Effect of Mo-Doping on the Proton-Conducting BaCe0.9-xMoxY0.1O3-δ Electrolyte at Intermediate Temperature SOFCs

Abstract

Perovskites have been attracting much attention because of their many potential applications as solid electrolytes in solid oxide fuel cells (SOFC). Among various kinds of perovskite materials, the Y2+ doped BaCe0.9Y0.1O3-δ (BCY) have been investigated extensively. It is noted that the doped BCY have good stability and relatively high protonic conductivity. However, the sintering temperature of BCY is very high above 1600 °C to achieve the required densification. High sintering temperature leads to evaporation of barium and the subsequent segregation of doped elements. As a result of this, the electrochemical properties of BaCe0.7Zr0.1Y0.2O3-δ electrolyte are reduced. At high temperatures, it’s difficult to maintain the porous structure of electrodes and causes the formation of impurity phases. So, in order to overcome this issue, we doped Mo- to BCY and reduce the sintering temperature of the electrolyte without comprising its performance. The sol-gel method was followed for the preparation of Ba1Ce0.9-xMoxY0.1O3-δ (BCMY, x=0.025%-0.2%) powder. The precursor's Ba(NO3)2, Ce(NO3)3.6H2O, Y(NO3)3.6H2O, and (NH4)6Mo7O24.4H2O in the stoichiometric ratio were dissolved in a mixture of water, citric acid, and glycine used as chelating agents in the molar ratio of 1:2:1. The solution was heated at 100 °C and was constantly stirred till it becomes a gel. The dried precursor was then heated at 350 °C for 2 hrs to remove the organic residues through combustion. Afterward, it was calcined at a temperature of 1100 °C for 10 hrs and finally, a white powder of BCMY was obtained. The synthesized BCMY electrolytes were sintered at 900, 1000, and 1100 °C to observe the effects of low sintering temperature on the structural, morphological, and electrical properties of BCMY. All BCMY electrolyte materials exhibited a crystalline perovskite structure and were found to be thermally stable as shown in XRD (Fig. 1 (a, b)). The morphology and element distribution of the BCY and BCMY electrolyte were observed by the scanning electron microscope (SEM, (Fig. 1c)) and energy-dispersive x-ray spectroscopy (EDX). SEM images show that BaCe0.9Y0.1O3-δ electrolyte sinterability and densifications are significantly improved. Fully dense pellets are sintered by using 0.025-0.2 mole% Mo. Energy dispersive spectroscopy shows that sintering aids are uniformly distributed throughout the structure. This study demonstrates BCMY as a dense proton-conducting electrolyte for intermediate-temperature solid oxide fuel cells. The BCMY with Mo-doping appears to be a potential candidate for sintering at low temperatures. Sintering facilitates addition from oxygen vaccines, which ease ionic conduction through the electrolyte, result in a low activation energy of at moderate temperatures. Fully dense pellets are sintered by using 0.025-0.2 mole% Mo. This method of decreasing the BCMY sintering temperature is useful in improving the SOFC performance.