Institute for Complex Systems - Sapienza - CNR

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ISC Sapienza Facilities Laboratories Nanomaterials for alternative energies: solid-state hydrogen storage

Nanomaterials for alternative energies: solid-state hydrogen storage

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I work in a joint Sapienza University and CNR Laboratory that has been active since 1968 in applying the anelastic spectroscopy, the acoustic emission, and the thermal analysis to study various solid systems,

from the investigation of the motion of hydrogen in metals and of its quantum behaviour down to the liquid helium temperatures, to the high TC superconductors and manganites, to the lithium-ion batteries and the polymer electrolytes fuel cells. Annalisa Paolone and Oriele Palumbo, researchers at CNR-ISC, collaborate to the activity of the Lab, which over the last 10 years has been focused on the novel complex hydrides for the solid-state hydrogen storage.

A large variety of experimental techniques is available. The Lab is equipped with four main experimental stations which can work independently. The anelastic spectroscopy facility allows measurements of elastic energy loss and dynamic modulus in high vacuum in the temperature range between 1.3 and 900 K. Anelastic spectroscopy is a well established experimental technique to quantitatively determine the dynamics and the diffusion parameters of mobile species in solids and the occurrence of phase transitions, including chemical reactions. An external stress, applied to a sample through its vibration perturbs the energy levels of atoms of fractions of meV and induces redistribution of mobile species in the material (defects or lattice atoms) among the perturbed levels. The motion parameters are measured while, by thermal activation, the new equilibrium is being attained. The analysis of the data provides the parameters of the local or long range diffusion processes, like the relaxation rates and their pre-exponential factors, the activation energies for classical processes, or the splitting of the energy levels and the power laws of the relaxation rates for quantum tunnelling phenomena. Moreover, anelastic spectroscopy can sensitively detect structural and magnetic phase transitions through the dynamic elastic modulus, which is extremely sensitive to the formation of new phases or of atom complexes in materials. It has been shown that the dynamic Young modulus allows the monitoring of the evolution of the decomposition reactions in complex hydrides as a function of temperature and time. Anelastic relaxation gives essential information often not obtainable by other techniques and is complementary to neutron scattering, NMR, and NQR.

Fig.1 The experimental apparatus for anelastic spectroscopy measurements.

The group uses a flexible system for concomitant measurements of thermogravimetry and differential scanning calorimetry. This apparatus can operate both in inert gas atmospheres and in high vacuum, and the exploitable temperature range is between 300 and 1300 K. The system is complemented by a quadrupole mass spectrometer which allows the identification of the released gaseous species.

Fig. 2 The system for concomitant thermogravimetry, differential scanning calorimetry and mass spectrometry.

The thermal analysis Section is equipped with a commercial Dynamic Mechanical Analyzer, which is able to measure, also in liquid corrosive environments, but at a lower performance level, the elastic moduli and the elastic energy dissipation of solid samples in a wide temperature range, between 78 and 900 K. This system is particularly well suited for the study of polymers.

Recently we also added to our Lab an infrared spectrometer for transmission measurements in the mid-infrared range.

By the home-made Sieverts apparatus, it is possible to determine the thermodynamic p-c-T curves of the various solid-hydrogen systems, through the volumetric measurement of absorbed/desorbed hydrogen. This system is operative in a wide range of temperatures (80-600 K) and pressures (0-200 bar).

Fig. 3 The home-made Sieverts apparatus.