Photonic crystals in biology - NanoTR-VI

Poster Session, Thursday, June 17Theme F686 - N1123Hydrothermal preparation and electrochemical properties of Sm 3+ and Gd 3+ ,codoped ceria-based electrolytes for intermediate temperature-solid oxide fuel cellsSibel Dikmen 1 , Hasan Aslanbay 1 , Erdal Dikmen 21 Department of Chemistry, Suleyman Demirel University, Isparta 32260, Turkey2 Department of Physics, Suleyman Demirel University, Isparta 32260, TurkeyAbstract- The structure, ionic and electronic conductivities of Ce 0.8 Sm 0.2-x M x O 2- (for M: Gd, and La, x = 0-0.1) solid solutions, prepared forthe first time hydrothermally, are investigated. The uniformly small particle size (23-64 nm) of the materials allows sintering of the samplesinto highly dense ceramic pellets at 1300-1400 o C, significantly lower temperature, compared to that at 1600-1650 o C required for ceria solidelectrolytes prepared by solid state techniques. The maximum conductivity, 700ºC 6.50 10 -2 Scm -1 , E a = 0.59 eV, is found at x = 0.1 for Gdcodoping.The electrolytic domain boundary (EDB) of Ce 0.8 Sm 0.1 La 0.1 O 2- has been found to be lower than that of singly doped samples.These results suggest that co-doping can further improve the electrical performance of ceria-based electrolytes.Fuel cells are electrochemical devices that directly convertthe chemical energy of a fuel into electrical energy in ahighly clean, cheap and efficient way [1]. Electrolytes usedfor fuel cells are usually the main components determiningthe performance of the cell. A typical solid oxide fuel cellelectrolyte, 8mol% yttria-stabilized zirconia (YSZ), havingthermal and mechanical strength both toward anode reductionand cathode oxidation requires to operate at hightemperatures (800–1000 C) to provide high level of ionicconductivity. This limits the range of materials used forinterconnection, electrodes and sealing due to the corrosionof metallic components [2]. Some singly doped-electrolytes,such as Ce 1x Gd x O 2 (GDC), Ce 1x Sm x O 2 (SDC),Ce 1x Y x O 2 (YDC), etc., show high oxide ion conductivity atintermediate temperatures (500–700C) [3–5].Substitution ofthe Ce 4+ cations by a lowervalent metal ion (e.g., M 3+ ) in thelattice results in the oxygen vacancy formation and increasesthe ionic conductivity.The ceria-based electrolytes easily develop n-type electronicconduction when exposed to the reducing atmosphere of thefuel cell anode which decreases the fuel cell efficiency. It istherefore important to make efforts towards the reductionof electronic conductivity. The dependence of totalconductivities of Ce 0.8 Sm 0.2x Gd x O 2 as a function of oxygenpartial pressure has been shown in Fig. 2. As can be seen, thetotal electrical conductivity ( t ) is predominantly ionic andremains constant at moderate P O2 , whereas at low P O2 , thetotal electrical conductivity increases as P O2 decreases and ispredominantly electronic..0.50.40.10 Ce 0.8Sm 0.2-xGd xO 2-0.05In this research, with the aim to develop new ceria-basedelectrolyte materials with improved electrochemicalproperties, Sm 3+ and Gd 3+ co-doped ceria materials wereprepared for the first time hydrothermally.Similar to the previously reported systems [6–7], theelectrical conductivity of Ce 0.8 Sm 0.2x Gd x O 2 increasessystematically with increasing gadolinium substitution andreaches a maximum for the composition Ce 0.8 Sm 0.1 Gd 0.1 O 2 ,( 700 C 6.50×10 2 Scm 1 ) Fig. 1)-1.0-2.0t(Scm -1 )0-25 -20 -15 -10 -5 0log PO (atm) 2Ce Sm Gd O 0.8 0.2-x x 2-0.30.20.1x = 0-3.0-4.0-5.0-6.0-7.0x = 00.050.10.150.20Fig.2 Oxygen partial pressure dependence of the totalconductivity of Ce 0.8 Gd 0.2x Sm x O 2 solid solutions at 973 K.The data are fitted with t = i +kP O21/4.From these results we can conclude that co-doping with Sm 3+and Gd 3+ can lead to an improvement of the stability of ceriabasedelectrolytes at intermediate temperatures.This study was supported by TUBTAK under the Grant No:106T536.-8.010 12 14 16 18 20 22 2410000/T (K -1 )Fig.1 Arrhenius plots of the ionic conductivity ofCe 0.8 Gd 0.2x Sm x O 2 solid solutions*Corresponding author: sdikmen@fef.sdu.edu.tr[1] S. Dikmen, Journal of Alloys and Compounds, 491 , 106 (2010)[2] H. Inaba, H. Tagawa, Solid State Ion., 83, 1 (1996)[3] S.W. Zha, C.R. Xia, G.Y. Meng, J. Power Sources, 115, 44 (2003)[4] D.J. Kim, J. Am. Ceram. Soc., 72 (8), 1415 (1989).[5] S.J. Hong, A.V. Virkar, J. Am. Ceram. Soc., 78 (2) (1995) 433–439.[6] S. Dikmen, P. Shuk, M. Greenblatt, Solid State Ion., 126, 89 (1999).[17] S. Dikmen, P. Shuk, M. Greenblatt, H. Gocmez, Solid State Sci., 4, 585(2002)6th Nanoscience and Nanotechnology Conference, zmir, 2010 763