General overview about the issues that we intend to tackle
The European Union and G8 leaders presented the goal of reducing greenhouse gas (GHG) emissions by 80% by 2050 relative to 1990 levels. The October 2018 IPCC special report, however, warns of those targets not being sufficient. Increased action is needed, aimed at achieving net zero emissions in less than 15 years . Moreover, lack of action and increase in resource-intensive consumption are key impediments to achieving 1.5 °C pathways, in line with current pledges under the Paris Agreement. These EU objectives align with Sustainable Developments Goal (SDG) 13 Climate Action declared, amongst other 16 SDGs, in the United Nations #Envision 2030 Agenda. SDG 6 Clean Water and Sanitation, SDG 7 Affordable and Clean Energy, SDG 11 Sustainable Cities and Communists and SDG 13 Climate Action forge the conviction that a transition to a net-zero emissions energy system, together with circular, sustainable and green economy with regards to processes, materials, transport, and consumption, shall be integrated in flexible and smart systems networks. Thus, electrification of the economy is the pathway to achieve these goals due to its efficiency in generation, transport, conversion in other types of energy, and use. An integrated, green, smart economy requires clean energy vectors able to flexibly adapt to frequent mismatch between supply and demand, requiring energy storage capacity to seamlessly harmonise that discrepancy. However, electricity fails to offer a simple and affordable method to enable storage. Hydrogen offers a solution to this dilemma. Hydrogen yields zero emissions for the end-user, either using fuel cells that convert back the H2 into electricity, or by reacting with O2 rendering water an energy, or by catalytic conversion into energy and materials. Moreover, green hydrogen produced in electrolysers with renewable electricity fully decarbonises hydrogen as an energy vector. Hydrogen storage technologies is a new and high-impact research area that demands innovative solutions in the quest for a green and sustainable energy future. The recently released Renewable Energy European Directive 2018/2021 pairs energy supply chain with hydrogen storage. Methods for reversible storage, which make H2 available again in its pure form, are essential building blocks in a circular and sustainable hydrogen economy.
More to the point…
The gravimetric energy density of hydrogen (H2) is high, but the volumetric storage density of the lightweight gas is low. Consequently, the most important technical and economic challenges to overcome in a practical H2-storage system are storage density, costs, safety, the hydrogenation-dehydrogenation energy cycle and the ability to deliver enough H2. According to the current state of the art, five ways of storing H2 have been proposed: pressurised H2, liquid H2, storage in solids, hybrid storage systems and regenerative off-board systems. Conventional first two methods, based on either high pressure or very low temperature, exhibit drawbacks or limitations , i.e. limited capacity of increasing the volumetric density at high pressures and safety in the former; cost, energy efficiency and losses in the later. H2 can be stored in solid materials by either Chemisorption (i.e., absorption of hydrogen), which involves dissociation of H2 molecules into hydrogen atoms and chemical bonding of the atoms to a host matrix (the hydrogen is integrated in the lattice of a metal, an alloy or a chemical compound); or Physisorption (i.e., adsorption) of H2 by weak van der Waals forces to the inner surface of a highly porous material. Chemisorption in solid materials requires a thermal management of the storage in order to remove or supply the heat of reaction needed to split or recombine the H2 and form chemical bonds with the material, what in turn hampers this storage solution by reducing energy efficiency. The chemical binding is so strong that high temperature is needed to dehydrogenate, although the substances used should be solid at ambient conditions. The problem with physisorption is to provide light carrier materials with a sufficient amount of bonding sites for the hydrogen per volume. Moreover, this physical bonding would require low temperatures, penalising the energy efficiency and cost.
New storage materials are needed, capable of synergistically maximise the advantages of both Chemisorption and Physisorption, whereas reducing or eliminating their drawbacks. Ionic Liquids (ILs) are tuneable materials able to dissolve hydrogen solid storage materials, allowing liquid storage and delivery, like traditional fuels, lowering temperature needed for faster dehydrogenation, increasing the places where the hydrogen can be bound per unit of volume, and enhancing the strength of binding without requiring low temperatures. One currently promising family of ILs is N-substituted amine-borane ionic liquids (N-ABILs) . Rigorous research is needed aiming at: 1) finding enhanced H2 storage pairs IL-solid material, balancing the advantages aforementioned with the decrease of gravimetric density storage from solid to liquid; 2) characterising the thermophysical properties of those pairs, at operational conditions, with and without H2 and other impurities including moisture; 3) investigating the adsorption-desorption kinetics, energy balances and efficiencies of the selected IL- Solid material pairs.
Ionic liquids together with ethylene diamine bisborane (EDB) and ammonia borane (AB) are very promising pairs able to enhance H2 storage capacity. However, neither the properties of these materials combined with H2 at relevant conditions, nor the efficiency nor kinetics have been investigated.
The EU’s hydrogen strategy explores the potential for renewable hydrogen to help decarbonise the EU in a cost-effective way. Information regarding this strategy.