efficiency and clean exhaust comprising only water. Unfortunately, hydrogen does not
exist naturally as gas on the earth, and it is manufactured primarily using steam reforming of hydrocarbon fossil resources [1,2]. There is considerable CO2 emission and energy loss during the steam reforming manufacture process [3,4]. Solid oxide fuel cells (SOFCs) are considered as one of the cleanest technologies that can directly convert chemical energy to electrical energy with higher energy conversion efficiency and lower environment [5,6]. However, conventional
* Corresponding author. ** Corresponding author. College of Materials Science and Engineering, Shenzhen University, Shenzhen 518060, China E-mail addresses: [email protected] (X.-Z. Fu), [email protected] (J.-L. Luo). 1 Lin Shao and Jie-Yuan Lin contributed equally to this work. https://doi.org/10.1016/j.ijhydene.2018.08.204 0360-3199/© 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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oxide ionic conducting SOFCs can use directly readily available hydrocarbon fuels, there still emit large amounts of CO2 [7]. Hydrocarbons are also important raw materials for production of petrochemicals. In addition, no value-added chemicals are produced as the hydrocarbon fuels are completely oxidized. Chemicals energy co-generation in SOFCs based on proton conducting electrolytes have been developed to utilize hydrocarbon fossil resources in more efficient and environmentally friendly processes [8e11]. “Hydrogen energy” in the hydrocarbons can be directly utilized to produce electrical energy without CO2 emission since the proton conducting ceramic electrolyte membrane insulates oxygen to hydrocarbons and only protons dehydrogenated from hydrocarbons in the anode migrate through solid electrolyte to react with oxygen in the cathode to form very clean exhaust of water [12]. For example, ethane is dehydrogenated to cogenerate valueadded ethylene with high selectivity and electrical power simultaneously in proton conducting SOFC membrane reactors, while producing almost zero CO2 emissions [13e15]. Proton conducting oxides have potentially higher ionic conductivity at intermediate or low temperatures relative to oxide ion conducting electrolytes since protons have lower activity energy of transportation than oxide ions [5,16e18]. Ydoped BaCeO3d perovskite exhibits high proton conductivity among conductive oxides [19]. However, Y-doped BaCeO3d is unstable in CO2 containing atmospheres, thus limiting its practical applications as electrolyte material in SOFCs [20,21]. While Zr doping may improve the stability of Y-doped barium cerate in CO2 atmospheres, there is a concomitant decrease in conductivity with the level of doping [22,23]; the level of doping in BaCe0$7Y0$2Zr0$1O3d provides good balance of chemical stability and conductivity among the BaeCeeZreY perovskite oxide family [24]. Small cations (Sc and In) led to the formation of relatively large and uniform average grains size; these cerate showed moderate proton conductivity [25,26]. In contrast, doping with larger cations (Y, Yb, Tu, Ni) led to the formation of grains with nonuniform and overall smaller average grain sizes showing comparatively higher protonic conductivity [27e30]. Herein, we report a proton conducting electrolyte, Zr, Y and Nd co-doped barium cerate perovskite oxide with the excellent sinterability, and good chemical stability toward CO2containing atmospheres at high temperature. And its utility in a hydrocarbon SOFC membrane reactor for conversion of ethane selectively to ethylene and power are evaluated.
reaction of mixtures. After a single perovskite phase was obtained, the powders were ball-milled again for 24 h, pressed at 5 ton to form discs, and sintered at 1500 C in air for 10 h. Then the sintered electrolyte pellets were polish to about 1.5 mm thickness. Gold paste was screen printed onto each side of polished pellets, then calcined at 900 C for 30 min to obtain membrane electrode assemblies (MEA) for conductivity measurements. Platinum paste was used to prepare porous electrodes on proton conducting electrolyte membranes to prepare MEA for SOFC membrane reactor performance tests, as Pt is an active catalyst for both conversion of ethane to ethylene and reduction of oxygen at the respective electrodes.
Characterization of multiple-doped barium cerate electrolytes The phase structure of doped barium cerate proton conductor was determined at room temperature using a Rigaku Rotaflex powder X-ray diffractometer (XRD) with Cu Ka radiation. The scanning electron microscope (Hitachi, S-2700) was carried out to characterize the morphology. The proton conductivity of doped barium cerate proton conductor was measured in humid 5% hydrogen (balanced Ar) atmosphere. The chemical stability of the electrolytes was evaluated using a TA SDT Q600 thermal gravity analysis (TGA) in CO2 atmosphere in the range of 30e1200 C with a heating rate of 10 C$min1.
Fabrication and testing of hydrocarbon fuel cell membrane reactors SOFC membrane reactor was fabricated by placing the Pt/ electrolyte/Pt MEA between concentric pairs of alumina tubes in a vertical Thermolyne F79300 tubular furnace. After the SOFC membrane reactor reached the prescribed operating temperature, 150 mL min1 pure dry ethane (99.9%) and oxygen (99.9%) were supplied as anode and cathode feed gas, respectively. The schematic of proton conducting SOFC membrane reactors was showed in Fig. 1. The current-voltage performance were carried out using an electrochemical analysis instrumentation (Solartron 1287 and 1255B). The gas chromatograph (Agilent, HP5890) was analyzed the effluent from the anode chamber. The ethane conversion and ethylene selectivity were calculated according to the previously reported method [9].
Experimental Preparation of multiple-doped barium cerate electrolytes
Results and discussion
Multiple-doped barium cerate proton conductors of BaCe0$7Y0$2Zr0$1O3d, BaCe0$7Y0.17Zr0.1Nd0.03O3d, BaCe0$7Y0$15 Zr0.1Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d powders were prepared using a solid state reaction method. Starting materials BaCO3, CeO2, ZrO2, Y2O3, and Nd2O3 were ball-milled in stoichiometric ratio for 24 h. The pressed mixtures of precursor for BaCe0$7Y0.2-xZr0.1NdxO3d then were calcined at temperatures in the range of 1100e1400 C in air for 10 h to determine the optimum perovskite phase formation temperature. Then the temperature was used for the solid state
Preparation of multiple-doped barium cerate electrolytes Solid state reaction reactions provide straightforward, proven means to prepare perovskite oxides. To determine the temperature required for formation of the perovskite phase of the doped barium cerate, separate pressed stoichiometric mixtures of BaCO3, CeO2, ZrO2, Y2O3, and Nd2O3 each were heated at 1100 C, 1200 C, 1300 C and 1400 C for 10 h in air. XRD patterns in Fig. 2 showed that the main phase is perovskite when sam ples were sintered at 1100 C or 1200 C, however these XRD
Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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Fig. 1 e Schematic of proton conducting SOFC membrane reactors for co-generation of ethylene and power from ethane.
Fig. 2 e XRD patterns for BaCe0.7Zr0.1Y0.15Nd0.05O3¡d precursor mixtures calcined at different temperatures for 10 h in air.
patterns also showed small diffraction peaks for ZrO2. When the sintered temperature was 1300 C or 1400 C, the XRD showed only perovskite phase diffraction peaks. Thus, it was necessary to heat samples at least 1300 C in air to convert the mixtures of BaCO3, CeO2, ZrO2, Y2O3, and Nd2O3 precursors to pure Nd, Zr, Y doped barium cerate perovskite oxide.
Properties of multiple-doped barium cerate electrolytes Barium cerate based conductors are hard to sinter, which is an obstacle to their application. We used SEM to evaluate the
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sinterability of electrolyte membranes. Fig. 3 showed surface SEM images of BaCe0$7Y0$2Zr0$1O3d, BaCe0$7Y0$17Zr0.1Nd0.03 O3d, BaCe0$7Y0$15Zr0.1Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d discs after sintering at 1500 C for 10 h in air. There were a few holes on the surface of the BaCe0$7Y0$2Zr0$1O3d discs without Nd doping, resulting from incomplete sintering of BaCe0$7Y0$2Zr0$1O3d powders. While there were no holes on the surface of BaCe0$7Y0$17Zr0.1Nd0.03O3d, BaCe0$7Y0.15Zr0.1 Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d membranes, which were very dense membrane. Furthermore, the grain sizes of BaCe0$7Y0$17Zr0.1Nd0.03O3d, BaCe0$7Y0$15Zr0.1Nd0.05O3d and BaCe0$7Y0$1Zr0.1Nd0.1O3d were much larger than that of BaCe0$7Y0$2Zr0$1O3d. The relative density of the sintered samples is shown in Fig. 4, suggesting that the relative density of BaCe0$7Zr0$1Y0.2-xNdxO3d (0 x 0.1) sintered membranes increased from 95.2% to 99.3% as the Nd doped amount of X increased from 0 to 0.1. It is consistent with the SEM results, which also indicating that Nd doping improved the sinterability of doped barium cerate perovskite oxide. All the conductivities increased with temperature for the BaCe0$7Y0$2Zr0$1O3d, BaCe0$7Y0$17Zr0.1Nd0.03O3d, BaCe0$7Y0$15 Zr0.1Nd0.05O3d, and BaCe0$7Y0$1Zr0.1Nd0.1O3d electrolyte membranes in 2.7% H2O humidified hydrogen atmosphere (Fig. 5). At the same test temperature, the conductivity of BaCe0$7Y0$17Zr0.1Nd0.03O3d was slightly higher than that of BaCe0$7Y0$2Zr0$1O3d, but the conductivity decreased as the Nd doping amount increased for the other Nd doped samples whose conductivity was lower than that of BaCe0$7 Y0$2Zr0$1O3d. The enhancement of conductivity by a small amount of Nd doping might be resulted from the enhancement of sinterability of barium cerate ceramic membrane. For the same electrolyte materials, better sintering density results higher electrical conductivity [31]. The lowering of conductivity by higher Nd doping which substituted Y than 0.05 might be due to the fact that the Nd-doped barium cerate has lower conductivity than Y-doped barium cerate [32]. Fig. 5 also shows that the electrical conductivity of BaCe0$7Zr0. lNd0.2O3d was lower than that of BaCe0$7Zr0. lY0.2O3d. Fig. 6 compares TGA curves for BaCe0$85Y0$15O3d (BCY) and multiple-doped barium cerate in the about 2% CO2 balance with He flow. When the temperature was above 500 C there was large weight uptake to a maximum of 10.1% for BaCe0$85Y0$15O3d due to formation of BaCO3. In contrast, there was negligible weight uptake when BaCe0$7Y0$17Zr0.1Nd0.03 O3d and BaCe0$7Y0$15Zr0.1Nd0.05O3d was heated in CO2, resulting from that Zr doping improved the chemical stability of barium cerate at high temperature. There is report that only 10% Zr doped barium cerate is unstable in 100% CO2 atmosphere [33]. However, the concentration of CO2 is very low as trace of amount in the hydrocarbon proton conducting SOFC membrane reactors0 condition [10]. Thus the BaCe0$7Zr0$1Y0.2-x NdxO3d proton conductors have enough chemical stability for application in the hydrocarbon SOFC membrane reactors.
Performance of the hydrocarbon fuel cell membrane reactor A hydrocarbon fuel cell membrane reactor was assembled using BaCe0$7Y0$17Zr0.1Nd0.03O3d proton conducting electrolyte membrane and Pt electrodes since BaCe0$7Y0$15Zr0.1 Nd0.05O3d displayed the highest conductivity among the as-
Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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Fig. 3 e Surface SEM images of discs sintered at 1500 C for 10 h in air: (a) BaCe0.7Zr0.1Y0.2O3¡d, (b) BaCe0.7Zr0.1Y0.17Nd0.03O3¡d, (c) BaCe0.7Zr0.1Y0.15Nd0.05O3¡d, and (d) BaCe0.7Zr0.1Y0.1Nd0.1O3¡d.
Fig. 4 e Relative density of BaCe0.7Zr0.1Y0.2-xNdxO3¡d discs after sintering at 1500 C for 10 h in air.
prepared proton conductors. A cross-sectional SEM image (Fig. 7a) showed that BaCe0$7Y0$17Zr0.1Nd0.03O3d electrolyte was very dense similar to the surface shown in Fig. 2. The Pt anode adhered very well to the electrolyte throughout fuel cell reactor tests (Fig. 7a). The surface SEM of Pt electrode (Fig. 7b) demonstrated that it was very porous which enabled good mass transport and an extensive reactive area. Ethane conversion increased from 3% to 23% while the ethylene selectivity decreased from 99.5% to 91% in the fuel cell reactor as the operating temperature increased from 600 C to 700 C (Fig. 8). The fueled anode gas was dry pure
Fig. 5 e Conductivity of BaCe0.7Zr0.1Y0.2-xNdxO3¡d in humid (2.7% H2O) hydrogen atmosphere: (a) x ¼ 0.03, (b) x ¼ 0, (c) x ¼ 0.05, and (d) x ¼ 0.1.
ethane with 150 mL min1. The ethane conversion decreased comparing to that in the fuel cell membrane reactor with the ethane flow rate of 100 mL min1 [9]. It might be attributed to the lower contact time of ethane in the fuel cell anode with higher flow rate. Dehydrogenation of ethane to ethylene was the major reaction over Pt porous catalyst in the anode chamber. BaCe0.7Y0.17Zr0.1Nd0.03O3d electrolyte predominantly is a proton conductor which separates anode feed and products from cathode feed. Thus, there should be essentially no oxide ion transport from cathode to anode, in contrast to
Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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Fig. 6 e Chemical stability of sintered (a) BaCe0.85Y0.15O3¡d, (b) BaCe0.7Zr0.1Y0.2O3¡d, (c) BaCe0.7Zr0.1Y0.17Nd0.03O3¡d, (d) BaCe0.7Zr0.1Y0.15Nd0.05O3¡d determined using TGA in dilute CO2 atmosphere. conventional oxide ion conducting SOFCs. Thus, the protonic SOFC avoided deep oxidization of ethane or ethylene to CO2 and ensured high ethylene selectivity. Water was the only exhaust product at the cathode, formation of which provided the thermodynamic driving force for the electrochemical
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oxidative dehydrogenation; as the anode and cathode reactions were separated, there was no equilibrium limitation of the dehydrogenation reaction. Nevertheless, trace amounts of carbon oxides were detected in the anode effluent when the SOFC membrane reactor operated at higher temperature which was possibly attributed to reaction with the very small oxide ion transport number in doped barium cerate electrolyte at higher temperature or, less probably, diffusion of oxygen through the sealant [9,34]. Although the dehydrogenation of ethane rate increased with temperature, formation of methane by-product increased more quickly. Methane formation was attributable to thermal cracking of the carbonecarbon bond of ethane, in competition with ethane dehydrogenation at higher temperature. Nevertheless, ethylene selectivity was much higher when compared with conventional oxidative dehydrogenation of ethane [35,36]. In addition, there was no detectable amount of acetylene in the anode effluent. Acetylene is usually produced as a by-product during ethylene manufacture using conventional steam cracking processes, and acetylene is a major poison for catalysts used in polymerization of ethylene [37]. Dehydrogenated of ethane to ethylene concurrently generated electrical power, derived from the energy from the partial oxidation reaction of C2H6 to C2H4 and H2O. The maximum power density of the fuel cell membrane reactor at 650 C was 82 mW cm2 (Fig. 9). When the operating
Fig. 7 e SEM images of (a) cross-section of BaCe0.7Zr0.1Y0.17Nd0.03O3¡d proton conducting electrolyte membrane supporting porous Pt anode, and (b) surface of Pt electrode after fuel cell membrane reactor test.
Fig. 8 e (a) Dependence on temperature of ethane conversion and ethylene selectivity in the ethane/oxygen SOFC membrane reactor with BaCe0.7Zr0.1Y0.17Nd0.03O3¡d proton conducting electrolyte; (b) change of ethane conversion and ethylene selectivity at different current densities in proton ceramic fuel cell reactors at 700 C. Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204
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from 650 C to 700 C compared to the electrochemical oxidation of hydrogen in the proton conducting fuel cells. Although both the ethane and hydrogen fuel cells demonstrated relatively low power density due to the thick electrolyte membrane used herein, the comparable power density at 700 C suggests that the “hydrogen energy” in ethane was efficiently utilized in the proton conducting SOFC membrane reactor at elevated temperature.
Conclusions
Fig. 9 e Current density-voltage and power density curves of the ethane/oxygen SOFC membrane reactor.
Fig. 10 e Current density-voltage and power density curves of the hydrogen/oxygen SOFC.
temperature was increased to 700 C, the maximum power density of the reactor increased to 123 mW cm2. Advantages of this energy production process using hydrocarbon electrochemical oxidative dehydrogenation in a proton conducting SOFC membrane reactor include: (1) chemical energy is converted more efficiently to high grade electricity than processes utilizing heat energy in chemical oxidative dehydrogenation reactions; and (2) as hydrogen atom (proton) is the only content of ethane feed consumed to produce electrical energy there is clean water as the cathode exhaust. Thus “hydrogen energy” in the hydrocarbon fuels is converted directly to electricity with co-production of value-added alkenes from hydrocarbon feed in the proton conducting fuel cell membrane reactor. For comparison, the electrochemical performance of the same proton conducting fuel cell while using hydrogen as fuel is shown in Fig. 10. The maximum power densities were 112 mW cm2 and 138 mW cm2 at 650 C and 700 C, respectively. The open circuit voltage of the hydrogen fuel cell was about 0.15 V higher than that of the ethane fuel cell. The maximum power density of the ethane fuel cell reactor was slightly smaller than that of the hydrogen fuel cell at 700 C while it was significantly lower at 650 C. This effect is attributed to enhanced electrochemical oxidative dehydrogenation of ethane to power as the temperature increased
Pure multiple-doped barium cerate of BaCe0$7Y0.2-xZr0.1NdxO3d perovskite proton conductors were synthesized by solid state reaction at least 1300 C. The BaCe0$7Y0$17Zr0.1Nd0.03O3d electrolyte has a combination of the highest conductivity, excellent sinterability, and good chemical stability toward CO2-containing atmospheres at high temperature. An intermediate temperature SOFC membrane reactor with BaCe0$7Y0$17Zr0.1Nd0.03O3d as proton conducting electrolyte and porous Pt electrodes exhibited excellent performance for conversion of ethane selectively to ethylene with cogeneration of electrical power. When the operating temperature increased from 600 C. to 700 C, ethane conversion increased from 3% to 23% while the ethylene selectivity decreased from 99.5% to 91% in the SOFC membrane reactor. The main by-product is methane and there is no detected acetylene in anode exhaust. The power density of BaCe0$7Y0$17Zr0.1Nd0.03O3d thick membrane electrolyte SOFC membrane reactor fueled by ethane is 123 mW cm2, compared to 138 mW cm2 generated the same SOFC fueled by hydrogen at 700 C. This suggests that barium cerate based proton conductors are not suitable for direct application under most hydrocarbon fuels. This suggests that BaCe0$7Y0$17Zr0.1Nd0.03O3d is an interesting candidate for electrolytes in SOFC membrane reactor for conversion of ethane to ethylene.
Acknowledgements This work was supported by National Natural Science Foundation of China (No.21203236), Natural Sciences and Engineering Research Council of Canada/NOVA Chemicals CRD Grant, Alberta Innovates Energy and Environment Solutions, and Micro Systems Technology Research Institute.
Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.ijhydene.2018.08.204.
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Please cite this article in press as: Lin J-Y, et al., Multiple-doped barium cerate proton-conducting electrolytes for chemical-energy cogeneration in solid oxide fuel cells, International Journal of Hydrogen Energy (2018), https://doi.org/10.1016/j.ijhydene.2018.08.204