Interesting Hydrogen Storage behaviour of volcanic powders

Two different volcanic samples were analysed for this study, in order to understand the composition and the purity influence on H2 storage capability. The first analysed sample (sample 1) consists in a 1892 Etna Vulcan eruption showing oxidized metals, due to a long exposition to the atmospheric agents. The second sample (sample 2) is a lava rock, sampled during a 2006 summit eruption and was not contaminated by the atmospheric agents. Both of these samples show phenocrysts assemblage, which are common to most Etnean volcanics. They consist of plagioclase, clinopyroxene, olivine and Ti-magnetite [1]. The bulk rock was analysed for major and trace elements at Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) using a ZSX Primus II X-ray fluorescence spectrometer [4]. Analytical uncertainty (1s) is <1% for SiO2, TiO2, Al2O3, MnO, Fe2O3 tot, MgO, CaO and K2O and <5% Na2O and P2O5 [4]; and between 5 and 10% for all trace elements (L. Miraglia in press). Morphological and structural analyses were carried out on both samples to verify the size, the homogeneity of agglomerates and the crystallographic profiles. Morphological measurements were carried out using a Philips mod. XL30 SFEG at different magnifications. Agglomerates with different size and shape were found for both samples. The EDX mapping performed during the SEM analysis on both samples, revealed the presence of the same elements found through XRF analyses. Structural analyses were performed by XRD investigation, using a Philips X-ray automated diffractometre (mod PW3710), in a 2? range 5-100°. Both the pristine samples were analysed. The XRD profiles evidenced a slight presence of metals with a high oxidation state for sample 1 [2]. This is in accordance to the atmospheric agent exposition, but in general the XRD patterns are overlapped and the fundamental peaks are in accordance to the oxides profile individuated through XRF elemental analyses. Volumetric analyses by Sievert apparatus were carried out to verify the capability to adsorb hydrogen as a function of the operative conditions (temperature and pressure). Sample 1 has shown a hydrogen storage capability of about 2,5wt% at 30°C and 40bar, while sample 2 has supplied a higher capability reaching a value of about 4wt% in the same operative conditions (Fig.1). This value was obtained in after 280hrs, on the contrary, the first sample, at the same time stores about one half, meaning that the hydrogen sorption kinetic of the second sample is faster than sample 1. This wide difference could be attributable to different factors such as high purity of sample 2, not polluted by the atmospheric agents, and finer and homogeneously dispersed granulometry. On both analysed samples, a structural post-mortem characterization was carried out in order to verify if the hydrogen sorption tests produce some modification in the structure of the materials. The XRD profiles do not reveal any substantial modification, in fact quite unaltered spectra were found for the investigated materials. In conclusion, good and promising results were obtained using natural samples based on volcanic rocks with higher values than materials reported in literature [3], in particular regarding to the hydrogen storage in very mild conditions.