Hydrogen, Volume 4, Issue 3 (September 2023) – 17 articles

This work introduces state-of-the-art water detritiation processes and discusses the main technologies and materials adopted. Focus is given to the gas chromatography (GC) and the thermal cycling absorption process (TCAP), which are studied as potential back-end technologies for tritium recovery through a water detritiation system designed for a small-scale unit. GC and the TCAP are evaluated critically in order to establish their applicability for the final purification of the DT stream recovered at the bottom of the cryo-distillation column of a water detritiation unit. Both solutions (GC and the TCAP with an inverse column) exhibit safe and feasible operation modes and are characterised by a good technological level; furthermore, both of these processes meet the main design specifications required by the proposed application. However, the use of GC is preferred, since this system can operate with modest temperature cycling and producing streams (D₂ and T₂) of better purity. Full article

Considering the clean, renewable, and ecologically friendly characteristics of hydrogen gas, as well as its high energy density, hydrogen energy is thought to be the most potent contender to locally replace fossil fuels. The creation of a sustainable energy system is currently one of the critical industrial challenges, and electrocatalytic hydrogen evolution associated with appropriate safe storage techniques are key strategies to implement systems based on hydrogen technologies. The recent progress made possible through nanotechnology incorporation, either in terms of innovative methods of hydrogen storage or production methods, is a guarantee of future breakthroughs in energy sustainability. This manuscript addresses concisely and originally the importance of including nanotechnology in both green electroproduction of hydrogen and hydrogen storage in solid media. This work is mainly focused on these issues and eventually intends to change beliefs that hydrogen technologies are being imposed only for reasons of sustainability and not for the intrinsic value of the technology itself. Moreover, nanophysics and nano-engineering have the potential to significantly change the paradigm of conventional hydrogen technologies. Full article

A series of Mg-Y-Ni alloys with different volume fractions of long-period stacking-ordered (LPSO) phase were prepared, by controlling the alloy composition, heat treatment, and single-pass extrusion, to assess the influence of increasing LPSO phase volume fraction on the hydrogen absorption and desorption properties of the extruded alloys. The LPSO phase volume fraction in the alloys increased with increasing solute concentration, from ~24% LPSO in Mg₉₇Y₂Ni₁ (at.%) to ~60% LPSO in Mg₉₃Y₄Ni₃ (at.%) up to ~92% LPSO in Mg₉₁Y₅Ni₄ (at.%). The most refined microstructure was obtained in the alloy with highest volume fraction of LPSO phase. After 100 s at 300 °C, the Mg₉₁Y₅Ni₄ alloy absorbed 4.6 ± 0.2 wt.% H while the Mg₉₇Y₂Ni₁ and Mg₉₃Y₄Ni₃ alloys each absorbed 3.8 ± 0.2 wt.% H. After 10,000 s at 300 °C, all three alloys had absorbed a maximum of 5.3 ± 0.2 wt.% H with no further significant difference in hydrogen absorption kinetics. The Mg₉₁Y₅Ni₄ alloy desorbed 1.8 ± 0.2 wt.% H after 100 s at 300 °C against a vacuum while the Mg₉₇Y₂Ni₁ and Mg₉₃Y₄Ni₃ alloys desorbed 0.8 ± 0.2 wt. H and 0.6 ± 0.2 wt.% H, respectively. After 10,000 s at 300 °C, the Mg₉₁Y₅Ni₄ and Mg₉₇Y₂Ni₁ alloys completely desorbed 5.2 ± 0.2 wt.% H and 5.4 ± 0.2 wt.% H, respectively, but the Mg₉₃Y₄Ni₃ alloy desorbed only 3.7 ± 0.2 wt.% H. Hydrogen absorption and desorption kinetics were fastest in the Mg₉₁Y₅Ni₄ alloy with the highest LPSO volume fraction, but no consistent trend with LPSO phase volume fraction was observed with the Mg₉₃Y₄Ni₃ alloy, which showed the slowest absorption and desorption kinetics. The hydrogen pressures corresponding to metal–hydride equilibrium did not vary with LPSO phase volume fraction or alloy composition, indicating that the (de)hydrogenation thermodynamics were not significantly changed in any of the alloys. Hydrogen absorption experiments with thin foils, made of extruded Mg₉₁Y₅Ni₄ alloy with the highest LPSO phase fraction, demonstrated that the LPSO structures decompose into Mg phase, Mg₂Ni phase, lamellar Mg/Mg-Y structures, and YH_x particles. This study shows that hydrogen kinetics can be impacted in Mg-Y-Ni alloys by controlling the LPSO phases using common metallurgical techniques. Full article

Single phase CuCoMgAl-layered hydroxides were obtained by making fine adjustment to their composition through changing the (Co + Cu)/Mg = 0.5; 1; 2; 3 and Co/Cu = 0.5; 1; 2 ratios. The rise of Co/Cu in systems contributed to the increase in their thermal stability. CuCoMgAl-catalysts showed high selectivity of carbonyl group hydrogenation in furfural and 5-hydroxymethylfurfural. In furfural hydrogenation, the selectivity to furfuryl alcohol was more than 99%, and in 5-hydroxymethylfurfural hydrogenation, the selectivity to 2,5-hydroxymethyl furfural was 95%. The surface of the samples with different Co/Cu after calcination and reduction was the same and had a «core-shell» structure (TEM). «Core» consisted of Cu and Co metallic particles. «Shell» consisted of CuCoMgAlO_x mixed no-stoichiometric spinel oxides. There was no sintering or change in size of the metallic particles after the reaction. For the sample with Co/Cu = 1, their phase composition after reaction remained unchangeable. The increase of Co/Cu led to the formation of an X-ray amorphous phase after the reaction. This suggests the decrease in structural stability of this sample. The obtained results prove the prospects of using bimetallic CoCu-systems for hydrogenation of furan aldehydes, and opens up new directions for further research and improvement. Full article

Solar photocatalytic H₂ production has drawn an increasing amount of attention from the scientific community, industry, and society due to its use of green solar energy and a photocatalyst (semiconductor material) to produce green H₂. Cu-based semiconductors are interesting as photocatalysts for H₂ production because Cu is earth-abundant, cheap, and the synthesis of its copper-containing semiconductors is straightforward. Moreover, Cu-based semiconductors absorb visible light and present an adequate redox potential to perform water splitting reaction. Nevertheless, pristine Cu-based semiconductors exhibit low photoactivity due to the rapid recombination of photo-induced electron-hole (e⁻-h⁺) pairs and are subject to photo corrosion. To remedy these pitfalls, the Cu semiconductor-based Z-scheme family (Z-schemes and S-schemes) presents great interest due to the charge carrier mechanism involved. Due to the interest of Z-scheme photocatalysts in this issue, the basic concepts of the Z-scheme focusing on Cu-based semiconductors are addressed to obtain novel systems with high H₂ photo-catalytic activity. Focusing on H₂ production using Cu-based Z-schemes photocatalyst, the most representative examples are included in the main text. To conclude, an outlook on the future challenges of this topic is addressed. Full article

Hydrogen has been studied extensively as a potential enabler of the energy transition from fossil fuels to renewable sources. It promises a feasible decarbonisation route because it can act as an energy carrier, a heat source, or a chemical reactant in industrial processes. Hydrogen can be produced via renewable energy sources, such as solar, hydro, or geothermic routes, and is a more stable energy carrier than intermittent renewable sources. If hydrogen can be stored efficiently, it could play a crucial role in decarbonising industries. For hydrogen to be successfully implemented in industrial systems, its impact on infrastructure needs to be understood, quantified, and controlled. If hydrogen technology is to be economically feasible, we need to investigate and understand the retrofitting of current industrial infrastructure. Currently, there is a lack of comprehensive knowledge regarding alloys and components performance in long-term hydrogen-containing environments at industrial conditions associated with high-temperature hydrogen processing/production. This review summarises insights into the gaps in hydrogen embrittlement (HE) research that apply to high-temperature, high-pressure systems in industrial processes and applications. It illustrates why it is still important to develop characterisation techniques and methods for hydrogen interaction with metals and surfaces under these conditions. The review also describes the implications of using hydrogen in large-scale industrial processes. Full article

Refuelling hydrogen-powered cars, buses, trucks, trains, ships, and planes is a technological challenge. The absence of contemporary CFD models of refuelling through the entire hydrogen refuelling station (HRS) equipment is one of the scientific bottlenecks. Detailed refuelling protocols for more than 10 kg of hydrogen, e.g., for heavy-duty vehicles, are absent. A thoroughly validated CFD model for simulations of the refuelling process through the entire equipment of the HRS is needed for protocols’ development. This study aims to numerically simulate the start-up phase of the refuelling procedure at HRS using the developed CFD model. The simulations through the entire HRS equipment are compared against unique experimental data of NREL and demonstrated agreement with measured pressure and temperature dynamics in onboard storage tanks during the start-up phase while having less than 5% deviation. The CFD model demonstrates excellent predictive capability and is time efficient. The simulation time of the start-up phase of 14 s duration is about 2 h on a 32-core CPU. Full article

We present the analysis of the stability of the (TiO₂)_n nanoclusters, where n = 2–4, supported on the Fe₃O₃-hematite (100) surface. The analysis is focused on the size and geometry of the nanocluster, which defines the contact with the supporting hematite surface. The aim of the work is to explore the role of the interaction within the nanocluster as well as between the nanocluster and the surface in the structure of the composite system. We have used an in-house developed variant of the solids docking procedure to determine the most stable initial configurations of the nanoclusters with respect to the surface. Subsequently, we have carried out molecular dynamics simulations to enable finding a more stable configurations by the systems. The results show the three possible binding modes for the (TiO₂)₂ systems, but many more such modes for the larger clusters. Additionally, we have found that the partial dissociation of the nanocluster takes place upon the contact with the surface. Full article

Oxygen bubble accumulation on the anodic side of a polymer exchange membrane water electrolyzer (PEMWE) may cause a decrease in performance. To understand the behavior of these bubbles, a deep-learning-based bubble flow recognition tool dedicated to a PEMWE is developed. Combining the transparent side of a single PEMWE cell with a high-resolution high-speed camera allows us to acquire images of the two-phase flow in the channels. From these images, a deep learning vision system using a fine-tuned YOLO V7 model is applied to detect oxygen bubbles. The tool achieved a high mean average precision of 70%, confirmed the main observations in the literature, and provided exciting insights into the characteristics of two-phase flow regimes. In fact, increasing the water flow rate from 0.05 to 0.4 L/min decreases the bubble coverage (by around 32%) and the mean single-bubble area. In addition, increasing the current density from 0.3 to 1.4 A/cm² leads to an increase in bubble coverage (by around 40%) and bubble amount. Full article

A proton exchange membrane (PEM) electrolyzer is fed with water and powered by electric power to electrochemically produce hydrogen at low operating temperatures and emits oxygen as a by-product. Due to the complex nature of the performance of PEM electrolyzers, the application of an artificial neural network (ANN) is capable of predicting its dynamic characteristics. A handful of studies have examined and explored ANN in the prediction of the transient characteristics of PEM electrolyzers. This research explores the estimation of the transient behavior of a PEM electrolyzer stack under various operational conditions. Input variables in this study include stack current, oxygen pressure, hydrogen pressure, and stack temperature. ANN models using three differing learning algorithms and time delay structures estimated the hydrogen mass flow rate, which had transient behavior from 0 to 1 kg/h, and forecasted better with a higher count (>5) of hidden layer neurons. A coefficient of determination of 0.84 and a mean squared error of less than 0.005 were recorded. The best-fitting model to predict the dynamic behavior of the hydrogen mass flow rate was an ANN model using the Levenberg–Marquardt algorithm with 40 neurons that had a coefficient of determination of 0.90 and a mean squared error of 0.00337. In conclusion, optimally fit models of hydrogen flow from PEM electrolyzers utilizing artificial neural networks were developed. Such models are useful in establishing an agile flow control system for the electrolyzer system to help decrease power consumption and increase efficiency in hydrogen generation. Full article

For the few past decades, study of new hydrogen storage materials has been captivating scientists worldwide. Magnesium hydride, MgH₂, is considered one of the most promising materials due to its low cost, high hydrogen capacity, reversibility and the abundance of Mg. However, it requires further research to improve its hydrogen storage performance as it has some drawbacks such as poor dehydrogenation kinetic, high operational temperature, which limit its practical application. In this study, we introduce an overview of recent progress in improving the hydrogen storage performance of MgH₂ by the addition of titanium-based additives, which are one of the important groups of additives. The role of Ti-based additive hydrides, oxides, halides, carbides and carbonitrides are overviewed. In addition, the existing challenges and future perspectives of Mg-based hydrides are also discussed. Full article

Ceria-based nanostructures, employed as catalytic supports for noble and non-noble metals, are well-known for their remarkable activity in steam-reforming reactions, exceptional resistance to degradation, and thermal stability. However, the catalytic activity and selectivity of such systems are strongly dependent on the size and shape of ceria, making it possible to tune the oxide properties, affecting catalyst design and performance. The rational manipulation of ceria nanostructures offers various features that directly impact steam-reforming transformations, including the possibility of tuning oxygen vacancies, redox properties, and oxygen storage capacity. Thus, the importance of shape control in ceria nanomaterials is highlighted herein, emphasizing how the surface atomic configurations (exposure of different facets) significantly impact their efficiency. Although the main focus of this review is to discuss how the catalyst design may affect the performance of hydrogen production, some other elemental studies are shown, when necessary, to exemplify the level of deepness (or not) that literature has reached. Thus, an overview of ceria properties and how the physicochemical control of nanostructures contributes to their tuning will be presented, as well as a discussion regarding elemental materials design and the most prominent synthetic procedures; then, we select some metals (Ni, Co, and Pt) to discuss the understanding of such aspects for the field. Finally, challenges and perspectives for nanoengineering catalysts based on shape-controlled ceria nanostructures will be described to possibly improve the performance of designed catalysts for steam-reforming reactions. Although there are other literature reviews on ceria-based catalysts for these reactions, they do not specifically focus on the influence of the size and shape of the oxide. Full article

Working towards a more sustainable future with zero emissions, the International Future Laboratory for Hydrogen Economy at the Technical University of Munich (TUM) exhibits concerted efforts across various hydrogen technologies. The current research focuses on pre-reforming processes for high-quality reversible solid oxide cell feedstock preparation. An AI-based machine learning model has been developed, trained, and deployed to predict and optimise the controlled utilisation of methane gas. Using a blend of design of experiments and a validated 3D computational fluid dynamics model, pre-reforming process data have been generated for various syngas mixtures. The results of this study indicate that it is possible to achieve a targeted methane utilisation rate of 20% while decreasing the amount of catalyst material by 11%. Furthermore, it was found that precise process parameters could be determined efficiently and with minimal resource consumption in order to achieve higher methane fuel utilisation rates of 25% and 30%. The machine learning model has been effectively employed to analyse and optimise the fuel outlet conditions of the pre-reforming process, contributing to a better understanding of high-quality syngas preparation and furthering sustainable research efforts for a safe reversible solid oxide cell (r-SOC) process. Full article

Determining how to apply hydrogen as a therapeutic/preventive antioxidant for oxidative-stress-related diseases practically in daily life has not been studied. The effects of bathtubs and buckets filled with hydrogen water (41 °C, >10 min bathing) were investigated on six subjects, without a medical prescription, suffering from skin roughness on the foot, hand, finger, or elbow. They were also treated with an electrolyzer composed of a lattice-shaped, microscopically flat, platinum-plated three-layer electrode, except for one subject who was treated with a micro-porous emittance terminal hydrogen-jetting apparatus, resulting in improvements in both cases. For another subject with similar skin roughness on both hands, immersing the right hand in an electrolytically generated hydrogen water bucket showed more marked improvement than immersing the left hand in a bucket with normal water. The nano-bubbles (average, mode, and median sizes of 157 nm, 136 nm, and 94 nm, respectively) increased 3.79 fold to 2.20 × 10⁸/mL after 30 min electrolysis with 2 L of tap water and were boiling (98 °C, 2 min)-resistant, with heat stability in nano-bubbles as small as 69–101 nm, as evaluated by laser-beam-based Brownian movement trailing Nano-Sight analysis. The marked increase in nano-bubbles caused by electrolysis correlated with an increase in dissolved hydrogen (<15 μg/L to 527 μg/L) but not a decrease in dissolved oxygen (9.45 mg/L to 6.94 mg/L). Thus, the present study proposed the novelty of hydrogen regarding its contribution to health from the perspective that hydrogen-nano-bubble-rich water in a foot bucket, which was additively used together with a conventional bathtub and can be frequently used in daily life, improved diverse types of skin roughness. Full article

Hydrogen represents a promising renewable fuel, and its broad application can lead to drastic reductions in greenhouse gas emissions. Keeping hydrogen in liquid form helps achieve high energy density, but also requires cryogenic conditions for storage as hydrogen evaporates at temperatures of about 20 K, which can lead to a large pressure build-up in the tank. This paper addresses the unsteady thermal modeling of cryogenic tanks with liquid hydrogen. Considering the liquid and vapor phases in the tank as two nodes with averaged properties, a lumped-element method of low computational cost is developed and used for simulating two regimes: self-pressurization (also known as autogenous pressurization, or pressure build-up in the closed tank due to external heat leaks) and constant-pressure venting (when some hydrogen is let out of the tank to maintain pressure at a fixed level). The model compares favorably (within several percent for pressure) to experimental observations for autogenous pressurization in a NASA liquid hydrogen tank. The two processes of interest in this study are numerically investigated in tanks of similar shapes but different sizes ranging from about 2 to 1200 m³. Pressure and temperature growth rates are characterized in closed tanks, where the interfacial mass transfer manifests initial condensation followed by more pronounced evaporation. In tanks where pressure is kept fixed by venting some hydrogen from the vapor domain of the tank, the initial venting rate significantly exceeds evaporation rate, but after a settling period, magnitudes of both rates approach each other and continue evolving at a slower pace. The largest tank demonstrates a six-times-lower pressure rise than the smallest tank over a 100 h period. The relative boil-off losses in continuously vented tanks are found to be approximately proportional to the inverse of the tank diameter, thus generally following simple Galilean scaling with a few percent deviation due to scale effects. The model developed in this work is flexible for analyzing a variety of processes in liquid hydrogen storage systems, raising efficiencies, which is critically important for a future economy based on renewable energy. Full article

In this work, the production of hydrogen from the sodium borohydride (NaBH₄) reaction was studied using an experimental bench test in a passive device operating with or without minimal external energy input. The system consists of a reactor in which a mixture based on sodium borohydride powders and an organic acid is confined. A flow of water feeds the area in which the solid mixture is confined, which undergoes a hydrolysis reaction and this generates gaseous hydrogen. The hydrogen thus produced, already saturated with water vapor, is particularly suitable for feeding polymer electrolyte fuel cells for the production of electricity because it does not require further humidification. The borohydride–organic acid coupling studied for this device, and its chemical process, provides high reaction and conversion kinetics, presenting remarkable chemical stability over time. Full article

The realization of a carbon-neutral civilization, which has been set as a goal for the coming decades, goes directly hand-in-hand with the need for an energy system based on renewable energies (REs). Due to the strong weather-related, daily, and seasonal fluctuations in supply of REs, suitable energy storage devices must be included for such energy systems. For this purpose, an energy system model featuring hybrid energy storage consisting of a hydrogen unit (for long-term storage) and a lithium-ion storage device (for short-term storage) was developed. With a proper design, such a system can ensure a year-round energy supply by using electricity generated by photovoltaics (PVs). In the energy system that was investigated, hydrogen (${\mathrm{H}}_2$) was produced by using an electrolyser (ELY) with a PV surplus during the summer months and then stored in an ${\mathrm{H}}_2$ tank. During the winter, due to the lack of PV power, the ${\mathrm{H}}_2$ is converted back into electricity and heat by a fuel cell (FC). While the components of such a system are expensive, a resource- and cost-efficient layout is important. For this purpose, a Matlab/Simulink model that enabled an energy balance analysis and a component lifetime forecast was developed. With this model, the results of extensive parameter studies allowed an optimized system layout to be created for specific applications. The parameter studies covered different focal points. Several ELY and FC layouts, different load characteristics, different system scales, different weather conditions, and different load levels—especially in winter with variations in heating demand—were investigated. Full article