Researches and developments on hydrogen storage materials are turning to a new status of laying stress on basic science. Although many trials have been made with hydrogen storage materials classified to four categories, targets of DOE (U. S. Department of Energy) have not yet attained. Brief review on advanced materials with emphasis on new concepts leads to expectation of break through inspired by novel effluents out of leading big science.
Science and technology concerning hydrogen storage materials are advancing towards the nanometer scale. X-rays, which have wave lengths matched to this length scale, are an ideal tool to study materials in nanometer scale. SPring-8, the world-biggest synchrotron radiation facility, provides ultra-brilliant, high-directional, polarized and pulsed X-rays. These excellent lights enable us to investigate precisely, accurately and even time dependently the structural and electronic properties of materials on hydrogenation and/or dehydrogenation. We present the synchrotron radiation based X-rays experiments that are powerful and useful particularly for the functional study of hydrogen storage materials. The latest results on metal hydrides are presented as example.
Gas hydrates allow for compact storage of various gases in the hydrate-cages composed of water molecules. The storage and transport systems of natural gas or hydrogen, which take advantage of the characteristics of gas hydrates, have been a focus of constant attention as new techniques. The formation of hydrogen hydrate, however, requires severe conditions of high pressures over 100 MPa or extremely low temperatures. The addition of another guest species has been thought to be most likely way to overcome severe conditions, while it decreases the storage density of hydrogen. In this review, the thermodynamic stabilities of mixed gas hydrates and the hydrate-cage occupancies of hydrogen and additional guest species are described. From the viewpoints of the formation condition and storage density for the mixed gas hydrate, the capability of gas hydrates as hydrogen storage medium is briefly discussed.
Thermodynamical stabilities of metal borohydrides, M(BH4)n, which are potential candidates for hydrogen storage materials due to their high gravimetric hydrogen density, have been investigated using the first-principles calculation based on density functional theory. The results indicate that the charge compensation by Mn+ is a key feature for the stability of the internal bonding of [BH4]− anion. A good correlation between the heats of formation and the Pauling electronegativities of cations is found for M(BH4)n. The intermediate phase during the hydrogen desorption reaction is also studied theoretically for LiBH4.
The high voltage stabilities of Pt/sulfated-ZrO2 and Pt/C electrocatalysts for a cathode of polymer electrolyte fuel cells (PEFCs) have been investigated using a constant cell voltage method. The cell performance, the electrochemical surface area (ESA) of Pt, and the cell resistance of the cells with Pt/sulfated-ZrO2 and Pt/C cathodes were measured after the cell voltage was kept at the constant voltage of 1.3 V. The severe degradation of the cell performance was observed on the Pt/C cathode. On the other hand, the cell performance and ESA of the Pt/sulfated-ZrO2 cathode hardly deteriorated with holding the cell voltage of 1.3 V for 120 min. It was clarified that the Pt/sulfated-ZrO2 had sufficiently higher voltage stability and might be a candidate for a stable cathode at high potential for PEFC.
Kyoto Protocol, which is fired in 2005 introduced emission trade as one option of the Kyoto Mechanism. Although Japan has been struggling to reduce its GHG emissions, it seems so hard to meet the Kyoto Target, namely 6% reduction from 1990 level. Therefore Kyoto Mechanism is much attractive option for Japan and many companies are trying to arrange the CDM projects or purchasing the credits directly. In Japan, concerning the GHG emission, no mandate regulation has been introduced. On the contrary, EU-ETS defined an aggressive emission cap for each business institution. As a result, EU-ETS has occupied the position of the de-fact standard about emission trade. Moreover, EU may lead the fundamental discussion of the future framework of climate change.
Since 2004, oil and gas prices has showed abnormal hikes and remained at higher level. But, this problem is not caused by resource depletion of oil and gas. Weakened supply cushions in USA and activities of energy future market are true reasons for price hikes. On the other hand, environment constraints to energy use will be more severe. We need to concentrate our efforts to developments of innovative technologies such as hydrogen fuel.