Italy

This work explores the integration of Proton Exchange Membrane (PEM) electrolysis waste heat with district heating networks (DHN) aiming to enhance the overall energy efficiency and economic viability of hydrogen production systems. PEM electrolysers generate substantial amounts of low-temperature waste heat during operation which is often dissipated and left unutilised. By recovering such thermal energy and selling it to district heating systems a synergistic energy pathway that supports both green hydrogen production and sustainable urban heating can be achieved. The study investigates how the electrolyser’s operating temperature ranging between 50 and 80 ◦C influences both hydrogen production and thermal energy availability exploring trade-offs between electrical efficiency and heat recovery potential. Furthermore the study evaluates the compatibility of the recovered heat with common heat emission systems such as radiators fan coils and radiant floors. Results indicate that valorising waste heat can enhance the overall system performance by reducing the electrolyser’s specific energy consumption and its levelized cost of hydrogen (LCOH) while supplying carbon-free thermal energy for the end users. This integrated approach contributes to the broader goal of sector coupling offering a pathway toward more resilient flexible and resource-efficient energy systems.

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.

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.

This study investigates the combustion process in a marine spark-ignition engine fueled with an ammonia–hydrogen blend (15% hydrogen by volume) using a passive pre-chamber. A 3D-CFD model supported by a 1D engine model was employed to analyze equivalence ratios between 0.7 and 0.9 and pre-chamber nozzle diameters from 7 to 3 mm. Results indicate that combustion is consistently initiated by turbulent jets but at an equivalence ratio of 0.7 the charge combustion is incomplete. For lean mixtures reducing nozzle size improves flame propagation although not sufficiently to ensure stable operation. At an equivalence ratio of 0.8 reducing the nozzle diameter from 7 to 5 mm advances CA50 by about 6 CAD while further reduction causes minor variations. At richer conditions nozzle diameter plays a negligible role. Optimal performance was achieved with a 7 mm nozzle at equivalence ratio 0.8 delivering about 43% efficiency and 1.17 MW per cylinder.

This study evaluates the performance of three anion-exchange membranes (FAS-50 AMX Fujifilm-AEM) and a diaphragm separator (Zirfon® UTP 500) in alkaline water sono-electrolysis using a 25 % KOH electrolyte at ambient temperature. Energy efficiency hydrogen production kinetics and membrane stability were assessed experimentally and through modeling. Among the tested separators Zirfon achieved the highest energy efficiency outperforming AEM AMX and FAS-50. Hydrogen production rates under silent conditions ranged from 2.55 µg/s (AEM) to 2.92 µg/s (FAS-50) while sonication (40 kHz 60 W) increased rates by 0.03–0.12 µg/s with the strongest relative effect observed for FAS-50 (≈4.0 % increase). By contrast Zirfon and AEM showed slight efficiency reductions (0.5–2 %) under ultrasound due to their higher structural resistance. Ion-exchange capacity tests confirmed significant degradation of polymeric membranes (IEC losses of 60–90 %) while Zirfon maintained stability in 25 % KOH. Modeling results showed that the diaphragm resistance was dominated by the ohmic losses (55–86 %) with ultrasound reducing bubble coverage and associated resistance only marginally (<0.02 V). Overall Zirfon demonstrated superior stability and efficiency for long-term operation while ultrasound primarily enhanced hydrogen evolution kinetics in mechanically weaker polymeric membranes.