Scholarly article on topic 'Synthesis and Characterization of PdO-NiO-SDC Nano-powder by Glycine-Nitrate Combustion Synthesis for Anode of IT-SOFC'

Synthesis and Characterization of PdO-NiO-SDC Nano-powder by Glycine-Nitrate Combustion Synthesis for Anode of IT-SOFC Academic research paper on "Materials engineering"

CC BY-NC-ND
0
0
Share paper
Academic journal
Energy Procedia
OECD Field of science
Keywords
{"Low temperature SOFC" / "PdO-NiO-SDC anode" / "Glycine nitrate combustion synthesis"}

Abstract of research paper on Materials engineering, author of scientific article — B.B. Patil, S. Basu

Abstract Ni-samaria doped ceria (SDC) is reported as potential anode material for intermediate temperature solid oxide fuel cells (SOFCs). The performances of SOFCs are mostly dependent on anodic microstructure which is related to anode preparation processes. In the present study, PdO-NiO-SDC nano-composite powder is synthesized by single step glycine nitrate combustion process (GNP) for the first time. The powder is prepared by using different glycine to nitrate ratio and respective properties are studied using X-ray Diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Brunauer Emmett Teller (BET) surface area and electrochemical impedance spectroscopy (EIS). XRD study showed the formation of cubic NiO, SDC and PdO phases upto 600°C and Ni-Pd solid solutions above 800°C. Crystallite size and porosity of the PdO-NiO-SDC powders are found to increase with increase in glycine to fuel ratio. The porosity of sintered pellets is found to be 40-45% which is sufficient for anode of SOFC. The conductivity of the pellet sintered at 1200°C is 99 and 72 S/cm at 450°C and 800°C, respectively. The electrical conductivity is observed to be increased with the increase in sintering temperature. Thus ultra fine, composite PdO-NiO-SDC powders with high surface area, better porosity and conductivity is synthesized successfully by simple, low cost, energy efficient single step glycine nitrate method for its possible application as an anode for intermediate temperature solid oxide fuel cells (IT-SOFCs) such as metal supported SOFCs.

Academic research paper on topic "Synthesis and Characterization of PdO-NiO-SDC Nano-powder by Glycine-Nitrate Combustion Synthesis for Anode of IT-SOFC"

CrossMark

Available online at www.sciencedirect.com

ScienceDirect

Energy Procedia 54 (2014) 669 - 679

4th International Conference on Advances in Energy Research 2013, ICAER 2013

Synthesis and Characterization of PdO-NiO-SDC Nano-Powder by Glycine-Nitrate Combustion Synthesis for Anode of IT-SOFC

B. B. Patil and S. Basu*

Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi 110016, India

Abstract

Ni-samaria doped ceria (SDC) is reported as potential anode material for intermediate temperature solid oxide fuel cells (SOFCs). The performances of SOFCs are mostly dependent on anodic microstructure which is related to anode preparation processes. In the present study, PdO-NiO-SDC nano-composite powder is synthesized by single step glycine nitrate combustion process (GNP) for the first time. The powder is prepared by using different glycine to nitrate ratio and respective properties are studied using X-ray Diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), Brunauer Emmett Teller (BET) surface area and electrochemical impedance spectroscopy (EIS). XRD study showed the formation of cubic NiO, SDC and PdO phases upto 600 °C and Ni-Pd solid solutions above 800 °C. Crystallite size and porosity of the PdO-NiO-SDC powders are found to increase with increase in glycine to fuel ratio. The porosity of sintered pellets is found to be 40-45 % which is sufficient for anode of SOFC. The conductivity of the pellet sintered at 1200 °C is 99 and 72 S/cm at 450 °C and 800 °C, respectively. The electrical conductivity is observed to be increased with the increase in sintering temperature. Thus ultra fine, composite PdO-NiO-SDC powders with high surface area, better porosity and conductivity is synthesized successfully by simple, low cost, energy efficient single step glycine nitrate method for its possible application as an anode for intermediate temperature solid oxide fuel cells (IT-SOFCs) such as metal supported SOFCs.

© 2014S.Basu.PublishedbyElsevierLtd.Thisisan open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of Organizing Committee of ICAER 2013 Keywords: Low temperature SOFC; PdO-NiO-SDC anode; Glycine nitrate combustion synthesis

* Corresponding author. Tel.: +91 11 26591035; fax: +91 11 26581120. E-mail address: sbasu@iitd.ac.in

1876-6102 © 2014 S. Basu. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of Organizing Committee of ICAER 2013 doi: 10.1016/j.egypro.2014.07.308

1. Introduction

Ni is still the most popular anode material for low and intermediate temperature solid oxide fuel cell (ITSOFC). However, Ni-based anodes catalysis the formation of graphitic carbon at low H2O/C ratios [1]. Ni is also liable to agglomerate and change shape during consolidation and subsequent operation at higher temperatures due to its low melting point. Due to this, decrease in electrical conductivity of the anodes is observed which affects the performance of SOFCs [2]. Previous studies of bimetallic anodes suggests that improved hydrogen oxidation rates and carbon deposition resistance is possible [3, 4]. It is reported that, the alloyed anode, Ni1-xMx-SDC may improve the anodes performance by improving its mechanical, thermal or chemical properties. The electro-catalytic activity of SOFC can also be improved by the addition of metal catalysts such as Ni, Pt, Pd, Ru, Ir and Rh [4, 5, 6]. For example, Mcintosh et al. [6] studied the effect of precious metals on ceria based anodes and found that maximum power density increases from 0.02 to 0.28 W/cm2 with addition of 1 wt% Pd at 700 °C.

The performance of SOFC mostly depends on anode microstructure which is related to starting powder preparation and anode forming processes. Different synthesis methods such as solid state reaction, sol gel, hydrothermal, co-precipitation and solution combustion synthesis have been used for the ceramic powder processing. The conventional solid state method is a lengthy process which requires multi-sintering steps. The synthesized powder also shows large particle size and low purity [7]. While sol gel method is also time consuming process and it is difficult to control the reaction mechanism for the synthesis of binary and ternary oxides and to select appropriate precipitator. Among the available wet chemical processes, combustion technique is capable of producing ultra fine powders [8, 9]. The solution combustion starts at lower temperature with the help of external heating source, followed by subsequent exothermic reactions between the oxidizer and fuel. This exothermic reaction provides necessary heat to further carry the reaction in forward direction to produce nanocrystalline powders as the final product. In glycine nitrate combustion synthesis (GNP), glycine is used as a fuel, being oxidized by nitrate ions. It is inexpensive, has high energy efficiency, fast heating rates, short reaction times and high compositional homogeneity [10, 11]. In literature, ternary and binary nickel- based anodes materials such as NiO-Ce1-x Zrx O2 [12], Ni1-xCux-SDC [13], Ni + Fe + SDC [14] , FexCo0.5XNi0.5-SDC anodes [15] is synthesized by GNP combustion synthesis method. There is only one reference where NiO-SDC is synthesized by single step urea combustion method [16].

PdO-NiO-SDC anode material is earlier synthesized by different methods [17, 18]. Although the GNP method is used to synthesize binary and ternary and multi-component oxides, to our best our knowledge it has not been used to synthesize Ni1-xPdxCe0.8Sm0.2O1.9 (PdO-NiO-SDC) powders. Hence in the present work, attempts have been made to synthesize the (PdO-NiO-SDC) powder by single step glycine nitrate combustion synthesis with different glycine to nitrate ratios. The prepared PdO-NiO-SDC powders are physically and electrochemically characterized to evaluate its applicability as anode of IT-SOFC.

2. Experimental Procedure

2.1. Powder synthesis

For the synthesis of 2 wt % PdO-NiO-SDC powder, solution was prepared by dissolving stoichiometric amount of palladium nitrate [Pd(NO3)2], nickel (II) nitrate hexahydrate [Ni (NO3)3.6H2O], cerium (III) nitrate [Ce(NO3)3.6H2O], samarium (III) nitrate [Sm(NO3)3.6H2O] in deionised water with Ni:Ce08Sm02Oi.9 as 7:3. Ce: Sm was selected as 8:2 in order to have high conductivity [19]. All chemicals were supplied by Alfa Aesar (India). Glycine (NH2-CH2-COOH) was first dissolved in deionised water and glycine and metal nitrate solutions were then mixed thoroughly, to ensure molecular level mixing, to form a clear, homogeneous solution. The powder characteristics such as crystallite size, surface area, extent and nature of agglomeration are primarily governed by enthalpy or flame temperature generated during combustion [20]. After homogenization the solution was heated on hot plate at 80 °C till brown color gel forms. Then the temperature of the hot plate was raised to 180-250 °C. The resultant viscous gel ignited automatically and an intense and self sustaining flame was formed, which rapidly

propagates to the whole material. It results in to the formation of foamy, highly porous brown color powder. The conversion process lasts for about a minute.

To remove the residual carbon and to promote the crystallization, ash was sintered at 600 °C for 2 h. Since during combustion reaction enthalpy was very high, powder synthesized is light in weight and hence it was difficult to capture the powder. To get rid of this a stainless steel mesh was put onto the steel reactor. By doing this, the exhaust gas was allowed to leave the steel reactor and ash was collected inside the reactor. The ash was then grounded in agate mortar for 5-10 min. Further, 10 wt % starch was added to the anode powder to increase its porosity. The powder was then uni-axially pressed at a pressure of about 16 MPa to obtain green compact pellets with thickness about 1 mm and diameter 13 mm. These pellets were sintered at 1100, 1200 and 1300 °C for 4 hours with a heating rate 3 °C /min in air for conductivity measurements.

2.2. Powder characterization

Thermo-gravimetry and derivative thermogravimetry (TG-DTG) of as synthesized powders were carried out by using TG instrument (TG 209 F3 Tarsus) with heating rate of 10 °C/min from 10-1000 °C in air environment. The morphology of the powders was observed using a high resolution transmission electron microscope (TECNAI G2, SEI (Netherland), equipped with an energy dispersive X-ray (EDX) analyzer. The micro-structural analysis of the synthesized powders was conducted with scanning electron microscope (2ELSS EVO series, model EVO 50). The phase identification of synthesized PdO-NiO-SDC powders with different g/n ratios was made with the powder X-ray diffraction (XRD) technique using Phillips PW-1710 diffractometer with CuKa radiations with wavelength

I.5424 A and scanning range 10-100°. The relative densities and porosity of the sintered pellets were measured by the standard Archimedes method. BET surface area of the as formed powders heated at 600°C for 2 h was measured with isothermal nitrogen absorption/desorption method using, Micrometritics Gemini, model 2375. The conductivity of the pellets sintered at 1100, 1200 and 1300 °C for 4 h was obtained from two probe conductivity measurements using impedance spectroscopy. Two electrodes were formed by applying silver paste on both the surfaces of the pellet and sintered at 200 °C for 20 min, measurements were made with an impedance analyzer (Versa STAT 3, Ametek) over a frequency range of 1 Hz to 1 MHz in the temperature range of 200-800 °C, at AC voltage amplitude 10 mV.

3. Results and Discussion

In the case of GNP, the precursor mixture of strong oxidizer and a readily combustible fuel, glycine after thermal dehydration causes nitrate decomposition giving N2, CO2 and H2O as the gaseous products. Therefore carbon and hydrogen are considered as reducing elements with their valancies +4 and +1, whereas oxygen is considered as an oxidizing element with the valency -2, and nitrogen is assumed to have zero valency. Cerium and samarium are onsidered as reducing elements with valency +3 in their nitrates. Palladium and nickel are also reducing elements with valency +2 in their nitrates. Using these valencies of individual element, total oxidizing valency of nitrate is

II.5 and total reducing valency of NH2-CH2-COOH is 9. A possible reaction equation of combustion for complete oxidation, called as stoichiometric [10] is given by equation 1.

Stoichiometric (n/g =0.78)

0 .02Pd(NO3)2 + 0.68Ni(NO3)2.6H2O+0.24Ce(NO3)3.6H2O + 0.06Sm(NO3)3.6H2O+1.277NH2 -CH2 -COOH +0.4048O2 ^ Pd0.02Ni0.68Ce024Sm0MO2-s + 2.5554CO2 + 1.788N2 + 9.074H2O (1)

Below and above the glycine to nitrate molar ratio of 0.78 is called a fuel lean and fuel rich ratio. Here selected fuel lean and rich ratios are 0.97 and 0.56 respectively. Redox reactions during combustion involving these ratios are given by equation (2 and 3)

0.02Pd (NO3)2 + 0.68 Ni(NO3)2.6H 2O + n.24Ce(NO3)3.6H2O + 0.06Sm( NO3)3.6H2O + 1.78NH2 - CH2 - COOH +1.535O, ^Pdnn,Nin68Cen,4Smnn6O, , + 3.56CO, + 2.04N, + m^^O (2)

2 0.02 0.68 0.24 0.06 2-d 2 2 2

0.02Pd(NO3)2 + 0.68Ni(NO3)2.6H2O + 0.24Ce(NO3)3.6H2O + Q.Q6Sm(NO3)3.6H2O + 1.03NH2 -CH2 -COOH +1.535O2 ^ Pd0mNi068Ce0MSm0MO2-s+ 2.054CO2 + 1.6635N2 + 8.4475H2O + 1.1897O2 (3)

3.1. TGA/DTG study

Figs.1(a-c) shows the simultaneous thermo-gravimetry and derivative thermogravimetry (TG/DTG) plots of as synthesized powders with different g/n ratios. From Fig. 1 it is seen that for all powders there is increase in the weight of the powders after heating them in air environment. Nature of the reactions observed during TG and DTG are almost same for different g/n ratios studied. It suggests that some amount of un-reacted glycine and nitrates left behind and react with each other during further heating in air environment. For all samples a sharp endothermic peak is observed at about 950 °C showing the complete formation of the desired product. This suggests that the PdO-NiO-SDC has been crystallized almost perfectly at this temperature.

3.2. XRD Analysis

In GNP, different g/n rations as fuel lean (0.97); stoichiometric (0.78) and fuel rich (0.56) strongly affect the powder characteristics. Fig. 2(a) shows the XRD patterns of powders synthesized by using these ratios. The synthesized powders are well crystalline in nature, showing separate peaks corresponding to the cubic PdO - (222)

-0.30 -0.25 1 - 0.20 j -0.15 ; -0.10 j

- 0.05 !

- 0.00 ; - -0.05 f --0.10

200 400 600

Temperature ( DC)

Fig. 1. Simultaneous TG-DTG plots of as synthesized PdO-NiO-SDC powders with (a) g/n ratio 0.78, (b) g/n ratio 0.56 and (c) g/n ratio (0.97).

Fig. 2. XRD patterns of PdO-NiO-SDC powder (a) as synthesized and (b) heat treated at 600 °C for different g/n ratios as fuel lean (0.97), stoichiometric (0.78) and fuel rich (0.56).

(420); cubic NiO - (111), (200), (220), (311), (222) and cubic fluorite SDC phases (111), (002), (022), (113), (222), (004), (133), (024), (224) and (115). The average values of the lattice parameters 'a' for fuel lean, stoichiometric and fuel rich compositions are found to be 5.4550, 5.4415, 5.4411 °A for cubic SDC, 5.6766, 5.6842, 5.6828 for cubic PdO and 4.2062, 4.1889, 4.1867 for cubic NiO, respectively. The calculated lattice parameter matches well with the reported values [21, 22]. Fig. 2(b) shows the XRD patterns of the powders synthesized with different g/n ratios and heat treated at 600°C for 2 h. The average values of the lattice parameters 'a' for fuel lean, stoichiometric and fuel rich compositions are found to be 5.4360 A, 5.4361 A, 5.4415 A for cubic SDC, 5.6772 A, 5.6776 A, 5.6842 A for cubic PdO and 4.1924 A, 4.1886 A, 4.1889 A for cubic NiO, respectively. The crystallite size is calculated by using Scherer's formula and found to be 11.5, 23.8 and 43.2 nm for fuel lean, stoichiometric and fuel rich ratios. The powders prepared from fuel lean ratio are having small crystallite size as compared to others due to the less amount of heat evolved during the combustion of fuel. Since nano-crystalline ceramics have superior powder properties such as large surface area, better sinterability, higher conductivity [12, 13], hence we have optimized fuel lean ratio (0.97) for further studies.

Fig. 3 shows XRD patterns of the powder synthesized from fuel lean ration (0.97) and heat treated at 600 °C, 800 °C and 1000 °C for 2 h. The characteristic peaks corresponding to PdO phases is not observed for 800 °C and 1000 °C heat treated powders, showing the formation of Ni1-x-PdxO alloys. The calculated crystallite size of the powders heated at 600 °C, 800 °C and 1000 °C are 11.57, 15.53 and 35.92 nm. It is found that the crystallinity of the powder

Fig. 3. XRD patterns of PdO-NiO-SDC powder synthesized with g/n ratio 0.97 and heat treated at 600 °C, 800 °C, 1000 °C during combustion synthesis process.

30000-

* - NiO ?- SDC

25000-

1 20000-

f 10000-

1300 '1200 1100

26 (degrees)

Fig. 4. XRD plots of PdO-NiO-SDC pellets sintered at 1100, 1200, 1300 °C for 4 h

increases with the increase in the calcination temperature. Fig. 4 shows XRD plots of the pellets prepared from fuel lean ration (0.97) and sintered at 1100 °C, 1200 °C and 1300 °C for 4 h. The characteristic peaks corresponding to PdO phases are not observed, showing the formation of Ni(1-x)-PdxO alloys. The peaks from the solid solution shifted slightly to the lower angles due to dissolution of Pd2+ in Ni2+. The calculated crystallite size of the pellets sintered at 1100 °C, 1200 °C and 1300 °C is found to be 52.97, 61.94 and 98.20 nm. The crystalline nature of the pellets increases with the increase in the sintering temperature. It may be noted that overall powder synthesized by using glycine nitrate combustion synthesis is ultra fine with nanometer size grains. The reason for nano-crystalline nature may be due to atomic and molecular level mixing of reagents. During combustion, the nucleation process occurs through the rearrangement and short path diffusion of nearby atoms and molecules [23]. The large volume of the gases evolved during the combustion reaction limits the inter particle contact. Also the combustion process occurs at such a fast rate that sufficient energy and time are not available for long path diffusion or migration of the atoms or molecules as a result of which the initial nano-size of the powder is retained [24].

3.3. SEM and BET Analysis

Fig. 5 shows SEM images of as synthesized PdO-NiO-SDC powders with (a) g/n ratio 0.78 (b) g/n ratio 0.56 (c) g/n ratio 0.97 and respectively heat treated at 600°C for 2 h (d, e, f). All the powders are found to be highly porous. During combustion synthesis, exothermic reaction takes place and large amount of gases evolved which makes the powder highly porous. Powders heated at 600 °C for 2 h are also porous but increase in particle size is observed after calcinations. In case of anode a certain amount of porosity is required in order to facilities the gas transfer and to enlarge the three phase boundary region. Thus the presence of micro and macro porous in the powder will help to increase the reaction area and will significantly decreases the electrode polarization resistance. It is seen that fuel rich (g/n = 0.56) composition shows increase in the crystallite size of the powder and hence decrease the surface area due to local sintering of the powder particles. This is due to large amount of heat evolved during combustion of fuel rich composition [20].

Fig. 6 shows the SEM images (30 KX) of cross-section of PdO-NiO-SDC pellets sintered at 1100, 1200 and 1300 °C in air. After sintering, pore former burn off which increases the porosity of pellets. The porosity of sintered pellets is measured by Archimede's principle and the respective values are presented in Table 1. It can be seen that open porosity of the pellets decreases and grain to grain connectivity increases with increase in sintering temperature.

Fig. 5. SEM images of as synthesized PdO-NiO-SDC powders with (a) g/n ratio 0.78 (b) g/n ratio 0.56 (c) g/n ratio 0.97 and respectively heat treated at 600°C for 2 h (d, e, f).

Fig. 6. SEM images of of cross-section of PdO-NiO-SDC pellets sintered at (a) 1100 °C (b) 1200 °C and (c) 1300°C

Table 1. Variation of porosity of pellets with respect to sintering temperature.

Sintering temperature (°C) Porosity (%)

1100 45

1200 38

1300 16

Table 2 shows BET surface area of the powders synthesized by stoichiometric, fuel rich and fuel lean compositions and heat treated at 600 °C for 2 h. The powder synthesized from the fuel lean ratio has high surface area as compared to the powder synthesized from the stoichiometric and fuel rich compositions. High flame temperature in the case of stoichiometric and fuel rich compositions may have affected the powder characteristics adversely. This results into the increase in the crystallite size, premature partial local sintering among the active primary particles produced during combustion, thereby reducing the surface area [15, 16]. BET results are in accordance to the XRD results.

3.4. TEM and EDS Analysis Figs. 7(a-d) shows the TEM images of the PdO-NiO-SDC powders at different magnifications for g/n fuel rich (

Table 2. Effect of glycine to nitrate molar ratio on BET surface area.

g/n molar BET (m2/g) Average pore

ratio diameter (nm)

0.97 mo 2

0.78 5.11 1.9

0.56 3.34 2.2

g/n=0.56) and fuel lean (g/n=0.97) ratios. TEM images confirms the nano-crystalline nature of the synthesized powders. The average particle size of the powders are in the range of 5-10 nm for fuel rich and fuel lean compositions and is in agreement with the average crystallite size calculated from the XRD. The corresponding EDS images in figs. 7 (e, f) represent the presence of all the desired elements Pd, Ni, Ce Sm and O in both the powders. The carbon peaks appears due to the conductive carbon tape used during sample mounting.

3.5. Electrical Properties

The conductivity of PdO-NiO-SDC pellets sintered at 1100, 1200 and 1300 °C is measured in temperature range of 500 to 800 °C in humidified hydrogen as shown in Fig. 8. It is observed that the conductivity of the pellets increase with increase in sintering temperature. With increase in sintering temperature, the grain size of the material increases

1 ¡L^Jfc". (f) Li..........

Fig. 7. TEM and EDS micrographs of PdO-NiO-SDC powders synthesized with g/n ratio 0.97 (a, b, e) and g/n ratio 0.56 (c, d, f) and heat treated at 600°C for 2 h

= u 1.84-

g 1.80-

O 1.78-

* : : .4 i » • • -

0.90 0.95

1.05 1.10 1.15 1000/T (K1)

1.20 1.25

Fig. 8. Variation of log of conductivity vs 1000/T of the pellets sintered at (■)1100 °C, (•) 1200 °C, and (A)1300 °C

and porosity decreases, which intern increase the connectivity of the material and thereby the conductivity. Moreover, conductivity of all pellets decreases with increase in operating temperature showing metallic behavior. The conductivity is less than that reported for NiO-SDC [16, 25] but are better than that reported for LSCM anode [26]. Hence one can conclude that the conductivity of the cermet is high enough to use it as anode in intermediate temperature SOFC. The activation energy was calculated by using, a T = a° exp (-Ea/kT) where, Ea is the activation energy for conduction, T the absolute temperature, and a° is a pre-exponential factor. Activation energies is found to be 0.21, 0.22 and 0.21 eV for the pellets sintered at 1100, 1200 and 1300°C for 4 h, respectively which is lower than that reported for SDC [21], NiO-SDC [27], and PdO-NiO-SDC [22]. The anode for SOFC should have high electronic conductivities, adequate porosity for gas transport, and high oxygen-ion conductivities. In the present case, PdO-NiO-SDC anode synthesized by glycine nitrate combustion synthesis can be considered as the anode for IT-SOFC.

NiO-SDC anode and SDC as electrolyte has been used in metal supported SOFC by S.Hui et al. [28, 29]. In the present case, crystallite size of the synthesized PdO-NiO-SDC is in nano scale. In nano-crystalline materials grain boundaries have high defect densities and the atoms there have high mobility, and hence when the grain size decreases from the few micrometers to the nano level, the grain boundaries show unusually high conductivity [30], enhance sintering properties due to nano scale nature. This also leads to the better BET surface area value of 15 m2/g. Also pellets formed shows highly porous microstructure with porosity in the range 38-45 %, better electrical conductivity 99 S/cm at 450 °C and 72 S/cm at 500 °C. Due to the presence of mixed phases such as SDC, Ni and Pd, the anode will have mixed ionic and electronic conductivity; and will have high three phase boundary area, sulfur and coking resistance [22].

4. Conclusions

PdO-NiO-SDC mixed ionic electronic conducting nano-powder is synthesized by simple, rapid and cost effective glycine- nitrate combustion method, for the first time. XRD shows that the crystalline size increases with increase in calcinations temperature from 11.57 to 35.92 nm. SEM shows that synthesized powders are highly porous. The maximum BET surface area of the powder is found to be 15 m2/g for fuel lean g/n ratio. TEM confirms that particle size is in nm range whereas EDS shows the presence of all the desired elements. Pellets sintered in the temperature range 1100-1300 °C for 4 h shows porosity in the range of 16-45 % which decreases with increase in sintering

temperature. The conductivity of prepared material is observed to be 99 S/cm at 450 °C and 72 S/cm at 800 °C. The prepared PdO-NiO-SDC fulfills all the requirements as anode for IT SOFC.

Acknowledgements

Authors are thankful to the Ministry of New and Renewable Energy (MNRE), New Delhi and I.I.T. Delhi for providing financial assistance.

References

[1] Toebes ML, Bitter JH, Dillen AJvan, Jong, KPde. Impact of the structure and reactivity of nickel particles on the catalytic growth of carbon nanofibers. Cataly Today 2002;76:33-42.

[2] Simwonis D, Tietz F, Stover D. Nickel coarsening in annealed Ni/8YSZ anode substrates for solid oxide fuel cells. Solid State Ionics 2000; 132: 241-251.

[3] Azad AM, Duran MJ, McCoy AK, Abraham MA. Development of ceria-supported sulfur tolerant nanocatalysts: Pd-based formulations Appl Cataly A: Gen 2007; 332:225-236.

[4] Lu XC, Zhu JH. Cu(Pd)-impregnated Lan.75Srn.25Crn.5Mnn.5O3 - 5 anodes for direct utilization of methane in SOFC. Solid State Ionics 2007; 178:1467-1475.

[5] Uchida H, Mochizuki N, Watanabe M. High performance electrode for medium temperature operating solid oxide fuel cells. Polarization property of ceria based anode with highly dispersed ruthenium catalysts in (H2+CO2+H2O) gas. J Electrochem Soc 1996; 143:1700-1704.

[6] McIntosh S, Vohs JM and Gorte RJ. Effect of precious-metal dopants on SOFC anodes for direct utilization of hydrocarbons. Electrochem Solid state Lett 2003; 6:A240-A243.

[7] Sin A, Odier P. Gelation by acrylamide, a quasi universal medium for the synthesis of fine oxide powders for electroceramic applications. J Adv Mat 2000; 12: 649-652.

[8] Kingsley JJ, Suresh K, Patil KC. Combustion synthesis of fine-particle metal aluminates. J Mater Sci 1990;25:1305-1312.

[9] Ferreira, VM, Azough F, Baptista, JL, Freer R. DiC12: Magnesium titanate microwave dielectric ceramics. Ferrolectrics 1992;133:127-132.

[10] Chick LA, Pederson LR, Maupin GD, Bates JL, Thomas LE, Exarhos GJ. Glycine-nitrate combustion synthesis of oxide ceramic powders.

Mater Lett 1990;10: 6-12.

[11] Kingsley JJ, Pederson LR. Combustion synthesis of perovskite LnCrO3 powders using ammonium dichromate. Mater Lett 1993; 18: 89-96.

[12] Prasad DH, Jung HY, Jung HG, Kim BK, Lee KW and Lee JH. Single step synthesis of nano- sized NiO-Cen.75Zrn.25O2 composite

powders by glycine nitrate process. Mater Lett 2008; 62: 587-590.

[13] Xia Z, Xia C, Zhang M, Zhu, W, Wang H. Ni1-xCux alloy-based anodes for low-temperature solid oxide fuel cells with biomass-produced

gas as fuel. J Power Sources 2006;161:1056-1061.

[14] Lu XC, Zhu JH. Ni-Fe + SDC composite as anode material for intermediate temperature solid oxide fuel cell. J Power Sources 2007;165: 678-684.

[15] Xie Z, Zhu W, Zhu B, Xia C. FexCon.5-xNin.5-SDC anodes for low-temperature solid oxide fuel cells. Electrochem Acta 2006;51:3052-

[16] Chen M, Kim BH, Xu Q, Nam OJ, Ko J H. Synthesis and performances of Ni-SDC cermets for IT-SOFC anode. J Europ Ceram Soc

2008;28: 2947-2953.

[17] Hibino T, Hashimoto A, Yano M, Suzuki M, Yoshida S, Sano M. High Performance Anodes for SOFCs operating in methane-air mixture

at reduced temperatures. J Electrochem Soc 2002;149:A133-A136.

[18] Buergler BE, Siegrist ME, Gauckler LJ. Single chamber solid oxide fuel cells with integrated current-collectors. Solid State Ionics 2005;176

:1717-1722.

[19] Jose R, James J, John AM, Sundararaman D, Divakar R. A new combustion process for nanosized YBa2ZrO5.5 powders. Nanostruct Mater

1999; 11 (5): 623-629.

[20] Purohit, RD, Saha S, Tyagi AK. Nanocrystalline thoria powders via glycine-nitrate combustion, J Nuclear Mater 2001;288:7-10.

[21] Patil BB, Pawar SH. Spray pyrolytic synthesis of samarium doped ceria (Ce0.8Sm0.2O19) films for solid oxide fuel cell applications. Appl Surf Scien 2007;253: 4994-5002.

[22] Patil BB, Pawar SH. Synthesis and characterization of spray deposited PdO-NiO-SDC composite anode material for potential application in IT-SOFC. J Alloys Compounds 2011;509: 3644-3650.

[23] Bansal NP and Zhong Z. Combustion synthesis of Sm0.5Sr0.5CoO3-x and La0.6Sr0.4CoO3-x nanopowders for solid oxide fuel cell cathodes. J

Power Sources 2006;158:148-153.

[24] Liu B, Zhang Y. Ba0.5Sr0.5Co0.8Fe0.2O3 nanopowders prepared by glycine-nitrate process for solid oxide fuel cell cathode. J Alloys and compounds 2008;453: 418-422.

[25] Yin Y, Zhu W, Xia C, Meng G. Gel-cast NiO-SDC composites as anodes for solid oxide fuel cells. J Power Sources 2004;132: 36-41.

[26] Ronghui L, Qingshon D, Wenhui M, Hua W, Bin Y, Yongnian D, Xueju M. Preparation and characterization of component materials for intermediate temperature solid oxide fuel cell by glycine nitrate process. J Rare Earths 2006; 24: 98-103.

[27] Patil BB, Ganesan VS, Pawar H. Studies on spray deposited NiO-SDC composite films for solid oxide fUel cells, J Alloys and Compounds 2008;46: 680-687.

[28] Hui R, Berghaus JO, Petit CD, Qu W, Yick S, Legoux JG, Moreau C. High performance metal-supported solid oxide fuel cells fabricated by thermal spray. J Power Sources 2009;191:371-376.

[29] Hui S, Yang D, Wang Z, Yick S, Petit CD, Ou, W, Tuck A, Maric R, Ghosh D. Metal supported solid oxide fuel cell operated at 400-600 °C. J Power Sources 2007;167: 336-339.

[30] Tuller HL. Ionic conduction in nanocrystalline materials. Solid State Ionics 2000; 131:143-157.