Publications

This study aims to advance the understanding of hydrogen embrittlement (HE) in low-carbon and low-alloy steels by developing a predictive framework for assessing fracture toughness (FT) a critical parameter for mitigating HE in hydrogen infrastructure. A machine learning (ML) model was constructed by analyzing data from relevant literature to evaluate the fracture toughness of steels exposed to hydrogen environments. Seven ML modeling techniques were initially considered with four selected for detailed evaluation based on predictive accuracy. The chosen modeling techniques were k-nearest neighbors (KNN) random forest (RF) gradient boosting (GB) and decision tree regression (DT). The selected models were further evaluated for their predictive accuracy and reliability and the best model was used to perform parametric studies to investigate the impact of relevant parameters on FT. According to the results the KNN model demonstrated reliable predictive performance supported by high R-squared values and low error metrics. Among the variables considered hydrogen pressure and yield strength emerged as the most influential with hydrogen pressure alone accounting for 32% of the variation in FT. The model revealed a distinct trend in FT behavior showing a significant decline at low hydrogen pressures (0–6.9 MPa) and a plateau at higher pressures (>8 MPa) indicating a saturation point. Alloying element contents specifically those of carbon and phosphorus also played a notable role in FT prediction. Additionally the study confirmed that low concentrations of oxygen (

Green hydrogen production is a sustainable energy solution with great potential offering advantages such as adaptability storage capacity and ease of transport. However there are challenges such as high energy consumption production costs demand and regulation which hinder its largescale adoption. This study explores the role of simulation models in optimizing the technical and economic aspects of green hydrogen production. The proposed system which integrates photovoltaic and energy storage technologies significantly reduces the grid dependency of the electrolyzer achieving an energy self-consumption of 64 kWh per kilogram of hydrogen produced. By replacing the high-fidelity model of the electrolyzer with a reduced-order model it is possible to minimize the computational effort and simulation times for different step configurations. These findings offer relevant information to improve the economic viability and energy efficiency in green hydrogen production. This facilitates decision-making at a local level by implementing strategies to achieve a sustainable energy transition.

This study investigates the integration of green hydrogen into building energy systems using local solar power with the electricity grid serving as a backup plan. A comprehensive bottom-up analysis compares six energy system configurations: the natural gas grid boiler system all-electric heat pump system natural gas and hydrogen blended system hydrogen microgrid boiler system cogeneration hydrogen fuel cell system and hybrid hydrogen heat pump system. Energy efficiency evaluations were conducted for 25 homes within one block in a neighborhood across five typological house stocks located in Stoke-on-Trent UK. This research was modeled using a spreadsheet-based approach. The results highlight that while the all-electric heat pump system still demonstrates the highest energy efficiency with the lowest consumption the hybrid hydrogen heat pump system emerges as the most efficient hydrogen-based solution. Further optimization through the implementation of a peak-shaving strategy shows promise in enhancing system performance. In this approach hybrid hydrogen serves as a heating source during peak demand hours (evenings and cold seasons) complemented by a solar energy powered heat pump during summer and daytime. An hourly operational configuration is recommended to ensure consistent performance and sustainability. This study focuses on energy performance excluding cost-effectiveness analysis. Therefore the cost of the energy is not taken into consideration requiring further development for future research in these areas.

In rotating machinery unbalanced mass is one of the most common causes of system vibration. This paper presents an experimental investigation of the unbalance response of a gas foil bearing-rotor system based on a 30 kW-rated commercial hydrogen fuel cell vehicle air compressor. The study examines the response of the system to varying unbalanced masses at different rotational speeds. Experimental results show that after adding unbalanced mass subsynchronous vibration of the rotor is relatively slight while synchronous vibration is the main source of vibration; when unbalanced mass is added to one side of the rotor the synchronous vibration on that side initially decreases and then increases with speed while synchronous vibration on the opposite side continuously increases with speed; when unbalanced mass is added to both sides the synchronous vibration on each side increases with the phase difference of the unbalanced mass at low speed while the opposite trend occurs at high speed. The analysis of the gas foil bearingrotor system dynamics model established based on the dynamic coefficient of the bearing shows that the bending of the rotor offsets the displacement caused by the unbalanced mass which is the primary reason for the nonlinear behavior of the synchronous vibration of the rotor. These findings contribute to an improved understanding of GFB-rotor interactions under unbalanced conditions and provide practical guidance for optimizing dynamic balancing strategies in hydrogen fuel cell vehicle compressors.

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.

Global attention is being given to hydrogen as it is seen as a versatile energy carrier and a flexible energy vector in transitioning to a low-carbon economy. Hydrogen production/storage/conveyance is metal intensive and it is crucial to understand if there is material availability to fulfil the committed plans. Using the material intensity of electrolysers pipelines and desalinators along with the projected Portuguese and European Union roadmaps we are able to identify possible bottlenecks in the supply chains. The availability of the vast majority of raw materials does not represent a threat to hydrogen technologies implementation with electrolysers requiring almost up to 3 Mt of raw materials and pipelines up to 2.5 Mt. The evident exception is iridium although representing less than 0.001 % of the material requirements it may hinder the widespread implementation of proton exchange membrane electrolysers. Desalinators have the least material footprint of the studied infrastructure.

This study focuses on the potential valorization of brewers’ spent grain (BSG) through gasification for ultra-pure green hydrogen production via membrane separation. First a fundamental physicochemical characterization of BSG samples from two different Spanish brewing industries was conducted revealing high energy content and good reproducibility of elemental composition thus providing great potential for hydrogen generation in the context of circular economy for the brewery industry. The syngas composition reached by BSG gasification has been predicted and main operating conditions optimized to maximize the hydrogen yield (25–75 vol% air-steam mixture ratio GR = 0.75 T = 800 ◦C and P = 5 bar). For gas purification two Pd-membranes were fabricated by ELP-PP onto tubular PSS supports with high reproducibility (Pd-thickness in the range 8.22–8.75 μm) exhibiting an almost complete H2-selectivity good fitting to Sieverts’ law and hydrogen permeate fluxes ranging from 175 to 550 mol m− 2 h− 1 under ideal gas feed composition conditions. The mechanical resistance of membranes was maintained at pressure driving forces up to 10 bar thus highlighting their potential for commercialization and industrial application. Furthermore long-term stability tests up to 75 h indicated promising membrane performance for continuous operation offering valuable insights for stakeholders in the brewery industry to enhance economic growth and environmental sustainability through green hydrogen production from BSG.

CO2 emission reduction of sectors such as aviation maritime shipping road haulage and chemical production is challenging but necessary. Although these sectors will most likely continue to rely on carbonaceous energy carriers they are expected to gradually shift away from fossil fuels. In order to do so the prominent option is to utilize alternative carbon sources—like biomass and CO2 originating from carbon capture—for the production of non-fossil carbonaceous vectors (biofuels and e-fuels). However the limited availability of biomass and the varying nature of other carbon sources necessitate a comprehensive evaluation of trade-offs between potential carbon uses and existing sources. Then it is primordial to understand the origin of carbon used in sustainable aviation fuel (SAF) to understand the implications of defossilizing aviation for the energy system. Moreover the production of SAF implies deep changes to the energy system that are quantified in this work. This study utilizes the linear programming cost optimization tool EnergyScope TD to analyze the holistic French energy system encompassing transport industry electricity and heat sectors while ensuring net greenhouse gas neutrality. A novel method to model and quantify carbon flows within the system is introduced enabling a comprehensive assessment of greenhouse gas neutrality. This study highlights the significance of fulfilling clean energy requirements and implementing carbon dioxide removal measures as crucial steps toward achieving climate neutrality. Indeed to reach climate neutrality a production of 1046 TWh of electricity by non-fossil sources is needed. Furthermore the findings underscore the critical role of efficient carbon and energy valorization from biomass providing evidence that producing fuels by combining biomass and hydrogen is optimal. The study also offers valuable insights into the future cost and impact of SAF production for air travel originating from France. That is the European law ReFuelEU would increase the price of plane tickets by +33% and would require 126 TWh of hydrogen and 50 TWh of biomass to produce the necessary 91 TWh of jet fuel. Finally the implications of the assumption behind the production of SAF are discussed.

Addressing the critical need for sustainable high-density hydrogen (H2) carriers to decarbonize the global energy landscape this paper presents a comprehensive critical review of ammonia’s pivotal role in the energy transition with a specific focus on its application in the transportation sector. While H2 is recognized as a future fuel its storage and distribution challenges necessitate alternative vectors. Ammonia (NH3) with its compelling advantages including high volumetric H2 density established global infrastructure and potential for near-zero greenhouse gas emissions emerges as a leading candidate. This review uniquely synthesizes the evolving landscape of sustainable NH3 production pathways (e.g. green NH3 from renewable electricity) with a systematic analysis of technological advancements to investigate its direct utilization as a transportation fuel. The paper critically examines the multifaceted challenges and opportunities associated with NH3-fueled vehicles refueling infrastructure development and comprehensive safety considerations alongside their environmental and economic implications. By providing a consolidated forward-looking perspective on this complex energy vector this paper offers crucial insights for researchers policymakers and industry stakeholders highlighting NH3’s transformative potential to accelerate the decarbonization of hard-to-abate transportation sectors and contribute significantly to a sustainable energy future.

Decarbonizing long-haul heavy-duty transport in Europe focuses on batteryelectric trucks with high-power chargers or electric road systems and fuel-cell-electric vehicles with hydrogen refueling stations. We present a comparative life cycle assessment and total cost of ownership analysis of these technologies for 20% of Germany’s heavy-duty long-haul transport alongside internal combustion engine vehicles. The results show that fuel cell vehicles with on-site hydrogen have the highest life cycle emissions (65 Mt CO2e) followed by internal combustion engine vehicles (55 Mt CO2e). Battery-electric vehicles using electric road systems achieve the lowest emissions (21 Mt CO2e) and the lowest costs (EUR 45 billion). In contrast fuel cell vehicles with on-site hydrogen have the highest costs (EUR 69 billion). Operational costs dominate total expenses making them a compelling target for subsidies. The choice between battery and fuel cell technologies depends on the ratio of vehicles to infrastructure transport performance and range. Fuel cell trucks are better suited for remote areas due to their longer range while integrating electric road systems with high-power charging could offer synergies. Recent advancements in battery and fuel cell durability further highlight the potential of both technologies in heavy-duty transport. This study provides insights for policymakers and industry stakeholders in the shift towards sustainable transport. The greenhouse gas emission savings from adopting battery-electric trucks are 54% in our high-power charging scenario and 62% in the electric road system scenario in comparison to the reference scenario with diesel trucks.