Hydrogen, Volume 5, Issue 2 (June 2024) – 7 articles

Onboard hydrogen storage tanks are currently fitted with thermally activated pressure relief devices (TPRDs), enabling hydrogen to blowdown in the event of fire. For release diameters below the critical diameter, the flame from the TPRD may blow-out during a pressure drop. Flame blow-outs pose a safety concern for an indoor or covered environment, e.g., a garage or carpark, where hydrogen can accumulate and deflagrate. This study describes the application of a validated computational fluid dynamics (CFD) model to simulate the dynamic flame behaviour from a TPRD designed to exclude its blow-out. The dynamic behaviour replicates a real scenario. Flame behaviour during tank blowdown through two TPRDs with different nozzle geometries is presented. Simulations confirm flame blow-out for a single-diameter TPRD of 0.5 mm during tank blowdown, while the double-diameter nozzle successfully excludes flame blow-out. The pressure at which the flame blow-out process is initiated during blowdown through a single-diameter nozzle was predicted. Full article

Hydrogen storage in general is an indispensable prerequisite for the introduction of a hydrogen energy-based infrastructure. In this respect, high-pressure metal hydride (MH) tank systems appear to be one of the most promising hydrogen storage techniques for automotive applications using proton exchange membrane (PEM) fuel cells. These systems bear the potential of achieving a beneficial compromise concerning the comparably large volumetric storage density, wide working temperature range, comparably low liberation of heat, and increased safety. The debatable term “unstable metal hydride” is used in the literature in reference to metal hydrides with high dissociation pressure at a comparably low temperature. Such compounds may help to improve the merits of high-pressure MH tank systems. Consequently, in the last few years, some materials for possible on-board applications in such tank systems have been developed. This review summarizes the state-of-the-art developments of these metal hydrides, mainly including intermetallic compounds and complex hydrides, and offers some guidelines for future developments. Since typical laboratory hydrogen uptake measurements are limited to 200 bar, a possible threshold for defining unstable hydrides could be a value of their equilibrium pressure of p_eq > 200 bar for T < 100 °C. However, these values would mark a technological future target and most current materials, and those reported in this review, do not fulfill these requirements and need to be seen as current stages of development toward the intended target. For each of the aforementioned categories in this review, special care is taken to not only cover the pioneering and classic research but also to portray the current status and latest advances. For intermetallic compounds, key aspects focus on the influence of partial substitution on the absorption/desorption plateau pressure, hydrogen storage capacity and hysteresis properties. For complex hydrides, the preparation procedures, thermodynamics and theoretical calculation are presented. In addition, challenges, perspectives, and development tendencies in this field are also discussed. Full article

Water is a potential green source for the generation of clean elemental hydrogen without contaminants. One of the most convenient methods for hydrogen generation is based on the oxidation of different metals by water. The inspection of the catalytic activity toward hydrogen formation from water performed in this study was carried out using four different metals, namely, zinc, magnesium, iron, and manganese. The process is catalyzed by in situ-generated nickel nanoparticles. The zinc–water system was found to be the most effective and exhibited 94% conversion in 4 h. The solid phase in the latter system was characterized by PXRD and SEM techniques. Several blank tests provided a fundamental understanding of the role of each constituent within the system, and a molecular mechanism for the catalytic cycle was proposed. Full article

Long-duration energy storage is the key challenge facing renewable energy transition in the future of well over 50% and up to 75% of primary energy supply with intermittent solar and wind electricity, while up to 25% would come from biomass, which requires traditional type storage. To this end, chemical energy storage at grid scale in the form of fuel appears to be the ideal option for wind and solar power. Renewable hydrogen is a much-considered fuel along with ammonia. However, these fuels are not only difficult to transport over long distances, but they would also require totally new and prohibitively expensive infrastructure. On the other hand, the existing natural gas pipeline infrastructure in developed economies can not only transmit a mixture of methane with up to 20% hydrogen without modification, but it also has more than adequate long-duration storage capacity. This is confirmed by analyzing the energy economies of the USA and Germany, both possessing well-developed natural gas transmission and storage systems. It is envisioned that renewable methane will be produced via well-established biological and/or chemical processes reacting green hydrogen with carbon dioxide, the latter to be separated ideally from biogas generated via the biological conversion of biomass to biomethane. At the point of utilization of the methane to generate power and a variety of chemicals, the released carbon dioxide would be also sequestered. An essentially net zero carbon energy system would be then become operational. The current conversion efficiency of power to hydrogen/methane to power on the order of 40% would limit the penetration of wind and solar power. Conversion efficiencies of over 75% can be attained with the on-going commercialization of solid oxide electrolysis and fuel cells for up to 75% penetration of intermittent renewable power. The proposed hydrogen/methane system would then be widely adopted because it is practical, affordable, and sustainable. Full article

The global push for sustainable energy has heightened the demand for green hydrogen, which is crucial for decarbonizing heavy industry. However, current electrolysis plant capacities are insufficient. This research addresses the challenge through optimizing large-scale electrolysis construction via standardization, modularization, process optimization, and automation. This paper introduces H₂Giga, a project for mass-producing electrolyzers, and HyPLANT100, investigating large-scale electrolysis plant structure and construction processes. Modularizing electrolyzers enhances production efficiency and scalability. The integration of AutomationML facilitates seamless information exchange. A digital twin concept enables simulations, optimizations, and error identification before assembly. While construction site automation provides advantages, tasks like connection technologies and handling cables, tubes, and hoses require pre-assembly. This study identifies key tasks suitable for automation and estimating required components. The Enapter Multicore electrolyzer serves as a case study, showcasing robotic technology for tube fittings. In conclusion, this research underscores the significance of standardization, modularization, and automation in boosting the electrolysis production capacity for green hydrogen, contributing to ongoing efforts in decarbonizing the industrial sector and advancing the global energy transition. Full article

Hydrogen plays a leading role in achieving a future with net zero greenhouse gas emissions. The present challenge is producing green hydrogen to cover the fuel demands of transportation and industry to gain independence from fossil fuels. This review’s goal is to critically demonstrate the existing methods of biomass treatment and assess their ability to scale up. Biomass is an excellent hydrogen carrier and biomass-derived processes are the main target for hydrogen production as they provide an innovative pathway to green hydrogen production. Comparing the existing processes, thermochemical treatment is found to be far more evolved than biological or electrochemical treatment, especially with regard to scaling prospects. Full article

Hydrogen permeation sparked a renewed interest in the second half of the 20th century due to the favorable features of this element as an energy factor. Furthermore, niche applications such as nuclear fusion gained attention for the highest selectivity ensured by self-supported dense metallic membranes, especially those consisting of Pd-based alloys. In this framework, the ENEA Frascati laboratories have decades of experience in the manufacturing, integration, and operation of Pd-Ag permeators. Most of the experimental investigations were performed on single-tube membranes, proving their performance under relevant operational conditions. Nowadays, once the applicability of this technology has been demonstrated, the scalability of the single-tube experience over medium- and large-scale units must be verified. To do this, ENEA Frascati laboratories have designed and constructed a multi-tube permeator, namely the Medium-Scaled Membrane Reactor (MeSMeR), focused on scalability assessment. In this work, the results obtained with the MeSMeR facility have been compared with previous experimental campaigns conducted on single-tube units, and the scalability of the permeation results has been proven. Moreover, post-test simulations have been performed based on single-tube finite element modeling, proving the scalability of the numerical outcomes and the possibility of using this tool for scale-up design procedures. Full article