Successful development of hydrogen separation membranes based on mixed ionic and electronic conductors would improve the economics of hydrogen production. The combination of high proton conductivity and good chemical stability is desirable for practical applications. In this paper, we report a new compound, BZCY6 [Ba(Zr0.2Ce0.6Y0.2)O-3], as an alternative to BCY20 (BaCe0.8Y0.2O3). The hydrogen permeation rate and chemical stability of the Ni-BZCY6 membrane were studied under various conditions. It appears that the membrane is stable in atmospheres containing up to 30% CO2 at 900 C. These results suggest that the Ni-BZCY6 membrane is suitable for hydrogen separation from hydrocarbon fuels. (c) 2005 The Electrochemical Society.