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For the commercial viability of a hydrogen-based transportation, hydrogen infrastructure is key. One of the major issues of hydrogen infrastructure is related to the deployment and costs of the Hydrogen Refuelling Stations (HRSs), where up to 40% of the cost is related to hydrogen compression. The introduction of Metal Hydride Hydrogen Compressors (MHHCs) in the HRSs as compression elements is a potential technology to reduce operational costs, ensure noiseless operation and increase efficiency, if renewable-based thermal energy (and/or industrial waste heat) is supplied to the system. In this work, four different two-stage MHHCs are introduced and examined in terms of compression ratio, hydrogen flow rate (compression duration), thermal energy requirements and efficiency. In addition, for comparison purposes, a three-stage MHHC is also studied. The properties of five different materials are used for the individual compression stages of the MHHCs, where all the necessary thermodynamic properties are extracted experimentally and incorporated in a commercial Multiphysics software. The unsteady heat and mass transfer equations are employed for the development of the numerical model. The hydrogenation/dehydrogenation kinetics and the temperature profile were validated against solid experimental results. In addition, to improve and accelerate the storage/release kinetics, an internal thermal management scenario has been introduced. The results show that for compression at the temperature range of 10–90 °C, the most favourable two-stage compression case (Case 3) showed a compression ratio of 11.18 ÷ 1, an isentropic efficiency of 4.54% with a thermal energy demand of 322 kJ/molH2 and a cycle time of almost 34 min.

There has been a continuously growing trend in international commercial air traffic, with the exception of COVID-19 crises; however, after the recovery, the trend is expected to even sharpen. The consequences of released emissions and by-products in the environment range from human health hazards, low air quality and global warming. This study is aimed to investigate the role of aviation emissions in global warming. For this purpose, data on different variables including global air traffic and growth rate, air traffic in different continents, total global CO2emissions of different airlines, direct and indirect emissions, air traffic in various UK airports and fuel-efficient aircraft was collected from various sources like EU member states, Statista, Eurostat, IATA, CAA and EUROCONTROL. The results indicated that in 2019, commercial airlines carried over 4.5 × 109passengers on scheduled flights. However, due to the COVID-19 pandemic in 2020, the global number of passengers was reduced to 1.8 × 109, representing around a 60% reduction in air traffic. Germany was the largest contributor to greenhouse gas (GHG) from the EU, releasing 927 kt of emissions in 3 years. In the UK, Heathrow airport had the highest number of passengers in 2019 with over 80 million, and the study of monthly aircraft movement revealed that Heathrow Airport also had the highest number of EU and International flights, while Edinburgh had the domestic flights in 2018. These research findings could be beneficial for airlines, policymakers and governments targeting the reduction of aircraft emissions.Graphical abstract

The development of a Ni@SiO2 partial oxidation (POx) catalyst with the potential to support indirect internal reforming (IIR) is reported. The paper explores how the silica shell proves vital in resisting the deactivation of the catalyst by re-oxidation. The results show that the silica shell maintained the nickel in its reduced state by limiting the rate of oxygen diffusion to the nickel surface. Retaining the Ni0 state allows for partial oxidation to proceed. The investigated catalysts were characterised by TGA, XRD, BET and TEM and the performance of the catalysts was assessed by gas chromatography. The tested catalysts showed greater than 95% methane conversion at 750 °C with a high selectivity towards syngas production. The stability of the catalyst was monitored over a time frame of 100 h, with minor degradation occurring due to nickel particle agglomeration.

In the current study, an experimental approach for the further understanding of the LiH hydrolysis reaction for hydrogen production is considered. The experimental work has been undertaken under small scale conditions by utilising fixed bed reactors. The hydrolysis reaction has been studied at several oven temperatures (150 °C, 300 °C and 500 °C). The favourable driving potentials for the hydrolysis reactions were identified by the utilisation of the Gibbs free energy analysis. The main outcome of the study is the deceleration of the reaction pace due to the formation of the by-product layers during the reaction. At the initial stage, due to the contact of steam with the unreacted and fresh LiH surface, the reaction proceeds on a fast pace, while the formation of the layers tends to decelerate the diffusion of steam into the core of material, forcing the production step to be slower. The hydrogen yield was found to be more than 90% of the theoretical value for all the reaction temperatures. Finally, a scenario of a hybrid-electric propulsion system for Unmanned Aerial Vehicles (UAVs) including Li-ion battery, Proton Membrane Fuel Cell (PEMFC) and an on-board hydrogen production system based on LiH hydrolysis is introduced and studied.

A numerical study fully validated with solid experimental results is presented and analysed, regarding the hydrogenation process of rectangular metal hydride tanks for green building applications. Based on a previous study conducted by the authors, where the effective heat management of rectangular tanks by using plain embedded cooling tubes was analysed, in the current work the importance of using extended surfaces to enhance the thermal properties and the hydrogenation kinetics is analysed. The studied extended surfaces (fins) were of rectangular shape; and several combinations regarding the number of fins and the fin thickness were examined and analysed. The values for fin thickness were 2-3-5 and 8 mm and the number of fins studied were 10-14-18 and 20. To evaluate the effect of the heat management process, a modified version of a variable named as Non-Dimensional Conductance (NDC) is introduced and studied. A novel AB 2 -Laves phase intermetallic was considered as the metal hydride for the study. The results of the hydrogenation behaviour for the introduced parameters (fin number and thickness) showed that the rectangular tank equipped with the cooling tubes in combination with 14 fins of 5 mm fin thickness has the capability of storing hydrogen over 90% of its theoretical capacity in less than 30 min.

The present chapter focuses on hydrogen technologies for both stationary and mobility/transportation applications. Hydrogen production from sustainable resources for the generation of pure and low cost hydrogen is described in the chapter. Several potential hydrogen production techniques are introduced and analyzed. The challenges and the advantages of each production method will be discussed. Furthermore, the chapter will introduce hydrogen infrastructure development for mobility applications and will discuss hydrogen storage challenges. Hydrogen production for fuel cell technologies requires an improvement regarding sustainability of the hydrogen supply and an improvement regarding decentralized hydrogen production. Moreover, hydrogen economy as far requires a large scale and long term storage solution to meet the increasing demand.

This work investigates the catalytic performance of bimetallic Ni-Cu/Al2O3 catalysts for syngas production by methanol steam reforming. The synthesis and characterization of a series of Nix-Cuy/Al2O3 catalysts with various stoichiometric fractions (x = 10, 7, 5, 3 and 0 wt% and y = 0, 3, 5, 7 and 10 wt% to Al2O3 support, respectively) are investigated and discussed. The catalytic performance is evaluated experimentally at temperature range of 225–325 °C. Both mono-metallic catalyst (10wt%Cu/Al2O3 and 10wt%Ni/Al2O3) and bi-metallic catalysts (7wt%Cu-3wt%Ni/Al2O3, 5wt%Cu-5wt%Ni/Al2O3 and 3wt%Cu-7wt%Ni/Al2O3) are synthesized using an impregnation method and characterized by means of SEM, temperature programmed reduction (TPR), BET analysis, XRD and TGA. It is found that the bimetallic Ni-Cu catalyst had a strong influence on the amount of CO2 and CO produced due to the different selectivity towards the water gas shift reaction and methanol decomposition reaction. The increase of the Ni content leads to an increase in CO and decrease in CO2 yields. The bimetallic catalyst did not produce CH4, revealing that Cu alloying in Ni catalyst had an inhibiting effect for CO and/or CO2 hydrogenation.

In the current work, a parametric numerical analysis of MmNi4.6Al0.4 is studied during the hydrogenation process; under effective heat management. A fully validated with solid experimental results mathematical model including the heat, mass and momentum conservation equations is introduced, described and incorporated on a Multiphysics software (COMSOL Multiphysics). The target of the current study was the storage of 200g of hydrogen per hydrogenation/dehydrogenation cycle within 5000s. The heat management during the hydrogenation process was performed by the usage of plain-embedded cooling tubes in combination with extended surfaces. The parameters examined in the current work were; the fin thickness, the fin number (metal hydride thickness) and the coolants’ flowrate within the tubes. A non-dimensional parameter was utilised for the evaluation of the heat management process. The results showed that the optimum fin number was 60, in combination with fin thickness 5-8mm and the value of the heat transfer coefficient 2000-5000 Wm-2K-1.

A numerical study on multistage metal hydride hydrogen compression (MHHC) systems is presented and analyzed. Multistage MHHC systems use a combination of different materials to increase the final compression ratio at the end of the compression process. In the current work a numerical model is proposed to describe the operation of a complete three-stage MHHC cycle, which can be divided in seven steps (for a three-stage compression system): first stage hydrogenation process, sensible heating of first stage, coupling process between the first and the second stage, sensible heating of the second stage, second coupling with the upcoming sensible heating of the third stage material and finally the delivery of high pressure hydrogen to a high pressure hydrogen tank. Three scenarios concerning the combination of different materials for the compression stages are introduced and analyzed in terms of maximum compression ratio, cycle time and energy consumption. According to the results, the combination of LaNi 5 (stage 1), MmNi 4.6 Al 0.4 (stage 2) and a novel synthesized AB 2 -Laves phase intermetallic (stage 3) present a compression ratio 22:1 while operating between 20 and 130 °C.

The solar photovoltaic cells received special attention during the past few years due to their rapid renewability consideration, particularly in international airports because of sustainability and high cost of fossil fuel. The present study aims to evaluate the feasibility performance of a novel 12 MWp capacity solar photovoltaic (PV) power plant at Doncaster Sheffield Airport, UK and to develop a mathematical model to provide a greater understanding of glare from solar panels and subsequently outline methods to avoid its effects. SISIFO and Global Solar Atlas software (GSA) simulations were used to obtain the results. Results reported that the proposed plant produced average energy of 1,034.31 MWh monthly and 12,411.69 MWh annually. The maximum electricity production was observed in May, June, and July as 1,772.71, 1,872.32, and 1,818.25 MWh, with 20.51, 21.67, and 21.04% of Capacity Utilization Factor (CUF), respectively. The average energy yield per month was achieved as 2585.74 kWh/kWp with an average performance ratio of 82.59%. Results also showed that 12 MWp PV plant at DSA reduced an average CO2 emission of 10,562,270 kg (11,642.90 tons) annually. The results revealed that glaring is very unlikely to occur throughout the year; however, winter period produced the lowest trajectory of reflected light. Overall, the proposed solar plant at Doncaster Sheffield airport (DSA) was found to be feasible and generates almost double electricity of overall energy demand (6,951.55 MWh) at Doncaster Sheffield airport. However, it is recommended that the excessive produced energy during summer could be transfer into the national grid, which would be returned during the winter season to facilitate PV plant.

This study presents a full operation and optimisation of a mixing unit; an innovative approach is developed to address the behaviour of gas-liquid mixing by using Electrical Resistance Tomography (ERT). The validity of the method is investigated by developing the tomographic images using different numbers of baffles in a mixing unit. This technique provided clear visual evidence of better mixing that took place inside the gasliquid system and the effect of a different number of baffles on mixing characteristics. For optimum gas flow rate (m3/s) and power input (kW), the oxygen absorption rate in water was measured. Dynamic gassingout method was applied for five different gas flow rates and four different power inputs to find out mass transfer coefficient (KLa). The rest of the experiments with one up to four baffles were carried out at these optimum values of power input (2.0 kW) and gas flow rate (8.5×10-4 m3/s). The experimental results and tomography visualisations showed that the gasliquid mixing with standard baffling provided near the optimal process performance and good mechanical stability, as higher mass transfer rates were obtained using a greater number of baffles. The addition of single baffle had a striking effect on mixing efficiency and additions of further baffles significantly decrease mixing time. The energy required for complete mixing was remarkably reduced in the case of four baffles as compared to without any baffle. The process economics study showed that the increased cost of baffles installation accounts for less cost of energy input for agitation. The process economics have also revealed that the optimum numbers of baffles are four in the present mixing unit and the use of an optimum number of baffles reduced the energy input cost by 54%.

In this study, methane and methanol steam reforming reactions over commercial Ni/Al2O3, commercial Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al2O3 catalyst with respect to the commercial Ni/Al2O3 (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al2O3 (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H2 selectivity, CO2 and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H2, with H2 selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al2O3 catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al2O3 (8.9%) and commercial Cu/ZnO/Al2O3 catalysts (3.5%).

In the current work, a three-dimensional computational study regarding coupled heat and mass transfer during both the hydrogenation and dehydrogenation process in upscale cylindrical metal hydride reactors is presented, analysed and optimized. Three different heat management scenarios were examined at the degree to which they provide improved system performance. The three scenarios were: 1) plain embedded cooling/heating tubes, 2) transverse finned tubes and 3) longitudinal finned tubes. A detailed optimization study was presented leading to the selection of the optimized geometries. In addition, two different types of hydrides, LaNi5 and an AB2-type intermetallic were studied as possible candidate materials for using as the first stage alloys in a two-stage metal hydride hydrogen compression system. As extracted from the above results, it is clear that the case of using a vessel equipped with 16 longitudinal finned tubes is the most efficient way to enhance the hydrogenation kinetics when using both LaNi5 and the AB2-alloy as the hydride agents. When using LaNi5 as the operating hydride the case of the vessel equipped with 60 embedded cooling tubes presents the same kinetic behaviour with the case of the vessel equipped with 12 longitudinal finned tubes, so in that way, by using extended surfaces to enhance the heat exchange can reduce the total number of tubes from 60 to 12. For the case of using the AB2-type material as the operating hydride the performance of the extended surfaces is more dominant and effective compared to the case of using the embedded tubes, especially for the case of the longitudinal extended surfaces.

Low-temperature methane and methanol steam-reforming catalysts Ni/Al 2 O 3 , Cu/Al 2 O 3 and Ni–Cu/Al 2 O 3 with various loadings of Ni and Cu were prepared using a wet impregnation method. The samples were characterized using scanning electron microscope, surface area (BET) test, X-ray diffraction (XRD), infrared test, CO chemisorption test and temperature-programmed reduction tests. XRD testing showed that NiO and CuO were present. Ni–Cu-alloyed catalyst shows a significant change in the catalyst characteristics compared with those of individual metals. The results presented in this paper show the main changes in the catalyst properties using ex situ testing. Copyright , Oxford University Press.