Advanced hybrid architecture (power & hydrogen) in low temp. methane steam reforming, which allows a significant improvement in energy efficiency, require developing effective and stable H2 sepn. membranes. We compare here the performances and stability of two membranes based on a thin Pd-Ag alloy film supported over tubular ceramic asym. membrane. These two samples were prepd. by co-plating and sequential electroless plating. They show macroscopic similar characteristics and absence of cracks and defects, but the co-plating leads to a dendritic structure and the presence of clear grain boundaries in the alloy film. In the sequential plating, a compact and uniform thin film is instead present. The membrane prepd. by sequential deposition show better performance in terms of sepn. H2/CO2 and H2 permeability. The different nanoscale morphol. of membrane layer influences the mechanisms of transport, as well as the changes in the morphol. induces by the presence of CO2 in the feed. [on SciFinder(R)]