Evaluation of thin film fuel cells with Zr-rich BaZr(x)Ce(0.8−x)Y(0.2)O(3−δ) electrolytes (x ≥ 0.4) fabricated by a single-step reactive sintering method

This paper reports a survey of power generation characteristics of anode-supported thin film fuel cells with Zr-rich BaZr(x)Ce(0.8−x)Y(0.2)O(3−δ) (x = 0.4, 0.6, 0.7, and 0.8) proton-conducting electrolytes, which were fabricated by single step co-firing with Zn(NO(3))(2) additives at a relatively low temperature (1400 °C). The grain sizes significantly increased to several μm for x = 0.4 and 0.6, whereas the grain sizes remained in the sub-μm ranges for x = 0.7 and 0.8, which resulted in large gaps of the fuel cell performances at x over and below 0.6. The cells for x = 0.4 and 0.6 exhibited efficient power generation, yielding peak powers of 279 and 336 mW cm(−2) at 600 °C, respectively, which were higher than those of the corresponding cells previously reported. However, the performances abruptly deteriorated with the increasing x to more than 0.7 because the electrolyte films were highly resistive due to the coarse-grained microstructures. Impedance spectroscopy for the dense sintered BaZr(x)Ce(0.8−x)Y(0.2)O(3−δ) discs confirmed that the total proton conductivity of BaZr(0.6)Ce(0.2)Y(0.2)O(3−δ) was higher than that of BaZr(0.4)Ce(0.4)Y(0.2)O(3−δ) at temperatures above 500 °C despite relatively small grain sizes. In addition, BaZr(0.6)Ce(0.2)Y(0.2)O(3−δ) cells could gain a stable current throughout a continuous run for a few days under CO(2)-containing fuel supply, which was due to high fraction of thermodynamically stable BaZrO(3) matrices. It was demonstrated that BaZr(0.6)Ce(0.2)Y(0.2)O(3−δ) is a promising electrolyte for proton-conducting ceramic fuel cells with excellent proton conductivity and CO(2) tolerance at intermediate temperatures.