Phase formation and properties of composite electrolyte BaCe_(0.8)Y_(0.2)O_(3-δ)-Ce_(0.8)Gd_(0.2)O_(1.9) for intermediate temperature solid oxide fuel cells

摘要

In this study, we have investigated the feasibility of forming a new ionic conducting electrolyte from a proton conducting phase, BaCe_(0.8)Y_(0.2)O_(3-δ) (BCY), and an oxygen conducting phase, Ce_(0.8)Gd_(0.2)O_(1.9) (GDC), in order to decrease the reduction of Ce~(4+) ions to Ce~(3+) ions in reducing atmospheres at high temperatures. BCY-GDC composite powders (molar ratio 1:1) are synthesized via a one-step citric acid-nitrate gel combustion method. The reaction between the BCY and GDC in these composite powders at 1550 C results in the formation of a new perovskite phase with a nominal composition of BaCe_(1.6)Y_(0.2)Gd_(0.2)O_(4.9-ū) The conductivity of the new perovskite phase is found to be substantially (~150%) higher than that of the composite electrolyte made from the mixture of BCY and GDC with the same nominal composition as the new perovskite phase. The single fuel cells with the new perovskite electrolyte exhibit better electrochemical performance than the cells with the composite electrolyte made of the mixture of BCY and GDC. The maximum power density of single cells with the new perovskite electrolyte can reach 0.657 Wcm~2 at 700℃ using humidified hydrogen (3% H_2O) as the fuel. This maximum power density is ~65% higher than that of the cells with the BCY + GDC composite electrolyte.