The thermodynamics of the LaNi5-H2 system by differential heat flow calorimetry II: The α and β single-phase regions

Hydrogen quantum effects in hydride LaNi(5)H(7)

Energy eigenvalues and wave functions of hydrogen atoms in hydride LaNi(5)H(7) are calculated. First-principles electronic structure calculations are employed to obtain the three-dimensional potential energy structure of each hydrogen site. These quantum effects are not negligibly small in evaluation of enthalpy of formation, an important property of hydrogen storage. Including the temperature effect from hydrogen gas, experimental values are well reproduced. The excitation probability of inelastic neutron scattering is also calculated using the wave functions obtained.

Testing facility for hydrogen storage materials designed to simulate application based conditions

For the daily use of hydrogen storage materials, not only their intrinsic storage properties are important, but also equally important is the performance under practical conditions. Besides the techniques already available for the fundamental characterization of storage materials, there is a growing need to test storage materials under conditions resembling day-to-day use. For that we developed and tested a downscaled hydrogen storage reactor with which it is possible to monitor the hydrogenation behavior under nonideal conditions. Here we present a characterization of the developed reactor setup which enables a fast screening of storage materials. For characterization and calibration purposes, we use the rather well-documented LaNi(5)-Al alloy as reference. The found experimental results agree well with the properties of LaNi(5)-Al as reported in literature. Our results show that this reactor setup enables an efficient screening of new developed storage alloys under realistic conditions and is therefore complementary to the already existing characterization setups.

High-pressure and high-temperature differential scanning calorimeter for combined pressure-concentration-temperature measurements of hydrides

The design and construction of a high-pressure (200 bar) and high-temperature (600 degrees C) heat-flow differential scanning calorimeter (DSC) for the in situ investigation of the hydrogenation and dehydrogenation reactions of hydrides is presented. In combination with a pressure-concentration-temperature (pcT) system, simultaneous thermodynamic and volumetric measurements become accessible. Due to the high thermal conductivity of hydrogen, only the sample cell and the reference cell are exposed to hydrogen and the remaining system is under ambient conditions. This separation has the advantage that the calibration factor is independent of the hydrogen pressure. The internal empty volume of the combined system is as low as possible to maximize the precision of the pcT measurements. The calorimetric block of the DSC is designed with a silver/copper alloy and the temperature measurements are made resistively with platinum temperature sensors (Pt 100). The instrument was calibrated and its operability was successfully studied on the example of the hydrogen sorption behavior of LaNi(5).