TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The enclosure has a coefficient of thermal expansion that is within 2% of the coefficient of thermal expansion of the hydrogen-selective membrane(s). It may have a coefficient of thermal expansion that is greater than 13 mum/m/degreesC or less than 16 mum/m/degreesC. The support has a coefficient of thermal expansion that is within 10% of the coefficient of thermal expansion of the hydrogen-selective membrane. The support is not hydrogen-selective. It includes screen components.The enclosure further includes a perimeter shell portion interconnecting the end plates. Each end plate includes a perimeter region. At least a portion of the shell portion is integrally formed with a first one of the end plates. It projects from the perimeter region toward a second one of the end plates. The shell portion includes an end portion distal the first one of the end plates that is adapted to form a fluid-tight interface with a sealing region of the second one of the end plates. The shell portion is a first shell portion that is integrally formed with the first one of the pair of end plates. A seal extends between the perimeter regions. The enclosure includes only a single sealed interface between the pair of end plates. A pair of hydrogen-selective membranes are oriented such that the pair of hydrogen-selective membranes are spaced apart from each other with their permeate surfaces facing each other to define a membrane envelope with a harvesting conduit extending between the permeate surfaces. The product stream is formed from the portion of the mixed gas stream that passes through the membranes to the harvesting conduit. The remaining portion of the mixed gas stream remains on the first surface of the membranes forming at least a portion of the byproduct stream.The purification device further comprises a heating assembly adapted to heat the device to 250-500degreesC and including electrically powered heater(s) external the enclosure. The purification device is in combination with a fuel processor adapted to produce the mixed gas stream. The fuel processor is adapted to produce the mixed gas stream from feed stream(s) comprising water or a carbon-containing feedstock. The purification device is in combination with a fuel cell stack adapted to receive at least a portion of the product stream.    TECHNOLOGY FOCUS - METALLURGY - Preferred Materials: The support is at least partially formed from an alloy comprising nickel and copper.