In this work, the inert gas leak evolution problem in electrolessly-plated palladium (Pd)-based composite membranes has been revisited. Pd was doped with a higher melting point element such as ruthenium (Ru) or platinum (Pt) and the thermal stability of the membranes was evaluated. Pd, Pd-Ru and Pd-Pt composite membranes were synthesized by electroless plating techniques and the rate of increase of the nitrogen leak in the temperature range of 773-873 K for these membranes in a pure hydrogen atmosphere was determined. The results showed that doping Pd with Pt or Ru significantly reduces the rate at which the nitrogen leak increased compared to a pure Pd membrane by almost one order of magnitude. The effect of these Pd-alloys on the hydrogen permeance stability at high temperatures ( >= 823 K) was also investigated. The addition of a trace amount, less than 1 wt%, of Ru to Pd was sufficient to enhance the thermal stability of pure Pd membrane by lowering the nitrogen leak growth rate, though the hydrogen permeance stability was not improved. The Pd-Pt alloy membrane, despite having a lower hydrogen permeance, had a very stable hydrogen permeation flux at higher temperatures (up to 873 K). (C) 2014 Elsevier B.V. All rights reserved.