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In the past material innovation has changed society through new material-induced technologies adding a new value to society. In the present world engineers and scientists are expected to invent new materials to solve the global problem of climate change. For the transport sector the challenge for material engineers is to change the oil-based world into a sustainable world. After witnessing the recent high oil price and its adverse impact on the global economy it is time to accelerate our efforts towards this change.

Industries are tackling global energy issues such as oil and CO₂ as well as local environmental problems such as NOx and particulate matter. Hydrogen is the most promising candidate to provide carbon-free emission-free and oil-free mobility. As such engineers are working very hard to bring this technology into the real society. This paper describes recent progress of vehicle technologies as well as hydrogen-storage technologies to extend the cruise range and ensure the easiness of refuelling and requesting material scientists to collaborate with industry to fight against global warming.

Link to document download on Royal Society Website  

To examine the effect of initial turbulence on vented explosions experiments were performed for lean hydrogen–air mixtures with hydrogen concentrations ranging from 12 to 15% vol. at elevated initial turbulence. As expected it was found that an increase in initial turbulence increased the overall flame propagation speed and this increased flame propagation speed translated into higher peak overpressures during the external explosion. The peak pressures generated by flame–acoustic interactions however did not vary significantly with initial turbulence. When flame speeds measurements were examined it was found that the burning velocity increased with flame radius as a power function of radius with a relatively constant exponent over the range of weak initial turbulence studied and did not vary systematically with initial turbulence. Instead the elevated initial turbulence increased the initial flame propagation velocities of the various mixtures. The initial turbulence thus appears to act primarily by generating higher initial flame wrinkling while having a minimal effect on the growth rate of the wrinkles. For practical purposes of modelling flame propagation and pressure generation in vented explosions the increase in burning velocity due to turbulence is suggested to be approximated by a single constant factor that increases the effective burning velocity of the mixture. When this approach is applied to a previously developed vent sizing correlation the correlation performs well for almost all of the peaks. It was found however that in certain situations this approach significantly under predicts the flame–acoustic peak. This suggests that further research may be necessary to better understand the influence of initial turbulence on the development of flame–acoustic peaks in vented explosions.

At the JRC-IET on-board hydrogen tanks have been subjected to filling–emptying cycles to investigate their long-term mechanical and thermal behaviour and their safety performance. The local temperature history inside the tanks has been measured and compared with the temperatures outside and at the tank metallic bosses which is the measurement location identified by some standards. The outcome of these activities is a set of experimental data which will be made publicly available as reference for safety studies and validation of computational fluid dynamics.

In this work the validity of simplified mathematical models for predicting dispersion of turbulent buoyant jet or plume within a confined volume is evaluated. In the framework of the HYSAFE Network of Excellence CEA performed experimental tests in a full-scale Garage facility in order to reproduce accidental gas leakages into an unventilated residential garage. The effects of release velocities diameters durations mass flow rates and flow regimes on the vertical distribution of the gas concentration are investigated. Experimental data confirm the formation for the release conditions of an almost well-mixed upper layer and a stratified lower layer. The comparison of the measurements and the model predictions shows that a good agreement is obtained for a relatively long-time gas discharge for jet like or plume like flow behaviour.

Hydrogen energy applications often require that systems are used indoors (e.g. industrial trucks for materials handling in a warehouse facility fuel cells located in a room or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons to isolate them from the end-user and the public or from weather conditions.<br/>Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture or can result in jet-fires. Within Hyindoor European Project carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation vented deflagrations jet fires and including under-ventilated flame regimes (e.g. extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.

Jordan's energy diversification strategy is centred around renewables which are expected will provide the low-cost reliable secure and environmentally sustainable energy required to power its new engines of economic growth – manufacturing transport construction and agriculture.

The National Energy Strategy 2020–2030 presents the evolution of the energy sector under its vision for stimulating demand achieving efficiency and improving electricity system flexibility.

This Renewables Readiness Assessment (RRA) highlights key actions for the short and medium-term that could create more conductive conditions for renewable energy development. It aims to help unlock Jordan's renewable energy potential and provide the means to meet the energy diversification goals of its national strategy.

The study was undertaken by the Ministry of Energy and Mineral Resources (MEMR) in collaboration with the International Renewable Energy Agency (IRENA).

Key recommendations:

• Provide the necessary conditions for renewables growth in the power sector.
• Foster continued growth of renewable power generation.
• Plan the integration of higher shares of renewable power.
• Incentivise the use of renewables for heating and cooling.
• Support renewable transport and mobility options.
• Catalyse renewable energy investment. Strengthen local industries and create jobs in renewables.

Laminar burning velocities (SL) of hydrogen/ammonia mixtures in air at atmospheric pressure were studied experimentally and numerically. The blending of hydrogen with ammonia two fuels that have been proposed as promising carriers for renewable energy causes the laminar flame speed of the mixture SL to decrease significantly. However details of this have not previously available. Systematic measurements were therefore performed for a series of hydrogen/ammonia mixtures with wide ranges of mole fractions of blended ammonia (XNH3) and equivalence ratio using a heat flux method based on heat flux of a flat flame transferred to the burner surface. It was found that the mixture of XNH3 = 40% has a value of SL close to that of methane which is the dominant component of natural gas. Using three chemical kinetic mechanisms available in the literature i.e. the well-known GRI-Mech 3.0 mechanism and two mechanisms recently released SL were also modelled for the cases studied. However the discrepancies between the experimental and numerical results can exceed 50% with the GRI-Mech 3.0 mechanism. Discrepancies were also found between the numerical results obtained with different mechanisms. These results can contribute to an increase in both the safety and efficiency of the coutilization of these two types of emerging renewable fuel and to guiding the development of better kinetic models.

A precise understanding of the flame turbulence induced by cellular instabilities is indispensable to perform an appropriate risk assessment of hydrogen fuelled gas explosion. In this research Darrieus Landau instability (DL instability) whose effect on gas explosion is  remarkable was experimentally examined. The DL instability is essentially caused by a volumetric expansion of burned gas at flame front. Therefore in order to examine the effects of volumetric expansion ratio the experiments were conducted using H2-O2-N2-Ar gas mixtures of various volumetric expansion ratio conditions by changing N2-Ar ratio. When Ar content ratio is increased the flame temperature becomes higher and volumetric expansion ratio is increased owing to lower specific heat of Ar. The experiments were conducted in nearly unconfined conditions of laboratory-scale and large-scale. Gas mixtures were filled in a 10 cm diameter soap bubble for the laboratory-scale and in a plastic tent of thin vinyl sheet of 1m3  for the large-scale. The gas mixtures were ignited by an electric spark and blast wave and flame speed were measured simultaneously by using a pressure sensor and a high-speed video camera. The DL instability owing to volumetric expansion accelerates flame propagation. In addition the intensity of blast wave was greatly raised depending on flame acceleration which can be explained by an acoustic theory. The effects of expansion ratio and experimental scales on flame propagation and blast wave were analyzed in detail. These results are quite important to perform an appropriate consequence analysis of accidental explosion of hydrogen.

Type IV pressure vessels are commonly used for hydrogen on-board stationary or bulk storages. During their lifetime they can be submitted to mechanical impacts creating damage within the composite structure not necessarily correlated to what is visible from the outside. When an impact is suspected or when a cylinder is periodically inspected it is necessary to determine whether it can safely stay in service or not. The FCH JU project Hypactor aims at creating a large database of impacts characterized by various non destructive testing (NDT) methods in order to provide reliable pass-fail criteria for damaged cylinders. This paper presents some of the tests results investigating short term burst) and long term (cycling) performance of impacted cylinders and the recommendations that can be made for impact testing and NDT criteria calibration.

The HyDeploy project has undertaken a programme of work to assess the effect of hydrogen addition on the safety and performance of gas appliances and installations. A representative set of eight appliances have been assessed in laboratory experiments with a range of test gases that explored high and low Wobbe Number and hydrogen concentrations up to 28.4 % mol/mol. Tests have demonstrated that the addition of hydrogen does not affect the key hazard areas of CO production light back flame out or the operation of flame failure devices. It was identified that for some designs of gas fire appliances the operation of the oxygen depletion sensors may be affected by the addition of hydrogen and further studies in this area are planned. A laboratory based study was supported by an onsite testing programme where 133 installations were assessed for gas tightness appliance combustion safety and operation against normal line natural gas G20 reference gas and two hydrogen blended gases. Where installations were gas tight for natural gas analysis showed that no additional leakage occurred with hydrogen blended gases. There were also no issues identified with the combustion performance of appliances and onsite results were in line with those obtained in the laboratory testing programme.

Liquid hydrogen (LH2) storage is viewed as a viable approach to assure sufficient hydrogen capacity at commercial fuelling stations. Presently LH2 is produced at remote facilities and then transported to the end-use site by road vehicles (i.e. LH2 tanker trucks). Venting of hydrogen to depressurize the transport storage tank is a routine part of the LH2 delivery and site transfer process. The behaviour of cold hydrogen plumes has not been well characterized because of the sparsity of empirical field data which can lead to overly conservative safety requirements. Committee members of the National Fire Protection Association (NFPA) Standard 2 [1] formed the Hydrogen Storage Safety Task Group which consists of hydrogen producers safety experts and computational fluid dynamics modellers has identified the lack of understanding of hydrogen dispersion during LH2 venting of storage vessels as a critical gap for establishing safety distances at LH2 facilities especially commercial hydrogen fuelling stations. To address this need the National Renewable Energy Laboratory Sensor Laboratory in collaboration with the NFPA Hydrogen Storage Task Group developed a prototype Cold Hydrogen Plume Analyzer to empirically characterize the hydrogen plume formed during LH2 storage tank venting. The prototype analyzer was field deployed during an actual LH2 venting process. Critical findings included

• Hydrogen above the lower flammable limit (LFL) was detected as much as 2 m lower than the release point which is not predicted by existing models.
• Personal monitors detected hydrogen at ground level although at levels below the LFL.
• A small but inconsistent correlation was found between oxygen depletion and the hydrogen concentration.
• A negligible to non-existent correlation was found between in-situ temperature measurements and the hydrogen concentration.

The prototype analyzer is being upgraded for enhanced metrological capabilities including improved real-time spatial and temporal profiling of hydrogen plumes and tracking of prevailing weather conditions. Additional deployments are planned to monitor plume behaviour under different wind humidity and temperature conditions. The data will be shared with the Hydrogen Storage Task Group and ultimately will be used support theoretical models and code requirements prescribed in NFPA 2.

To define a strategy of mitigation for containerized hydrogen systems (fuel cells for example) against explosion the main characteristics of flammable atmosphere (size concentration turbulence…) shall be well-known. This article presents an experimental study on accidental hydrogen releases and dispersion into an enclosure of 4 m3 (2 m x 2 m x 1 m). Different release points are studied: two circular releases of 1 and 3 mm and a system to create ring-shaped releases. The releases are operated with a pressure between 10 and 40 bars in order to be close to the process conditions. Different positions of the release inside the enclosure i.e. centred on the floor or along a wall are also studied. A specific effort is made to characterize the turbulence in the enclosure during the releases. The objectives of the experimental study are to understand and quantify the mechanisms of formation of the explosive atmosphere taking into account the geometry and position of the release point and the confinement. Those experimental data are analyzed and compared with existing models and could bring some new elements to improve them.

The uncertainty on the laminar flame speed extracted from spherically expanding flames can be minimized by using large flame radius data for the extrapolation to zero stretch-rate. However at large radii the hydrodynamic and thermo-diffusive instabilities induce the formation of a complex cellular flame front and limit the range of usable data. In the present study we have employed the flame stability theory of Matalon to optimize the properties of the initial mixture so that transition to cellularity may occur at a pre-determined large radius. This approach was employed to measure the laminar flame speeds of H2/O2/N2/He mixtures with equivalence ratios from 0.6 to 2.0 at pressures of 50/80/100 kPa and a temperature of 300 K. For all the performed experiments the uncertainty related to the extrapolation to zero stretch-rate (performed with the linear curvature model) was below 2% as shown by the position of the data points in the (Lb/Rf;U Lb/Rf;L) plan where Lb is the burned Markstein length; and Rf;L and Rf;U are the flame radii at the lower and upper bounds of the extrapolation range. Comparison of the predictions of four chemical mechanisms with the present unstretched laminar flame speed data indicated an error below 10% for most conditions. In addition unsteady 1-D simulations performed with A-SURF demonstrated that the flame dynamical response to stretch rate could not be captured by the mechanisms. The present work indicates that although the stability theory of Matalon provides a well defined framework to optimize the mixture properties for improved flame speed measurement the uncertainty of some of the required parameters can result in largely over-estimated critical radius for cellularity onset which compromise the accuracy of the optimization procedure.

We have implemented a portable large-scale shadowgraph system for use in flow visualization relating to hydrogen safety. Previous large-scale shadowgraph and schlieren implementations have often been limited to background- oriented techniques which are subject to noise. The system built is based on a large-scale shadowgraph technique developed by Settles which allows for high-quality visualization. We have applied the shadowgraph system to complex phenomena and current issues in hydrogen safety including DDT in long channels jet releases and unconfined deflagrations. Shadowgrams taken are compared to a Z-schlieren system. This shadowgraph system allows analysis of these phenomena at longer length scales.

Element One Inc. Boulder CO is developing novel hydrogen gas leak indicators to improve the safety and maintenance operations of hydrogen production and chemical processing facilities and hydrogen fueling stations. These technologies can be used to make visual gas leak indicators such as paints decals and conformal plastic films as well as RF sensors for wireless networks. The primary advantage of the Element One hydrogen gas indicators is their low cost and easy deployment which allows them to be used ubiquitously at each and every potential hydrogen leak site. They have the potential to convert safety problems into routine maintenance problems thereby improving overall safety and decreasing operational costs.

Hydrogen used in hydrogen fuel cell vehicles is the flammable gas which has wide flammable range and flame propagation speed is very fast. This fuel cell vehicle equipped with high-pressure vessel in the form of fuel to supply the high pressure hydrogen storage system needs to be checked carefully about a special safety design and exact weak point for high pressure repeated fatigue. 70 L liner and 70 MPa Type-3 vessel were tested using the equipments which can perform ambient hydraulic cycling test and burst test in the Korea Gas Safety Corporation. And it was performed to identify the internal external behaviour through the Finite Element Analysis (FEA) and real leakage mode for high pressure repeated fatigue when subjected to be pressurized in vessel. 70 L liner and 70 MPa Type-3 vessel were tested using the equipments which can perform ambient hydraulic cycling test and burst test in the Korea Gas Safety Corporation. And it was performed to identify the internal external behaviour through the Finite Element Analysis (FEA) and real leakage mode for high pressure repeated fatigue when subjected to be pressurized in vessel. Through this study liner of type-3 hydrogen vessel is ruptured first on cylindrical (body) part than Dome part in 8.5 MPa. Also the same Phenomena are confirmed through the Finite Element Analysis (FEA). External composite leakage mode in ambient hydraulic cycling test was occurred in different area such as the Dome Dome knuckle and cylindrical (body) parts. But cracks of inner liner for gas tight were occurred in only cylindrical (body) parts. Also in FEA results when vessel is pressurized Dome knuckle and cylindrical (body) parts is weakest among all parts because of expansion of cylindrical (body) parts.

The commercial deployment of hydrogen will often involve housing portable hydrogen fuel cell power units in 20-foot or 40-foot shipping containers. Due to the unique properties of hydrogen hazards identification and consequence analysis is essential to safe guard the installations and design measures to mitigate potential hazards. In the present study the explosion of a premixed hydrogen-air cloud enclosed in a 20-foot container of 20’ x 8’ x 8’.6” is investigated in detail numerically. Numerical simulations have been performed using HyFOAM a dedicated solver for vented hydrogen explosions developed in-house within the frame of the open source computational fluid dynamics (CFD) code OpenFOAM toolbox. The flame wrinkling combustion model is used for modelling turbulent deflagrations. Additional sub-models have been added to account for lean combustion properties of hydrogen-air mixtures. The predictions are validated against the recent experiments carried out by Gexcon as part of the HySEA project supported by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) under the Horizon 2020 Framework Programme for Research and Innovation. The effects of congestion within the containers on the generated overpressures are also investigated.

Polymers for O-rings valve seats gaskets and other sealing applications in the hydrogen infrastructure face extreme conditions of high-pressure H2 (0.1 to 100 MPa) during normal operation. To fill current knowledge gaps and to establish standard test methods for polymers in H2 environments these materials can be tested in laboratory scale H2 manifolds mimicking end use pressure and temperature conditions. Beyond the influence of high pressure H2 the selection of gases used for leak detection in the H2 test manifold their pressures and times of exposure gas types relative diffusion and permeation rates are all important influences on the polymers being tested. These effects can be studied ex-situ with post-exposure characterization. In a previous study four polymers (Viton A Buna N High Density Polyethylene (HDPE) and Polytetrafluoroethylene (PTFE)) commonly used in the H2 infrastructure were exposed to high-pressure H2 (100 MPa). The observed effects of H2 were consistent with typical polymer property-structure relationships; in particular H2 affected elastomers more than thermoplastics. However since high pressure He was used for purging and leak detection prior to filling with H2 a study of the influence of the purge gas on these polymers was considered necessary to isolate the effects of H2 from those of the purge gas. Therefore in this study Viton A Buna N and PTFE were exposed to the He purge procedure without the subsequent H2 exposure. Additionally six polymers Viton A Buna N PTFE Polyoxymethylene (POM) Polyamide 11 (Nylon) and Ethylenepropylenediene monomer rubber (EPDM) were subjected to high pressure Ar (100 MPa) followed by high pressure H2 (100 MPa) under the same static isothermal conditions to identify the effect of a purge gas with a significantly larger molecular size than He. Viton A and Buna N elastomers are more prone to irreversible changes as a result of H2 exposure from both Ar and He leak tests as indicated by influences on storage modulus extent of swelling and increased compression set. EPDM even though it is an elastomer is not as prone to high-pressure gas influences. The thermoplastics are generally less influenced by high pressure regardless of the gas type. Conclusions from these experiments will provide insight into the influence of purging processes and purge gases on the subsequent testing in high pressure gaseous H2. Control for the influence of purging on testing results is essential for the development of robust test methods for evaluating the effects of H2 and other high-pressure gases on the properties of polymers.

In the United States requirements for liquid motor vehicle fuelling stations have been in place for many years. Requirements for motor vehicle fuelling stations for gaseous fuels including hydrogen are relatively new. These requirements have in the United States been developed along different code and standards paths. The liquid fuels have been addressed in a single document and the gaseous fuels have been addressed in documents specific to an individual gas. The result of these parallel processes is that multi-fuel stations are subject to requirements in several fuelling regulations codes and standards (RCS). This paper describes a configuration of a multi-fuel motor vehicle fuelling station and provides a detailed breakdown of the codes and standards requirements. The multi-fuel station would dispense what the U.S. Department of Energy defines as the six key alternative fuels: biodiesel electricity ethanol hydrogen natural gas and propane. The paper will also identify any apparent gaps in RCS and potential research projects that could help fill these gaps.

We are addressing hydrogen release into a single-vented facility with wind blowing onto the opposite side of the vent wall. Earlier work based on tests performed by HSL with wind (within the HyIndoor project) and comparative CFD simulations with and without wind ([1]within the H2FC project) has shown that the hydrogen concentrations inside the enclosure are increased compared to the case with no wind. This was attributed to the fact that wind is disrupting the passive ventilation. The present work is based on the GAMELAN tests (within the HyIndoor project) performed with one vent and no wind. For this enclosure simulations were performed with and without wind and reproduced the disrupting wind effect. In order to remove this effect and enhance the ventilation additional simulations were performed by considering different geometrical modifications near the vent. A simple geometrical layout around the vent is here proposed that leads to elimination of the disrupting wind effect. The analysis has been performed using the ADREA-HF code earlier validated both for the HSL and the GAMELAN tests. The current work was performed partly within HyIndoor project

Catastrophic rupture of onboard hydrogen storage in a fire is a safety concern. Different passive e.g. fireproofing materials the thermally activated pressure relief device (TPRD) and active e.g. initiation of TPRD by fire sensors safety systems are being developed to reduce hazards from and associated risks of high-pressure hydrogen storage tank rupture in a fire. The probability of such low-frequency highconsequences event is a function of fire resistance rating (FRR) i.e. the time before tank without TPRD ruptures in a fire the probability of TPRD failure etc. This safety issue is “confirmed” by observed recently cases of CNG tanks rupture due to blocked or failed to operate TPRD etc. The increase of FRR by any means decreases the probability of tank rupture in a fire particularly because of fire extinction by first responders on arrival at an accident scene.<br/>This study of socio-economic effects of safety applies a quantitative risk assessment (QRA) methodology to an example of hydrogen vehicles with passive tank protection system on roads in London.<br/>The risk is defined here through the cost of human loss per fuel cell hydrogen vehicle (FCHV) fire accident and fatality rate per FCHV per year. The first step in the methodology is the consequence analysis based on validated deterministic engineering tools to estimate the main identified hazards: overpressure in the blast wave at different distances and the thermal hazards from a fireball in the case of catastrophic tank rupture in a fire. The population can be exposed to slight injury serious injury and fatality after an accident. These effects are determined based on criteria by Health and Safety Executive (UK) and a cost metrics is applied to the number of exposed people in these three harm categories to estimate the cost per an accident. The second step in the methodology is either the frequency or the probability analysis. Probabilities of a vehicle fire and failure of the thermally activated pressure relief device are taken from published sources. A vulnerability probit function is employed to calculate the probability of emergency operations’ failure to prevent tank rupture as a function of a storage tank FRR and time of fire brigade arrival. These later results are integrated to estimate the tank rupture frequency and fatality rate. The risk is presented as a function of fire resistance rating.<br/>The QRA methodology allows to calculate the cost of human loss associated with an FCHV fire accident and demonstrates how the increase of FRR of onboard storage as a safety engineering measure would improve socio-economics of FCHV deployment and public acceptance of the technology.

Integral type models to describe stationary plumes and jets in cross-flows (wind) have been developed since about 1970. These models are widely used for risk analysis to describe the consequences of many different scenarios. Alternatively CFD codes are being applied but computational requirements still limit the number of scenarios that can be dealt with using CFD only. The integral models however are not suited to handle transient releases such as releases from pressurized equipment where the initially high release rate decreases rapidly with time. Further on gas ignition a second model is needed to describe the rapid combustion of the flammable part of the plume (flash fire) and a third model has to be applied for the remaining jet fire. The objective of this paper is to describe the first steps of the development of an integral-type model describing the transient development and decay of a jet of flammable gas after a release from a pressure container. The intention is to transfer the stationary models to a fully transient model capable to predict the maximum extension of short-duration high pressure jets. The model development is supported by conducting a set of transient ignited and unignited spontaneous releases at initial pressures between 25bar and 400bar. These data forms the basis for the presented model development approach.

The numerical simulations on the high-pressure hydrogen jet are performed by using the unsteady three-dimensional compressible Navier-Stokes equations with multi-species conservation equations. The present numerical results show that the highly expanded hydrogen free jet observes and the distance between the Mach disc and the nozzle exit agrees well with the empirical equation. The time-averaged H2 concentration of the numerical simulations agrees well with the experimental data and the empirical equation. The numerical simulation of ignition in a hydrogen jet is performed to show the flame behaviour from the calculated OH iso surface. We predicted the ignition and no-ignition region from the present numerical results about the forced ignition in the high-pressurized hydrogen jet.

Hydrogen safety is a relevant topic for both nuclear fission and fusion power plants. Hydrogen generated in the course of a severe accident may endanger the integrity of safety barriers and may result in radioactive releases. In the case of the ITER fusion facility accident scenarios with water ingress consider the release of hydrogen into the suppression tank (ST) of the vacuum vessel pressure suppression system (VVPSS). Under the assumption of additional air ingress the formation of flammable gas mixtures may lead to explosions and safety component failure.<br/>The installation of passive auto-catalytic recombiners (PARs) inside the ST which are presently used as safety devices inside the containments of nuclear fission reactors is one option under consideration to mitigate such a scenario. PARs convert hydrogen into water vapor by means of passive mechanisms and have been qualified for operation under the conditions of a nuclear power plant accident since the 1990s.<br/>In order to support on-going hydrogen safety considerations simulations of accident scenarios using the CFD code ANSYS-CFX are foreseen. In this context the in-house code REKO-DIREKT is coupled to CFX to simulate PAR operation. However the operational boundary conditions for hydrogen recombination (e.g. temperature pressure gas mixture) of a fusion reactor scenario differ significantly from those of a fission reactor. In order to enhance the code towards realistic PAR operation a series of experiments has been performed in the REKO-4 facility with specific focus on ITER conditions. These specifically include operation under sub-atmospheric pressure (0.2–1.0 bar) gas compositions ranging from lean to rich H2/O2 mixtures and superposed flow conditions.<br/>The paper gives an overview of the experimental program presents results achieved and gives an outlook on the modelling approach towards accident scenario simulation.

The hydrogen vector stands as a potentially important tool to achieve the decarbonization of the energy sector. It represents an option to store the periodic excesses of energy generation from renewable electrical sources to be used as it is as a substitute for fossil fuels in some applications or reconverted into electricity when needed. In this context hydrogen can significantly decarbonize the building sector as an alternative fuel for gas-driven devices. Along with hydrogen the European strategic vision indicates the electrification of heat among the main energy transition pathways. The potential environmental benefits achievable from renewable hydrogen in thermally-driven appliances and the electrification of residential heat through electric heat pumps were evaluated and compared in this work. The novelty of the research consists of a consequential comparative life cycle assessment (16 impact categories) evaluation for three buildings (old old retrofitted and new) supplied by three different appliances (condensing boiler gas absorption heat pump and electric heat pump) never investigated before. The energy transition was evaluated for 2020 and 2030 scenarios considering the impact of gaseous fuels (natural gas and European green hydrogen) and electricity based on the pathway of the European electricity grid (27 European member states plus the United Kingdom). The results allowed to compare the environmental profile in deterministic and stochastic approaches and confirm if the increase of renewables reduces the impact in the operational phase of the appliances. The results demonstrate that despite the increased renewable share the use phase remains the most significant for both temporal scenarios contributing to 91% of the environmental profile. Despite the higher footprint in 2020 compared to the electric heat pump (198–200 vs. 170–196 gCO2eq/kWhth) the gas absorption heat pump offered a lower environmental profile than the others in all the scenarios analyzed.

This paper focuses on hydrogen production for green mobility applications (other applications are currently under investigation). Firstly a brief state of the art of hydrogen generation by hydrolysis with magnesium is shown. The hydrolysis performance of Magnesium powder ball–milled along with different additives (graphite and transition metals TM = Ni Fe and Al) is taken for comparison. The best performance was observed with Mg–10 wt.% g mixtures (95% of theoretical hydrogen generation yield in about 3 min). An efficient solution to control this hydrolysis reaction is proposed to produce hydrogen on demand and to feed a PEM fuel cell. Tests on a bench fitted with a 100 W Proton Exchange Membrane (PEM) fuel cell have demonstrated the technological potential of this solution for electric assistance applications in the field of light mobility.

Hydrogen is an alternative to conventional heavy marine fuel oil following the initial strategy of the International Maritime Organization (IMO) for reducing greenhouse gas emissions. Although hydrogen energy has many advantages (zero-emission high efficiency and low noise) it has considerable fire and explosion risks due to its thermal and chemical characteristics (wide flammable concentration range and low ignition energy). Thus safety is a key concern related to the use of hydrogen. Whereas most previous studies focused on the terrestrial environment we aim to analyze the effects of the ship’s motion on hydrogen dispersion (using commercial FLUENT code) in an enclosed area. When compared to the steady state our results revealed that hydrogen reached specific sensors in 63% and 52% less time depending on vessel motion type and direction. Since ships carry and use a large amount of hydrogen as a power source the risk of hydrogen leakage from collision or damage necessitates studying the correspondence between leakage diffusion and motion characteristics of the ship to position the sensor correctly.

This Insight continues the OIES series considering the future of gas. The clear message from previous papers is that on the (increasingly certain) assumption that governments in major European gas markets remain committed to decarbonisation targets the existing natural gas industry is under threat.   It is therefore important to develop a decarbonisation narrative leading to a low- or zero-carbon gas implementation plan.



Previous papers have considered potential pathways for gas to decarbonise specifically considering biogas and biomethane and power-to-gas (electrolysis) . This paper goes on to consider the potential for production transport and use of hydrogen in the decarbonising energy system. Previous papers predominately focused on Europe which has been leading the way in decarbonisation. Hydrogen is now being considered more widely in various countries around the world so this paper reflects that wider geographical coverage.



Since the term ‘hydrogen economy’ was first used in 1970 there have been a number of ‘false dawns’ with bold claims for the speed of transition to hydrogen.  This Insight argues that this time for some applications at least there are grounds for optimism about a future role for decarbonised hydrogen but the lesson from history is that bold claims need to be examined carefully and treated with some caution. There are no easy or low-cost solutions to decarbonisation of the energy system and this is certainly the case for possible deployment of low-carbon hydrogen. A key challenge is to demonstrate the technical commercial economic and social acceptability of various possibilities at scale. Hydrogen will certainly play a role in decarbonisation of the energy system although the size of the role may be more limited than envisaged in some more optimistic projections.



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The Health and Safety Laboratory (HSL) has carried out an investigation into the gas characteristics that may influence the leakage dispersion and flammability hazards associated with blended natural gas-hydrogen mixtures containing up to 20 % mol/mol hydrogen. The work was carried out under contract to Cadent & Northern Gas Networks as part of the HyDeploy project which was commissioned to investigate the feasibility of using blended hydrogen-natural gas mixtures in UK mains gas distribution networks.

Under the HyDeploy project a demonstration scheme is being carried out at Keele University in which it is planned to inject up to 20 % mol/mol hydrogen. Keele is Britain’s largest campus university and an ideal test site for a demonstration scheme as its gas distribution network is largely independent of the national gas network but still subject to UK gas industry procedural controls. It is anticipated that a successful demonstration scheme will facilitate the use of blended natural gas-hydrogen mixtures throughout the UK leading to significant reductions in carbon dioxide emissions. The project is being led by Cadent & Northern Gas Networks and also involves ITM Power Progressive Energy Keele University and HSL in consortium.

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With the development of the natural gas industry gas transmission pipelines have been developed rapidly in terms of safety economy and efficiency. Our recent studies have shown that an important factor of main pipelines serviceability loss under their long-term service is the in-bulk metal degradation of the pipe wall. This leads to the loss of the initial mechanical properties primarily resistance to brittle fracture which were set in engineering calculations at the pipeline design stage. At the same time stress corrosion cracking has been identified as one of the predominant failures in pipeline steels in humid environments which causes rupture of high-pressure gas transmission pipes as well as serious economic losses and disasters.

In the present work the low-carbon pipeline steels with different strength levels from the point of view of their susceptibility to stress corrosion cracking in the as-received state and after in-laboratory accelerated degradation under environmental conditions similar to those of an acidic soil were investigated. The main objectives of this study were to determine whether the development of higher strength materials led to greater susceptibility to stress corrosion cracking and whether degraded pipeline steels became more susceptible to stress corrosion cracking than in the as-received state. The procedure of accelerated degradation of pipeline steels was developed and introduced in laboratory under the combined action of axial loading and hydrogen charging. It proved to be reliable and useful to performed laboratory simulation of in-service degradation of pipeline steels with different strength. The in-laboratory degraded 17H1S and X60 pipeline steels tested in the NS4 solution saturated with CO₂ under open circuit potential revealed the susceptibility to stress corrosion cracking reflected in the degradation of mechanical properties and at the same time the degraded X60 steel showed higher resistance to stress corrosion cracking than the degraded 17H1S steel. Fractographic observation confirmed the pipeline steels hydrogen embrittlement caused by the permeated hydrogen.

We report volumetric analysis techniques to analyze the transport properties of hydrogen dissolved in cylindrical-shaped polymers. The techniques utilize the volume measurement of the released hydrogen from rubber by gas collection in a graduated cylinder after charging sample with high-pressure hydrogen and subsequent decompression. We further improve the graduated cylinder with some modifications such as reading the electrical capacitance of the water level using electrodes and changing the sample loading position. From the measurement results the uptake (C∞) diffusion coefficient (D) and solubility (S) of hydrogen are quantified with an upgraded diffusion analysis program. These methods are applied to three cylindrical rubbers. Dual adsorption behaviors with increasing pressure are observed for all the samples. C∞ follows Henry’s law up to ~15 MPa whereas Langmuir model applies up to 90 MPa. D shows Knudsen and bulk diffusion behavior below and above pressure respectively. A COMSOL simulation is compared with experimental observations.

New technological solutions are required to control the impact of the increasing presence of renewable energy sources connected to the electric grid that are characterized by unpredictable production (i.e. wind and solar energy). Energy storage is becoming essential to stabilize the grid when a mismatch between production and demand occurs. Among the available solutions Power to Hydrogen (P2H) is one of the most attractive options. However despite the potential many barriers currently hinder P2H market development. The literature reports general barriers and strategies to overcome them but a specific analysis is fundamental to identifying how these barriers concretely arise in national and regional frameworks since tailored solutions are needed to foster the development of P2H local market. The paper aims to identify and to analyze the existing barriers for P2H market uptake in Italy. The paper shows how several technical regulatory and economic issues are still unsolved resulting in a source of uncertainty for P2H investment. The paper also suggests possible approaches and solutions to address the Italian barriers and to support politics and decision-makers in the definition and implementation of the national hydrogen strategy.

In a fuel cell electric vehicle (FCEV) powered by a metal hydride tank the performance of the tank is an indicator of the overall health status which is used to predict its behaviour and make appropriate energy management decisions. The aim of this paper is to investigate how to evaluate the effects of charge/discharge cycles on the performance of a commercial automotive metal hydride hydrogen storage system applied to a real FCEV. For this purpose a mathematical model is proposed based on uncertain physical parameters that are identified using the stochastic particle swarm optimisation (PSO) algorithm combined with experimental measurements. The variation of these parameters allows an assessment of the degradation level of the tank’s performance on both the quantitative and qualitative aspects. Simulated results derived from the proposed model and experimental measurements were in good agreement with a maximum relative error of less than 2%. The validated model was used to establish the correlations between the observed degradations in a hydride tank recovered from a real FCEV. The results obtained show that it is possible to predict tank degradations by developing laws of variation of these parameters as a function of the real conditions of the use of the FCEV (number of charging/discharging cycles pressures mass flow rates temperatures).

Biomass gasification for energy purposes has several advantages such as the mitigation of global warming and national energy independency. In the present work the data from an innovative and intensified steam/oxygen biomass gasification process integrating a gas filtration step directly inside the reactor are presented. The produced gas at the outlet of the 1 MWth gasification pilot plant was analysed in terms of its main gaseous products (hydrogen carbon monoxide carbon dioxide and methane) and contaminants. Experimental test sets were carried out at 0.25–0.28 Equivalence Ratio (ER) 0.4–0.5 Steam/Biomass (S/B) and 780–850 °C gasification temperature. Almond shells were selected as biomass feedstock and supplied to the reactor at approximately 120 and 150 kgdry/h. Based on the collected data the in-vessel filtration system showed a dust removal efficiency higher than 99%-wt. A gas yield of 1.2 Nm³dry/kgdaf and a producer gas with a dry composition of 27–33%v H2 23–29%v CO 31–36%v CO₂ 9–11%v CH₄ and light hydrocarbons lower than 1%v were also observed. Correspondingly a Low Heating Value (LHV) of 10.3–10.9 MJ/Nm³dry and a cold gas efficiency (CGE) up to 75% were estimated. Overall the collected data allowed for the assessment of the preliminary performances of the intensified gasification process and provided the data to validate a simulative model developed through Aspen Plus software.

Northern Ireland has achieved its 2020 targets in the electricity sector ahead of time with 46.8% of its electricity demand supplied by renewable generators. When it comes to heat the progress is less impressive – 68% of domestic heating is provided by oil and only around 2500 customers use low carbon heat generators in their homes. In addition 22% of consumers live in fuel poverty. Fuel poverty support programmes still propose the replacement of old oil boilers with new models or with gas boilers where a connection to the grid is possible.<br/>Failure of the commercial RHI scheme and the knock-on effect of the closure of the domestic RHI scheme caused significant damage to the industry and to the reputation of low carbon heat technologies leaving NI consumers without any explicit supporting mechanisms for low carbon heat supply. Decreases in carbon emissions from the heat sector are mainly achieved through switching from oil to gas heating. Gas infrastructure is under development in NI and promises to reach 60% of customers by 2022.

There is no inherent property of hydrogen that makes it unsuitable for metering at distribution or transmission pressures. Towns gas containing large percentages of hydrogen was used for many years in the UK and continues to be in use in Hong Kong and Singapore. Many manufacturers sell their ordinary mechanical gas meters as suitable for hydrogen in a laboratory or industrial situation; unfortunately lack of demand has meant that none of these meters seem to have certified under appropriate metering regulations for gaseous hydrogen (e.g. the Measuring Instruments Directive)<br/>Some of the more sophisticated modern inferential meters (e.g. thermal or ultrasonic) currently designed specifically for natural gas (or LPG if suitably calibrated) are likely to unsuitable for repurposing directly to hydrogen but none of the problems appear fundamental or insuperable. The largest potential hurdle probably surrounds the physical size of current meters. A hydrogen appliance will consume about 3.3 more hydrogen than natural gas (on a volumetric basis) and using traditional designs this would have been measured through a meter probably too large to fit within an existing meter box. Unless unsolved such an increase in size would add materially to any hydrogen re-purposing programme.<br/>The meter trade thus need to be challenged to come up with a hydrogen meter that is the same physical size as a natural gas meter on a power rating basis (i.e. in kW). Ultrasonic and thermal mass meters should be included in the necessary Research and Development programme.<br/>A meter test programme is suggested that will provide evidence to meter manufacturers that the metering of hydrogen is not inherently difficult and thus convince them to make the necessary investments and/or approach the GDNO’s for assistance with such a programme.

Sustainable energy conversion requires zero emissions of greenhouse gases and criteria pollutants using primary energy sources that the earth naturally replenishes quickly like renewable resources. Solar and wind power conversion technologies have become cost effective recently but challenges remain to manage electrical grid dynamics and to meet end-use requirements for energy dense fuels and chemicals. Renewable hydrogen provides the best opportunity for a zero emissions fuel and is the best feedstock for production of zero emission liquid fuels and some chemical and heat end-uses. Renewable hydrogen can be made at very high efficiency using electrolysis systems that are dynamically operated to complement renewable wind and solar power dynamics. Hydrogen can be stored within the existing natural gas system to provide low cost massive storage capacity that (1) could be sufficient to enable a 100% zero emissions grid; (2) has sufficient energy density for end-uses including heavy duty transport; (3) is a building block for zero emissions fertilizer and chemicals; and (4) enables sustainable primary energy in all sectors of the economy.

This work investigates the connection between electrification of the industry transport and heat sector and the integration of wind and solar power in the electricity system. The impact of combining electrification of the steel industry passenger vehicles and residential heat supply with flexibility provision is evaluated from a systems and sector perspective. Deploying a parallel computing approach to the capacity expansion problem the impact of flexibility provision throughout the north European electricity system transition is investigated. It is found that a strategic collaboration between the electricity system an electrified steel industry an electrified transport sector in the form of passenger electric vehicles (EVs) and residential heat supply can reduce total system cost by 8% in the north European electricity system compared to if no collaboration is achieved. The flexibility provision by new electricity consumers enables a faster transition from fossil fuels in the European electricity system and reduces thermal generation. From a sector perspective strategic consumption of electricity for hydrogen production and EV charging and discharging to the grid reduces the number of hours with very high electricity prices resulting in a reduction in annual electricity prices by up to 20%.

Mg attracts much research interest as anode material for Ni-MH batteries thanks to its lightweight cost-effectiveness and high theoretical capacity (2200 mA h g⁻¹). However its practical application is tremendously challenged by the poor hydrogen sorption kinetics passivation from aggressive aqueous electrolytes and insulating nature of MgH₂. Mg-based alloys exhibit enhanced hydrogen sorption kinetics and electrical conductivity but significant amount of costly transition metal elements are required. In this work we have for the first time utilized non-alloyed but catalyzed Mg as anode for Ni-MH batteries. 5 mol.% TiF3 was added to nanosized Mg for accelerating the hydrogen sorption kinetics. Several strategies for preventing the problematic passivation of Mg have been studied including protective encapsulation of the electrode and utilizing room-temperature/high-temperature ionic liquids and an alkaline polymer membrane as working electrolyte. Promising electrochemical performance has been achieved in this Mg–TiF₃ composite anode based Ni-MH batteries with room for further improvements.

Interest in the low-cost production of clean hydrogen is growing. Anion exchange membrane water electrolyzers (AEMWEs) are considered one of the most promising sustainable hydrogen production technologies because of their ability to split water using platinum group metal-free catalysts less expensive anode flow fields and bipolar plates. Critical to the realization of AEMWEs is understanding the durability-limiting factors that restrict the long-term use of these devices. This article presents both durability-limiting factors and mitigation strategies for AEMWEs under three operation modes i.e. pure water-fed (no liquid electrolyte) concentrated KOH-fed and 1 wt% K₂CO₃-fed operating at a differential pressure of 100 psi. We examine extended-term behaviors of AEMWEs at the single-cell level and connect their behavior with the electrochemical chemical and mechanical instability of single-cell components. Finally we discuss the pros and cons of AEMWEs under these operation modes and provide direction for long-lasting AEMWEs with highly efficient hydrogen production capabilities.

Pipelines during their service life subjected to operational degradation i.e. their mechanical characteristics worsened with time. Pronounced texture of pipe steels associated with their manufacturing process revealed itself in an essential difference in impact toughness determined for specimens cut in mutually perpendicular directions with respect to the pipe axis. Higher KCV values for longitudinal specimens as compared with transverse ones were explained by the difference in a length of perlite grain strips separated by ferrite grains in specimens of different orientation. A role of hydrogen absorbed my metal during its operation in steel degradation was discussed.<br/>The main fractographic peculiarity for the operated steels comparing to the steels in the initial state is the appearance of delamination on the fracture surfaces which are oriented in the rolling direction. Correlation was found for the tested steels between fractographic sings of their embrittlement due to operational degradation and their loss of brittle fracture resistance. It is concluded that a decrease of impact toughness caused by long term operation of pipeline steels is definitely concerned with the amount of delamination on the fracture surfaces.

Electrocatalytic water splitting is the key process for the formation of green fuels for energy transport and storage in a sustainable energy economy. Besides electricity it requires water an aspect that seldomly has been considered until recently. As freshwater is a limited resource (<1% of earth's water) lately plentiful reports were published on direct seawater (around 96.5% of earth's water) splitting without or with additives (buffers or bases). Alternatively the seawater can be split in two steps where it is first purified by reverse osmosis and then split in a conventional water electrolyser. This quantitative analysis discusses the challenges of the direct usage of non-purified seawater. Further herein we compare the energy requirements and costs of seawater purification with those of conventional water splitting. We find that direct seawater splitting has substantial drawbacks compared to conventional water splitting and bears almost no advantage. In short it is less promising than the two-step scenario as the capital and operating costs of water purification are insignificant compared to those of electrolysis of pure water.

A 100% renewable economy would give a lasting solution to the challenges raised by climate change energy security sustainability and pollution. The conversion of the present transport system appears to be one of the most difficult aspects of such renewable transition. This study reviews the technologies and systems that are being proposed or proven as alternative to fossil-fuel based transportation and their prospects for their entry into the post-carbon era from both technological and energetic viewpoints. The energetic cost of the transition from the current transportation system into global 100% renewable transportation is estimated as well as the electrical energy required for the operation of the new renewable transportation sector. A 100% renewable transport providing the same service as global transport in 2014 would demand about 18% less energy. The main reduction is expected in road transport (69%) but the shipping and air sectors would notably increase their consumptions: 163% and 149% respectively. The analysis concludes that a 100% renewable transportation is feasible but not necessarily compatible with indefinite increase of resources consumption. The major material and energy limitations and obstacles of each transport sector for this transition are shown.

Strategic networks of hydrocarbon pipelines in long time service are adversely affected by the action of aggressive chemicals transported with the fluids and dissolved in the environment. Material degradation phenomena are amplified in the presence of hydrogen and water elements that increase the material brittleness and reduce the safety margins. The risk of failure during operation of these infrastructures can be reduced if not prevented by the continuous monitoring of the integrity of the pipe surfaces and by the tracking of the relevant bulk properties. A fast and potentially non-destructive diagnostic tool of material degradation which may be exploited in this context is based on the instrumented indentation tests that can be performed on metals at different scales. Preliminary validation studies of the significance of this methodology for the assessment of pipeline integrity have been carried out with the aid of interpretation models of the experiments. The main results of this ongoing activity are illustrated in this contribution.

After the Fukushima Daiichi nuclear power plant (NPP) accident new regulatory requirements were enforced in July 2013 and a backfit was required for all existing nuclear power plants. It is required to take measures to prevent severe accidents and mitigate their radiological consequences. The Regulatory Standard and Research Department Secretariat of Nuclear Regulation Authority (S/NRA/R) has been conducting numerical studies and experimental studies on relevant severe accident phenomena and countermeasures. This article highlights fission product (FP) release and hydrogen risk as two major areas. Relevant activities in the S/NRA/R are briefly introduced as follows: 1. For FP release: Identifying the source terms and leak mechanisms is a key issue from the viewpoint of understanding the progression of accident phenomena and planning effective countermeasures that take into account vulnerabilities of containment under severe accident conditions. To resolve these issues the activities focus on wet well venting pool scrubbing iodine chemistry (in-vessel and ex-vessel) containment failure mode and treatment of radioactive liquid effluent. 2. For hydrogen risk: because of three incidents of hydrogen explosion in reactor buildings a comprehensive reinforcement of the hydrogen risk management has been a high priority topic. Therefore the activities in evaluation methods focus on hydrogen generation hydrogen distribution and hydrogen combustion.

The global policy solution seeks to reduce the usage of fossil fuels and greenhouse gas (GHG) emissions and biogas (BG) represents a solutions to these problems. The use of biogas could help cope with increased amounts of waste and reduce usage of fossil fuels. Biogas could be used in compressed natural gas (CNG) engines but the engine electronic control unit (ECU) needs to be modified. In this research a spark ignition (SI) engine was tested for mixtures of biogas and hydrogen (volumetric hydrogen concentration of 0 14 24 33 and 43%). In all experiments two cases of spark timing (ST) were used: the first for an optimal mixture and the second for CNG. The results show that hydrogen increases combustion quality and reduces incomplete combustion products. Because of BG’s lower burning speed the advanced ST increased brake thermal efficiency (BTE) by 4.3% when the engine was running on biogas. Adding 14 vol% of hydrogen (H2 ) increases the burning speed of the mixture and enhances BTE by 2.6% at spark timing optimal for CNG (CNG ST) and 0.6% at the optimal mixture ST (mixture ST). Analyses of the rate of heat release (ROHR) temperature and pressure increase in the cylinder were carried out using utility BURN in AVL BOOST software.

Tropical climate is characterized by hot temperatures throughout the year. In areas subject to this climate air conditioning represents an important share of total energy consumption. In some tropical islands there is no electric grid; in these cases electricity is often provided by diesel generators. In this study in order to decarbonize electricity and cooling production and to improve autonomy in a standalone application a microgrid producing combined cooling and electrical power was proposed. The presented system was composed of photovoltaic panels a battery an electrolyzer a hydrogen tank a fuel cell power converters a heat pump electrical loads and an adsorption cooling system. Electricity production and storage were provided by photovoltaic panels and a hydrogen storage system respectively while cooling production and storage were achieved using a heat pump and an adsorption cooling system respectively. The standalone application presented was a single house located in Tahiti French Polynesia. In this paper the system as a whole is presented. Then the interaction between each element is described and a model of the system is presented. Thirdly the energy and power management required in order to meet electrical and thermal needs are presented. Then the results of the control strategy are presented. The results showed that the adsorption cooling system provided 53% of the cooling demand. The use of the adsorption cooling system reduced the needed photovoltaic panel area the use of the electrolyzer and the use of the fuel cell by more than 60% and reduced energy losses by 7% (compared to a classic heat pump) for air conditioning.

Transitioning German road transport partially to hydrogen energy is among the possibilities being discussed to help meet national climate targets. This study investigates impacts of a hypothetical complete transition from conventionally-fuelled to hydrogen-powered German transport through representative scenarios. Our results show that German emissions change between −179 and +95 MtCO₂eq annually depending on the scenario with renewable-powered electrolysis leading to the greatest emissions reduction while electrolysis using the fossil-intense current electricity mix leads to the greatest increase. German energy emissions of regulated pollutants decrease significantly indicating the potential for simultaneous air quality improvements. Vehicular hydrogen demand is 1000 PJ annually requiring 446–525 TWh for electrolysis hydrogen transport and storage which could be supplied by future German renewable generation supporting the potential for CO₂-free hydrogen traffic and increased energy security. Thus hydrogen-powered transport could contribute significantly to climate and air quality goals warranting further research and political discussion about this possibility.

This paper discusses the numerical modeling of an automobile fuel cell system using a two-stage turbo-compressor for air supply. The numerical model incorporates essential input parameters for air and hydrogen flow. The model also performed mass and energy balances across different components such as pump fan heat-exchanger air compressor and keeps in consideration the pressure losses across flow pipes and various mechanical parts. The compressor design process initiates with numerical analysis of the preliminary design of a highly efficient two-stage turbo compressor with an expander as a single-stage compressor has several limitations in terms of efficiency and pressure ratio. The compressor’s design parameters were carefully studied and analyzed with respect to the highly efficient fuel cell stack (FCS) used in modern hydrogen vehicles. The model is solved to evaluate the overall performance of PEM FCS. The final compressor has a total pressure and temperature of 4.2 bar and 149.3°C whereas the required power is 20.08kW with 3.18kW power losses and having a combined efficiency of 70.8%. According to the FC model with and without expander the net-power outputs are 98.15kW and 88.27kW respectively and the maximum efficiencies are 65.1% and 59.1% respectively. Therefore it can be concluded that a two-stage turbo compressor with a turbo-expander can have significant effects on overall system power and efficiency. The model can be used to predict and optimize system performance for PEM FCS at different operating conditions.

Due to their ability to reversibly absorb/desorb hydrogen without hysteresis Pd–Au nanoalloys have been proposed as materials for hydrogen sensing. For sensing it is important that absorption/desorption isotherms are reproducible and stable over time. A few studies have pointed to the influence of short and long range chemical order on these isotherms but many aspects of the impact of chemical order have remained unexplored. Here we use alloy cluster expansions to describe the thermodynamics of hydrogen in Pd–Au in a wide concentration range. We investigate how different chemical orderings corresponding to annealing at different temperatures as well as different external pressures of hydrogen impact the behavior of the material with focus on its hydrogen absorption/desorption isotherms. In particular we find that a long-range ordered L12 phase is expected to form if the H₂ pressure is sufficiently high. Furthermore we construct the phase diagram at temperatures from 250 K to 500 K showing that if full equilibrium is reached in the presence of hydrogen phase separation can often be expected to occur in stark contrast to the phase diagram in para-equilibrium. Our results explain the experimental observation that absorption/desorption isotherms in Pd–Au are often stable over time but also reveal pitfalls for when this may not be the case.