Characterization of Y-Doped SrTi1-XVxO3 (Y = 0.1, x = 0.1 and 0.2) Anodes for SOFCs

Doped-SrTiO3 (STO) perovskites have been proven to be one of the promising candidates for the development of SOFC anode materials. The performance of STO is comparable to Ni/YSZ cermet anode at higher temperature [1]. However, its performance is still judged insufficient because of the high operating temperature and inadequate electronic conductivity. Substitution of A and B site of the perovskite is believed could further improve the ionic and electronic conductivity of the materials thus maximizing the performance of STO.

In this research, the effect of substitution of A and B site of the STO perovskite was investigated using Y-doped SrTi_1-xV_xO₃ with compositions Sr_0.9 Y_0.1 Ti_0.9 V_0.1 O₃ and Sr_0.9 Y_0.1 Ti_0.8 V_0.2 O₃. Both samples were prepared using solid state synthesis reaction sintered at temperature of 1450°C and 1250°C for duration of 4 hrs for Sr_0.9 Y_0.1 Ti_0.9 V_0.1 O₃ and Sr_0.9 Y_0.1 Ti_0.8 V_0.2 O_3, respectively. The microstructures of the samples were analyzed using scanning electron microscope (SEM) and the porous structure of the materials fulfills the essential characteristic as anode materials. X-ray diffraction (XRD) analysis of the materials confirmed that both samples formed single phase tetragonal structure (space group: I 4/m c m).

The thermal expansion coefficient (TEC) values of the samples are closed to the reported value of yttrium stabilized zirconia (YSZ) which show good thermomechanical compatibility of the materials with YSZ(TEC~ 10.8 x 10^-6 K^-1) [2]. Figure 1 illustrates the effect of TEC values with increasing B site doping concentration.

The electronic conductivity of the samples was measured under normal atmospheric pressure using four probe DC techniques at a temperature range of between 500°C to 1000°C. The measured conductivity of the samples is within the range of 0.0032 Scm^-1 to 0.2042 Scm^-1which is considered to be very low. The Arrhenius plot of the samples is shown in figure 2 below.

The average zeta potential of the samples is within the range of moderate stability of colloidal suspension with measured values of -29.9 mV and -31.2 mV for Sr_0.9 Y_0.1 Ti_0.9 V_0.1 O₃ and Sr_0.9 Y_0.1 Ti_0.8 V_0.2 O₃respectively. This suggests that the materials are able to resists aggregation. Refer to Table 1 below for the interpretation of the zeta potential values [3].

TG analysis of the samples was plotted in figure 3 below. 18.81% decrease in weight was accounted for Sr_0.9 Y_0.1 Ti_0.9 V_0.1 O₃ while an increase of 2.28% in weight was seen for Sr_0.9 Y_0.1 Ti_0.8 V_0.2 O₃.

References:

[1] M. Gong, X. Liu, J. Trembly, C. Johnson, “Sulfur-tolerant anode materials for solid oxide fuel cell application”, J. Power Sources 168 (2007) 289.

[2] O.A. Marina, N.L. Canfield, J.W. Stevenson, “Thermal, electrical, and electrocatalytical properties of lanthanum-doped strontium titanate” Solid State Ionics, 149 (2002) 21-28.

[3] Riddick, Thomas M. (Thomas Moore), 1907-1975. Control of colloid stability through zeta potential. Wynnewood, Pa., Livingston [1968]