- Email: [email protected]
Highly efficient composite electrolyte for natural gas fed fuel cell
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Highly efficient composite electrolyte for natural gas fed fuel cell Akhlaq Ahmed a, Rizwan Raza a,b,*, Muhammad Saeed Khalid c, Muhammad Saleem a, Farah Alvi a, Muhammad Sufyan Javed a,d, Tauqir A. Sherazi e, Majid Niaz Akhtar a, Nadeem Akram a, Muhammad Ashfaq Ahmad a, Asia Rafique a, Javed Iqbal f, Amjad Ali a, M. Kaleem Ullah a, S. Khalid Imran b, Imran Shakir g, M. Ajmal Khan a, Bin Zhu b,h,** a Department of Physics, COMSATS Institute of Information Technology, Defence Road, off Raiwind Road, Lahore, 54000, Pakistan b Department of Energy Technology, Royal Institute of Technology, KTH, Stockholm, 10044, Sweden c National University of Sciences & Technology (NUST), Islamabad, Pakistan d Department of Applied Physics, Chongqing University, Chongqing 400044, PR China e Department of Chemistry, COMSATS Institute of Information Technology, Abbotabad 22060, Pakistan f Department of Chemical Engineering, COMSATS Institute of Information Technology, Defence Road, off Raiwind Road, Lahore 54000, Pakistan g Deanship of Scientific Research, College of Engineering, King Saud University, P. O. Box 800, Riyadh 11421, Saudi Arabia h Hubei Collaborative Innovation Center for Advanced Materials, Faculty of Physics and Electronic Science, Hubei University, Wuhan, Hubei, 430062, PR China
article info
abstract
Article history:
Solid oxide fuel cells (SOFCs) have the ability to operate with different variants of hydro
Received 30 April 2015
carbon fuel such as biogas, natural gas, methane, ethane, syngas, methanol, ethanol,
Received in revised form
hydrogen and any other hydrogen rich gas. Utilization of these fuels in SOFC, especially the
10 January 2016
natural gas, would significantly reduce operating cost and would enhance the viability for
Accepted 22 February 2016
commercialization of FC technology. In this paper, the performance of two indigenously
Available online xxx
manufactured nanocomposite electrolytes; barium and samarium doped ceria (BSDCcarbonate); and lanthanum and samarium doped ceria (co-precipitation method LSDC-
Keywords:
carbonate) using natural gas as fuel is discussed. The nanocomposite electrolytes were
LT-SOFCs
synthesized using co-precipitation and wet chemical methods (here after referred to as
Proton conductor
nano electrolytes). The structure and morphology of the nano electrolytes were examined
High conductivity
by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fuel cell perfor-
Fuel cell performance
mance (OCV) was tested at temperature (300e600 C). The ionic conductivity of the nano electrolytes were measured by two probe DC method. The detailed composition analysis of nano electrolytes was performed with the help of Raman Spectroscopy. Electrochemical study has shown an ionic conductivity of 0.16 Scm1 at 600 C for BSDC-carbonate in hydrogen atmosphere, which is higher than conventional electrolytes SDC and GDC under
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (R. Raza), [email protected] (B. Zhu). http://dx.doi.org/10.1016/j.ijhydene.2016.02.095 0360-3199/Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
2
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
same conditions. In this article reasonably good ionic conductivity of BSDC-carbonate, at 600 C, has also been achieved in air atmosphere which is comparatively greater than the conventional SDC and GDC electrolytes. Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Solid oxide fuel cells (SOFC) have found great interest since last two decades due to their ability to provide high efficiency, tolerance towards the fuels and being environmental friendly. However many complications still exist which need to be addressed, before making SOFC economically inexpensive in the market [1,2]. Major hurdles are expensive electrolyte/ electrode materials, high working temperatures, and expensive hydrogen fuel. Many research groups are working to make efficient electrolytes and electrodes but preparing a cheap electrolyte is still a big challenge to commercialize SOFC [1]. Another challenge is to operate SOFC on hydrocarbon fuels instead of pure hydrogen. Hydrogen gas as a fuel has some major issues related to cost, difficulty in handling, transportation and other technological technology aspects [3]. Since 1988 more than 86% of hydrogen is produced from fossil fuels which include 30% from refinery, 48% from natural gas, and 18% from coal; and remaining from electrolysis of water [2,3]. Instead of producing pure hydrogen form hydrocarbon fuels for SOFC which is not cost effective, the direct use of these hydrocarbons as fuel especially natural gas (95% methane) needs to be explored. SOFC offers the possibility to be used with wide range of fuels like hydrogen, coal gas, natural gas, methanol and diesel etc. [5,7,8]. Among different types of fuel cells, SOFC is a solid state fuel cell based on a solid oxide electrolyte which possess the maximum electrical efficiency (45e60%) and with cogeneration with other technologies its efficiency increases (60e80%) with minimum emissions [6]. SOFCs offer extensive potential for power and heat generation called CHP (combined heat and power). SOFCs normally operate between the temperature range of 300e600 C are called low temperature SOFC (LTSOFC). The electrolyte is the most important part of SOFC [9]. For SOFC, yttrium stabilized zirconia (YSZ), gadolinium doped ceria (GDC), samarium doped ceria (SDC) and calcium doped ceria (CDC) are commonly used materials for electrolytes [10,11]. Since high temperature SOFCs operate above 800 C, which is responsible for efficient material degradation, technological complications and high cost of ceramic materials etc. [1] and leads major obstacles for commercialization. Therefore to achieve fuel cell operating temperature below 600 C is a big challenge in the field of SOFC [12]. In SOFC, when pure electrolytes (YSZ, GDC, SDC, and CDC) are used, it operates at high temperatures and exhibits low power density, low current density and low conductivity [13,14]. However the usage of nano electrolytes in SOFC shows
good performance with high power density and improved conductivity at low operating temperatures. During the synthesis of nano electrolytes lowering the sintering temperature lead to smaller size of grains, which increases the conductivity of material [15,16]. Among hydrocarbon fuels, natural gas is economical and easily available world-wide. The possibility to use natural gas, as a fuel, in SOFC needs to be investigated extensively. Direct hydrocarbon fuel cells, will increase the possibility to commercialize the FC technology. SOFC can utilize natural gas directly without external reforming. Internal reforming in SOFC has advantages like system simplicity, cost effectiveness and also enhances the system efficiency, by utilizing the extra heat produced during the chemical reaction. When natural gas is fed to SOFC, following chemical reactions may occur during the internal reforming [4]. CH4 /2H2 þ C C þ O2 /CO H2 þ O2 /H2 O CH4 þ O2 /CH3 OH þ 2e A general reaction for family of methane is given by Cn H2nþ2 þ ð3n þ 1ÞO2 /nCO2 þ ðn þ 1ÞH2 O þ ð6n þ 2Þe Natural gas, supply infrastructure, is available throughout the world, more efficient, easy to store, transport, can be directly used without any external processing as compared to hydrogen in case of producing energy. Natural gas (Methane) is also more efficient fuel, as compared to hydrogen, in case of producing energy. Methane releases eight electrons for each mole while hydrogen releases only two electrons per mole. Methane is more appropriate and promising as compared to hydrogen for FC-technology [9]. Many researcher have studied different electrolyte i.e. Mr J. Pena-Martinez et al. (2006), investigated the performance of SOFC by using Strontium, Magnesium-doped Lanthanum Gallate (LSGM) ceramics as electrolyte and nanocomposite LSM as cathode. The maximum power density was recorded 160 mW cm2 at 800 C [15]. Mr Jacquin et al. (2007), developed proton conducting BaCe0.9Y0.1O2.95 e type ceramic oxide from nano-powders. The total conductivity at 500 C was 1.2 102 S cm1 [16]. Mr. X. Chen et al. (2008), synthesized a proton and oxide ion conductor, Sn0.9In0.1P2O7. The conductivity of Sn0.9In0.1P2O7 and performance of Sn0.9In0.1P2O7 membrane fuel cell were investigated under various atmospheres in the range of 130e230 C temperature. The
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
conductivity of Sn0.9In0.1P2O7 obtained 0.019 S/cm at 200 C which was improved performance than pure proton conductive fuel cells at 235 C. These nanocomposite electrolytes were equally useful for SOFCs and PEMFCs [17]. Mr L. Fan et al. (2012), synthesized samarium doped ceriacarbonates nanocomposite electrolytes using citric acidnitrate combustion method and solid state reaction method for SOFC. The maximum power densities of 839.5 at 600 C and around 437 mW cm2 at 450 C were reported. These nanocomposites show very low resistance and high ionic conductivity [18]. Mr A. Elleuch et al. (2012), using oxalate coprecipitation process, synthesized nanocomposite electrolytes composed of Samarium-Doped Ceria (SDC) and a binary carbonate phase (67 mol% Li2CO3/33 mol% Na2CO3) for intermediate temperature direct carbon fuel cells (ITDCFCs) [19]. But no many researchers have focused on natural gas based composite electrolyte. In this article, synthesis and performance of newly developed nano electrolytes for LTSOFC with natural gas as well as pure hydrogen as fuel is being reported. Barium and Lanthanum nano electrolytes
3
have shown excellent conductivity, improved power density, higher current density at lower temperature as compared to conventional electrolytes for SOFC. In start, we discuss the synthesis of nanocomposite electrolytes in detail. The structure, morphology, ionic conductivities and performance of the nanocomposite electrolytes with natural gas as fuel are discussed in detail.
Experimental Synthesis of barium and samarium doped ceria composite (BSDC-carbonate) [Sample-1, 3 and 4] using co-precipitation and wet chemical methods BSDC-carbonate (barium and samarium doped ceriacarbonate) nano electrolytes named as sample-1, sample 3 and sample 4were synthesized using co-precipitation and wet chemical methods. The detail synthesis procedure is shown in Fig. 1.
Flow Chart for BSDC . 0.02MCe (NO3) 3·6H2O + 0.5L distilled water 0
Stirred for 2 minutes at 80 C Added 0.005M Sm (NO ) ·6H O in above solution 3 3
2
0
Stirred for 30 minutes at 80 C After 30 min., added drop wise 0.0125M Na2CO3 solution === (prepared in 50ml distilled water) in above solution 0
Stirred for few minutes at 80 C Samarium Doped Ceria Solution (SDC) SDC soluƟon + Ba(NO3)2 soluƟon 0
Stirred for 30 minutes at 80 C FiltraƟon AŌer 30 minutes Precipitate like composite obtained
0
Drying in Oven at 150 C for 2 hours
0
Sintering by Furnace at 800 C for 4 hours
Nanocomposite Powder of BSDC
Fig. 1 e Flow chart of synthesis procedure of nanocomposite electrolyte. Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
4
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
The optimized ratio between SDC and Ba(NO3)2 are considered to be 1:1 for these samples. The ratio between samarium (Sm) and cerium (Ce) are considered 1:4(20%:80%) for each electrolyte. 0.02 mol of cerium nitrate (Ce(NO3)3$6H2O (Sigma Aldrich, USA)) is prepared in 0.5 L distilled water and stirred for 2 min at frequency 800 rev/min with temperature 80 C. Further 0.005 mol of Sm(NO3)3$6H2O (Sigma Aldrich, USA) was added in the cerium nitrate solution and continued stirring for further 30 min to get samarium doped ceria (SDC) solution to be used in all samples. For BSDC-carbonate (sample 1), 0.0125 mol/L solution of sodium carbonate (Na2CO3) was added drop wise in the SDC solution and was stirred for 2 min. 0.025 mol/L solution of Ba (NO3)2 (Sigma Aldrich, USA) was added in the solution of SDC and kept on stirring for further 30 min. After 30 min stirring, solution was filtered to get precipitates. The wet precipitate was dried in an oven at 150 C for 2 h. Later the precipitate powdered was sintered in a furnace at 800 C for 4 h. After sintering, the BSDC-carbonate nanocomposite (sample 1)has obtained which is further grinded for to be used as smart electrolyte. Wet chemical method has investigated for synthesis of BSDC (sample 3). Separate solutions of 2.66 g of Na2CO3 and 0.025 mol/L of Ba(NO3)2 were prepared and stirred for several minutes at 80 C. Both solutions were mixed and stirred at 80 C for 30 min before mixing with the aforementioned SDC solution. The solution is kept stirred till drying. Later dried material was sintered at 800 C for 4 h and grinded afterwards to obtain BSDC (sample-3). Whereas BSDC-carbonate (sample-4) was synthesized using citric acid (C6H8O7) as chelating agent in wet chemical approach. In SDC solution, we added 0.0125 mol/L of Ba (NO3)2 and 0.0125 mol of C6H8O7 in it and started heating the solution at 140 C till dry. It takes nearly 2 h and 30 min for complete drying and grinded the powder. In the end grinded powder
was sintered at 800 C for 4 h before pellet formation and characterization study.
Synthesis of lanthanum and samarium doped ceria composite (LSDC) [Sample-2] LSDC-carbonate (lanthanum and samarium doped ceria with carbonate) nanocomposite electrolyte (sample-2) was synthesized by using co-precipitation method. The ratio between SDC and La (NO3)3$6H2O is considered 1:1. The ratio between samarium (Sm) and cerium (Ce) was considered 1:4. However synthesis method for SDC solution is nearly same as in aforementioned samples. We synthesized La (NO3)3$6H2O solution by using 50 ml distilled water in a beaker and added 0.025 mol of La (NO3)3$6H2O and stirred for few minutes at 80 C. After 2 min as described in preparation of sample-1, added the above solution in SDC solution and stirred at 80 C for 30 min. In the end solution was filtered and washed to get precipitate like composite. Precipitate was kept for drying in an oven at 150 C for another 2 h which later sintered in a furnace for 4 h at 800 C to improve overall quality of product. After sintering for 4 h, LSDC nanocomposite has obtained and eventually grinded to obtain fine powder.
Results and discussion Micro structure of the synthesized electrolytes The crystalline structure of the synthesized electrolytes was examined by X-ray diffraction (XRD) technique. XRD pattern was captured using a Philips X'pert pro super diffractometer with CueKa radiation of wavelength (l ¼ 1.5418 Å) working at 40 kV, 30 mA.
Fig. 2 e Combined XRD Pattern of synthesized electrolytes. Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
5
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
Table 1 e Comparison of XRD of synthesized electrolytes.
BSDC [Sample-1] LSDC [Sample-2] BSDC [Sample-3] BSDC [Sample-4]
FWHM [2q]
d-spacing [ A]
Crystallite size [nm]
0.7085 0.9446 0.1771 0.2952
3.17626 3.21475 3.13579 3.16072
11.58 8.68 46.40 27.82
XRD patterns of synthesized electrolytes are shown in Fig. 2. The BSDC-carbonate (sample 1) and LSDC-carbonate (sample 2) composite prepared by co-precipitation method have the cubic structure with a space group Pm-3m-(221), and JCPDS Card 83-0533, SDC has the Cubic fluorite structure with a space group Fm-3m-(225), and JCPDS Card 75-0159,whereasCubic Lanthanum oxide has the space group Fm-3m-(223), with JCPDS Card 88-2336 consecutively phases are identified. It has been observed that the Lanthanum contents are not reacted with the SDC oxide, when they are fired at 800 C for 4 h. But the barium content reacted with the SDC oxide at 800 C for 4 h to make phase barium cerate oxide. The comparison of XRD measurements of electrolytes is shown in Table 1. The crystallite size of BSDC-carbonate (samples 1,3,4) electrolyte are 11.58 nm and 46.40 nm measured by using DebyeeScherrer formula. The LSDCcarbonate (sample 2) electrolyte has a crystalline size of 8.68 nm. The diffraction patterns of nano electrolytes provide the proof that composites have nanocrystalline structure. Fig. 3 depicts the microstructure of the Barium and Samarium Co-doped Ceria (BSDC-carbonate) [Sample-3], obtained by scanning electron microscopy (SEM) (Hitachi, SU3500, Japan). The morphology of the synthesized BSDCcarbonate seems to be largely homogeneous and with a dense structure. A range of particle sizes from 100 nm to 500 nm has been observed. It is perceived that due to small particle size; the ionic conductivity of synthesized nanocomposite electrolyte is high. There is possibility of, due to large boundary size of grains, reducing the contact resistance between particles which allows the ions to pass through interfaces of particles easily.
Fig. 4 e Comparison of Raman spectroscopy.
The structural analysis of synthesized materials was also performed using Raman Spectroscopy. The Raman spectra of the synthesized materials is obtained by Raman spectrometer (model HR 800 Horiba, Japan) at room temperature. HeeNe laser source with wave length 632.8 nm was used with spectra resolution of 1 cm1. The powders of all samples are sintered at 800 C for 4 h before characterization. A combined diagram for comparison is shown in Fig. 4. The most intense peaks appear at about 454 cm1in all four synthesized electrolytes, which belong to SDC. It means Samarium (Sm) has completely doped in Ceria (CeO2) in synthesized nano electrolytes. The other small peaks may be of Barium Oxide, Lanthanum or other impurities present in composites.
Fuel cell performance (electrochemical characterization) For performance of fuel cell with, nano electrolytes, pellets of nano electrolytes were made by hydraulic press. The mixture of LiNiCuZnO & nanoelectrolyte [0.50 g (Electrode powder) þ 0.20 g (Electrolyte powder)] was used to prepare 1.0
0.20
300 350 400 450 500
Cell Voltage(V)
0.8
C C C C C
0.16
0.6
0.12
0.4
0.08
0.2
0.04
0.0
Power density (W/cm )
Material
0.00 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Current density (A/cm )
Fig. 3 e SEM image of BSDC [Sample-3].
Fig. 5 e FC performance BSDC-carbonate [Sample-1] under natural gas.
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
6
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
0.18 0.9 0.8
Cell voltage (V)
0.7
0.12
0.6
0.10
0.5
0.08
0.4 0.3
0.06
0.2
0.04
0.1
0.02 0.00 0.7
0.0 0.0
0.1
0.2
0.3
0.4
0.5
Power density (W/cm2)
0
300 C 0.16 0 400 C 0 500 C 0.14 0 600 C
0.6
2
Current density (A/cm )
Fig. 6 e FC performance LSDC-carbonate [Sample-2] under natural gas.
electrodes material. The thickness of the pallet was kept 1 mm with diameter of 13 mm. Nickel foil was used on the anode side which prevents pellet from breakdown and also acts as a catalyst. Pellets were sintered at 500 C for 30 min before doing performance test. The performance of these FCs was investigated at temperature range 300e500 C by using natural gas as fuel. Natural gas was supplied at anode with flow rate of 100 ml min1 at 1 atm pressure and oxygen from air was provided at cathode side with the help of an air pump. The IV/IP characteristics were observed using fuel cell testing unit (SM-102). The performances of all prepared samples are shown in Figs. 5, 6,7 and 8 at different temperature. A comparison of fuel cell performance for all four nano electrolytes is shown in Table 2. It can be seen that BSDC-carbonate electrolyte (sample 3) synthesized by using wet chemical method has shown highest power density 350 mW cm2 at low temperatures (300e500 C) with minimum losses. 100 200 300 400 500 600 700 800 900 100011001200130014001500 480 500 550 580
0.7
Cell voltage (V)
0.6
400 350 300
0.5
250
0.4
200
0.3
150
0.2
100
0.1
50
0.0
2
0
Power density (mW/cm )
0.8
0 0
300
600
900
1200
1500
2
Current density (mA/cm )
Fig. 7 e FC performance BSDC-carbonate [Sample-3] under natural gas.
Fig. 8 e FC performance BSDC-carbonate [Sample-4] under natural gas.
Ionic conductivity and nanostructure of BSDC nanocomposite electrolyte In this section, we discuss ionic conductivity and nanostructure of BSDC nanoelectrolyte [Sample-3] which shows highest power density among other synthesized electrodes in this contribution. The ionic conductivity measurements for BSDC nanocomposite were measured using two probe DC method. A pellet of 2.05 mm thickness with diameter of 13 mm and effective area of 0.64 cm2 was prepared using hydraulic press. In order to collect current, silver paste was coated on both side of the pellet. The conductivity measurements are done under hydrogen atmosphere at 600 C which is shown in Fig. 9. An ionic conductivity of 0.16 S/cm at 600 C is measured which is significantly higher, as compared to the conventional SDC and GDC electrolytes, for LTSOFC under hydrogen atmosphere. Under air atmosphere, an ionic conductivity of 0.015 S/cm at 600 C was recorded which is also greater than conventional SDC and GDC electrolytes at same temperature for SOFC under air atmosphere. Fig. 9 shows conductivity comparison of BSDC with conventional electrolytes under air atmosphere. It has been seen that conductivity increases with increase in temperature. With aging, no material degradation is occurred. As prepared material has shown stable conductivity with aging.
Conclusion In this article BSDC-carbonate nanocomposites electrolytes are successfully synthesized by co-precipitation and wet chemical methods. Microstructure characterization by SEM, XRD and Raman Spectroscopy confirms the formation of BSDC nanocomposite electrolytes. BSDC nanocomposite electrolyte synthesized by wet chemical method has shown high conductivity at low temperatures when natural gas is used as fuel. For natural gas, the obtained ionic conductivities at low temperatures (600 C) under air and hydrogen atmosphere are 0.015 S/cm and 0.16 S/cm respectively which
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
7
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
Table 2 e Fuel cell performance of different cells. Prepared samples BSDC [Sample-1] LSDC [Sample-2] BSDC [Sample-3] BSDC [Sample-4]
Electrode material LiNiCuZn LiNiCuZn LiNiCuZn LiNiCuZn
0.20
Operating temp.
(Oxide)þBSDC (Oxide)þLSDC (Oxide)þBSDC (Oxide)þBSDC
550 550 550 550
C C C C
BaSDC(Samp ple-3)-in H2atmos sphere BaSDC (Sample-3)-in air atmosp phere
SDC GDC
0.15
σ(s/cm)
[2] 0.10
[3] [4]
0.05
[5] 0.00 1.1
1.2
1.3
1.4
1.5
1.6
[6]
-1
1000/T (K ) Fig. 9 e Conductivity comparison of BSDC-carbonate [Sample-3] with conventional electrolytes under air and H2 atmosphere.
[7]
[8]
[9]
are significantly higher than the conventional SDC and GDC at similar conditions. These synthesized electrolytes offer the possibility to reduce the working temperature of SOFC. The FC containing BSDC-carbonate (sample 3) as electrolyte gives excellent performance with maximum power density of 350 mW cm2 at 550 C. This high conductive nanocomposite electrolyte for Low Temperature Solid Oxide Fuel Cells (LTSOFCs) are appropriate for natural gas as fuel and provides a way forward to commercialization of the FCtechnology.
[10]
[11] [12]
[13]
Acknowledgements A start-up research grant funded by the HEC Pakistan (No. PM-IPFP/HRD/HEC/2012/3597), COMSATS Research Grant Program (CRGP) and research grant from the Swedish Research Council (VR, Contract No. 621-2011-4983) are gratefully acknowledged.
[14]
[15]
[16]
references [17] [1] (a)Shaowu Z, Ashley M, Abernathy H, Meilin L. GDC-based low-temperature SOFCs powered by hydrocarbon fuels. J Electrochem Soc 2004;151:A1128e33.
OCV (V)
Fuel cell performance (mW/cm2)
0.927 0.854 0.750 0.858
168 175 375 230
(b)Lee JG, Park JH, Shul YG. Tailoring gadolinium-doped ceria-based solid oxide fuel cells to achieve 2 W cm 2 at 550 . Nat Commun 2014;5. Article number: 4045. (c)Brett Daniel JL, Atkinson A, Brandon NP, Skinner SJ. Intermediate temperature solid oxide fuel cells. Chem Soc Rev 2008;37:1568e78. Ge XM, Chan SH, Liu QL, Sun Q. Solid oxide fuel cell anode materials for direct hydrocarbon utilization. Adv Energy Mater 2012;10:1156e81. McIntosh Steven, Raymond JG. Direct hydrocarbon solid oxide fuel cells. Chem Rev 2004;104:4845e66. San Martı´n JI, Zamora I, San Martı´n JJ, Aperribay V, Eguı´a P. Hybrid technologies: fuel cells and renewable energies. University of Basque Country; 2007. Zuo C, Liu M, Liu M. Solid oxide fuel cells. In: Sol-gel processing for conventional and alternative energy. US: Springer; 2012. p. 7e36. Qin H, Zhu Z, Liu Q, Jing Y, Raza R, Imran S, et al. Direct biofuel low-temperature solid oxide fuel cells. Energy & Environ Sci 2011;4:1273e6. Vielstich H, Yokokawa H, Gasteiger H. Handbook of fuel cells: fundamentals technology and applicationsvolume 5. John Wiley & Sons; 2009. Carrette L, Friedrich KA, Stimming U1. Fuel cellsefundamentals and applications. Fuel cells 2001;1:5e39. Stambouli A, Boudghene, Traversa E. Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy. Renew Sustain Energy Rev 2002;6(5):433e55. Laosiripojana Navadol, Wiyaratn W, Kiatkittipong W, Arpornwichanop A, Soottitantawat A, Assabumrungrat S. Reviews on solid oxide fuel cell technology. Eng J 2009;1:65e84. Steele Brian CH, Heinzel Angelika. Materials for fuel-cell technologies. Nature 2001;6861:345e52. Miura Norio, Nakatou M, Zhuiykov S. Impedancemetric gas sensor based on zirconia solid electrolyte and oxide sensing electrode for detecting total NO at high temperature. Sens Actuators B Chem 2003;93:221e8. Raza R, Ahmad MA, Iqbal J, Akram N, Gao Z, Javed S, et al. Ce0.8(SmZr)0.2O2-carbonate nanocomposite electrolyte for solid oxide fuel cell. Int J Energy Res 2014;38:524e9. Chiang YM, Lavik EB, Kosacki I, Tuller HL, Ying JY. Defect and transport properties of nanocrystalline CeO2x. Appl Phys Lett 1996;69:185. pez D, Ruiz-Morales JC, Pena-Martinez J, Marrero-Lo ~ ez P, Gauckler LJ. Fuel cell studies of Buergler BE, Nu´n perovskite-type materials for IT-SOFC. J Power Sources 2006;159:914e21. Jacquin M, Jing Y, Essoumhi A, Taillades G, Jones DJ, re J. Flash combustion synthesis and characterisation Rozie of nanosized proton conducting yttria-doped barium cerate. J New Mater Electrochem Syst 2007;10:243e8. Chen X, Wang C, Payzant EA, Xia C, Chu D. An oxide ion and proton co-ion conducting Sn0.9In0.1P2O7 electrolyte for intermediate-temperature fuel cells. J Electrochem Soc 2008;155(12):B1264e9.
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
8
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
[18] Fan L, Wang C, Di J, Chen M, Zhen J, Zhu B. Study of ceriacarbonate nanocomposite, electrolytes for lowtemperature solid oxide fuel cells. J Nanosci Nanotechnol 2012;12:1e5.
[19] Elleuch A, Yu J, Boussetta A, Halouani K, Li Y. Electrochemical oxidation of graphite in an intermediate temperature direct carbon fuel cell based on two-phases electrolyte. Int J Hydrogen Energy 2013;38:8514e23.
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Highly efficient composite electrolyte for natural gas fed fuel cell Akhlaq Ahmed a, Rizwan Raza a,b,*, Muhammad Saeed Khalid c, Muhammad Saleem a, Farah Alvi a, Muhammad Sufyan Javed a,d, Tauqir A. Sherazi e, Majid Niaz Akhtar a, Nadeem Akram a, Muhammad Ashfaq Ahmad a, Asia Rafique a, Javed Iqbal f, Amjad Ali a, M. Kaleem Ullah a, S. Khalid Imran b, Imran Shakir g, M. Ajmal Khan a, Bin Zhu b,h,** a Department of Physics, COMSATS Institute of Information Technology, Defence Road, off Raiwind Road, Lahore, 54000, Pakistan b Department of Energy Technology, Royal Institute of Technology, KTH, Stockholm, 10044, Sweden c National University of Sciences & Technology (NUST), Islamabad, Pakistan d Department of Applied Physics, Chongqing University, Chongqing 400044, PR China e Department of Chemistry, COMSATS Institute of Information Technology, Abbotabad 22060, Pakistan f Department of Chemical Engineering, COMSATS Institute of Information Technology, Defence Road, off Raiwind Road, Lahore 54000, Pakistan g Deanship of Scientific Research, College of Engineering, King Saud University, P. O. Box 800, Riyadh 11421, Saudi Arabia h Hubei Collaborative Innovation Center for Advanced Materials, Faculty of Physics and Electronic Science, Hubei University, Wuhan, Hubei, 430062, PR China
article info
abstract
Article history:
Solid oxide fuel cells (SOFCs) have the ability to operate with different variants of hydro
Received 30 April 2015
carbon fuel such as biogas, natural gas, methane, ethane, syngas, methanol, ethanol,
Received in revised form
hydrogen and any other hydrogen rich gas. Utilization of these fuels in SOFC, especially the
10 January 2016
natural gas, would significantly reduce operating cost and would enhance the viability for
Accepted 22 February 2016
commercialization of FC technology. In this paper, the performance of two indigenously
Available online xxx
manufactured nanocomposite electrolytes; barium and samarium doped ceria (BSDCcarbonate); and lanthanum and samarium doped ceria (co-precipitation method LSDC-
Keywords:
carbonate) using natural gas as fuel is discussed. The nanocomposite electrolytes were
LT-SOFCs
synthesized using co-precipitation and wet chemical methods (here after referred to as
Proton conductor
nano electrolytes). The structure and morphology of the nano electrolytes were examined
High conductivity
by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fuel cell perfor-
Fuel cell performance
mance (OCV) was tested at temperature (300e600 C). The ionic conductivity of the nano electrolytes were measured by two probe DC method. The detailed composition analysis of nano electrolytes was performed with the help of Raman Spectroscopy. Electrochemical study has shown an ionic conductivity of 0.16 Scm1 at 600 C for BSDC-carbonate in hydrogen atmosphere, which is higher than conventional electrolytes SDC and GDC under
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (R. Raza), [email protected] (B. Zhu). http://dx.doi.org/10.1016/j.ijhydene.2016.02.095 0360-3199/Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
2
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
same conditions. In this article reasonably good ionic conductivity of BSDC-carbonate, at 600 C, has also been achieved in air atmosphere which is comparatively greater than the conventional SDC and GDC electrolytes. Copyright © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Solid oxide fuel cells (SOFC) have found great interest since last two decades due to their ability to provide high efficiency, tolerance towards the fuels and being environmental friendly. However many complications still exist which need to be addressed, before making SOFC economically inexpensive in the market [1,2]. Major hurdles are expensive electrolyte/ electrode materials, high working temperatures, and expensive hydrogen fuel. Many research groups are working to make efficient electrolytes and electrodes but preparing a cheap electrolyte is still a big challenge to commercialize SOFC [1]. Another challenge is to operate SOFC on hydrocarbon fuels instead of pure hydrogen. Hydrogen gas as a fuel has some major issues related to cost, difficulty in handling, transportation and other technological technology aspects [3]. Since 1988 more than 86% of hydrogen is produced from fossil fuels which include 30% from refinery, 48% from natural gas, and 18% from coal; and remaining from electrolysis of water [2,3]. Instead of producing pure hydrogen form hydrocarbon fuels for SOFC which is not cost effective, the direct use of these hydrocarbons as fuel especially natural gas (95% methane) needs to be explored. SOFC offers the possibility to be used with wide range of fuels like hydrogen, coal gas, natural gas, methanol and diesel etc. [5,7,8]. Among different types of fuel cells, SOFC is a solid state fuel cell based on a solid oxide electrolyte which possess the maximum electrical efficiency (45e60%) and with cogeneration with other technologies its efficiency increases (60e80%) with minimum emissions [6]. SOFCs offer extensive potential for power and heat generation called CHP (combined heat and power). SOFCs normally operate between the temperature range of 300e600 C are called low temperature SOFC (LTSOFC). The electrolyte is the most important part of SOFC [9]. For SOFC, yttrium stabilized zirconia (YSZ), gadolinium doped ceria (GDC), samarium doped ceria (SDC) and calcium doped ceria (CDC) are commonly used materials for electrolytes [10,11]. Since high temperature SOFCs operate above 800 C, which is responsible for efficient material degradation, technological complications and high cost of ceramic materials etc. [1] and leads major obstacles for commercialization. Therefore to achieve fuel cell operating temperature below 600 C is a big challenge in the field of SOFC [12]. In SOFC, when pure electrolytes (YSZ, GDC, SDC, and CDC) are used, it operates at high temperatures and exhibits low power density, low current density and low conductivity [13,14]. However the usage of nano electrolytes in SOFC shows
good performance with high power density and improved conductivity at low operating temperatures. During the synthesis of nano electrolytes lowering the sintering temperature lead to smaller size of grains, which increases the conductivity of material [15,16]. Among hydrocarbon fuels, natural gas is economical and easily available world-wide. The possibility to use natural gas, as a fuel, in SOFC needs to be investigated extensively. Direct hydrocarbon fuel cells, will increase the possibility to commercialize the FC technology. SOFC can utilize natural gas directly without external reforming. Internal reforming in SOFC has advantages like system simplicity, cost effectiveness and also enhances the system efficiency, by utilizing the extra heat produced during the chemical reaction. When natural gas is fed to SOFC, following chemical reactions may occur during the internal reforming [4]. CH4 /2H2 þ C C þ O2 /CO H2 þ O2 /H2 O CH4 þ O2 /CH3 OH þ 2e A general reaction for family of methane is given by Cn H2nþ2 þ ð3n þ 1ÞO2 /nCO2 þ ðn þ 1ÞH2 O þ ð6n þ 2Þe Natural gas, supply infrastructure, is available throughout the world, more efficient, easy to store, transport, can be directly used without any external processing as compared to hydrogen in case of producing energy. Natural gas (Methane) is also more efficient fuel, as compared to hydrogen, in case of producing energy. Methane releases eight electrons for each mole while hydrogen releases only two electrons per mole. Methane is more appropriate and promising as compared to hydrogen for FC-technology [9]. Many researcher have studied different electrolyte i.e. Mr J. Pena-Martinez et al. (2006), investigated the performance of SOFC by using Strontium, Magnesium-doped Lanthanum Gallate (LSGM) ceramics as electrolyte and nanocomposite LSM as cathode. The maximum power density was recorded 160 mW cm2 at 800 C [15]. Mr Jacquin et al. (2007), developed proton conducting BaCe0.9Y0.1O2.95 e type ceramic oxide from nano-powders. The total conductivity at 500 C was 1.2 102 S cm1 [16]. Mr. X. Chen et al. (2008), synthesized a proton and oxide ion conductor, Sn0.9In0.1P2O7. The conductivity of Sn0.9In0.1P2O7 and performance of Sn0.9In0.1P2O7 membrane fuel cell were investigated under various atmospheres in the range of 130e230 C temperature. The
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
conductivity of Sn0.9In0.1P2O7 obtained 0.019 S/cm at 200 C which was improved performance than pure proton conductive fuel cells at 235 C. These nanocomposite electrolytes were equally useful for SOFCs and PEMFCs [17]. Mr L. Fan et al. (2012), synthesized samarium doped ceriacarbonates nanocomposite electrolytes using citric acidnitrate combustion method and solid state reaction method for SOFC. The maximum power densities of 839.5 at 600 C and around 437 mW cm2 at 450 C were reported. These nanocomposites show very low resistance and high ionic conductivity [18]. Mr A. Elleuch et al. (2012), using oxalate coprecipitation process, synthesized nanocomposite electrolytes composed of Samarium-Doped Ceria (SDC) and a binary carbonate phase (67 mol% Li2CO3/33 mol% Na2CO3) for intermediate temperature direct carbon fuel cells (ITDCFCs) [19]. But no many researchers have focused on natural gas based composite electrolyte. In this article, synthesis and performance of newly developed nano electrolytes for LTSOFC with natural gas as well as pure hydrogen as fuel is being reported. Barium and Lanthanum nano electrolytes
3
have shown excellent conductivity, improved power density, higher current density at lower temperature as compared to conventional electrolytes for SOFC. In start, we discuss the synthesis of nanocomposite electrolytes in detail. The structure, morphology, ionic conductivities and performance of the nanocomposite electrolytes with natural gas as fuel are discussed in detail.
Experimental Synthesis of barium and samarium doped ceria composite (BSDC-carbonate) [Sample-1, 3 and 4] using co-precipitation and wet chemical methods BSDC-carbonate (barium and samarium doped ceriacarbonate) nano electrolytes named as sample-1, sample 3 and sample 4were synthesized using co-precipitation and wet chemical methods. The detail synthesis procedure is shown in Fig. 1.
Flow Chart for BSDC . 0.02MCe (NO3) 3·6H2O + 0.5L distilled water 0
Stirred for 2 minutes at 80 C Added 0.005M Sm (NO ) ·6H O in above solution 3 3
2
0
Stirred for 30 minutes at 80 C After 30 min., added drop wise 0.0125M Na2CO3 solution === (prepared in 50ml distilled water) in above solution 0
Stirred for few minutes at 80 C Samarium Doped Ceria Solution (SDC) SDC soluƟon + Ba(NO3)2 soluƟon 0
Stirred for 30 minutes at 80 C FiltraƟon AŌer 30 minutes Precipitate like composite obtained
0
Drying in Oven at 150 C for 2 hours
0
Sintering by Furnace at 800 C for 4 hours
Nanocomposite Powder of BSDC
Fig. 1 e Flow chart of synthesis procedure of nanocomposite electrolyte. Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
4
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
The optimized ratio between SDC and Ba(NO3)2 are considered to be 1:1 for these samples. The ratio between samarium (Sm) and cerium (Ce) are considered 1:4(20%:80%) for each electrolyte. 0.02 mol of cerium nitrate (Ce(NO3)3$6H2O (Sigma Aldrich, USA)) is prepared in 0.5 L distilled water and stirred for 2 min at frequency 800 rev/min with temperature 80 C. Further 0.005 mol of Sm(NO3)3$6H2O (Sigma Aldrich, USA) was added in the cerium nitrate solution and continued stirring for further 30 min to get samarium doped ceria (SDC) solution to be used in all samples. For BSDC-carbonate (sample 1), 0.0125 mol/L solution of sodium carbonate (Na2CO3) was added drop wise in the SDC solution and was stirred for 2 min. 0.025 mol/L solution of Ba (NO3)2 (Sigma Aldrich, USA) was added in the solution of SDC and kept on stirring for further 30 min. After 30 min stirring, solution was filtered to get precipitates. The wet precipitate was dried in an oven at 150 C for 2 h. Later the precipitate powdered was sintered in a furnace at 800 C for 4 h. After sintering, the BSDC-carbonate nanocomposite (sample 1)has obtained which is further grinded for to be used as smart electrolyte. Wet chemical method has investigated for synthesis of BSDC (sample 3). Separate solutions of 2.66 g of Na2CO3 and 0.025 mol/L of Ba(NO3)2 were prepared and stirred for several minutes at 80 C. Both solutions were mixed and stirred at 80 C for 30 min before mixing with the aforementioned SDC solution. The solution is kept stirred till drying. Later dried material was sintered at 800 C for 4 h and grinded afterwards to obtain BSDC (sample-3). Whereas BSDC-carbonate (sample-4) was synthesized using citric acid (C6H8O7) as chelating agent in wet chemical approach. In SDC solution, we added 0.0125 mol/L of Ba (NO3)2 and 0.0125 mol of C6H8O7 in it and started heating the solution at 140 C till dry. It takes nearly 2 h and 30 min for complete drying and grinded the powder. In the end grinded powder
was sintered at 800 C for 4 h before pellet formation and characterization study.
Synthesis of lanthanum and samarium doped ceria composite (LSDC) [Sample-2] LSDC-carbonate (lanthanum and samarium doped ceria with carbonate) nanocomposite electrolyte (sample-2) was synthesized by using co-precipitation method. The ratio between SDC and La (NO3)3$6H2O is considered 1:1. The ratio between samarium (Sm) and cerium (Ce) was considered 1:4. However synthesis method for SDC solution is nearly same as in aforementioned samples. We synthesized La (NO3)3$6H2O solution by using 50 ml distilled water in a beaker and added 0.025 mol of La (NO3)3$6H2O and stirred for few minutes at 80 C. After 2 min as described in preparation of sample-1, added the above solution in SDC solution and stirred at 80 C for 30 min. In the end solution was filtered and washed to get precipitate like composite. Precipitate was kept for drying in an oven at 150 C for another 2 h which later sintered in a furnace for 4 h at 800 C to improve overall quality of product. After sintering for 4 h, LSDC nanocomposite has obtained and eventually grinded to obtain fine powder.
Results and discussion Micro structure of the synthesized electrolytes The crystalline structure of the synthesized electrolytes was examined by X-ray diffraction (XRD) technique. XRD pattern was captured using a Philips X'pert pro super diffractometer with CueKa radiation of wavelength (l ¼ 1.5418 Å) working at 40 kV, 30 mA.
Fig. 2 e Combined XRD Pattern of synthesized electrolytes. Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
5
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
Table 1 e Comparison of XRD of synthesized electrolytes.
BSDC [Sample-1] LSDC [Sample-2] BSDC [Sample-3] BSDC [Sample-4]
FWHM [2q]
d-spacing [ A]
Crystallite size [nm]
0.7085 0.9446 0.1771 0.2952
3.17626 3.21475 3.13579 3.16072
11.58 8.68 46.40 27.82
XRD patterns of synthesized electrolytes are shown in Fig. 2. The BSDC-carbonate (sample 1) and LSDC-carbonate (sample 2) composite prepared by co-precipitation method have the cubic structure with a space group Pm-3m-(221), and JCPDS Card 83-0533, SDC has the Cubic fluorite structure with a space group Fm-3m-(225), and JCPDS Card 75-0159,whereasCubic Lanthanum oxide has the space group Fm-3m-(223), with JCPDS Card 88-2336 consecutively phases are identified. It has been observed that the Lanthanum contents are not reacted with the SDC oxide, when they are fired at 800 C for 4 h. But the barium content reacted with the SDC oxide at 800 C for 4 h to make phase barium cerate oxide. The comparison of XRD measurements of electrolytes is shown in Table 1. The crystallite size of BSDC-carbonate (samples 1,3,4) electrolyte are 11.58 nm and 46.40 nm measured by using DebyeeScherrer formula. The LSDCcarbonate (sample 2) electrolyte has a crystalline size of 8.68 nm. The diffraction patterns of nano electrolytes provide the proof that composites have nanocrystalline structure. Fig. 3 depicts the microstructure of the Barium and Samarium Co-doped Ceria (BSDC-carbonate) [Sample-3], obtained by scanning electron microscopy (SEM) (Hitachi, SU3500, Japan). The morphology of the synthesized BSDCcarbonate seems to be largely homogeneous and with a dense structure. A range of particle sizes from 100 nm to 500 nm has been observed. It is perceived that due to small particle size; the ionic conductivity of synthesized nanocomposite electrolyte is high. There is possibility of, due to large boundary size of grains, reducing the contact resistance between particles which allows the ions to pass through interfaces of particles easily.
Fig. 4 e Comparison of Raman spectroscopy.
The structural analysis of synthesized materials was also performed using Raman Spectroscopy. The Raman spectra of the synthesized materials is obtained by Raman spectrometer (model HR 800 Horiba, Japan) at room temperature. HeeNe laser source with wave length 632.8 nm was used with spectra resolution of 1 cm1. The powders of all samples are sintered at 800 C for 4 h before characterization. A combined diagram for comparison is shown in Fig. 4. The most intense peaks appear at about 454 cm1in all four synthesized electrolytes, which belong to SDC. It means Samarium (Sm) has completely doped in Ceria (CeO2) in synthesized nano electrolytes. The other small peaks may be of Barium Oxide, Lanthanum or other impurities present in composites.
Fuel cell performance (electrochemical characterization) For performance of fuel cell with, nano electrolytes, pellets of nano electrolytes were made by hydraulic press. The mixture of LiNiCuZnO & nanoelectrolyte [0.50 g (Electrode powder) þ 0.20 g (Electrolyte powder)] was used to prepare 1.0
0.20
300 350 400 450 500
Cell Voltage(V)
0.8
C C C C C
0.16
0.6
0.12
0.4
0.08
0.2
0.04
0.0
Power density (W/cm )
Material
0.00 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Current density (A/cm )
Fig. 3 e SEM image of BSDC [Sample-3].
Fig. 5 e FC performance BSDC-carbonate [Sample-1] under natural gas.
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
6
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
0.18 0.9 0.8
Cell voltage (V)
0.7
0.12
0.6
0.10
0.5
0.08
0.4 0.3
0.06
0.2
0.04
0.1
0.02 0.00 0.7
0.0 0.0
0.1
0.2
0.3
0.4
0.5
Power density (W/cm2)
0
300 C 0.16 0 400 C 0 500 C 0.14 0 600 C
0.6
2
Current density (A/cm )
Fig. 6 e FC performance LSDC-carbonate [Sample-2] under natural gas.
electrodes material. The thickness of the pallet was kept 1 mm with diameter of 13 mm. Nickel foil was used on the anode side which prevents pellet from breakdown and also acts as a catalyst. Pellets were sintered at 500 C for 30 min before doing performance test. The performance of these FCs was investigated at temperature range 300e500 C by using natural gas as fuel. Natural gas was supplied at anode with flow rate of 100 ml min1 at 1 atm pressure and oxygen from air was provided at cathode side with the help of an air pump. The IV/IP characteristics were observed using fuel cell testing unit (SM-102). The performances of all prepared samples are shown in Figs. 5, 6,7 and 8 at different temperature. A comparison of fuel cell performance for all four nano electrolytes is shown in Table 2. It can be seen that BSDC-carbonate electrolyte (sample 3) synthesized by using wet chemical method has shown highest power density 350 mW cm2 at low temperatures (300e500 C) with minimum losses. 100 200 300 400 500 600 700 800 900 100011001200130014001500 480 500 550 580
0.7
Cell voltage (V)
0.6
400 350 300
0.5
250
0.4
200
0.3
150
0.2
100
0.1
50
0.0
2
0
Power density (mW/cm )
0.8
0 0
300
600
900
1200
1500
2
Current density (mA/cm )
Fig. 7 e FC performance BSDC-carbonate [Sample-3] under natural gas.
Fig. 8 e FC performance BSDC-carbonate [Sample-4] under natural gas.
Ionic conductivity and nanostructure of BSDC nanocomposite electrolyte In this section, we discuss ionic conductivity and nanostructure of BSDC nanoelectrolyte [Sample-3] which shows highest power density among other synthesized electrodes in this contribution. The ionic conductivity measurements for BSDC nanocomposite were measured using two probe DC method. A pellet of 2.05 mm thickness with diameter of 13 mm and effective area of 0.64 cm2 was prepared using hydraulic press. In order to collect current, silver paste was coated on both side of the pellet. The conductivity measurements are done under hydrogen atmosphere at 600 C which is shown in Fig. 9. An ionic conductivity of 0.16 S/cm at 600 C is measured which is significantly higher, as compared to the conventional SDC and GDC electrolytes, for LTSOFC under hydrogen atmosphere. Under air atmosphere, an ionic conductivity of 0.015 S/cm at 600 C was recorded which is also greater than conventional SDC and GDC electrolytes at same temperature for SOFC under air atmosphere. Fig. 9 shows conductivity comparison of BSDC with conventional electrolytes under air atmosphere. It has been seen that conductivity increases with increase in temperature. With aging, no material degradation is occurred. As prepared material has shown stable conductivity with aging.
Conclusion In this article BSDC-carbonate nanocomposites electrolytes are successfully synthesized by co-precipitation and wet chemical methods. Microstructure characterization by SEM, XRD and Raman Spectroscopy confirms the formation of BSDC nanocomposite electrolytes. BSDC nanocomposite electrolyte synthesized by wet chemical method has shown high conductivity at low temperatures when natural gas is used as fuel. For natural gas, the obtained ionic conductivities at low temperatures (600 C) under air and hydrogen atmosphere are 0.015 S/cm and 0.16 S/cm respectively which
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
7
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
Table 2 e Fuel cell performance of different cells. Prepared samples BSDC [Sample-1] LSDC [Sample-2] BSDC [Sample-3] BSDC [Sample-4]
Electrode material LiNiCuZn LiNiCuZn LiNiCuZn LiNiCuZn
0.20
Operating temp.
(Oxide)þBSDC (Oxide)þLSDC (Oxide)þBSDC (Oxide)þBSDC
550 550 550 550
C C C C
BaSDC(Samp ple-3)-in H2atmos sphere BaSDC (Sample-3)-in air atmosp phere
SDC GDC
0.15
σ(s/cm)
[2] 0.10
[3] [4]
0.05
[5] 0.00 1.1
1.2
1.3
1.4
1.5
1.6
[6]
-1
1000/T (K ) Fig. 9 e Conductivity comparison of BSDC-carbonate [Sample-3] with conventional electrolytes under air and H2 atmosphere.
[7]
[8]
[9]
are significantly higher than the conventional SDC and GDC at similar conditions. These synthesized electrolytes offer the possibility to reduce the working temperature of SOFC. The FC containing BSDC-carbonate (sample 3) as electrolyte gives excellent performance with maximum power density of 350 mW cm2 at 550 C. This high conductive nanocomposite electrolyte for Low Temperature Solid Oxide Fuel Cells (LTSOFCs) are appropriate for natural gas as fuel and provides a way forward to commercialization of the FCtechnology.
[10]
[11] [12]
[13]
Acknowledgements A start-up research grant funded by the HEC Pakistan (No. PM-IPFP/HRD/HEC/2012/3597), COMSATS Research Grant Program (CRGP) and research grant from the Swedish Research Council (VR, Contract No. 621-2011-4983) are gratefully acknowledged.
[14]
[15]
[16]
references [17] [1] (a)Shaowu Z, Ashley M, Abernathy H, Meilin L. GDC-based low-temperature SOFCs powered by hydrocarbon fuels. J Electrochem Soc 2004;151:A1128e33.
OCV (V)
Fuel cell performance (mW/cm2)
0.927 0.854 0.750 0.858
168 175 375 230
(b)Lee JG, Park JH, Shul YG. Tailoring gadolinium-doped ceria-based solid oxide fuel cells to achieve 2 W cm 2 at 550 . Nat Commun 2014;5. Article number: 4045. (c)Brett Daniel JL, Atkinson A, Brandon NP, Skinner SJ. Intermediate temperature solid oxide fuel cells. Chem Soc Rev 2008;37:1568e78. Ge XM, Chan SH, Liu QL, Sun Q. Solid oxide fuel cell anode materials for direct hydrocarbon utilization. Adv Energy Mater 2012;10:1156e81. McIntosh Steven, Raymond JG. Direct hydrocarbon solid oxide fuel cells. Chem Rev 2004;104:4845e66. San Martı´n JI, Zamora I, San Martı´n JJ, Aperribay V, Eguı´a P. Hybrid technologies: fuel cells and renewable energies. University of Basque Country; 2007. Zuo C, Liu M, Liu M. Solid oxide fuel cells. In: Sol-gel processing for conventional and alternative energy. US: Springer; 2012. p. 7e36. Qin H, Zhu Z, Liu Q, Jing Y, Raza R, Imran S, et al. Direct biofuel low-temperature solid oxide fuel cells. Energy & Environ Sci 2011;4:1273e6. Vielstich H, Yokokawa H, Gasteiger H. Handbook of fuel cells: fundamentals technology and applicationsvolume 5. John Wiley & Sons; 2009. Carrette L, Friedrich KA, Stimming U1. Fuel cellsefundamentals and applications. Fuel cells 2001;1:5e39. Stambouli A, Boudghene, Traversa E. Solid oxide fuel cells (SOFCs): a review of an environmentally clean and efficient source of energy. Renew Sustain Energy Rev 2002;6(5):433e55. Laosiripojana Navadol, Wiyaratn W, Kiatkittipong W, Arpornwichanop A, Soottitantawat A, Assabumrungrat S. Reviews on solid oxide fuel cell technology. Eng J 2009;1:65e84. Steele Brian CH, Heinzel Angelika. Materials for fuel-cell technologies. Nature 2001;6861:345e52. Miura Norio, Nakatou M, Zhuiykov S. Impedancemetric gas sensor based on zirconia solid electrolyte and oxide sensing electrode for detecting total NO at high temperature. Sens Actuators B Chem 2003;93:221e8. Raza R, Ahmad MA, Iqbal J, Akram N, Gao Z, Javed S, et al. Ce0.8(SmZr)0.2O2-carbonate nanocomposite electrolyte for solid oxide fuel cell. Int J Energy Res 2014;38:524e9. Chiang YM, Lavik EB, Kosacki I, Tuller HL, Ying JY. Defect and transport properties of nanocrystalline CeO2x. Appl Phys Lett 1996;69:185. pez D, Ruiz-Morales JC, Pena-Martinez J, Marrero-Lo ~ ez P, Gauckler LJ. Fuel cell studies of Buergler BE, Nu´n perovskite-type materials for IT-SOFC. J Power Sources 2006;159:914e21. Jacquin M, Jing Y, Essoumhi A, Taillades G, Jones DJ, re J. Flash combustion synthesis and characterisation Rozie of nanosized proton conducting yttria-doped barium cerate. J New Mater Electrochem Syst 2007;10:243e8. Chen X, Wang C, Payzant EA, Xia C, Chu D. An oxide ion and proton co-ion conducting Sn0.9In0.1P2O7 electrolyte for intermediate-temperature fuel cells. J Electrochem Soc 2008;155(12):B1264e9.
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095
8
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e8
[18] Fan L, Wang C, Di J, Chen M, Zhen J, Zhu B. Study of ceriacarbonate nanocomposite, electrolytes for lowtemperature solid oxide fuel cells. J Nanosci Nanotechnol 2012;12:1e5.
[19] Elleuch A, Yu J, Boussetta A, Halouani K, Li Y. Electrochemical oxidation of graphite in an intermediate temperature direct carbon fuel cell based on two-phases electrolyte. Int J Hydrogen Energy 2013;38:8514e23.
Please cite this article in press as: Ahmed A, et al., Highly efficient composite electrolyte for natural gas fed fuel cell, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.02.095