FLYHY

Fluorine substituted High Capacity Hydrides for Hydrogen Storage at low working temperatures

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 Obiettivo del progetto (Objective)

'At present there is no solid state hydrogen storage material available fulfilling all requirements for practical use in mobile applications. These are 1. high storage density, 2. temperatures and heats of operation compatible with PEM fuel cells, 3. high hydrogen loading and unloading speeds in the range of a few minutes and 4. low production costs. FlyHy focuses especially on the first three points while using commercially upscalable materials preparation processes. High hydrogen capacity materials like alane or borohydrides as well as so called Reactive Hydride Composites (mixtures of borohydrides with selected other hydrides), nowadays suffering from too high or too low reaction temperatures and heats, shall be modified by substituting halogens for part of the hydrogen or hydrogen containing complexes. The project partners IFE, GKSS and AU have shown that by this approach novel mixed hydrido-halogenide compounds can be prepared. Fluorine substituted Sodium Alanate exhibited drastically increased desorption pressures at the same reaction temperature or lowered reaction temperatures at the same pressure resp. Targets of the FlyHy project are (i) to exploit these findings on materials destabilisation and stabilisation resp. by halogen substitution for alane, borohydrides and Reactive Hydride Composites , in order to achieve a breakthrough in the thermodynamic properties of these materials exhibiting the highest hydrogen capacities known at present, (ii) to obtain an in depth scientific understanding of the sorption properties of the substituted materials by extended structural and thermodynamical characterisation and modelling, for materials optimisation, (iii) determine tank relevant materials properties like e.g. densification behaviour and heat conductivity, and, if applicable, do first tests in a prototype tank.'

Introduzione (Teaser)

Hydrogen is typically stored in compressed gas or liquid form. Scientists developed solid state hydrogen storage materials to address the needs of the transport and stationary energy supply sector for low pressure, low volume hydrogen storage.

Descrizione progetto (Article)

Nature's solar, wind and water resources are promising candidates to help relieve dependence on a dwindling supply of fossil fuels whose combustion is increasingly associated with global climate change. However, these alternative energy forms are plagued by some of the same issues facing fossil fuel-based energy, namely inconsistent supply (changing over time) and uneven geographical distribution.

Hydrogen is the most abundant element in the Universe and could solve both those problems. However, it is difficult to store at room temperature with the density and compactness required for mobile applications. Scientists initiated the 'Fluorine substituted high-capacity hydrides for hydrogen storage at low working temperatures' (FLYHY) project to develop novel materials and processes for hydrogen storage in the solid state.

FLYHY focused on modifying high hydrogen-capacity materials by substituting some hydrogen atoms with halogens (fluorine, chlorine, bromine and iodine) using commercially up-scalable preparation processes. The goal was to achieve high storage density, fast hydrogen loading and unloading speeds, and heats of operation compatible with fuel cells (proton exchange membrane (PEM)).

Several promising borohydrides were investigated including lithium borohydride (LiBH4) and calcium borohydride (Ca(BH4)2). Substitution of the BH4- groups was evaluated for the various halogens and resulting compounds characterised with respect to the desired properties. Fluorine substitution in calcium, lithium and sodium-based reactive hydride composites (RHCs) and the expected lowering of hydrogen release temperatures was observed. Optimisation of reaction temperatures, pressures and additives is expected to yield reaction pathways that maintain the high storage capacity and cycling stability of the parent compounds.

Life-cycle analysis and comparisons of cost of fuelling support the competitiveness of solid state hydrogen storage with conventional compressed gas or liquid technologies with one caveat. Raw materials must be obtained in bulk from large-scale industrial suppliers rather than in gramme amounts from fine chemicals suppliers. However, effects of lower purities must be assessed.

FLYHY made important progress in the development of solid state hydrogen storage materials with storage densities, rapid hydrogen cycling and temperatures compatible with integration with fuel cells for mobile and stationary applications. Hydrogen's potential to replace fossil fuels as a clean, renewable and secure energy source may be one step closer to large-scale realisation.