Experimental and Theoretical Studies of Non-Galvanic Hydrogen Separations Using Doped-Strontium Cerates for Application in Clean Energy Production

Abstract

Hydrogen is one of the leading choices for alternative environmentally friendly clean energy sources and there is an increasing worldwide interest in the hydrogen economy and hydrogen technologies. One of the main technical challenges presently faced in the production of hydrogen is the cost of purification or the separation of hydrogen from gas mixtures. Non-galvanic hydrogen separation by dense ceramic membranes with mixed protonic–electronic conduction seems to be one of the most promising technologies for hydrogen separation for environmentally friendly energy. There are several issues associated with the applications of dense ceramic membranes for (non-galvanic) hydrogen separation, for example, impractical hydrogen separation rates, the stability of the materials, and the shortages of experimental data and theoretical models of hydrogen permeation for those membranes. The present project has undertaken the following investigations:  Analysis of a currently available model for non-galvanic hydrogen permeation of the membranes;  Development of a method for fabrication of asymmetric dense membranes to improve the filling technique to aid the conventional dry pressing, to develop a simple, cost-effective and highly reproducible method to prepare thin dense membranes;  Study of material stability in a reducing atmosphere to confirm the effect of hydrogen on the phase stability of commonly reported perovskite type material;  Investigation of non-galvanic hydrogen permeation data for dense perovskite type membranes in both dry and wet hydrogen; and  Comparison of the experimental results with the model predictions. This project demonstrated that the settlement method is an effective filling technique which aids the conventional dry pressing, in order to prepare a thin uniform layer on a porous support. The method can provide advantages such as ease of control of the membrane thickness. The settlement methods can also be applied to prepare a thin uniform nano porous layer on a porous support, which can possibly be utilised as a molecular sieve type membrane for hydrogen separations from syngas. The phase stability study confirmed that some of the perovskite phase of the SrCe0.95Yb0.05O3-α decomposed to cerium oxide under strongly reducing conditions such as in dry hydrogen at 900 ○C. It was interesting to find that the extent of decomposition of the perovskite phase in a reducing condition was most influenced by the status of the SrCe0.95Yb0.05O3-α sample (i.e. either disk or powder form) while the temperature or the extent of the reducing atmosphere produced a smaller effect. The finding indicated that relaxation kinetics may play an important role in the phase stability of perovskite materials, and that it is vital to conduct hydrogen permeation tests using a ‘wet’ hydrogen atmosphere, in order to avoid strongly reducing conditions.