Bipolar plates for electrochemical cell stacks

A separator for electrochemical cells, comprises two porous, electrically conducting sheets selected from the group consisting of expanded metal mesh, metal foam, conducting polymer foam, porous conductive carbon material and combinations thereof, and an electrically conducting gas barrier disposed in electrical contact between the sheets. The electrically conducting gas barrier is a metal sheet, made of titanium, and the separator has a polymeric ceU frame peripherally enclosing a porous electrically conducting sheet.