T.H. Lee

Use of mixed conducting membranes to produce hydrogen by water dissociation

Abstract We have studied the production of hydrogen by water dissociation at moderate temperatures (700–900°C) with novel mixed-conducting membranes. Hydrogen production rates were investigated as a function of temperature, water partial pressure, membrane thickness, and oxygen chemical potential gradient across the membranes. The hydrogen production rate increased with both increasing moisture concentration and oxygen chemical potential gradient. A hydrogen production rate of 6 cm 3 ( STP )/ min cm 2 was measured with a 0.10-mm-thick membrane at 900°C and 50 vol % water vapor on one side of the membrane and 80% hydrogen (balance helium) on the other side. Hydrogen was used as a model gas on one side of the membrane to establish a high oxygen potential gradient; however, another reducing gas, methane, was substituted in one experiment to maintain the high oxygen potential gradient. The hydrogen production rate increased with decreasing membrane thickness, but surface kinetics played an important role as membrane thickness decreased.

Palladium based film-type cermet membranes for hydrogen separation

Thin-film type cermet (i.e., ceramic–metal composite) membranes were made by a paste painting method, and their hydrogen transport properties were evaluated. The hydrogen permeability of a 30 μm thick Pd/YSZ (palladium/yttrium-stabilized zirconia) film was compared with that of Pd foil (thickness of 0.1 mm). To test the reproducibility of the results and stability of the Pd/YSZ film, the films permeability was measured over a period of ∼300 h as a function of temperature, gas flow rate, and hydrogen partial pressure. In addition, the influence of a porous alumina substrate was investigated by measuring the hydrogen flux of the Pd foil with and without an Al2O3 substrate in front of the foil. The differences between the hydrogen permeability of the cermet film and that of the Pd foil are discussed. As additional practical information about the cermet film, its thermal expansion behavior was studied in air and in nitrogen, and changes in its microstructure were examined during stability tests. Taken together, the results indicate that thin-film Pd/YSZ cermet membranes can meet the requirements of hydrogen transport membranes.

Development of dense ceramic membranes for hydrogen separation.

We developed novel cermet (i.e., ceramic-metal composite) membranes for separating hydrogen from gas mixtures at high temperature and pressure. The hydrogen permeation rate in the temperature range of 600-900 C was determined for three classes of cermet membranes (ANL-1, ANL-2, and ANL-3). Among these membranes, ANL-3 showed the highest hydrogen permeation rate, with a maximum flux of 3.2 cm{sup 3}/min-cm{sup 2} for a 0.23-mm-thick membrane at 900 C. Effects of membrane thickness and hydrogen partial pressure on permeation rate indicated that bulk diffusion of hydrogen is rate-limiting for ANL-3 membranes. The lack of degradation in permeation rate during exposure to a simulated syngas mixture suggests that ANL-3 membranes are chemically stable and suitable for long-term operation.