Nanosized systems and mesoporous materials for hydrogen production, storage, and conversion

The development of innovative systems for energy production, storage and delivery represents today one of the most investigated area in materials science. The so called “hydrogen cycle,” based on the production of this combustible by photocatalytic water splitting processes, its solid state storage and finally its conversion by PEM fuel cell devices, is considered a promising approach to meet the increasing energy storage and conversion demand for several applications: portable devices, electric vehicles, as well as stationary installations. Among the characteristics required to advanced materials with improved properties for the above applications are proper chemical reactivity and the possibility to tailor geometric and electronic factors. To this regard, quite recently the attention has been focusing to nanosized materials and mesoporous scaffolds, which combine thermodynamic metastability with several advantageous morphological features as high surface area, pore diameter between 2-50 nm, good corrosion resistance etc. In this work we present the recent activity developed in our laboratories concerning new materials for the above cited hydrogen related technologies. Object of intense investigation is the development of a new class of chemical systems with such properties as well as the study of the mechanisms related to their synthesis and the optimization of experimental conditions needed for their preparation. A series of mesoporous materials are synthesized by sol-gel methods, using EISA (Evaporation Induced Self-Assembly) and Hard Templating approaches. Composite systems were also prepared by melting infiltration or wet impregnation of nanosized phases within the porous matrixes. The obtained samples were characterized by several techniques as ex-situ X-ray Diffraction, Thermogravimetry coupled with Differential Thermal Analysis, Differential Scanning Calorimetry, Scanning and Transmission Electron Microscopy, nitrogen adsorption-desorption isotherms and UV-Vis spectrophotometry. Sorption properties of the hydrides confined into mesoporous matrixes were investigated by Thermal Desorption Spectroscopy, and by manometric-volumetric Sievert type apparatuses connected to high pressure DSC. Performances of composite materials assembled in PEM fuel cells electrodes were evaluated by electrochemical methods. Concerning TiO2 photoanodes, tested in water splitting process, all samples synthesized using soft template method showed a better photoactivity than those prepared by hard template, as evidenced by the increased number of hydrogen moles evolved at the cathode. Regarding the materials for hydrogen storage, nanosized hydrides embedded in the mesoporous matrixes SBA-15 and CMK-3, desorb hydrogen at a temperature lower than the corresponding bulk materials. Composite systems for PEM fuel cells electrodes, based on nanosized Pt and Pt/NbO2 embedded within mesoporous CMK3, displayed better performances and improved ageing properties than the commercial ones.