Decomposition of steam under a chemical driving force at moderate temperatures offers a simple and economical way to generate hydrogen. A significant amount of hydrogen can be generated and separated by splitting steam and removing the oxygen using Gd0.2Ce0.8O1.9-delta (GDC)-Gd0.08Sr0.88Ti0.95Al0.05O3 +/-delta (GSTA) mixed oxygen ionic and electronic conducting membranes. Hydrogen generation experiments for the self-supported thick membranes and porous supported thin membranes were conducted at different oxygen partial pressure gradients across the membrane established using H-2-H2O mixture gas. Experimental results indicate that the hydrogen generation from steam using GDC-GSTA MIEC membranes at elevated temperatures is mainly controlled by the bulk diffusion of oxygen for the self-supported thick membranes, while the permeation process for the porous supported thin membranes is mixed controlled, i.e. the hydrogen generation/oxygen permeation process is controlled by the surface exchange reactions and bulk diffusion of oxygen through the MIEC membrane. A mathematical model for the calculation of the area specific hydrogen generation rate is proposed in this paper based on the measured oxygen partial pressures, gas compositions, and gas flow rates of the inlet and outlet gases on feed side of the membrane, as well as the permeation area of the membrane. (C) 2011 Elsevier Ltd. All rights reserved.