Effect of La3+ and Gd3+ for Bi3+ in Bismuth Vanadate Electrolyte

Abstract

The modern scientific and technological approach, in the area of energy production is to develop inexpensive devices, which could satisfy the current drive for cleaner and more efficiently distributed power, particularly in combination of heat and power systems. In this context, fuel cells represent a promising and viable alternative for large scale generation of electricity, with minimal undesirable chemical, thermal and acoustic emissions. A fuel cell is a device that directly converts the chemical energy of reactants (a fuel such as hydrogen, natural gas, methane or methanol and an oxidant air or oxygen), into electricity. Solid Oxide Fuel Cell (SOFC) is the most advancing field in the science of fuel cell due to higher efficiency than other fuel cells. The obstacle in the commercialization of SOFCs is their high operating temperature. Solid electrolyte is the most important part of SOFCs. Its performance is critical to the development and commercialization of SOFC. Therefore several efforts have been made to develop a suitable solid electrolyte which has higher ionic conductivity in intermediate temperature range (800- 600oC). Several electrolyte materials have been studied and it is found that bismuth oxide based electrolytes shows higher conductivity at lower temperatures when doped with various aliovalent cations. Basically, bismuth vanadate exhibits three phase transition i.e. α → β and β → γ in room temperature to 700oC temperature range. In these phases disordered γ-phase shows higher conductivity than α and β phases. γ-phase could be stabilized at room temperature after doping of various cations. In present study, a series of Bi4-xMxV2O11 (0 ≤ x ≥0.4; M= Gd, La) have been synthesized and characterized by using various techniques such as X-ray diffraction, Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA) and ac conductivity measurement. All the samples exhibit either α-Bi4V2O11 or β-Bi4V2O11 phase. These phase formations is further confirmed by DSC and ac conductivity measurement. The conductivity variation has been discussed on the base of defect mechanism.