Evaluation of thin film fuel cells with Zr-rich BaZrxCe0.8-xY0.2O3-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 BaZrxCe0.8-xY0.2O3-delta (x = 0.4, 0.6, 0.7, and 0.8) proton-conducting electrolytes, which were fabricated by single step co-firing with Zn(NO3)(2) additives at a relatively low temperature (1400 degrees C). The grain sizes significantly increased to several mu m for x = 0.4 and 0.6, whereas the grain sizes remained in the sub-mu m 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 degrees 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 BaZrxCe0.8-xY0.2O3-delta discs confirmed that the total proton conductivity of BaZr0.6Ce0.2Y0.2O3-delta was higher than that of BaZr0.4Ce0.4Y0.2O3-delta at temperatures above 500 degrees C despite relatively small grain sizes. In addition, BaZr0.6Ce0.2Y0.2O3-delta cells could gain a stable current throughout a continuous run for a few days under CO2-containing fuel supply, which was due to high fraction of thermodynamically stable BaZrO3 matrices. It was demonstrated that BaZr0.6Ce0.2Y0.2O3-delta is a promising electrolyte for proton-conducting ceramic fuel cells with excellent proton conductivity and CO2 tolerance at intermediate temperatures.