To provide a device which purifies so that impurity which is not desirable may be removed from a mixed stream before carrying the impure hydrogen stream made on the occasion of hydrogen purification to a fuel cell or fuel cell stack.

The hydrogen purification device (10) includes an enclosure (12) which contains a separation membrane assembly (20) adapted to receive a mixed gas stream (24) containing hydrogen gas to produce a stream (34) that contains pure or at least substantially pure hydrogen gas therefrom. The separation assembly (20) includes at least one hydrogen-permeable and/or hydrogen-selective membrane (46), and in some embodiments includes at least one membrane envelope that includes a pair of generally opposed membrane regions that define a harvesting conduit therebetween and which are separated by a support. The enclosure (12) includes components that are formed from materials having similar or the same coefficients of thermal expansion as the membrane or membranes (46).