Publications

Liquid organic hydrogen carriers (LOHC) are a technology that allows storing hy-drogen in a safe and dense manner by reversible chemical conversion. They consti-tute a very promising option for energy storage transport and release combined withelectric power generation by fuel cells in large-scale applications like trains. In orderto establish trains running on LOHC it is mandatory to ensure the reliability of thesystem. This study evaluates various system configurations concerning reliabilityand resilience. The fault tree analysis method has been used to quantify the prob-ability of failure. The S-P matrix was applied to assess the different failure modes incontext of severity as well as their probability. The MTTF of the system can be morethan doubled by introducing single redundancy for the fuel cell and the reactor whilemore than two redundant components diminish the positive effect on reliability dueto higher complexity. It is estimated that the systems full functionality is available formore than 97% of its operating time.

Hydrogen energy as clean and efcient energy is considered signifcant support for the construction of a sustainable society in the face of global climate change and the looming energy revolution. Hydrogen is one of the most important chemical substances on earth and can be obtained through various techniques using renewable and nonrenewable energy sources. However the necessity for a gradual transition to renewable energy sources signifcantly hampers eforts to identify and implement green hydrogen production paths. Therefore this paper’s objective is to provide a technological review of the systems of hydrogen production from solar and wind energy utilizing several types of water electrolyzers. The current paper starts with a short brief about the diferent production techniques. A detailed comparison between water electrolyzer types and a complete illustration of hydrogen production techniques using solar and wind are presented with examples after which an economic assessment of green hydrogen production by comparing the costs of the discussed renewable sources with other production methods. Finally the challenges that face the mentioned production methods are illuminated in the current review.

In the energy transition from fossil fuels to renewables hydrogen is a realistic alternative to achieving the decarbonization target. However its chemical and physical properties make its storage and transport expensive. To ensure the cost-effective H2 usage as an energy vector other chemicals are getting attention as H2 carriers. Among them ammonia is the most promising candidate. The value chain of NH3 as a H2 carrier considering the long-distance ship transport includes NH3 synthesis and storage at the loading terminal NH3 storage at the unloading terminal and its cracking to release H2. NH3 synthesis and cracking are the cost drivers of the value chain. Also the NH3 cracking at large scale is not a mature technology and a significant effort has to be made in intensifying the process as much as possible. In this respect this work reviews the available technologies for NH3 cracking critically analyzing them in view of the scale up to the industrial level.

The exploration and evaluation of new composites possessing both processability and enhanced hydrogen storage capacity are of signifcant interest for onboard hydrogen storage systems and fuel cell based electric vehicle development. Here we demonstrate the fabrication of composite membranes with sufcient mechanical properties for enhanced hydrogen storage that are based on a polymer of intrinsic microporosity (PIM-1) matrix containing nano-sized fllers: activated carbon (AX21) or metal–organic framework (MIL-101). This is one of the frst comparative studies of diferent composite systems for hydrogen storage and in addition the frst detailed evaluation of the difusion kinetics of hydrogen in polymer-based nanoporous composites. The composite flms were characterised by surface area and porosity analysis hydrogen adsorption measurements mechanical testing and gas adsorption modelling. The PIM-1/AX21 composite with 60 wt% AX21 provides enhanced hydrogen adsorption kinetics and a total hydrogen storage capacity of up to 9.35 wt% at 77 K; this is superior to the US Department of Energy hydrogen storage target. Tensile testing indicates that the ultimate stress and strain of PIM-1/ AX21 are higher than those of the MIL-101 or PAF-1 containing composites and are sufcient for use in hydrogen storage tanks. The data presented provides new insights into both the design and characterisation methods of polymer-based composite membranes. Our nanoporous polymer-based composites ofer advantages over powders in terms of safety handling and practical manufacturing with potential for hydrogen storage applications either as means of increasing storage or decreasing operating pressures in high-pressure hydrogen storage tanks.

Integrated steelworks off-gases are generally exploited to produce heat and electricity. However further valorization can be achieved by using them as feedstock for the synthesis of valuable products such as methane and methanol with the addition of renewable hydrogen. This was the aim of the recently concluded project entitled “Intelligent and integrated upgrade of carbon sources in steel industries through hydrogen intensified synthesis processes (i3 upgrade)”. Within this project several activities were carried out: from laboratory analyses to simulation investigations from design development and tests of innovative reactor concepts and of advanced process control to detailed economic analyses business models and investigation of implementation cases. The final developed methane production reactors arerespectively an additively manufactured structured fixedbed reactor and a reactor setup using wash-coated honeycomb monoliths as catalyst; both reactors reached almost full COx conversion under slightly over-stoichiometric conditions. A new multi-stage concept of methanol reactor was designed commissioned and extensively tested at pilot-scale; it shows very effective conversion rates near to 100% for CO and slightly lower for CO2 at one-through operation for the methanol synthesis. Online tests proved that developed dispatch controller implements a smooth control strategy in real time with a temporal resolution of 1 min and a forecasting horizon of 2 h. Furthermore both offline simulations and cost analyses highlighted the fundamental role of hydrogen availability and costs for the feasibility of i 3 upgrade solutions and showed that the industrial implementation of the i 3 upgrade solutions can lead to significant environmental and economic benefits for steelworks especially in case green electricity is available at an affordable price.

The automotive industry sees hydrogen-powered fuel cell(FC) drives as a promising option with a high range and shortrefueling time. Current research aims to increase the profitabil-ity of the fuel cell system by reducing hydrogen consumption.This study suggests the use of an electrochemical hydrogencompressor (EHC) for hydrogen recirculation. Compared tomechanical compressors the EHC is very efficient due to thealmost isothermal conditions and due to its modular structurecan only take up a minimal amount of space in vehicles. Inaddition gas separation and purification of the hydrogentakes place in an EHC which is a significant advantage overthe standard recirculation with a blower or a jet pump. Thehigh purity of the hydrogen at the cathode outlet of the EHCalso increased partial pressure of the hydrogen at the fuel cellinlet and its efficiency. The study carried out shows that repla-cing the blower with the EHC reduces the hydrogen loss bypurging by up to ~95% and the efficiency of the FC systemcould be further improved. Thus the EHC has a great poten-tial for recycling hydrogen in FC systems in the automotiveindustry and is a great alternative to the current blower.

Underground hydrogen storage in depleted hydrocarbon reservoirs and aquifers has been proposed as a potential long-term solution to storing intermittently produced renewable electricity as the subsurface formations provide secure and large storage space. Various phenomena can lead to hydrogen loss in subsurface systems with the key cause being the trapping especially during the withdrawal cycle. Capillary trapping in particular is strongly related to the hysteresis phenomena observed in the capillary pressure/saturation and relative-permeability/saturation curves. This paper address two key points: (1) the sole impact of hysteresis in capillary pressure on hydrogen trapping during withdrawal cycles and (2) the dependency of optimal operational parameters (injection/withdrawal flow rate) and the reservoir characteristics such as permeability thickness and wettability of the porous medium on the remaining hydrogen saturation.<br/>Model<br/>To study the capillary hysteresis during underground hydrogen storage Killough [1] model was implemented in the MRST toolbox [2]. A comparative study was performed to quantify the impact of changes in capillary pressure behaviour by including and excluding the hysteresis and scanning curves. Additionally this study investigates the impact of injection/withdrawal rates and the aquifer permeability for various capillary and Bond numbers in a homogeneous system.<br/>Findings<br/>It was found that although the hydrogen storage efficiency is not considerably impacted by the inclusion of the capillary-pressure scanning curves the impact of capillary pressure on the well properties (withdrawal rate and pressure) can become significant. Higher injection and withdrawal rates does not necessarily lead to a better performance in terms of productivity. The productivity enhancement depends on the competition between gravitational capillary and viscous forces. The observed water upconing at relatively high capillary numbers resulted in low hydrogen productivity. highlighting the importance of well design and placement.

The energy transition is pushing towards a considerable diffusion of local energy communities based on renewable energy systems and coupled with energy storage systems or energy vectors to provide independence from fossil fuels and limit carbon emissions. Indeed the variable and intermittent nature of renewables make them inadequate to satisfy the end-users’ electricity demand throughout the whole day; thus the study of energy storage systems considering their seasonal storage behaviour (e.g. energy-power coupling selfdischarge loss and minimum state of charge) is fundamental to guarantee the proper energy coverage. This work aims at identifying the off-grid operation of a local energy community powered by a 220 kW small-scale hydropower plant in the center of Italy using either a battery energy storage system or a hydrogen one with the Calliope framework. Results show that whereas the hydrogen storage system is composed of a 137 kW electrolyser a 41 kW fuel cell and a storage of 5247 kgH2 a battery system storage system would have a capacity of 280 MWh. Even though the battery storage has a better round-trip efficiency its self-discharge loss and minimum state of charge limitation involve a discharging phase with a steeper slope thus requiring considerable economic investments because of the high energy-to-power ratio.

This article investigates the economic and environmental implications of implementing green ammonia production plants in Spain. To this end one business-as-usual scenario for gray ammonia production was compared with three green ammonia scenarios powered with different renewable energy sources (i.e. solar photovoltaic (PV) wind and a combination of solar PV and wind). The results illustrated that green ammonia scenarios reduced the environmental impacts in global warming stratospheric ozone depletion and fossil resource scarcity when compared with conventional gray ammonia scenario. Conversely green ammonia implementation increased the environmental impacts in the categories of land use mineral resource scarcity freshwater eutrophication and terrestrial acidification. The techno-economic analysis revealed that the conventional gray ammonia scenario featured lower costs than green ammonia scenarios when considering a moderate natural gas cost. However green ammonia implementation became the most economically favorable option when the natural gas cost and carbon prices increased. Finally the results showed that developing efficient ammonia-fueled systems is important to make green ammonia a relevant energy vector when considering the entire supply chain (production/transportation). Overall the results of this research demonstrate that green ammonia could play an important role in future decarbonization scenarios.

This work presents a study of the effects that integration of electrolysis facilities for Power-to-X processes have on the power grid. The novel simulation setup combines a high-resolution grid optimization model and a detailed scheduling model for alkaline water electrolysis. The utilization and congestion of power lines in northern Germany is investigated by setting different installed capacities and production strategies of the electrolysis facility. For electrolysis capacities up to 300 MW (~50 ktH2/a) local impacts on the grid are observed while higher capacities cause supra-regional impacts. Thereby impacts are defined as deviations from the average line utilization greater than 5%. In addition the minimum line congestion is determined to coincide with the dailyconstrained production strategy of the electrolysis facility. Our result show a good compromise for the integrated grid-facility operation with minimum production cost and reduced impact on the grid.