Italy

This paper presents the development of a thermodynamic model for the hydrogen refuelling station (HRS) to simulate the process of refuelling which involves the transfer of hydrogen gas from a high-pressure storage tank to the onboard tank of a fuel cell electric vehicle (FCEV). This model encompasses the fundamental elements of an HRS which consists of a storage tank compressor piping system heat exchanger and an on-board vehicle tank. The model is implemented and validated using experimental data from SAE J2601. Various simulations are conducted to assess the impact of the Joule-Thomson effect and compression on the temperature of hydrogen flow specifically focusing on an average pressure rate of 18 MPa/min. Furthermore a comprehensive analysis is conducted to examine the impact of pressure variations in the storage tank (10–90 MPa) and the initial pressure within the vehicle tank (5–35 MPa) as well as variations in ambient temperature (0–40 °C). The study revealed that the energy consumption in the cooling system surpasses the average power consumption in the more advantageous scenario of 60 MPa by a range of 36% to over 220% when the pressure in the storage system drops below 30 MPa. Furthermore it was noted that the impact of ambient temperature is comparatively less significant when compared to the initial pressure of the vehicle's tank. The impact of an ambient temperature change of 10 °C on the final temperature of a hydrogen vehicle is found to be approximately 2 °C. Similarly a variation in the initial vehicle pressure of 10 MPa results in a modification of the final hydrogen vehicle temperature by approximately 8.5 °C.

This study explores the potentiality of low/zero carbon fuels such as methanol methane and hydrogen for motor applications to pursue the goal of energy security and environmental sustainability. An experimental investigation was performed on a spark ignition engine equipped with both a port fuel and a direct injection system. Liquid fuels were injected into the intake manifold to benefit from a homogeneous charge formation. Gaseous fuels were injected in direct mode to enhance the efficiency and prevent abnormal combustion. Tests were realized at a fixed indicated mean effective pressure and at three different engine speeds. The experimental results highlighted the reduction of CO and CO2 emissions for the alternative fuels to an extent depending on their properties. Methanol exhibited high THC and low NOx emissions compared to gasoline. Methane and even more so hydrogen allowed for a reduction in THC emissions. With regard to the impact of gaseous fuels on the NOx emissions this was strongly related to the operating conditions. A surprising result concerns the particle emissions that were affected not only by the fuel characteristics and the engine test point but also by the lubricating oil. The oil contribution was particularly evident for hydrogen fuel which showed high particle emissions although they did not contain carbon atoms.

The maritime transportation sector is a large and growing contributor of greenhouse gas and other emissions. Therefore stringent measures have been taken by the International Maritime Organization to mitigate the environmental impact of the international shipping. These lead to the adoption of new technical solutions involving clean fuels such as hydrogen and high efficiency propulsion technologies that is fuel cells. In this framework this paper proposes a methodological approach aimed at supporting the retrofit design process of a car-passenger ferry operating in the Greece’s western maritime zone whose conventional powertrain is replaced with a fuel cell hybrid system. To this aim first the energy/power requirements and the expected hydrogen consumption of the vessel are determined basing on a typical operational profile retrieved from data provided by the shipping company. Three hybrid powertrain configurations are then proposed where fuel cell and batteries are balanced out according to different design criteria. Hence a new vessel layout is defined for each of the considered options by taking into account on-board weight and space constraints to allocate the components of the new hydrogen-based propulsion systems. Finally the developed vessel configurations are simulated in a virtual towing tank environment in order to assess their hydrodynamic response and compare them with the original one thus providing crucial insights for the design process of new hydrogen-fueled vessel solutions. Findings from this study reveal that the hydrogen-based configurations of the vessel are all characterized by a slight reduction of the payload mainly due to the space required to allocate the hydrogen storage system; instead the hydrodynamic behavior of the H2 powered vessels is found to be similar to the one of the original Diesel configuration; also from a hydrodynamic point of view the results show that mid load operating conditions get relevance for the design process of the hybrid vessels.

The coupling of a reversible Solid Oxide Cell (rSOC) with an offshore wind turbine is investigated to evaluate the mutual benefits in terms of local energy management. This integrated system has been simulated with a dynamic model under a control algorithm which manages the rSOC operation in relation to the wind resource implementing a local hydrogen storage with a double function: (i) assure power supply to the wind turbine auxiliary systems during power shortages (ii) valorize the heat produced to cover the desalinization system needs. With an export-based strategy which maximize the rSOC capacity factor up to 15 tons of hydrogen could be produced for other purposes. The results show the compatibility between the auxiliary systems supply of a 2.3 MW wind turbine and a 120/21 kWe rSOC system which can cover the auxiliaries demand during wind shortages or maintenance. The total volume required by such a system occupy less than the 2% if compared with the turbine tower volume. Additionally thermal availability exceeds the desalination needs representing a promising solution for small-scale onsite desalination in offshore environments.

The energy sector constitutes a dynamic and complex system indicating that its actions are influenced not just by its individual components but also by the emergent behavior resulting from interactions among them. Moreover there are crucial limitations of previous approaches for addressing the sustainability challenge of the energy sector. Changing transforming and integrating paradigms are the most relevant leverage points for transforming a given system. In other words nowadays the integration of new predominant paradigms in order to provide a unified framework could aim at this actual transformation looking for a sustainable future. This research aims to develop a new unified framework for the integration of the following three paradigms: (1) Sustainability (2) Complexity and (3) Systems Thinking which will be applied to achieving sustainable energy production (using hydrogen production as a case study). The novelty of this work relies on providing a holistic perspective through the integration of the aforementioned paradigms considering the multiple and complex interdependencies among the economy the environment and the economy. For this purpose an integrated seven-stage approach is introduced which explores from the starting point of the integration of paradigms to the application of this integration to sustainable energy production. After applying the Three-Paradigm approach for sustainable hydrogen production as a case study 216 feedback loops are identified due to the emerged complexity linked to the analyzed system. Additionally three system dynamics-based models are developed (by increasing the level of complexity) as part of the application of the Three-Paradigm approach. This research can be of interest to a broad professional audience (e.g. engineers policymakers) as looks into the sustainability of the energy sector from a holistic perspective considering a newly developed Three-Paradigm model considering complexity and using a Systems Thinking approach.

This paper analyzes the hydrogen refueling process for heavy-duty vehicles according to the SAE J2601/2 protocol. Attention is paid to two key aspects of the protocol that affect the refueling process: treatment of the storage system from a thermodynamic and geometric point of view and the maximum deliverable flow rate of the station in the refueling process. The effect of the ratio of the inner diameter to the inner length of the total volume on the refueling process was then analyzed and it was shown how far the new approach results deviate from the results obtained by applying the SAE protocol. A total supply of 28 kg was simulated but with three different configurations: 14*2 kg tanks 7*4 kg tanks and 4*7 kg tanks. When analyzing the effect of varying the ratio of inner diameter to inner length it was noted that in the most conservative case there is an overestimation in terms of final temperature for the three configurations of about: 2.1 ◦C 1.4 ◦C and 1.1 ◦C respectively. This aspect has a significant impact on the refueling time which could be reduced by about 9.9% in the first case and about 7.1% and 5.4% in the other two. In addition refueling using the multi-tank approach was simulated for some case studies assimilated to heavy vehicles currently on the market in terms of the amount of hydrogen stored. These refuelings were carried out with stations capable of delivering a maximum flow rate of 120 g/s 180 g/s and 240 g/s. It is inferred that increasing the flow rate from 120 g/s to 180 g/s results in time savings for the three cases of: 35% 34% and 37%. On the other hand running up to 240 g/s results in time savings of: 54% 52% and 55%.

The decarbonization of sectors such as aviation maritime transport and heavy-duty mobility—where direct electrification is not yet feasible—requires alternative fuels with high energy density and compatibility with existing infrastructure. This review investigates the potential of liquid synthetic fuels known as liquid electrofuels (or e-fuels) to replace fossil fuels in these hard-to-abate sectors. The objective is to provide a comprehensive integrative assessment of liquid e-fuel development by analyzing production pathways feedstock demands regulatory frameworks and industrial implementation trends. The study reviews three major production processes—Fischer–Tropsch synthesis methanol synthesis and the Haber–Bosch process—used to produce six key synthetic fuels: e-kerosene e-diesel e-methanol e-dimethyl ether e-gasoline and e-ammonia. The methodology includes a systematic review of literature life cycle assessments for water and energy demand and analysis of over 30 large-scale projects worldwide in terms of plant capacity (10–200 MW) production volume capital investment and technology readiness level. Results show that process efficiencies range from 59 % to 89 % with current production costs for synthetic kerosene and methanol varying between 1200–4200 €/ton depending on the pathway and technology maturity. The study finds that polymer electrolyte membrane electrolysis and industrial point-source carbon dioxide capture are the most prevalent technologies among operational plants. Regulatory complexity high capital expenditure and the lack of harmonized sustainability criteria remain key barriers to commercial scaling. This review advances the scientific literature by presenting a novel multi-dimensional framework that connects technical environmental and policy considerations offering a strategic roadmap for accelerating the global deployment of liquid synthetic fuels.

This paper presents an assessment of the levelized cost of clean hydrogen produced in Sicily a region in Southern Italy particularly rich in renewable energy and where nearly 50% of Italy’s refineries are located making a comparison between on-site production that is near the end users who will use the hydrogen and centralized production comparing the costs obtained by employing the two types of electrolyzers already commercially available. In the study for centralized production the scale factor method was applied on the costs of electrolyzers and the optimal transport modes were considered based on the distance and amount of hydrogen to be transported. The results obtained indicate higher prices for hydrogen produced locally (from about 7 €/kg to 10 €/kg) and lower prices (from 2.66 €/kg to 5.80 €/kg) for hydrogen produced in centralized plants due to economies of scale and higher conversion efficiencies. How-ever meeting the demand for clean hydrogen at minimal cost requires hydrogen distribution pipelines to transport it from centralized production sites to users which currently do not exist in Sicily as well as a significant amount of renewable energy ranging from 1.4 to 1.7 TWh per year to cover only 16% of refineries’ hydrogen needs.

Green hydrogen (H2 ) a promising clean energy source garnering increasing attention worldwide can be derived through various pathways resulting in differing levels of greenhouse gas emissions. Notably Green H2 production can utilize different methods such as integrating standard photovoltaic panels thermal photovoltaic or concentrated photovoltaic thermal collectors with electrolyzers. Furthermore it can be conditioned to different states or carriers including liquefied H2 compressed H2 ammonia and methanol and stored and transported using various methods. This paper employs the Life Cycle Assessment methodology to compare 18 different green hydrogen pathways and provide recommendations for greening the hydrogen supply chain. The findings indicate that the production pathway utilizing concentrated photovoltaic thermal panels for electricity generation and hydrogen compression in the conditioning and transportation stages exhibits the lowest environmental impact emitting only 2.67 kg of CO2 per kg of H2 .

A new model is presented to predict hydrogen-assisted fatigue. The model combines a phase field description of fracture and fatigue stress-assisted hydrogen diffusion and a toughness degradation formulation with cyclic and hydrogen contributions. Hydrogen-assisted fatigue crack growth predictions exhibit an excellent agreement with experiments over all the scenarios considered spanning multiple load ratios H2 pressures and loading frequencies. These are obtained without any calibration with hydrogen-assisted fatigue data taking as input only mechanical and hydrogen transport material properties the material’s fatigue characteristics (from a single test in air) and the sensitivity of fracture toughness to hydrogen content. Furthermore the model is used to determine: (i) what are suitable test loading frequencies to obtain conservative data and (ii) the underestimation made when not pre-charging samples. The model can handle both laboratory specimens and large-scale engineering components enabling the Virtual Testing paradigm in infrastructure exposed to hydrogen environments and cyclic loading.

This paper addresses the problem of the reduction in the huge energy demand of hospitals and health care facilities. The sharp increase in the natural gas price due to the Ukrainian–Russian war has significantly reduced economic savings achieved by combined heat and power (CHP) units especially for hospitals. In this framework this research proposes a novel system based on the integration of a reversible CHP solid oxide fuel cell (SOFC) and a photovoltaic field (PV). The PV power is mainly used for balancing the hospital load. The excess power production is exploited to produce renewable hydrogen. The SOFC operates in electrical tracking mode. The cogenerative heat produced by the SOFC is exploited to partially meet the thermal load of the hospital. The SOFC is driven by the renewable hydrogen produced by the plant. When this hydrogen is not available the SOFC is driven by natural gas. In fact the SOFC is coupled with an external reformer. The simulation model of the whole plant including the reversible SOFC PV and hospital is developed in the TRNSYS18 environment and MATLAB. The model of the hospital is calibrated by means of measured data. The proposed system achieves very interesting results with a primary energy-saving index of 33% and a payback period of 6.7 years. Therefore this energy measure results in a promising solution for reducing the environmental impact of hospital and health care facilities.

In light of growing concerns regarding greenhouse gas emissions and the increasingly severe impacts of climate change the global situation demands immediate action to transition towards sustainable energy solutions. In this sense hydrogen could play a fundamental role in the energy transition offering a potential clean and versatile energy carrier. This paper reviews the recent results of Life Cycle Assessment studies of different hydrogen production pathways which are trying to define the routes that can guarantee the least environmental burdens. Steam methane reforming was considered as the benchmark for Global Warming Potential with an average emission of 11 kgCO2eq/kgH2. Hydrogen produced from water electrolysis powered by renewable energy (green H2 ) or nuclear energy (pink H2 ) showed the average lowest impacts with mean values of 2.02 kgCO2eq/kgH2 and 0.41 kgCO2eq/kgH2 respectively. The use of grid electricity to power the electrolyzer (yellow H2 ) raised the mean carbon footprint up to 17.2 kgCO2eq/kgH2 with a peak of 41.4 kgCO2eq/kgH2 in the case of countries with low renewable energy production. Waste pyrolysis and/or gasification presented average emissions three times higher than steam methane reforming while the recourse to residual biomass and biowaste significantly lowered greenhouse gas emissions. The acidification potential presents comparable results for all the technologies studied except for biomass gasification which showed significantly higher and more scattered values. Regarding the abiotic depletion potential (mineral) the main issue is the lack of an established recycling strategy especially for electrolysis technologies that hamper the inclusion of the End of Life stage in LCA computation. Whenever data were available hotspots for each hydrogen production process were identified.

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

This study examines hydrogen production across 27 European countries highlighting disparities due to varying energy policies and industrial capacities. Germany leads with 109 plants followed by Poland France Italy and the UK. Mid-range contributors like the Netherlands Spain Sweden and Belgium also show substantial investments. Countries like Finland Norway Austria and Denmark known for their renewable energy policies have fewer plants while Estonia Iceland Ireland Lithuania and Slovenia are just beginning to develop hydrogen capacities. The analysis also reveals that a significant portion of the overall hydrogen production capacity in these countries remains underutilized with an estimated 40% of existing infrastructure not operating at full potential. Many countries underutilize their production capacities due to infrastructural and operational challenges. Addressing these issues could enhance output supporting Europe’s energy transition goals. The study underscores the potential of hydrogen as a sustainable energy source in Europe and the need for continued investment technological advancements supportive policies and international collaboration to realize this potential.

To inject green hydrogen (H2) into the existing natural gas (NG) infrastructure is one way to decarbonize the European energy system. However asset readiness is necessary to be successful. Preliminary analysis and experimental results about the compatibility of hydrogen and natural gas mixtures (H2NG) with the actual gas grids make the scientific community confident about the feasibility. Nevertheless specific technical questions need more research. A significant topic of debate is the impact of H2NG mixtures on the performance of state-ofthe-art fiscal measuring devices which are essential for accurate billing. Identifying and addressing any potential degradation in their metrological performance due to H2NG is critical for decision-making. However the literature lacks data about the gas meters’ technologies currently installed in the NG grids such as a comprehensive overview of their readiness at different concentrations while data are fragmented among different sources. This paper addresses these gaps by analyzing the main characteristics and categorizing more than 20000 gas meters installed in THOTH2 project partners’ grids and by summarizing the performance of traditional technologies with H2NG mixtures and pure H2 based on literature review operators experience and manufacturers knowledge. Based on these insights recommendations are given to stakeholders on overcoming the identified barriers to facilitate a smooth transition.

In recent years the use of alternative fuels in thermal engine power plants has gained more and more attention becoming of paramount importance to overcome the use of fuels from fossil sources and to reduce polluting emissions. The present work deals with the analysis of the response to two different gas fuels—i.e. hydrogen and a syngas from agriculture product—of a 30 kW micro gas turbine integrated with a solar field. The solar field included a thermal storage system to partially cover loading requests during night hours reducing fuel demand. Additionally a Heat Recovery Unit was included in the plant considered and the whole plant was simulated by Thermoflex® code. Thermodynamics analysis was performed on hour-to-hour basis for a given day as well as for 12 months; subsequently an evaluation of cogeneration efficiency as well as energy saving was made. The results are compared against plant performance achieved with conventional natural gas fueling. After analyzing the performance of the plant through a thermodynamic analysis the study was complemented with CFD simulations of the combustor to evaluate the combustion development and pollutant emissions formation particularly of NOx with the two fuels considered using Ansys-Fluent code and a comparison was made.

The production of hydrogen from renewable sources could play a significant role in supporting the transition toward a decarbonized energy system. This study has involved investigating optimization strategies − mixedinteger linear programming (MILP) a hybrid particle swarm optimization (PSO)-MILP framework and PSO combined with a rule-based energy management strategy (EMS) − applied to a power-to-hydrogen system for industrial applications. The analysis evaluates the levelized cost of hydrogen production (LCOH) carbon emissions and the impact of key factors such as battery degradation electrolyzer efficiency real-time pricing and hydrogen load management. The obtained results indicated that the MILP-based models achieved moderate LCOH values (10.1–10.7 €/kg) but incurred higher CO2 emissions (20.2–24.6 kt/y). Instead the PSO model combined with the rule-based EMS lowered emissions to 14.3 kt/y (a 27–45% reduction) albeit with a higher LCOH (11.6 €/kg). The hybrid PSO-MILP models struck a balance achieving LCOH values of between 9.2 and 9.7 €/kg with CO2 emissions of 19.7–20.3 kt/y as they benefited from the integration of piecewise affine linearization for modeling electrolyzer efficiency and battery degradation. In terms of computational efforts the MILP-based models required more than 48 h to converge while the PSO-MILP models completed within 27–35 h and the PSO model with rule-based EMS achieved results in 1.5 h. These findings offer guidance that can be used to select the most suitable optimization method on the basis of the desired performance targets resource constraints and computational complexity thereby contributing to the design of more sustainable energy systems.

This study investigates the effect of Oxygen-Enriched Combustion on hydrogen-enriched natural gas (H2 -NG) fuel mixtures at a semi-industrial scale (up to 60 kW). The analysis focuses on flame structure temperature distribu tion in the furnace NOx emissions and potential fuel savings. A multi-fuel multi-oxidizer jet burner was used to compare two oxygen enrichment configurations: premixed with air (PM) and air-pure O2 (AO) independent feed. The O2 -enriched flames remained stable across the entire fuel range. OH* chemiluminescence imaging for the H2 -NG fuel mixture delivering 50 concentration kW revealed that higher O2 increases the OH* intensity narrows and elongates the flame transitions from buoyancy- to momentum-driven shape and relocates the reaction zone. At 50 % oxygen enrichment level (OEL) flame shape OH* intensity and temperature profiles resembled pure O combustion. Up to 29 % OEL furnace temperature profiles were similar to those 2 of air-fuel combustion. The power required to maintain 1300 ± 25 ◦C at the reference position decreases with O2 enrichment. Higher OELs resulted in a sharp increase in NOx emissions. The effect of hydrogen enrichment on NOx levels was significantly less pronounced than that of oxygen enrichment. The rise in NOx emissions correlates with increased OH* in tensities. For a 50 % H2 2 blend increasing the O concentration in the oxidizer from 21 % to 50 % resulted in a 27 % reduction in flue gas heat losses. Utilizing O2 co-produced with H2 could be strategic for reducing fuel consumption facilitating the adoption of hydrogen-based energy systems.

Dual fuel combustion has gained attention as a cost-effective solution for reducing the pollutant emissions of internal combustion engines. The typical approach is combining a conventional high-reactivity fossil fuel (diesel fuel) with a sustainable low-reactivity fuel such as bio-methane ethanol or green hydrogen. The last one is particularly interesting as in theory it produces only water and NOx when it burns. However integrating hydrogen into stock diesel engines is far from trivial due to a number of theoretical and practical challenges mainly related to the control of combustion at different loads and speeds. The use of 3D-CFD simulation supported by experimental data appears to be the most effective way to address these issues. This study investigates the hydrogen-diesel dual fuel concept implemented with minimum modifications in a light-duty diesel engine (2.8 L 4-cylinder direct injection with common rail) considering two operating points representing typical partial and full load conditions for a light commercial vehicle or an industrial engine. The numerical analysis explores the effects of progressively replacing diesel fuel with hydrogen up to 80% of the total energy input. The goal is to assess how this substitution affects engine performance and combustion characteristics. The results show that a moderate hydrogen substitution improves brake thermal efficiency while higher substitution rates present quite a severe challenge. To address these issues the diesel fuel injection strategy is optimized under dual fuel operation. The research findings are promising but they also indicate that further investigations are needed at high hydrogen substitution rates in order to exploit the potential of the concept.

The current solicitude in hydrogen production and its utilization as a greenhouse-neutral energy vector pushed deep interest in developing new and reliable systems intended for its detection. Most sensors available on the market offer reliable performance; however their limitations such as restricted dynamic range hysteresis reliance on consumables transducer–sample interaction and sample dispersion into the environment are not easily overcome. In this paper a non-dispersive Raman effect-based system is presented and compared with its dispersive alternative. This approach intrinsically guarantees no sample dispersion or preparation as no direct contact is required between the sample and the transducer. Moreover the technique does not suffer from hysteresis and recovering time issues. The results evaluated in terms of sample pressures and camera integration time demonstrate promising signal-to-noise ratio (SNR) and limit of detection (LOD) values indicating strong potential for direct field application.

This study offers a comprehensive analysis of the feasibility of green hydrogen economies in Western and Southern African regions focusing on the ECOWAS and SADC countries. Utilizing a novel approach based on composite indicators the research evaluates the potential readiness and overall feasibility of green hydrogen production and export across these regions. The study incorporates various factors including the technical potential of renewable energy sources water resource availability energy security and existing infrastructure for transport and export. Country-specific analyses reveal unique insights into the diverse potential of nations like South Africa Lesotho Ghana Nigeria Angola and Namibia each with its unique strengths and challenges in the context of green hydrogen. The research findings underscore the complexity of developing green hydrogen economies highlighting the need for nuanced region-specific approaches that consider technical socioeconomic geopolitical and environmental factors. The paper concludes that cooperation and integration between countries in the regions may be crucial for the success of a future green hydrogen economy

Green hydrogen has emerged as a promising energy vector for the decarbonisation of heavy industry. The EU and national governments have recently introduced incentives to address the high costs of green hydrogen production and accelerate the economic development of hydrogen. This study investigates the local production of green hydrogen to decarbonise the high-temperature process heat demand of a heavy industry located in Italy. The hydrogen generation is powered by PV electricity and from the electric grid. We have optimised the sizes of the energy system components including battery storage and hydrogen tanks. The Levelised Cost of Hydrogen (LCOH) was found to be 7.7 EUR/kg in the unincentivised base scenario but this amount significantly reduced to 3.3 EUR/kg when incentives on hydrogen production in abandoned industrial areas were considered. Thanks to such incentives the greenhouse gas emissions decreased by as much as 85 % with respect to the non-incentivised base case. Our results show that the effect of the incentives on the design and economics of the system is comparable with the expected reductions in equipment costs over the next decade. Importantly our findings reveal a linear relationship between Capital Costs and LCOH thereby enabling precise cost estimations to be made for the considered location without any further simulations. A side effect of the size optimisation in the presence of incentives is an increase of the plant footprint. However the limited availability of land could lead to non-optimal configurations with important impacts on emission intensity and LCOH.

This paper provides a comprehensive review and outlook on power converters devised for supplying polymer electrolyte membrane (PEM) electrolyzers from photovoltaic sources. The produced hydrogen known as green hydrogen is a promising solution to mitigate the dependence on fossil fuels. The main topologies of power conversion systems are discussed and classified; a loss analysis emphasizes the issues concerning the electrolyzer supply. The attention is focused on power converters of rated power up to a tenth of a kW since it is a promising field for a short-term solution implementing green hydrogen production as a decentralized. It is also encouraged by the proliferation of relatively cheap photovoltaic low-power plants. The main converters proposed by the literature in the last few years and realized for practical applications are analyzed highlighting their key characteristics and focusing on the parameters useful for designers. Future perspectives are addressed concerning the availability of new wide-bandgap devices and hard-to-abate sectors with reference to the whole conversion chain.

In this study a novel thermo-economic analysis on a membrane reactor adopted to generate hydrogen coupled to a carbon-dioxide capture system is proposed. Exergy destruction fuel and environmental as well as pur chased equipment costs have been accounted to estimate the cost of hydrogen production in the aforementioned integrated plant. It has been found that the integration of the CO2 capture system with the membrane reactor is responsible for the reduction of the hydrogen production cost by 12 % due to the decrease in environmental penalty cost. In addition the effects of operating parameters (steam-to-carbo ratio and biogas temperature) on the hydrogen production cost are investigated. Hence this work demonstrates that the latter can be decreased by approximately 2 $/kgH2 when steam to carbon ratio increases from 1.5 to 4. The analyses reveal that steam-tocarbo ratio increases exergy destruction cost affecting consequently also the hydrogen production cost. How ever from a thermodynamic point of view it enhances the hydrogen production in the membrane reactor mutually lowering the hydrogen production cost. It has been also estimated that a decrease in the biogas inlet temperature from 450 to 400◦C can reduce the hydrogen production cost by 7 %. This study demonstrates that the fuel cost is a major economic parameter affecting commercialization of hydrogen production while exergy destruction and environmental costs are also significant factors in determining the hydrogen production cost.

The Mediterranean basin has been characterized by a net flow of fossil commodities from the North African shore to Southern Europe and the Middle East for decades; however decarbonizing the energy system implies to substantially modify this situation turning the current “black dialogue” into a “green dialogue” (i.e. based on the exchange of renewable electricity and green hydrogen). This paper presents a feasibility study conducted to estimate the potential green hydrogen production by electrolysis in three Tunisian sites. It shows and compares several plant layouts varying the size and typology of renewable electricity generators and electrolyzers. The work adopts local weather data and technical features of the technologies in the computations and accounts for site specific topographical and infrastructural constraints such as land available for construction and local power grid connection capacities. It shows that configurations able to produce large quantities of green hydrogen may not be compliant with such constraints basically nullifying their contribution in any hydrogen strategy. Finally results show that the LCOH lies in the range 1.34 $/kgH2 and 4.06 $/kgH2 depending on both the location and the combination of renewable electricity generators and electrolyzers.

The aviation industry is facing challenges related to its environmental impact and thus the pressing need to develop aircraft technologies aligned with the society climate goals. Hydrogen is emerging as a potential clean fuel for aviation as it offers several advantages in terms of supply potential and weight specific energy. One of the key factors enabling the use of H2 in aviation is the development of reliable and safe storage technologies to be integrated into aircraft design. This work provides an overview of the technologies currently being investigated or developed for the storage of hydrogen within the aircraft which would enable the use of hydrogen as a sustainable fuel for aviation with emphasis on tanks material and structural aspects. The requirements dictated by the need of integrating the fuel system within existing or ex-novo aircraft architectures are discussed. Both the storage of gaseous and liquid hydrogen are considered and the main challenges related to the presence of either high internal pressures or cryogenic conditions are explored in the background of recent literature. The materials employed for the manufacturing of hydrogen tanks are overviewed. The need to improve the storage tanks efficiency is emphasized and issues such as thermal insulation and hydrogen embrittlement are covered as well as the reference to the main structural health monitoring strategies. Recent projects dealing with the development of onboard tanks for aviation are eventually listed and briefly reviewed. Finally considerations on the tank layout deemed more realistic and achievable in the near future are discussed.

The goal of achieving a zero-emission energy system by 2050 requires accurate energy planning to minimise the overall cost of the energy transition. Long-term energy models based on cost-optimal solutions are extremely dependent on the cost forecasts of different technologies. However such forecasts are inherently uncertain. The aim of the present work is to identify a cost-optimal pathway for the Italian energy system decarbonisation and assess how renewable cost scenarios can affect the optimal solution. The analysis has been carried out with the H2RES model a single-objective optimisation algorithm based on Linear Programming. Different cost scenarios for photovoltaics on-shore and off-shore wind power and lithium-ion batteries are simulated. Results indicate that a 100% renewable energy system in Italy is technically feasible. Power-to-X technologies are crucial for balancing purposes enabling a share of non-dispatchable generation higher than 90%. Renewable cost scenarios affect the energy mix however both on-shore and off-shore wind saturate the maximum capacity potential in almost all scenarios. Cost forecasts for lithium-ion batteries have a significant impact on their optimal capacity and the role of hydrogen. Indeed as battery costs rise fuel cells emerge as the main solution for balancing services. This study emphasises the importance of conducting cost sensitivity analyses in long-term energy planning. Such analyses can help to determine how changes in cost forecasts may affect the optimal strategies for decarbonising national energy systems.

Green hydrogen production and storage are vital in mitigating carbon emissions and sustainable transition. However the high investment cost and management requirements are the bottleneck of utilizing hybrid hydrogen-based systems in microgrids. Given the necessity of cost-effective and optimal design of these systems the present study examines techno-economic feasibility of integrating hybrid hydrogen-based systems into an outdoor test facility. With this perspective several solar-driven hybrid scenarios are introduced at two energy storage levels namely the battery and hydrogen energy storage systems including the high-pressure gaseous hydrogen and metal hydride storage tanks. Dynamic simulations are carried out to address subtle interactions in components of the hybrid system by establishing a TRNSYS model coupled to a Fortran code simulating the metal hydride storage system. The OpenStudio-EnergyPlus plugin is used to simulate the building load validate against experimental data according to the measured data and monitored operating conditions. Aimed at enabling efficient integration of energy storage systems a techno-enviro-economic optimization algorithm is developed to simultaneously minimize the levelized cost of the electricity and maximize the CO2 mitigation in each proposed hybrid scenario. The results indicate that integrating the gaseous hydrogen and metal hydride storages into the photovoltaic-alone scenario enhances 22.6% and 14.4% of the annual renewable factor. Accordingly the inclusion of battery system to these hybrid scenarios gives a 30.4% and 20.3 % boost to the renewable factor value respectively. Although the inclusion of battery energy storage into the hybrid systems increases the renewable factor the results imply that it reduces the hydrogen production rate via electrolysis. The optimized values of the levelized cost of electricity and CO2 emission for different scenarios vary in the range of 0.376–0.789 $/kWh and 6.57–9.75 ton respectively. The multi-criteria optimizations improve the levelized cost of electricity and CO2 emission by up to 46.2% and 11.3% with respect to their preliminary design.

Hydrogen refueling stations (HRSs) are key infrastructures rapidly spreading out to support the deployment of fuel cell electric vehicles for several mobility purposes. The research interest in these energy systems is increasing focusing on different research branches: research on innovation on equipment and technology proposal and development of station layout and research aiming to provide experimental data sets for perfor mance investigation. The present manuscript aims to present an overview of the most recent literature on hydrogen stations by presenting the technological status of the system at the global level and their research enhancement on the involved components and processes. After the review of the mentioned aspects this paper will present the already existing layouts and the potential configurations of such infrastructures considering several options of the delivery routes the end-user destination and hydrogen storage thermodynamic status whether liquid or gaseous.

The European Commission through the REPowerEU plan and the “Fit for 55” package aims to reduce fossil fuel dependence and greenhouse gas emissions by promoting electric and fuel cell hybrid electric vehicles (EV-FCHEVs). The transition to this mobility model requires energy systems that are able to provide both electricity and hydrogen while reducing the reliance of residential buildings on the national grid. This study analyses a poly-generative (PG) system composed of a Solid Oxide Fuel Cell (SOFC) fed by biomethane a Photovoltaic (PV) system and a Proton Exchange Membrane Electrolyser (PEME) with electric vehicles used as dynamic storage units. The assessment is based on simulation tools developed for the main components and applied to four representative seasonal days in Rende (Italy) considering different daily travel ranges of a 30-vehicle fleet. Results show that the PG system provides about 27 kW of electricity 14.6 kW of heat and 3.11 kg of hydrogen in winter spring and autumn and about 26 kW 14 kW and 3.11 kg in summer; it fully covers the building’s electrical demand in summer and hot water demand in all seasons. The integration of EV batteries reduces grid dependence improves renewable self-consumption and allows for the continuous and efficient operation of both the SOFC and PEME demonstrating the potential of the proposed system to support the green transition.

Underground hydrogen storage (UHS) in depleted oil and gas fields is pivotal for balancing large-scale renewable-energy systems yet the wettability of reservoir rocks in contact with hydrogen after decades of Enhanced Oil Recovery (EOR) operations remains poorly quantified. This work experimentally investigates how two common EOR legacies cationic surfactant (city-trimethyl-ammonium bromide CTAB) and supercritical carbon dioxide (SC–CO2) flooding alter rock–water–Hydrogen (H2) wettability in carbonate formations. Contact angles were measured on dolomite and limestone rock slabs at 30–75 ◦C and 3.4–17.2 MPa using a high-pressure captive-bubble cell. Crude-oil aging shifted clean dolomite from strongly water-wet (θ ~ 28–29◦) to intermediate-wet (θ ≈ 84◦). Subsequent immersion in dilute CTAB solutions (0.5–2 wt %) fully reversed this effect restoring or surpassing the original water-wetness (θ ≈ 21–28◦). Limestone samples exposed to SC-CO2 at 60–80 ◦C became more hydrophilic (θ ≈ 18–30◦) relative to untreated controls; moderate carbonate dissolution (≤6 × 103 ppm Ca2+) produced the most significant improvement in water-wetness whereas severe dissolution yielded diminishing returns. These findings show that many mature reservoirs are already water-wet (post-CO2) or can be easily re-wetted (via residual CTAB). Across all scenarios sample wettability showed little sensitivity to pressure but higher temperature consistently promoted stronger water-wetness. Future work should include dynamic core-flooding experiments with realistic reservoir.

In this paper developed in the context of the Clean Sky 2 project SIENA (Scalability Investigation of hybrid-Electric concepts for Next-generation Aircraft) an extensive analysis is carried out to identify and accelerate the development of innovative propulsion technologies and architectures that can be scaled across five aircraft categories from small General Aviation airplanes to long-range airliners. The assessed propulsive architectures consider various components such as batteries and fuel cells to provide electricity as well as electric motors and jet engines to provide thrust combined to find feasible aircraft architectures that satisfy certification constraints and deliver the required performance. The results provide a comprehensive analysis of the impact of key technology performance indicators on aircraft performance. They also highlight technology switching points as well as the potential for scaling up technologies from smaller to larger aircraft based on different hypotheses and assumptions concerning the upcoming technological advancements of components crucial for the decarbonization of aviation. Given the considered scenarios the common denominator of the obtained results is hydrogen as the main energy source. The presented work shows that for the underlying models and technology assumptions hydrogen can be efficiently used by fuel cells for propulsive and system power for smaller aircraft (General Aviation commuter and regional) typically driven by propellers. For short- to long-range jet aircraft direct combustion of hydrogen combined with a fuel cell to power the on-board subsystems appears favorable. The results are obtained for two different temporal scenarios 2030 and 2050 and are assessed using Payload-Range Energy Efficiency as the key performance indicator. Naturally introducing such innovative architectures will face a lack of applicable regulation which could hamper a smooth entry into service. These regulatory gaps are assessed detailing the level of maturity in current regulations for the different technologies and aircraft categories.

Hydrogen is considered a key alternative to fossil fuels in the broader context of ecological transition. Repurposing natural gas pipelines for hydrogen transport is one of the challenges of this approach. However hydrogen can diffuse into metallic lattices leading to hydrogen embrittlement (HE). For this reason typically ductile materials can experience unexpected brittle fractures and it is therefore necessary to assess the HE propensity of the current pipeline network to ensure its fitness for hydrogen transport. This study examines the relationship between the microstructure of the circumferential weld joint in X52 pipeline steel and hydrogen concentration introduced electrolytically. Base material heat affected zone and fused zone were subjected to 1800 3600 7200 and 14400 s of continuous charging with a current density J = − 10 mA/cm2 in an acid solution. Results showed that the fusion zone absorbed the most hydrogen across all charging times while the base material absorbed more hydrogen than the heat-affected zone due to the presence of non-metallic inclusions. Fracture toughness was assessed using single edge notch tension specimens (SENT) in air and electrolytic hydrogen. Results indicate that the base material is particularly vulnerable to hydrogen environments exhibiting the greatest reduction in toughness when exposed to hydrogen compared to air.

Hydrogen-based technologies prominently fuel cells are emerging as strategic solutions for decarbonization. They offer an efficient and clean alternative to fossil fuels for electricity generation making a tangible contribution to the European Green Deal climate objectives. The primary issue is the production and transportation of hydrogen. An on-site hydrogen production system that includes CO2 capture could be a viable solution. The proposed power system integrates an internal combustion engine (ICE) with a steam methane reformer (SMR) equipped with a CO2 capture and energy storage system to produce “blue hydrogen”. The hydrogen fuels a high-temperature polymer electrolyte membrane (HTPEM) fuel cell. A battery pack incorporated into the system manages rapid fluctuations in electrical load ensuring stability and continuity of supply and enabling the fuel cell to operate at a fixed point under nominal conditions. This hybrid system utilizes natural gas as its primary source reducing climate-altering emissions and representing an efficient and sustainable solution. The simulation was conducted in two distinct environments: Thermoflex code for the integration of the engine reformer and CO2 capture system; and Matlab/Simulink for fuel cell and battery pack sizing and dynamic system behavior analysis in response to user-demanded load variations with particular attention to energy flow management within the simulated electrical grid. The main results show an overall efficiency of the power system of 39.9% with a 33.5% reduction in CO2 emissions compared to traditional systems based solely on internal combustion engines.

This study explores the design and feasibility of a novel fuel cell-powered wind farm for residential electricity hydrogen/oxygen production and cooling/heating via a compression chiller. Wind turbine energy powers Proton Exchange Membrane (PEM) electrolyzers and a compression chiller unit. The proposed system was modeled using EES thermodynamic software and its economic viability was assessed. A case study across seven Italian regions with varying wind potentials evaluated the system’s feasibility in diverse weather conditions. Multi-objective optimization using Response Surface Methodology (RSM) determined the number of wind turbines as optimum number of electrolyzers & fuel cell units. Optimization results indicated that 37 wind turbines 1 fuel cell unit and 2 electrolyzer units yielded an exergy efficiency of 27.98 % and a cost rate of 619.9 $/h. TOPSIS analysis suggested 32 wind turbines 2 electrolyzers and 2 reverse osmosis units as an alternative configuration. Further twelve different scenarios were examined to enhance the distribution of wind farmgenerated electricity among the grid electrolyzers and reverse osmosis systems. revealing that directing 25 % to reverse osmosis 20 % to electrolyzers and 55 % to grid sales was optimal. Performance analysis across seven Italian cities (Turin Bologna Florence Palermo Genoa Milan and Rome) identified Genoa Palermo and Bologna as the most suitable locations due to favorable wind conditions. Implementing the system in Genoa the optimal site could produce 28435 MWh of electricity annually prevent 5801 tons of CO2 emissions (equivalent to 139218 $). Moreover selling this clean electricity to the grid could meet the annual clean electricity needs of approximately 5770 people in Italy

This study aimed to investigate the effectiveness of dark fermentation in biohydrogen production from agro-industrial wastes including apple pomace brewer’s grains molasses and potato powder subjected to different pretreatment methods. The experiments were conducted at a laboratory scale using 1000 cm3 anaerobic reactors at a temperature of 35 ◦C and anaerobic sludge as the inoculum. The highest yield of hydrogen was obtained from pre-treated apple pomace (101 cm3/g VS). Molasses a less complex substrate compared to the other raw materials produced 25% more hydrogen yield following pretreatment. Methanogens are sensitive to high temperatures and low-pH conditions. Nevertheless methane constituted 1–6% of the total biogas under these conditions. The key factor was appropriate treatment of the inoculum to limit competition from methanogens. Increasing the inoculum dose from 150 cm3/dm3 to 250 cm3/dm3 had no further effect on biogas production. The physicochemical parameters and VFA data confirmed the stability and usefulness of activated sludge as a source of microbial cultures for H2 production via dark fermentation.

From an environmental standpoint carbon-free energy carriers such as ammonia and hydrogen are essential for future energy systems. However their hightemperature chemical behavior remains insufficiently understood posing challenges for the development and optimization of advanced combustion technologies. Ammonia in particular is globally available and cost-effective especially for energy-intensive industries. The addition of ammonia or hydrogen to methane significantly reduces the accuracy of existing predictive models. Therefore validated and detailed data are urgently needed to enable reliable design and performance predictions. This review highlights the compatibility of ammonia with existing combustion infrastructure facilitating a smoother transition to more sustainable heating methods without the need for entirely new systems. Applications in high-temperature heating processes such as metal processing ceramics and glass production and power generation are of particular interest. This review focuses on the systematic assessment of alternative fuel mixtures comprising ammonia and hydrogen as well as natural gas with particular consideration of existing safety-related parameters and combustion characteristics. Fundamental quantities such as the laminar burning velocity are discussed in the context of their relevance for fuel mixtures and their scalability toward turbulent flame propagation which is of critical importance for industrial burner and reactor design. The influence of fuel composition on ignition limits is examined as these are essential parameters for safety margin definitions and operational boundary conditions. Furthermore flame stability in mixed-fuel systems is addressed to evaluate the practical feasibility and robustness of combustion under varying process conditions. A detailed overview of current diagnostic and analysis methods follows encompassing both pollutant measurement techniques and the detection of key radical species. These diagnostics form the experimental basis for reaction kinetics modeling and mechanism validation. Given the importance of emission formation in combustion systems a dedicated subsection summarizes major emission trends even though a comprehensive treatment would exceed the scope of this review. Thermal radiation effects which are highly relevant for heat transfer and system efficiency in large-scale applications are then reviewed. In parallel current developments in numerical simulation approaches for industrial-scale combustion systems are presented including aspects of model accuracy boundary conditions and computational efficiency. The review also incorporates insights from materials engineering particularly regarding high-temperature material performance corrosion resistance and compatibility with combustion products. Based on these interdisciplinary findings operational strategies for high-temperature furnaces are outlined and selected industrial reference systems are briefly presented. This integrated approach aims to support the design optimization and safe operation of next-generation combustion technologies utilizing carbon-free or low-carbon fuels.

Underground Hydrogen Storage (UHS) is a promising solution to maximize the use of hydrogen as an energy carrier. This study presents a standardized methodology for assessing UHS quality by introducing the Underground Hydrogen Storage Suitability Index (UHSSI) which integrates three sub-indices: the Caprock Potential Index (CPI) the Reservoir Quality Index (RQI) and the Site Potential Index (SPI). Parameters such as porosity permeability lithology caprock thickness depth temperature and salinity are evaluated and ranked from 0 (unsuitable) to 5 (excellent). The methodology was validated using data from six worldwide sites including salt caverns and aquifers. Sites like Moss Bluff Clemens Dome and Spindletop (USA) scored highly while Teesside (UK) Lobodice (Czech Republic) and Beynes (France) were classified as unsuitable due to shallow depths and microbial activity. A software tool the UHSSI Calculator was developed to automate site evaluations. This approach offers a cost-effective tool for preliminary screening and supports the safer development of UHS.

This paper explores cleaner and techno-economically viable solutions to provide electricity heat and cooling using green hydrogen (H2) and green ammonia (NH3) across the entire decarbonized value chain. We propose integrating a 100% hydrogen-fueled internal combustion engine (e.g. Jenbacher JMS 420) as a stationary backup solution and comparing its performance with other backup technologies. While electrochemical storage systems or battery energy storage systems (BESSs) offer fast and reliable short-term energy buffering they lack flexibility in relocation and typically involve higher costs for extended backup durations. Through five case studies we highlight that renewable-based energy supply requires additional capacity to bridge longer periods of undersupply. Our results indicate that for cost reasons battery–electric solutions alone are not economically feasible for longterm backup. Instead a more effective system combines both battery and hydrogen storage where batteries address daily fluctuations and hydrogen engines handle seasonal surpluses. Despite lower overall efficiency gas engines offer favorable investment and operating costs in backup applications with low annual operating hours. Furthermore the inherent fuel flexibility of combustion engines eventually will allow green ammonia-based backup systems particularly as advancements in small-scale thermal cracking become commercially available. Future studies will address CO2 credit recognition carbon taxes and regulatory constraints in developing more effective dispatch and master-planning solutions.

The ongoing digitalization of energy infrastructure is a crucial enabler for improving efficiency reliability and sustainability in gas distribution networks especially in the context of decarbonization and the integration of alternative energy carriers (e.g. renewable gases including biogas green hydrogen). This study presents the development and application of a Digital Twin framework for a real-world gas distribution network developed using open-source tools. The proposed methodology covers the entire digital lifecycle: from data acquisition through smart meters and GIS mapping to 3D modelling and simulation using tools such as QGIS FreeCAD and GasNetSim. Consumption data are collected processed and harmonized via Python-based workflows hourly simulations of network operation including pressure flow rate and gas quality indicators like the Wobbe Index. Results demonstrate the effectiveness of the Digital Twin in accurately replicating real network behavior and supporting scenario analyses for the introduction of greener energy vectors such as hydrogen or biomethane. The case study highlights the flexibility and transparency of the workflow as well as the critical importance of data quality and availability. The framework provides a robust basis for advanced network management optimization and planning offering practical tools to support the energy transition in the gas sector.

This study assesses the feasibility and profitability of marine hybrid clusters combining wave energy converters (WECs) and offshore wind turbines (OWTs) to power households and marine aquaculture. Researchers analyzed two coastal sites: La Serena Chile with high and consistent wave energy resources and Ensenada Mexico with moderate and more variable wave power. Two WEC technologies Wave Dragon (WD) and Pelamis (PEL) were evaluated alongside lithium-ion battery storage and green hydrogen production for surplus energy storage. Results show that La Serena’s high wave power (26.05 kW/m) requires less hybridization than Ensenada’s (13.88 kW/m). The WD device in La Serena achieved the highest energy production while PEL arrays in Ensenada were more effective. The PEL-OWT cluster proved the most cost-effective in Ensenada whereas the WD-OWT performed better in La Serena. Supplying electricity for seaweed aquaculture particularly in La Serena proves more profitable than for households. Ensenada’s clusters generate more surplus electricity suitable for the electricity market or hydrogen conversion. This study emphasizes the importance of tailoring emerging WEC systems to local conditions optimizing hybridization strategies and integrating consolidated industries such as aquaculture to enhance both economic and environmental benefits.

Hydrogen is increasingly recognized as a key energy vector for achieving deep decarbonization across urban and industrial sectors. Supporting global efforts to reduce greenhouse gas (GHG) emissions and achieve the Sustainable Development Goals (SDGs) it is essential to understand the multi-sectoral role of the hydrogen value chain spanning production storage and end-use applications with particular emphasis on smart city systems and industrial processes. Green hydrogen production technologies including alkaline water electrolysis (AWE) proton exchange membrane (PEM) electrolysis anion exchange membrane (AEM) electrolysis and solid oxide electrolysis cells (SOECs) are evaluated in terms of efficiency scalability and integration potential. Storage pathways are examined across physical storage (compressed gas cryo-compressed and liquid hydrogen) material-based storage (solid-state absorption in metal hydrides and chemical carriers such as LOHCs and ammonia) and geological storage (salt caverns depleted gas reservoirs and deep saline aquifers) highlighting their suitability for urban and industrial contexts. In the smart city domain hydrogen is analyzed as an enabler of zero-emission transportation low-carbon residential and commercial heating and renewable-integrated smart grids with long-duration storage capabilities. System-level studies demonstrate that coordinated integration of these applications can deliver higher overall energy efficiency deeper reductions in life-cycle GHG emissions and improved resilience of urban energy systems compared with sector-specific approaches. Policy frameworks safety standards and digitalization strategies are reviewed to illustrate how hydrogen infrastructure can be embedded into interconnected urban energy systems. Furthermore industrial applications focus on hydrogen’s potential to decarbonize energy-intensive processes and enable sector coupling between electricity heat and manufacturing. The environmental implications of hydrogen deployment are also considered including resource efficiency life-cycle emissions and ecosystem impacts. In contrast to reviews addressing isolated aspects of hydrogen technologies this study synthesizes technological infrastructural and policy dimensions integrating insights from over 400 studies to highlight the multifaceted role of hydrogen in sustainable urban development and industrial decarbonization and the added benefits achievable through coordinated cross-sector deployment strategies.

The urgent need to mitigate climate change and reduce greenhouse gas emissions has accelerated the search for sustainable and scalable energy carriers. Among the different alternatives ammonia stands out as a promising carbon-free fuel thanks to its high energy density efficient storage and compatibility with existing infrastructure. Moreover it can be produced through sustainable green processes. However its application in internal combustion engines is limited by several challenges including low reactivity narrow flammability limits and high ignition energy. These factors can compromise combustion efficiency and contribute to increased unburned ammonia emissions. To address these limitations hydrogen has emerged as a complementary fuel in dual-fuel configurations with ammonia. Hydrogen’s high reactivity enhances flame stability ignition characteristics and combustion efficiency while reducing emissions of unburned ammonia. This review examines the current status of dual-fuel ammonia and hydrogen combustion strategies in internal combustion engines and summarizes the experimental results. It highlights the potential of dual-fuel systems to optimize engine performance and minimize emissions. It identifies key challenges knowledge gaps and future research directions to support the development and widespread adoption of ammonia–hydrogen dual-fuel technologies.

In recent years governments have promoted the shift to low-emission transport systems with electric and hydrogen vehicles emerging as key alternatives for greener urban mobility. Evaluating zero- or near-zero tailpipe solutions requires a Lifecycle Assessment (LCA) approach accounting for emissions from energy production components and vehicle manufacturing. Such studies mainly address Greenhouse Gas (GHG) emissions while other pollutants are often overlooked. This study compares the Human Toxicity Potential (HTP) of Battery Electric Vehicles (BEVs) Fuel Cell Vehicles (FCVs) Hydrogen Internal Combustion Engine Vehicles (H2ICEVs) and hybrid H2ICEVs for public transport in the European Union. Current and future scenarios (2024 2030 2050) are examined considering evolving energy mixes and manufacturing impacts. Results underline that BEVs are characterized by the highest HTP in 2024 and that this trend is maintained even in future scenarios. As for hydrogen-based powertrains they show lower HTPs similar among them. This work underlines that current efforts must be intensified especially for BEVs to further limit harmful emissions from the mobility sector.

The decarbonization of remote energy systems presents both technical and economic challenges due to their dependance on fossil fuels and the variability of renewable energy sources. This study introduces a Two-Stage Stochastic Programming approach to optimize Hybrid Renewable Energy Systems under uncertainty in renewable energy production. The methodology is applied to the island of Pantelleria aiming to minimize Total Annualized Costs and CO2 emissions using an ε-constraint approach. Results show that within the set of optimized configurations stricter CO2 emissions constraints increase costs due to the need for oversized components to ensure supply reliability. Nevertheless even the zeroemissions scenario offers significant economic benefits compared to the current diesel-based system. Total Annualized Costs are reduced from 15.5 M€ to 8.10 M€ in the deterministic case and to 9.37 M€ in the stochastic one. The additional cost in the stochastic configuration is offset by improved reliability ensuring demand is met under all scenarios. A sensitivity analysis on electricity demand reveals the necessity of further larger components leading to a 27.0% cost increase in a fully renewable scenario with stochastic optimization for a 10% demand increase. These findings highlight the importance of stochastic optimization in designing cost-effective off-grid renewable energy systems.

In the pursuit of zero-emission mobility hydrogen represents a promising fuel for internal combustion engines. However its low volumetric energy density poses challenges especially for high-performance applications where compactness and lightweight design are crucial. This study investigates the feasibility of an innovative hydrogen-fueled two-stroke opposed-piston (2S-OP) engine targeting a specific power of 130 kW/L and an indicated thermal efficiency above 40%. A detailed 3D-CFD analysis is conducted to evaluate mixture formation combustion behavior abnormal combustion and water injection as a mitigation strategy. Innovative ring-shaped multi-point injection systems with several designs are tested demonstrating the impact of injector channels’ orientation on the final mixture distribution. The combustion analysis shows that a dual-spark configuration ensures faster combustion compared to a single-spark system with a 27.5% reduction in 10% to 90% combustion duration. Pre-ignition is identified as the main limiting factor strongly linked to mixture stratification and high temperatures. To suppress it water injection is proposed. A 55% evaporation efficiency of the water mass injected lowers the in-cylinder temperature and delays pre-ignition onset. Overall the study provides key design guidelines for future high-performance hydrogen-fueled 2S-OP engines.

The transition toward environmentally friendly steelmaking using hydrogen direct reduced iron as feed material in electric arc furnaces will eventually require process adjustments due to changes in the pellet properties when compared to e.g. blast furnace pellets. To this end the melting of hydrogen direct reduced iron pellets with 68 and 100% reduction degrees and Fe content of 67.24% was investigated in a laboratory-scale electric arc furnace. The presence of iron oxide-rich slag had a significant effect on the arc movement on the melt and an inhibiting effect on iron evaporation. The melting was monitored with video recording and optical emission spectroscopy. The videos were used to monitor the melting behavior whereas optical emissions revealed iron gangue elements and hydrogen from the pellets radiating in the plasma. Furthermore the flow of the melt is well seen in the videos as well as the movement of slag droplets on the melt surface. After the experiments the metal had silica-rich inclusions whereas slag had mostly penetrated into the crucible. The most notable differences in melting behavior can be attributed to the iron oxide-rich slag its interaction with the arc and penetration into the crucible and how it affects the arc movement and heat transfer.