TECHNOLOGY FOCUS - ELECTRONICS - Preferred Components: The substrate material is electrochemically active and the anode constitutes part of the substrate adjoining (m1). The anode comprises a thin layer of a different material interposed between (m1) and the substrate support.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: (m1) is oxygen deficient perovskite of formula ABO3-delta, BaCe0.9Y0.1O2.95 (BCY10), BaZr0.9Y0.1O2.95 (BZY) and members of the solid solution, BaCe0.9-xZrxY0.1O2.95 (BCZY) or the analogs of the previously mentioned phases with lanthanides such as Gd, Nd or Yb instead of Y and such phases with higher degree of substitution such as BaCe0.8Y0.2O2.95 (BCY20), Sr3CaZr0.5Ta1.5O8.75 (SCZTO) and Ba3Ca1.18Nb1.82O8.73 (BCN18) and composites of such materials; BaZrO3 based material; or BaZr1-xLnxO3-xdivide by2, which is prepared with the use of ZNO sintering aid (1 w/w.%). (m1) is provided with an outer protective layer. The membrane thickness is not greater than 25 (preferably 3 - 15) microns. The BaZrO3 based material is prepared with the use of a sintering aid. The substrate support is a metallized ceramic or a mixed conductive oxide having an electrical conductivity of not less than 10Scm-1 at the operating temperature of the steam electrolysis (preferably Cu:Al2O3, La0.8Sr0.2MnO3 (LSM), chromium doped LSM (i.e. La0.75Sr0.25Cr0.5Mn0.5O3) and La0.6Sr0.4CO0.2Fe0.8O3-d (LSCF). The substrate support pore size is not less than 0.5 microns or the substrate porosity is 30 - 60 %.A,B=metallic elements occupying A and B sites of the perovskite lattice structure;delta=degree of oxygen deficiency;X=0.02 - 0.25;Ln=lanthanide ion, La, Y or Sc.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The steam electrolysis is carried out at 400 - 800 degrees C.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: (m1) is oxygen deficient perovskite of formula ABO3-delta, BaCe0.9Y0.1O2.95 (BCY10), BaZr0.9Y0.1O2.95 (BZY) and members of the solid solution, BaCe0.9-xZrxY0.1O2.95 (BCZY) or the analogs of the previously mentioned phases with lanthanides such as Gd, Nd or Yb instead of Y and such phases with higher degree of substitution such as BaCe0.8Y0.2O2.95 (BCY20), Sr3CaZr0.5Ta1.5O8.75 (SCZTO) and Ba3Ca1.18Nb1.82O8.73 (BCN18) and composites of such materials; BaZrO3 based material; or BaZr1-xLnxO3-xdivide by2, which is prepared with the use of ZNO sintering aid (1 w/w.%). (m1) is provided with an outer protective layer. The membrane thickness is not greater than 25 (preferably 3 - 15) microns. The BaZrO3 based material is prepared with the use of a sintering aid. The substrate support is a metallized ceramic or a mixed conductive oxide having an electrical conductivity of not less than 10Scm-1 at the operating temperature of the steam electrolysis (preferably Cu:Al2O3, La0.8Sr0.2MnO3 (LSM), chromium doped LSM (i.e. La0.75Sr0.25Cr0.5Mn0.5O3) and La0.6Sr0.4CO0.2Fe0.8O3-d (LSCF). The substrate support pore size is not less than 0.5 microns or the substrate porosity is 30 - 60 %.A,B=metallic elements occupying A and B sites of the perovskite lattice structure;delta=degree of oxygen deficiency;X=0.02 - 0.25;Ln=lanthanide ion, La, Y or Sc. EXAMPLE - Porous La0.8Sr0.2MnO3 (LSM) substrates were prepared by tape casting. The liquid mixture used for tape casting consisted of commercial submicron size LSM powder (Praxair), graphite powder used as pore former, a (3:1) mixture of methyl ethyl ketone and ethanol as solvent, polyethylene glycol and di-n-butyl phthalate as dispersant and plasticizer, respectively and Butvar B-98 (RTM; polyvinyl butyral resin binder). The mixture comprising powder, solvent (1:1 mixture to the powder) and pore former (40 wt.%) was ball milled overnight for breaking the agglomerates and reducing the particle size. The organic additives (dispersant, plasticizer and binder, also LSM (40 wt.%)) were then added and the slurry was mixed for half an hour. A subsequent ball milling for 4 hours was performed for homogenization of the slurry. The slurry was then used for green tape deposition and the resultant dried tapes were cut, overlapped and cut into 2.5 cm diameter disks. The disks were then fired with a slow ramp rate of 0.5 - 1000 degrees C for burning the organic residues, kept there for 5 hours and then fired to 1300 degrees C for sintering and increasing the mechanical strength. The resulting substrate was placed on a hot plate and held at 300 - 350 degrees C while the electrolyte suspension (10 ml) (BaCe0.5Zr0.3Y0.16Zn0.04O3- (BCZZY electrolyte (2 g) ultrasonically dispersed in a mixture containing ethanol (35 ml))) was sprayed onto the substrate. The green bilayer was then sintered to 1325 - 1350 degrees C for 5 hours. The resultant structure was a porous LSM substrate deposited with a less porous very thin layer of LSM and a dense film of BCZZY of approximately 10 - 40 microns thickness. The BCZZY membrane was provided with a porous palladium cathode. At the anode there was provided a platinum mesh anode/current collector. The steam feed stream used was a pure oxygen supply as a carrier for the steam in order to avoid possible contamination of the cell components. The steam partial pressure of the steam feed stream gas was controlled by bubbling the gas through a water bath that was kept at ambient temperature achieving a steam partial pressure of 0.022 bar and providing a gas composition (vol.%) of H2O (2.2) and O2 (97.8), to the anode. A gas mixture comprising hydrogen and argon was similarly bubbled through ambient water to supply a gas having a composition (vol.%) of H2O (2.2), H2 (5) and Ar (92.8) to the cathode. Each of the gas flows was adjusted to 200 ml/cm3. The amount of hydrogen produced was determined from the potential on a zirconia oxygen sensor.