The reliability of a newly engineered palladium membrane diffuser for hydrogen purification has been investigated. The purifier was exposed to operating conditions that cause high failure rates in other Currently available commercial designs. Stress tests include repeated power outages. and rapidly increasing and decreasing, flow rates. Helium leak tests confirmed that the membranes maintained their integrity under these conditions, Atmospheric pressure ionization mass spectrometry (APIMS) verified sub-ppb efficiency of the purifier for impurity removal, Flow rate measurements as a function of pressure gradient and membrane temperature indicated that the flux across the membrane was not limited by external mass transfer resistance and followed basic laws of diffusion. (C) 2002 Elsevier Science B.V. All rights reserved.