Perovskite-structured ceramics with mixed protonic-electronic conductivity have attracted considerable attention in recent years for producing hydrogen of high purity (> 99.99%) from coal or methane conversion at high temperatures (> 600°C). Chemical stability and hydrogen flux of a solid solution between these compounds were studied to find a composition with both high electrical conductivity and good chemical stability against CO2. Doping of Zr into SrCe0.95Tm0.05O3 greatly enhanced its chemical stability, with 40% Zr doped material did not react with CO2. Introduction of Zr led to a decrease in the total electrical conductivity that was about three times less than that of basic SrCe0.95Tm0.05O3 without Zr doping. However, 40% Zr doped powders were difficult to sinter as they could reach only up to 90% of the theoretical density. Best Zr-doped membranes containing a pure perovskite phase, displaying good stability and high density were 30% Zr-doped SrCe0.65Zr0.30Tm0.05O3. It gave a good compromise between conductivity and stability for H2 separation applications. This is an abstract of a paper presented at the 2006 AIChE National Meeting (San Francisco, CA 11/12-17/2006).