Publications

A promising energy carrier and storage solution for integrating renewable energies into the power grid currently being investigated is hydrogen produced via electrolysis. It already serves various purposes but it might also enable the development of hydrogen-based electricity storage systems made up of electrolyzers hydrogen storage systems and generators (fuel cells or engines). The adoption of hydrogen-based technologies is strictly linked to the electrification of end uses and to multicarrier energy grids. This study introduces a generic method to integrate and optimize the sizing and operation phases of hydrogen-based power systems using an energy hub optimization model which can manage and coordinate multiple energy carriers and equipment. Furthermore the uncertainty related to renewables and final demands was carefully assessed. A case study on an urban microgrid with high hydrogen demand for mobility demonstrates the method’s applicability showing how the multi-objective optimization of hydrogen-based power systems can reduce total costs primary energy demand and carbon equivalent emissions for both power grids and mobility down to  −145%. Furthermore the adoption of the uncertainty assessment can give additional benefits allowing a downsizing of the equipment.

The technique of producing hydrogen by utilizing green and renewable energy sources is called green hydrogen production. Therefore by implementing this technique hydrogen will become a sustainable and clean energy source by lowering greenhouse gas emissions and reducing our reliance on fossil fuels. The key beneft of producing green hydrogen by utilizing green energy is that no harmful pollutants or greenhouse gases are directly released throughout the process. Hence to guarantee all of the environmental advantages it is crucial to consider the entire hydrogen supply chain involving storage transportation and end users. Hydrogen is a promising clean energy source and targets plan pathways towards decarbonization and net-zero emissions by 2050. This paper has highlighted the techniques for generating green hydrogen that are needed for a clean environment and sustainable energy solutions. Moreover it summarizes an overview outlook and energy transient of green hydrogen production. Consequently its perspective provides new insights and research directions in order to accelerate the development and identify the potential of green hydrogen production.

The Next Generation EU plan fosters the development of a large capacity for hydrogen generation. However water and energy resources are strictly connected to an indissoluble nexus. For that water electrolysis may counteract the coexistence of two primary UNO Sustainable Development Goals humankind must face to achieve a prosperous and equal society namely SDG 7 (Affordable access to renewable energy sources) and SDG 6 (clean water). To design innovative energy systems implementing hydrogen as an efficient and sustainable vector water resources need careful management and energy use ought not to compete with freshwater delivery. Therefore the present study reviews the technologies available for hydrogen production and their fitness to water quality standards. Among the feeding possibilities to be scrutinized wastewaters and saline waters are worth attention. Each source of water asks for a specific design and management of the water treatment pre-process. Since these steps are energydemanding in some applications the direct use of low-quality water to produce hydrogen may be envisaged. An example is the direct feeding of seawater to Solid Oxide Electrolysers (SOE). SOEs appear more promising than commercial low-temperature electrolysis systems since water steam production integrates the function of preliminary water treatment.

The conversion of solar to chemical energy is one of the central processes considered in the emerging renewable energy economy. Hydrogen production from water splitting over particulate semiconductor catalysts has often been proposed as a simple and a cost-effective method for largescale production. In this review we summarize the basic concepts of the overall water splitting (in the absence of sacrificial agents) using particulate photocatalysts with a focus on their synthetic methods and the role of the so-called “co-catalysts”. Then a focus is then given on improving light absorption in which the Z-scheme concept and the overall system efficiency are discussed. A section on reactor design and cost of the overall technology is given where the possibility of the different technologies to be deployed at a commercial scale and the considerable challenges ahead are discussed. To date the highest reported efficiency of any of these systems is at least one order of magnitude lower than that deserving consideration for practical applications.

By passing the delegated acts supplementing the revised Renewable Energy Directive the European Commission has recently set a regulatory benchmark for the classifcation of green hydrogen in the European Union. Controversial reactions to the restricted power purchase for electrolyser operation refect the need for more clarity about the efects of the delegated acts on the cost and the renewable characteristics of green hydrogen. To resolve this controversy we compare diferent power purchase scenarios considering major uncertainty factors such as electricity prices and the availability of renewables in various European locations. We show that the permission for unrestricted electricity mix usage does not necessarily lead to an emission intensity increase partially debilitating concerns by the European Commission and could notably decrease green hydrogen production cost. Furthermore our results indicate that the transitional regulations adopted to support a green hydrogen production ramp-up can result in similar cost reductions and ensure high renewable electricity usage.

Zero-carbon-dioxide-emitting hydrogen-powered aircraft have in recent decades come back on the stage as promising protagonists in the fght against global warming. The main cause for the reduced performance of liquid hydrogen aircraft lays in the fuel storage which demands the use of voluminous and heavy tanks. Literature on the topic shows that the optimal fuel storage solution depends on the aircraft range category but most studies disagree on which solution is optimal for each category. The objective of this research was to identify and compare possible solutions to the integration of the hydrogen fuel containment system on regional short/medium- and large passenger aircraft and to understand why and how the optimal tank integration strategy depends on the aircraft category. This objective was pursued by creating a design and analysis framework for CS-25 aircraft capable of appreciating the efects that diferent combinations of tank structure fuselage diameter tank layout shape venting pressure and pressure control generate at aircraft level. Despite that no large diferences among categories were found the following main observations were made: (1) using an integral tank structure was found to be increasingly more benefcial with increasing aircraft range/size. (2) The use of a forward tank in combination with the aft one appeared to be always benefcial in terms of energy consumption. (3) The increase in fuselage diameter is detrimental especially when an extra aisle is not required and a double-deck cabin is not feasible. (4) Direct venting has when done efciently a small positive efect. (5) The optimal venting pressure varies with the aircraft confguration performance and mission. The impact on performance from sizing the tank for missions longer than the harmonic one was also quantifed.

The storage of excess electrical generation enabled through the electrolytic production of hydrogen from water would allow “load-shifting” of power generation. This paves the way for hydrogen as an energy carrier to be further used as a zero‑carbon fuel for land air and sea transportation. However challenges in hydrogen storage and transportation ultimately pose restrictions on its wider adaption along horizontal and vertical vectors. This paper investigates chemical energy carriers ranging from small molecules such as ammonia and methane to formic acid as well as other more complex hydrocarbons in response to this timely engineering problem. The hydrogenation and dehydrogenation of such carrier molecules require energy lowering the effective net heating value of hydrogen up to 32 %. Different carrier approaches are discussed in the light of availability energetics water requirements and suitability for applications in power generation shipping trucking and aviation supplemented by a comprehensive safety review making this study unique in its field. It is found that hydrogen delivered without a carrier is ideal for power generation applications due to the large quantities required. Aviation would benefit from either ammonia or hydrogen and is generally a field challenging to decarbonize. Ammonia appears also to be a good medium for shipping hydrogen between continents and to power container ships due to its high energy density and lower liquid temperature compared with hydrogen. At the same time ammonia can also be used to power the ship's engine. Long-haul trucking would benefit the most from cryogenic or compressed hydrogen due to the lower quantities required and purity requirements of the fuel cells.

Hydrogen is becoming increasingly important to achieve the valid defossilization goals. However due to its physical properties especially the storage of hydrogen is challenging. One option in this regard are metal hy drides which are able to store hydrogen in chemically material-bound form. Against this background the goal of this paper is an analysis of possible technical application areas of such metal hydrides – both regarding transport and stationary application. These various options are assessed for metal hydrides as well as selected competing hydrogen storage options. The investigation shows that metal hydrides with a temperature range below 100 ◦C (e.g. TiFe) are of interest particularly for transportation applications; possible areas of application include rail and marine transportation as well as selected non-road vehicles. For stationary applications metal hydrides can be used on low and high temperature levels. Here metal hydrides with operating temperatures below 100 ◦C are particularly useful for selected small-scale applications (e.g. home storage systems). For applications with me dium storage capacities (100 kWh to 100 MWh) metal hydrides with higher temperature levels are also conceivable (e.g. NaAlH4). For even higher storage demands metal hydrides are less promising.

The growing demand for air travel in the commercial sector leads to an increase in global emissions whose mitigation entails transitioning from the current fossil-fuel based generation of aircrafts to a cleaner one within a short timeframe. The use of hydrogen and fuel cells has the potential to reach zero emissions in the aerospace sector provided that required innovation and research efforts are substantially accomplished. Development programs investments and new regulations are needed for this technology to be safe and economical. In this context it makes sense to develop a model-based preliminary design methodology for a hybrid regional aircraft assisted by a battery hybridized fuel cell powertrain. The technological assumptions underlying the study refer to both current and expected data for 2035. The major contribution of the proposed methodology is to provide a mathematical tool that considers the interactions between the choice of components in terms of installed power and energy management. This simultaneous study is done because of the availability of versatile control maps. The tool was then deployed to define current and future technological scenarios for fuel cell battery and hydrogen storage systems by quickly adapting control strategies to different sizing criteria and technical specifications. In this way it is possible to facilitate the estimation of the impact of different sizing criteria and technological features at the aircraft level on the onboard electrical system the management of in-flight power the propulsion methods the impact of the masses on consumption and operational characteristics in a typical flight mission. The proposed combination of advanced sizing and energy management strategies allowed meeting mass and volume constraints with state-of-the-art PEM fuel cell and Li-ion battery specifications. Such a solution corresponds to a high degree of hybridization between the fuel cell system and battery pack (i.e. 300 kW and 750 kWh) whereas projected 2035 specs were demonstrated to help reduce mass and volume by 23 % and 40 % respectively.

Because of their high surface areas crystallinity and tunable propertiesmetal−organic frameworks (MOFs) have attracted intense interest as next-generationmaterials for gas capture and storage. While much effort has been devoted to thediscovery of new MOFs a vast catalog of existing MOFs resides within the CambridgeStructural Database (CSD) many of whose gas uptake properties have not beenassessed. Here we employ data mining and automated structure analysis to identify“cleanup” and rapidly predict the hydrogen storage properties of these compounds.Approximately 20 000 candidate compounds were generated from the CSD using analgorithm that removes solvent/guest molecules. These compounds were thencharacterized with respect to their surface area and porosity. Employing the empiricalrelationship between excess H2 uptake and surface area we predict the theoretical total hydrogen storage capacity for the subsetof ∼4000 compounds exhibiting nontrivial internal porosity. Our screening identifies several overlooked compounds having hightheoretical capacities; these compounds are suggested as targets of opportunity for additional experimental characterization.More importantly screening reveals that the relationship between gravimetric and volumetric H2 density is concave downwardwith maximal volumetric performance occurring for surface areas of 3100−4800 m2 /g. We conclude that H2 storage in MOFswill not benefit from further improvements in surface area alone. Rather discovery efforts should aim to achieve moderate massdensities and surface areas simultaneously while ensuring framework stability upon solvent removal.