Old Technique for New Materials: Characterization of Solid State Hydrogen Storage Materials by Temperature Programmed Reaction

Abstract

ABSTRACTThe most common diagnostic tools in studying reversible solid-state hydrogen storage materials involve volumetric or gravimetric approaches. In this study, a mature gas solid analysis technique called Temperature Programmed Reaction (TPR) is presented as an alternative and complementary approach in investigating solid-state hydrogen storage materials. TPR is fast, simple and offers valuable information from a wide range of solid materials. This technique is routinely used to characterize the reduction behavior of metal oxide and sulfide catalysts. In a typical TPR experiment, a sample powder is heated at a constant rate under a non steady-state environment of constant pressure and flow of a hydrogen/inert gas mixture, while monitoring the rate of hydrogen absorption and desorption by a thermal conductivity detector. The principle behind TPR is the high thermal conductivity coefficient of hydrogen when compared to other gases. The detector is sensitive enough that a slight change in hydrogen concentration is reflected by significant changes in the thermal conductivity signal. Hydrogen storage materials exhibit fingerprint type TPR spectra, unique to their composition and structure. Specific rates of hydrogen intake, heats of absorption and desorption as well as extent of activation can be extracted from TPR curves. In addition, multiple absorption and desorption states can be identified from the number of absorption or desorption peaks. Material stability and potential structural or phase changes can also be inferred indirectly. The simplicity and the highly sensitive thermal conductivity measurement provide a number of advantages over the traditional volumetric or gravimetric methods. Metal hydride alloys of AB5-type are used to demonstrate the effectiveness of TPR technique in characterizing hydrogen storage materials.