Use of mixed conducting membranes to produce hydrogen by water dissociation

We have studied the production of hydrogen by water dissociation at moderate temperatures (700-900degreesC) 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 900degreesC 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. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.