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We present a quasi-elastic neutron scattering study of liquid deuterium hydride carried out using the Disk Chopper Spectrometer at the National Institute of Standards and Technology. Under saturated vapor pressure, the self-diffusion constant of deuterium hydride obeys an Arrhenius law D = D 0 exp − E A / k B T , where the prefactor D0 is given by D 0 = 9.5 ± 1.2 A ̊ 2 / p s and the activation energy is given by EA = 58 ± 2 K. We apply the quantum law of corresponding states to the known diffusion constants of the hydrogen isotopologues. From this application, we estimate that D 0 ≈ 9.1 A ̊ 2 / p s and EA ≈ 75 K in liquid tritium. Young's theory of quantum-mechanical effects in van der Waals fluids [Young, Phys. Rev. A 23, 1498 (1981)] is shown to apply to the diffusion constants of the liquid hydrogens. Our results underscore the importance of nuclear quantum effects in shaping the properties and behavior of the hydrogen isotopologues. [ABSTRACT FROM AUTHOR]

The reversible hydrogenation/dehydrogenation of aromatic molecules, known as liquid organic hydrogen carriers (LOHCs), is considered an attractive option for the safe storage and release of elemental hydrogen. The LOHC systems based on the alkoxy-naphthalene/alkoxy-decalin studied in this work can become potentially attractive from the point of view of the thermodynamic conditions of the reversible hydrogenation/dehydrogenation processes. This work reports the results of a complex experimental investigation of the thermochemical properties of the reactants of the LOHC systems. The enthalpies of formation were measured using high-precision combustion calorimetry, the enthalpies of vaporization and sublimation were derived from the vapor pressure–temperature dependencies measured using the transpiration method, and the melting temperatures and enthalpies of fusion were measured using the differential scanning calorimetry method. The liquid-phase enthalpies of formation of methoxy- and ethoxy-substituted naphthalenes and methoxy- and ethoxy-substituted decalins were derived and used for the thermodynamic analysis of hydrogenation/dehydrogenation reactions and transferhydrogenation reactions. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) combustion and solid oxide fuel cells (SOFCs) can potentially reduce aviation-produced greenhouse gas emissions compared to kerosene propulsion. This paper outlines a methodology for evaluating performance and emission tradeoffs when retrofitting conventional kerosene-powered aircraft with lower-emissionH2 combustion and SOFC hybrid alternatives. The proposed framework presents a constant-range approach for designing liquid hydrogen fuel tanks, considering insulation, sizing, center of gravity, and power constraints. A lifecycle assessment evaluates greenhouse gas emissions and contrail formation effects for carbon footprint mitigation, while a cost analysis examines retrofit implementation consequences. A Cessna Citation 560XLS+ case study shows a 5% mass decrease for H2 combustion and a 0.4% mass decrease for the SOFC hybrid, at the tradeoff of removing three passengers. The lifecycle analysis of green hydrogen in aviation reveals a significant reduction in CO2 emissions for H2 combustion and SOFC systems, except for natural-gas-produced H2 combustion, when compared to Jet-A fuel. However, this environmental benefit is contrasted by an increase in fuel cost per passenger-km for green H2 combustion and a rise for natural-gas-produced H2 SOFC compared to kerosene. The results suggest that retrofitting aircraft with alternative fuels could lower carbon emissions, noting the economic and passenger capacity tradeoffs.

The energy-intensive nature of hydrogen liquefaction underscores the critical need for efficiency improvements. This study presents an approach to enhance the design and performance of hydrogen heat exchangers by optimizing the cold-to-hot fluid mass flowrate ratios across various temperature ranges, leading to substantial improvements in the Continuous Conversion Proximity Index (CCPI). A dynamic simulation model is developed to explore the complex interactions between temperature distribution, mass flowrate ratio, inlet conversion rate, and the heat transfer and catalytic efficiency in cryogenic hydrogen heat exchangers. Optimal cold-to-hot fluid mass flowrate ratios, ranging from 3.31 to 8.44 across the 80-33 K temperature range, are identified. In particular, a 23.0% improvement in CCPI is observed in the 40-33 K range, significantly optimizing the continuous catalytic conversion process. The results show that inlet conversion rates between 96% and 94% ensure effective heat transfer and high ortho-para hydrogen conversion efficiency, whereas rates below 94% lead to rapid conversion but insufficient cooling. These findings provide a theoretical foundation for the design of highly efficient hydrogen heat exchangers and demonstrate that optimizing the mass flowrate ratio can enhance the process within the exchanger, bringing it closer to an ideal continuous conversion form. [Display omitted] • The CCPI index is introduced to evaluate deviation from ideal continuous conversion. • The optimal fluid flowrate ratios across various temperature ranges are determined. • The dynamic model reveals the impact of inlet conversion rates on heat transfer efficiency. • A 23% increase in CCPI is achieved with optimal flowrate in the 40-33 K temperature range. • The validated model supports improved design of cryogenic hydrogen heat exchangers. [ABSTRACT FROM AUTHOR]

In this study, the dispersion and explosion of liquid hydrogen (LH 2) in leakage accidents are investigated using the Flame Accelerator Simulator (FLACS) code. The study focus was a liquid hydrogen research facility in Gimhae, South Korea. Simulations were conducted under various conditions by varying the mass flow rates (0.61 and 0.3 kg/s), directions (lateral in areas with minimal structures, lateral towards a tube trailer truck, and downward), and durations (90 and 180 s) of leakage. The results indicated that higher leakage mass flow rates produce a larger flammable cloud volume (FCV), resulting in higher maximum overpressures than that caused by lower flow rates. Downward leakage generally resulted in a larger FCV and higher overpressure than lateral leakage. The explosion characteristics were also influenced by geometry of LH 2 facility, including the presence of structures in the leakage path. Contrastingly, leakage duration had a minimal effect on the maximum overpressure because an increased duration causes a greater dilution of hydrogen, only slightly expanding the FCV. According to the overpressure–impulse diagram, higher leakage flow rates cause severe health risks, approaching thresholds for lung rupture and 100% fatality. Contrary to the minor damages caused by lower leakage flow rates. High flow rates, particularly with downward leaks, can cause significant structural damage in brick buildings, potentially leading to partial demolition. • Higher leakage mass flow rates result in larger flammable cloud volumes and increased maximum overpressures. • Downward hydrogen leaks lead to larger flammable clouds and higher overpressures than lateral leaks. • Facility geometry and structures significantly affect explosion overpressure magnitude and distribution. • Leakage duration has a minimal effect on maximum overpressure due to hydrogen dilution during leakage. [ABSTRACT FROM AUTHOR]

The transition from traditional aviation fuels to low-emission alternatives such as hydrogen is a crucial step towards a sustainable future for aviation. Conventional jet fuels substantially contribute to greenhouse gas emissions and climate change. Hydrogen fuel, especially "green" hydrogen, offers great potential for achieving full sustainability in aviation. Hybrid/electric/fuel cell technologies may be used for shorter flights, while long-range aircraft are more likely to combust hydrogen in gas turbines. Liquid hydrogen is necessary to minimize storage tank weight, but the required fuel systems are at a low technology readiness level and differ significantly from Jet A-1 systems in architecture, operation, and performance. This paper provides an in-depth review covering the development of liquid hydrogen fuel system design concepts for gas turbines since the 1950s, compares insights from key projects such as NASA studies and ENABLEH2, alongside an analysis of recent publications and patent applications, and identifies the technological advancements required for achieving zero-emission targets through hydrogen-fuelled propulsion. [Display omitted] • Review the evolution and advancements in liquid hydrogen gas turbine fuel systems. • Compare different liquid hydrogen fuel systems for aviation and aerospace applications. • Analyze 11 relevant reports/projects and 15 patents on liquid hydrogen fuel systems. • Identification of the key technical challenges to adopting liquid hydrogen as a fuel. • Potential solutions to address the challenges for next-generation aero engines. [ABSTRACT FROM AUTHOR]

A typical feature that the LOHC technology shares with other types of chemical hydrogen storage is that the release of hydrogen from the carrier requires an input of heat. In many use cases where waste heat from external sources is not available (e.g. in heavy-duty mobility), this is seen as a major drawback. In this paper, we show that autothermal LOHC dehydrogenation offers a very attractive way to overcome this drawback. In detail, we demonstrate autothermal hydrogen release from dicyclohexylmethane using diphenylmethane oxidation to benzophenone as source of heat. The full storage cycle involves benzophenone hydrodeoxygenation to dicyclohexylmethane, dicyclohexylmethane dehydrogenation to diphenylmethane, and diphenylmethane oxidation to benzophenone. We studied both the individual reaction steps using pure feedstocks and the integral cycle in which the intermediates and by-products of each reaction remain in the system for the subsequent reaction step. Although no efforts have yet been made to develop special catalyst materials for this purpose, the results with the applied commercial hydrodeoxygenation (Pd/C), dehydrogenation (Pt on alumina) and partial oxidation (VO x /TiO 2) catalysts are already very promising. The storage cycle can be closed with high selectivity and with only minor total oxidation losses. The proposed concept of autothermal LOHC dehydrogenation offers the potential to increase the amount of useable hydrogen from a given amount of charged hydrogen carrier by up to 30%. • Autothermal dehydrogenation enables chemical hydrogen storage without external heat. • Dehydrogenation heat is provided through partial oxidation of the hydrogen carrier. • Regeneration takes place through hydrodeoxygenation at energy-rich locations. • Individual reaction steps and influencing parameters have been studied. • Full autothermal hydrogen storage cycle demonstrated for model system. [ABSTRACT FROM AUTHOR]

Axial liquid hydrogen pumps, essential for aerospace and energy sectors, offer high efficiency and reliability at extremely low temperatures. The significance of the tip clearance flow of axial liquid hydrogen pumps, in its interaction with the main flow, wall boundary layer, and wake flow, is paramount in determining the overall stability of the system. This study looked into the characteristics of axial liquid hydrogen pumps' tip leakage using numerical modeling methods. Regarding the leakage characteristics of hydrofoils (as a simplified form of pump blade), the predictive capabilities of three turbulence models—Shear Stress Transport (SST) k-ω , Stress-Blended Eddy Simulation (SBES), and Large Eddy Simulation (LES)—were compared. In terms of predicting the location of downstream tip leakage vortices, both the SBES and LES models align relatively well with experimental data. While the SST k-ω model offers computational efficiency, the SBES model demonstrates higher accuracy in predicting the velocity field near the core of the leakage vortex flow field, combining both efficiency and accuracy advantages. For the research on the pumps, with increasing flow rates, the leaky vortex's strength and effect range gradually decreased, and the vorticity value in the core region also decreased. This shift shows that as the flow rate increases, the leakage vortex becomes more stable. Additionally, the investigation was conducted on the pressure fluctuations on the blade surface. Under design conditions, the pressure fluctuations exhibited periodic changes, with their frequency primarily determined by the rotation frequency of the impeller. By establishing monitoring points on the blade surface, the study found that the amplitude of pressure fluctuations near the leading edge increased with increasing flow rates, whereas decreased at the suction and pressure sides. Under low flow conditions, due to the large amount of leakage and the poor stability of the leakage vortex, the pressure fluctuations on the back of the blade were more significant. This work offers theoretical assistance and technological direction for understanding and predicting the leakage characteristics and blade pressure fluctuations of axial liquid hydrogen pumps. [Display omitted] • Advanced turbulence model applied to axial liquid hydrogen pumps for precise tip leakage vortex analysis, enhancing performance prediction. • Unveiled the evolution law of leakage vortices in axial pumps, enabling more effective vortex control strategies for hydrogen pump systems. • Discovered how pressure pulsations affect leakage vortex stability in axial pumps, providing new insights for hydrogen pump optimization. [ABSTRACT FROM AUTHOR]

Liquid hydrogen plays a critical role in large-scale hydrogen storage and long-distance transport. The primary cost associated with liquid hydrogen supply is attributed to the liquefaction consumption. The hydrogen turbo-expander, a pivotal component in industrial hydrogen liquefaction plants, is instrumental in determining liquefaction costs. Improving the efficiency of the expander offers a significant opportunity for cost reduction. This paper commences by validating the loss model employed to assess the hydrogen turbo-expander using numerical simulation results. Subsequently, a regional division model is introduced for the expander impeller passage to identify the locations of various losses. Under diverse operational conditions, the boundaries of regions are determined through a comparison between the loss model and numerical simulation. Finally, an examination of losses in the hydrogen turbo-expander is conducted using Computational Fluid Dynamics (CFD) results under varying operating conditions, yielding the following insights. With an increase in the expansion ratio of the hydrogen turbo-expander, the isentropic efficiency initially rises and then declines. Among the various losses observed under variable working conditions, incidence loss emerges as the most critical factor. When the expansion ratio is small, a negative attack angle forms at the impeller inlet, causing chaotic flow within the channel and an increase in passage loss. • Correlations in loss model are validated for hydrogen turbo-expanders. • The proposed regional division model enables a quantitative loss analysis. • Efficiency decays more severely with the expansion ratio lower than design value. • Incidence loss is the primary driver for efficiency decline far from design condition. [ABSTRACT FROM AUTHOR]

The energy consumption of hydrogen liquefaction is often quantified as being approximately 40 % of hydrogen's lower heating value (LHV), making hydrogen liquefaction energy-intensive. Boundary conditions for energy consumption values in the literature are, however, often unclear, rendering these values questionable. Two methods can nevertheless significantly decrease energy consumption: (1) implementing improved liquefiers; and (2) utilising liquid hydrogen exergy – the reversible liquefaction work – stored in the liquid. Liquid hydrogen exergy equals 11.5 % LHV. And in comparison: per energy content, liquid hydrogen exergy is 5.5 times liquefied natural gas exergy. To estimate the energy savings potential of combining liquefier improvements and exergy utilisation, the exergy efficiency of improved liquefiers is calculated (44 %) and used as a quality measure. The same efficiency is assumed for exergy utilisation processes. The net energy consumption for the liquefaction - regasification chain is thereby reduced to 13-26 % LHV, depending on boundary conditions. • The H 2 liquefaction-regasification chain is evaluated by exergy analyses. • LH 2 exergy is 11.5 % of H 2 's lower heating value (LHV H 2 ), LNG exergy is 2.1 % of LHV CH 4 . • Improved H 2 liquefiers achieve 44 % exergy efficiency. • LH 2 exergy recovery during regasification estimated with liquefier exergy efficiency. • Energy consumption of H 2 liquefaction-regasification chain reducible to 13-26 % LHV H 2 . [ABSTRACT FROM AUTHOR]

In order to effectively improve the cold energy recovery efficiency and thermodynamic performance of liquid hydrogen regasification process, a novel type of liquid hydrogen cold energy cascade utilization (RC-HT-AS-DI-CS-AC) system is proposed, which includes Rankine cycle power generation (RC), hydrogen turbine power generation (HT), air separation (AS), production of dry ice (DI), cold storage (CS) and air conditioning (AC). A comprehensive energy, exergy and economic analysis is carried out to compare the proposed system with a comparison system scheme (CSS). For RC-HT-AS-DI-CS-AC system, the energy efficiency of overall system is 79.74%. The cold energy provided by the hydrogen stream achieve 182.31 kW, which is 61.18% increase compared with the CSS. The acquired exergy and exergy efficiency of the RC-HT-AS-DI-CS-AC system increase by 119.6% and 115.9% compared with the CSS. It reveals the importance of liquid hydrogen pressurization to improve exergy efficiency for overall system. However, in the economic analysis, the total annual cost (TAC) of the system of RC-HT-AS-DI-CS-AC system is 278,400 US $, which is significantly higher than TAC of CSS. As a result, the IRR of CSS and RC-HT-AS-DI-CS-AC systems are 87.39% and 15.10% respectively. Therefore, from a commercial point of view, CSS is more worthy of industrialization. [ABSTRACT FROM AUTHOR]

Cryogenic liquids such as liquid oxygen and liquid hydrogen are extensively used in many processes and manufacturing industries. In these industries, transferring cryogens via pipelines is a routine phenomenon. As the boiling points and latent heat of cryogens are low, excessive vaporization of these cryogens is innate. Therefore, ensuring that the cryogen reaches the utility in its liquid form is challenging. In the case of liquid hydrogen and liquid helium, the pipelines are jacketed with a high boiling cryogen like nitrogen. The idea is to dump most of the heat into cheap nitrogen to limit the loss of precious hydrogen or helium. From a heat inleak point, maximizing the amount of nitrogen in the jacket is advantageous by choosing large cross‐sectional areas. Also, larger flow cross sections would lower pressure drops and, therefore, lower pumping costs. However, such a choice would add to the mass of the pipeline. An increase in the mass of the pipeline increases the need for better structural support of the pipeline assembly. Therefore, the design of cryogen jackets for limiting heat inleak is a multi‐objective optimization problem. In this work, we model the heat leak into the hydrogen via the nitrogen jacket and the pressure drop of liquid nitrogen, and we find the mass of the pipeline assembly. Then, we optimize the design of nitrogen jackets fitted over hydrogen pipelines. We employ the evolutionary optimization technique, genetic algorithm (GA), to perform this optimization.cryogen; genetic algorithm; heat inleak; liquid hydrogen; optimization. [ABSTRACT FROM AUTHOR]

In this paper, an analytical model of an Unmanned Aerial Vehicle (UAV) propulsion system using liquid hydrogen to supply a fuel cell is presented. The article also describes experimental tests of the performance of a liquid hydrogen (LH 2) tank at different ambient temperatures and ground tests of the UAV propulsion system using LH 2. These tests were used to validate and calibrate the analytical model. The model is of reduced order and is based on the literature. Despite the simplicity of the model, the tank Boil-Off Gas (BOG) rate and pressure drop, the time for complete evaporation of LH 2 , the fuel cell performance, and the coolest temperature that the hydrogen can reach, were predicted with deviations not exceeding 0.3%, 0.5%, 2.2%, 0.6%, and 0.5% respectively. The final proposed model allows the incorporation of different conditions, materials, and geometries to suit each mission, all at low operational cost. • Analytical modeling of a UAV liquid hydrogen propulsion set. • Experimental data on liquid hydrogen tank and propulsion chain are presented. • Customization of conditions, materials, and geometries at a low operational cost. • Boil-off gas and pressure drop predicted with deviations below 0.3% and 0.55%. [ABSTRACT FROM AUTHOR]

This study proposes a pathway to improve the efficiency of the hydrogen liquefaction process by including single-phase turboexpanders in the final hydrogen expansion. A sensitivity study compares three configurations. All three expansions have the same inlet and outlet pressures, while the inlet temperature is the same for Cases A and C but not for Case B. Case A is a standard isenthalpic expansion using a Joule-Thomson valve. Case B uses a fully wet turboexpander which expands on the liquid side of the two-phase curve and hence requires more cooling prior to the expansion. Case C is a compromise where the single-phase expansion is done by a turboexpander and the two-phase expansion by a Joule-Thomson valve. For the WE-NET configuration analysed (and a 50-bar top pressure), Case C has an increase in yield of 13.3% points and in exergetic efficiency of 4.6% points, compared to the baseline (Case A). • Proposal of new expansion configurations to increase hydrogen liquefaction efficiency. • Three final hydrogen expansion configurations are compared. • Single-phase turboexpander and Joule-Thomson valve in series beneficial. • This new configuration increases both yield and exergetic efficiency. [ABSTRACT FROM AUTHOR]

The increasing demands for cryogenic liquid fuels pose serious challenges to storage and transportation technology. Hydrogen leakage occurs in cryogenic liquid storage tanks since hydrogen molecules can slowly diffuse through microscopic pores, which greatly weakens the performance of vacuum insulation layer. Various materials with high adsorption capacity have been developed to inhibit this phenomenon while few research focuses on the working performance inside tanks, which leads to the excessive dosage of adsorbents. This work aims to analyze the adsorption performance and economic benefits of hydrogen adsorbents in liquid hydrogen (LH) and liquid natural gas (LNG) tank, respectively. The results indicate that silver molecular sieve (SMS) is a cost-effective adsorbent in the long-term cryogenic liquid storage. LNG tank needs more ambient temperature adsorbents to maintain a similar performance to LH tank. For a 250 m3 LH tank, the optimal mass by using SMS ranges from 700 g to 800 g while a dosage of 900–1000 g is the best for a 250 m3 LNG tank. The excessive use of hydrogen adsorbents can't effectively improve the performance of cryogenic liquid storage tanks. These research findings may help the future vacuum maintenance in cryogenic liquid storage tanks. • Influence of different adsorbents on thermal insulation performance of tank is revealed. • Cost-effectiveness of SMS is verified by digital standards. • Adsorption performance of SMS in tank and its effect on tank are obtained. • The optimal dosages of SMS for 250 m3 LH and LNG tank are 800 g and 1000 g. [ABSTRACT FROM AUTHOR]

Liquid organic hydrogen carrier (LOHC) is a hydrogen storage and release technology of growing interest due to its excellent properties. Dibenzyltoluene is one of the best performing organic liquids for this purpose. In this work, we investigate the dehydrogenation reaction of perhydro-dibenzyltoluene (18H-DBT) in a batch reactor using Pt/Al 2 O 3 catalysts. The best catalytic results were obtained at 290 °C with the catalyst featuring lower Pt loading and higher dispersion, achieving a degree of dehydrogenation (DoD) of 88%. After 45 h of catalytic operation, the degree of dehydrogenation dropped by about 35%. The generation of by-products and physical changes in the Pt sites could be potential causes of the observed catalytic degradation. A cleaning treatment was carried out to restore the initial DoD, but only the productivity was improved, leading to a reduction in reaction times. The authors of the paper entitled Activity and degradation of Pt/Al2O3 catalyst assessment in hydrogen release from perhydro-dibenzyltoluene suggests the following highlights: • Hydrogen release increased with increasing temperature. • 0.5 wt % Pt/Al 2 O 3 reported higher catalytic efficiency than 1 wt % Pt/Al 2 O 3. • The catalysts showed a high catalytic efficiency after 45 h of operation. • Cleaning of the catalyst reduced the reaction times. • The generation of by-products and changes in the Pt centres lead to catalytic deactivation. [ABSTRACT FROM AUTHOR]

Hydrogen technologies will be necessary to decarbonize heavy-duty transportation, such as Class 8 trucks. While there have already been multiple successful hydrogen truck pilots, and multiple on-going commercial operations in Europe, there are still major challenges that can limit further deployment. The on-board storage technology utilized today, 700 bar Type 4 vessels, does not provide sufficient energy density to meet the demands of many truck fleet operators. One potential solution is on-board cryo-compressed hydrogen storage, which can offer greater energy densities, reduced storage cost, and help achieve diesel-like performance. Herein, we evaluate cryo-compressed hydrogen Class 8 trucks under a representative commercial operating profile. The thermodynamic evolution of state is evaluated, and key system design changes and their performance impact are detailed. We show useable hydrogen densities of 67 g/L, with no vent losses over the weekend, and a driving range of 1200 km (746 miles). We conclude with a comparison against 700 bar and liquid hydrogen storage technologies. Ultimately, this work provides a foundational framework to compare various hydrogen technologies for the heavy-duty truck market. • H 2 -fueled heavy trucks are necessary for mitigating climate change. • Cryo-compressed H 2 (CcH 2) holds promise for cost effective, long range heavy trucks. • CcH 2 weight and volume storage performance is similar to LH 2 and sLH 2 vessels. • Zero evaporative losses are anticipated due to robust thermal endurance. [ABSTRACT FROM AUTHOR]

Background: The issue of renewable energy (RE) source intermittency, such as wind and solar, along with the geographically uneven distribution of the global RE potential, makes it imperative to establish an energy transport medium to balance the energy demand and supply areas. A promising energy vector to address this situation is hydrogen, which is considered a clean energy carrier for various mobile and portable applications. Unfortunately, at standard pressure and temperature, its energy content per volume is very low (0.01 kJ/L). This necessitates alternative storage technologies to achieve reasonable capacities and enable economically viable long-distance transportation. Among the hydrogen storage technologies using chemical methods, liquid organic hydrogen carrier (LOHC) systems are considered a promising solution. They can be easily managed under ambient conditions, the H2 storage/release processes are carbon-free, and the carrier liquid is reusable. However, the evolution of the proposals from the carrier liquid type and catalyst elemental composition point of view is scarcely studied, considering that both are critical in the performance of the system (operational parameters, kinetic of the reactions, gravimetric hydrogen content, and others) and impact in the final cost of the technology deployed. The latter is due to the use of the Pt group elements (PGEs) in the catalyst that, for example, have a high demand in the hydrogen production sector, particularly for polymer electrolyte membrane (PEM) water electrolysis. With that in mind, our objective was to examine the evolution and the focus of the research in recent years related to proposals of LOHCs and catalysts for hydrogenation and dehydrogenation reactions in LOHC systems which can be useful in defining routes/strategies for new participants interested in becoming involved in the development of this technology. Data sources: For this systematic review, we searched the SCOPUS database and forward and backward citations for studies published in the database between January 2011 and December 2022. Eligibility criteria: The criteria include articles which assessed or studied the effect of the type of catalyst, type of organic liquid, reactor design(s)/configuration(s), and modification of the reactor operational parameters, among others, over the performance of the LOHC system (de/hydrogenation reaction(s)). Data extraction and analysis: The relevant data from each reviewed study were collected and organized into a pre-designed table on an Excel spreadsheet, categorized by reference, year, carrier organic liquid, reaction (hydrogenation and/or dehydrogenation), investigated catalyst, and primary catalyst element. For processing the data obtained from the selected scientific publications, the data analysis software Orbit Intellixir was employed. Results: For the study, 233 studies were included. For the liquid carrier side, benzyltoluene and carbazole dominate the research strategies. Meanwhile, platinum (Pt) and palladium (Pd) are the most employed catalysts for dehydrogenation reactions, while ruthenium (Ru) is preferred for hydrogenation reactions. Conclusions: From the investigated liquid carrier, those based on benzyltoluene and carbazole together account for over 50% of the total scientific publications. Proposals based on indole, biphenyl, cyclohexane, and cyclohexyl could be considered to be emerging within the time considered in this review, and, therefore, should be monitored for their evolution. A great activity was detected in the development of catalysts oriented toward the dehydrogenation reaction, because this reaction requires high temperatures and presents slow H2 release kinetics, conditioning the success of the implementation of the technology. Finally, from the perspective of the catalyst composition (monometallic and/or bimetallic), it was identified that, for the dehydrogenation reaction, the most used elements are platinum (Pt) and palladium (Pd), while, for the hydrogenation reaction, ruthenium (Ru) widely leads its use in the different catalyst designs. Therefore, the near-term initiatives driving progress in this field are expected to focus on the development of new or improved catalysts for the dehydrogenation reaction of organic liquids based on benzyltoluene and carbazole. [ABSTRACT FROM AUTHOR]

Hydrogen is a clean-burning fuel with water as its only by-product, yet its widespread adoption is hampered by logistical challenges. Liquid organic hydrogen carriers, such as alcohols from sustainable sources, can be converted to hydrogen through aqueous-phase reforming (APR), a promising technology that bypasses the energy-intensive vaporization of feedstocks. However, the hydrothermal conditions of APR pose significant challenges to catalyst stability, which is crucial for its industrial deployment. This review focuses on the stability of catalysts in APR, particularly in sustaining hydrogen production over extended durations or multiple reaction cycles. Additionally, we explore the potential of ultrasound-assisted APR, where sonolysis enables hydrogen production without external heating. Although the technological readiness of ultrasound-assisted or -induced APR currently trails behind thermal APR, the development of catalysts optimized for ultrasound use may unlock new possibilities in the efficient hydrogen production from alcohols. [ABSTRACT FROM AUTHOR]

As an important energy source to achieve carbon neutrality, green hydrogen has always faced the problems of high use cost and unsatisfactory environmental benefits due to its remote production areas. Therefore, a liquid-gaseous cascade green hydrogen delivery scheme is proposed in this article. In this scheme, green hydrogen is liquefied into high-density and low-pressure liquid hydrogen to enable the transport of large quantities of green hydrogen over long distances. After long-distance transport, the liquid hydrogen is stored and then gasified at transfer stations and converted into high-pressure hydrogen for distribution to the nearby hydrogen facilities in cities. In addition, this study conducted a detailed model evaluation of the scheme around the actual case of hydrogen energy demand in Chengdu City in China and compared it with conventional hydrogen delivery methods. The results show that the unit hydrogen cost of the liquid-gaseous cascade green hydrogen delivery scheme is only 51.58 CNY/kgH2, and the dynamic payback periods of long- and short-distance transportation stages are 13.61 years and 7.02 years, respectively. In terms of carbon emissions, this scheme only generates indirect carbon emissions of 2.98 kgCO2/kgH2 without using utility electricity. In sum, both the economic and carbon emission analyses demonstrate the advantages of the liquid-gaseous cascade green hydrogen delivery scheme. With further reductions in electricity prices and liquefication costs, this scheme has the potential to provide an economically/environmentally superior solution for future large-scale green hydrogen applications. [ABSTRACT FROM AUTHOR]

Though being attractive on railway decarbonisation for regional lines, excessive cost caused by immature hydrogen supply chain is one of the significant hurdles for promoting hydrogen traction to rolling stocks. Therefore, we conduct bespoke research on the UK's hydrogen supply chain for railway, concentrating on hydrogen transportation. Firstly, a map for the planned hydrogen production plants and potential hydrogen lines is developed with the location, capacity, and usage. A spatially explicit model for the hydrogen supply chain is then introduced, which optimises the existing grid-based methodology on accuracy and applicability. Compressed hydrogen at three pressures, and liquid hydrogen are considered as the mediums, incorporating by road and rail transport. Furthermore, three scenarios for hydrogen rail penetration are simulated respectively to discuss the levelised cost and the most suitable national transport network. The results show that the developed model with mix-integer linear programming (MILP) can well design the UK's hydrogen distribution for railway traction. Moreover, the hydrogen transport medium and vehicle should adjust to suit for different era where the penetration of hydrogen traction varies. The levelised cost of hydrogen (LCOH) decreases from 6.13 £/kg to 5.13 £/kg on average from the conservative scenario to the radical scenario. Applying different transport combinations according to the specific situation can satisfy the demand while reducing cost for multi-supplier and multi-targeting hydrogen transport. • A spatially explicit model with MILP for the UK's railway-bespoke hydrogen supply chain. • Scenarios on different penetration for UK's hydrogen railway to 2050. • Comprehensive and reliable data support for the entire supply chain. • Multi-supplier and multi-targeting hydrogen transport with various transportation technologies. • Satisfying demand while reducing LCOH with the developed hydrogen distribution model. [ABSTRACT FROM AUTHOR]

This work is aimed at a comprehensive solution to the problem of reliable and safe operation of a transport energy system with a high energy concentration based on a universal energy carrier - cryogenic liquid hydrogen. The article discusses the possibility of using various methods and techniques to assess the reliability of machines and equipment operated in emergency situations and extreme conditions. The obtained results are analyzed. Currently, the oil and gas complex pays great attention to the development of hydrogen technologies, as well as hydrogen energy in connection with the relevance of the Climate Agenda. In this regard, hydrogen energy facilities are of the greatest interest: cryogenic hydrogen reservoirs, cryogenic hydrogen pipelines, cryogenic oxygen reservoirs and cryogenic oxygen pipelines, as well as cryogenic reservoirs and pipelines for storing process nitrogen gas. An important role for global energy exchange is played by LH 2 tankers for transporting cryogenic hydrogen. For example, Australia and Japan built the first LH 2 tanker to transport hydrogen from Australia to Japan. In addition, another 85 LH 2 tankers are expected to be built. After transportation, cryogenic hydrogen is stored in cryogenic hydrogen storages, usually also representing cryogenic hydrogen tanks with piping in the form of cryogenic pipelines, as well as cryogenic nitrogen tanks for storing process nitrogen gas. Further, hydrogen is used in road transport, aviation, ship fleet, industry, and energy. The main elements of mobile, stationary and airborne hydrogen storage systems are under critical loads and are in the area of increased study and attention. In this regard, we considered the functions of changing the main operational characteristics, made proposals on the possibility of predicting the development of accumulated faults and proposals for ensuring safety and extending the life of objects, taking into account the determination of local and integral damage to cryogenic tanks and pipelines. Project for the creation of a main cryogenic hydrogen pipeline from Azerbaijan to Europe across the Adriatic Sea. [Display omitted] [ABSTRACT FROM AUTHOR]

Producing liquid hydrogen (LH 2) is an energy-intensive process as 30% of the LH 2 energy is consumed during liquefaction in the existing commercial plants. Thus, numerous innovative liquefaction processes were proposed to achieve a significant reduction in the specific energy consumption (SEC) of the LH 2 production systems. In particular, single-mixed refrigerant (SMR) and dual-mixed refrigerant (DMR) hydrogen precooling processes were introduced as efficient alternatives for conventional precooling processes. However, the SEC of the SMR is still high (>2 kWh/kg H2) and lacks efficient and practical optimization. On the other hand, the DMR demonstrates efficient operation (SEC close to 1.0 kWh/kg H2) but with a more complex configuration and higher capital cost. To address these gaps, this study (i) presents a new dual-pressure SMR precooling process (DP-SMR) that combines the simplicity of the SMR process and efficient operation of the DMR process, (ii) proposes a new optimization method for the cryogenic process with systematic implementation on the SMR, DMR, and the proposed DP-SMR processes, and (iii) conducts systematic thermoeconomic assessment for the optimized cases of the precooling processes. The proposed optimization method integrates knowledge-based optimization (KBO) procedures with other efficient optimization algorithms including genetic algorithm optimization (GAO), particle swarm optimization (PSO), and Bayesian optimization (BO). This method fosters the optimization process and ensures the achievement of optimal performance that satisfies all design constraints without performing penalty functions. The results show that the SEC of the proposed DP-SMR process is 1.29 kWh/kg H2 , which is 6%–10% lower than all SMR processes available in the literature. In addition, the levelized precooling cost of the DP-SMR process is 2.15% and 16.00% lower than that of the optimized DMR and SMR processes, respectively. The proposed optimization procedures in this study will facilitate the achievement of robust optimization performance for any cryogenic process including hydrogen, nitrogen, and natural gas liquefaction systems. • A new dual-pressure single mixed-refrigerant hydrogen precooling process is proposed. • A new optimization method for the cryogenic process is introduced. • Systematic thermoeconomic analysis for three H2 precooling processes is conducted. • The energy consumption of the proposed process is reduced by 10%. • The H 2 precooling cost is reduced by 16% compared to conventional SMR processes. [ABSTRACT FROM AUTHOR]

Liquid hydrogen (LH 2) is a promising and economical clean energy for achieving global carbon neutrality. Multi-layer insulation (MLI) with high performance is essential for the safe storage and operation of LH 2. To perform a better optimization of MLI, the second law of thermodynamics becomes a complement to the first law of thermodynamics. However, very few studies have carried out the optimization of MLI performance through the second law of thermodynamics. For the sake of achieving more efficient optimization of MLI as well as revealing the fundamental indicators limiting the performance of MLI, this paper analyzes the characteristics of entropy generation produced by the solid heat conduction, thermal radiation, and residual gas conduction distributed in the MLI schemes by a validated layer-by-layer model. For a 40-layer MLI arranged with a constant layer density of 20 layers/cm, the first 15 layers near the cold boundary occupy more than 98% of the total entropy generation, providing an effective range of layers for thermodynamic optimization. Besides, an optimization of variable-density MLI (VDMLI) separated into two segments based on the entropy generation minimization is conducted. The optimal VDMLI has substantially lowered the entropy generation from the solid heat conduction but at the cost of increasing the entropy generation from radiation and residual gas conduction. This study provides a reliable optimization method of MLI, which allows the safe storage of clean energy with a low boiling temperature. • A modified layer-by-layer model is built for entropy generation analysis. • Characteristics of entropy generation distributed in MLI are investigated. • Effect of layer density on components of entropy generation is detailed discussed. • Optimization of 2-segment VDMLI upon entropy generation minimization is conducted. [ABSTRACT FROM AUTHOR]

Adopting experience and best practices for stimulating the development of RES in individual regions that most successfully implement RES-based installations into their energy balance is a necessary element in the development of the energy sector of disadvantaged regions, while a methodology is needed to determine what factors influenced the success of implementation and what criteria should be used to compare and to determine the success of the implementation of RES in the region, however, a generally accepted methodology has not been formed to date. It was proposed to determine the leading regions and disadvantaged regions from the point of view of success in introducing renewable energy sources into the regional energy system based on the success of fulfilling the regional demand. To assess the success of the use and implementation of installations based on renewable energy in the regional energy system, it is necessary to identify parameters that reflect the potential of renewable energy sources, the initial state of energy supply in the region, the costs of construction of the installation, the profit received from the sale of generated energy, and the current state of the regional energy system. Based on the developed technique, the six most energy-intensive regions included in the operating area of the Southern Branch of United Dispatch Control Center of Russian Power System Operator which have renewable energy power plants were analyzed. The chosen indicator was the share of energy resources generated from renewable energy sources in the total amount of energy resources. Based on the results of the analysis, recommendations were drawn for disadvantaged regions. Energy donation for disadvantaged areas is proposed through the production of a universal energy carrier - hydrogen - in prosperous areas. For energy storage, hydrogen cryogenic storage facilities have been considered promising. The standard cryogenic hydrogen tank RSV-1400 was adopted as part of the main element of the hydrogen storage facility. The capacity of such tanks is 1 000 000 L. To transport energy to consumers, the possibilities of transporting hydrogen by cryogenic tankers and hydrogen transport tanks have been considered. In addition, at present there is a fairly large scientific, technical and practical base for the creation of gas and cryogenic liquid hydrogen pipelines. [ABSTRACT FROM AUTHOR]

Hydrogen is in the spotlight in the energy world, and it will remain so. In Europe, the necessity to integrate ever-growing amounts of Renewable Energy Sources (RES) in order to implement the ambitious European decarbonization policy (package Fit-for-55) and to preserve the security of energy supply (package Repower-EU) are feeding the interest in hydrogen. This paper will provide a thorough analysis of prospects and criticalities for the development of hydrogen both as a carrier and as a feedstock and, definitively, as a key element for the implementation of the European decarbonization policies. First, the present regulatory framework will be highlighted, taking the European Union as a main reference, since it presently has one of the most advanced hydrogen legislations in the world. Then, both hydrogen offer (technologies) and demand (both as a feedstock and as an energy carrier) will be dealt with in detail. Two additional sections will take care to illustrate, respectively, the interactions between hydrogen and the electricity grid and the issues related to the creation of a liquid hydrogen market. Finally, a conclusion section will wrap up and summarize the most urgent issues to be tackled to create a well-functioning hydrogen economy. [ABSTRACT FROM AUTHOR]

Cyclohexane is a high-valued chemical rece1vmg significant interest in liquid hydrogen storage technology. TiO2-based catalysts show high performance in the photocatalytic dehydrogenation of cyclohexane under mild conditions, but the detailed reaction mechanism is not well understood. With the surface science approaches, we have studied the adsorption and surface chemistry of cyclohexane on rutile TiO2(110). The thermal desorption spectroscopy and X-ray photoelectron spectroscopy results both demonstrate the molecular adsorption of cyclohexane on rutile TiO2(110). Upon the UV Hg light irradiation, photodesorption of cyclohexane occurs from both the chemisorbed monolayer and the multilayer. No decomposition nor dehydrogenation of cyclohexane occurs on rutile TiO2(110). These results deepen the fundamental understanding of the surface chemistry of cyclohexane on the TiO2 surface. [ABSTRACT FROM AUTHOR]

While hydrogen is regularly discussed as a possible option for storing regenerative energies, its low minimum ignition energy and broad range of explosive concentrations pose safety challenges regarding hydrogen storage, and there are also challenges related to hydrogen production and transport and at the point of use. A risk assessment of the whole hydrogen energy system is necessary to develop hydrogen utilization further. Here, we concentrate on the most important hydrogen storage technologies, especially high-pressure storage, liquid hydrogen in cryogenic tanks, methanol storage, and salt cavern storage. This review aims to study the most recent research results related to these storage techniques by describing typical sensors and explosion protection measures, thus allowing for a risk assessment of hydrogen storage through these technologies. [ABSTRACT FROM AUTHOR]

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This paper examines the atomization characteristics of liquid hydrogen fuel in a premixing tube under different operating conditions. Hydrogen fuel's unique injection morphology and atomization behavior were analyzed using the Volume of Fluid-to-Discrete Particle Model (VOF to DPM) approach, coupled with the SST k − ω turbulence model and adaptive mesh refinement. The study revealed that the breakup and transformation of liquid surfaces into particles are significantly impacted by varying air velocities and injection pressure. Specifically, higher air velocities caused the liquid sheet to lengthen and narrow due to intensified vortices. However, the breakup was delayed at higher velocities, occurring at distances of 0.037 m and 0.043 m for air velocities of 10 m/s and 20 m/s, respectively. The research also highlights the significant role that injection pressure plays in fluid sheet breakup. Higher pressures promote better atomization and fuel–lair mixing, resulting in more particles with increased diameters. Notably, the fluid sheet exhibited a small angle of about 43.79° when using the velocity component corresponding to p1 = 0.5 MPa. Similarly, for p2 = 1 MPa and p3 = 2 MPa, the angles were measured to be approximately 47.5° and 49.5°, respectively. Additionally, the study observed that the injection expands in length and diameter as time progresses, indicating fuel dispersion. These insights have significant implications for the design principles of injectors in power generation technologies that utilize liquid hydrogen fuel. [ABSTRACT FROM AUTHOR]

Hydrogen, as a sustainable fuel for transportation sector as well as some other heavy industries, should be stored or transferred in liquid phase. To prevent the evaporation of hydrogen in the tanks and the consequent hazards, it is common to lower its temperature below the saturation point known as subcooling of the fluid. When the subcooled liquid hydrogen flows through pipes with higher wall temperatures, the hydrogen can evaporate and flow boiling occurs, resulting in a complex heat transfer behavior of the fluid. In this study, we propose an advanced intelligent model based on the Cascade Forward Neural Network (CFNN) to predict Heat Transfer Coefficient (HTC) of subcooled liquid hydrogen under various flow conditions. Our model leverages on a dataset that is nearly twice the size of the largest previously used in the literature, significantly enhancing its generalization, reliability, and accuracy. The proposed CFNN model incorporates 19 input features, including crucial dimensionless parameters, orientation and thermodynamic condition of the fluid, and characteristics of the pipe that hydrogen flow through to accurately estimate HTC in unseen fluid conditions. The results demonstrate that the proposed model achieves an R-squared value of 0.9978, substantially outperforming the best empirical methods, which have an R-squared value of only 0.8058 for the same testing data. This innovative approach provides a highly accurate and reliable tool for predicting HTC, offering significant improvements over conventional methods and contributing valuable insights for real-world applications in the energy and transportation sectors. • Subcooling hydrogen seems necessary for safe storing in aircraft. • Modelling of heat transfer of LH2 in the pipes is vital for designing the system. • Use of artificial intelligence enables highly accurate heat transfer predictions. • Cascade Forward Neural Network estimates HTC of subcooled LH2 with 99.78% accuracy. • A comparison of findings is made with existing AI models and empirical correlation. [ABSTRACT FROM AUTHOR]

Pure organic films consisting of polypyrrole, polyaniline and a composite of polypyrrole and polyaniline electrodeposited in the ionic liquid EMIM‐TFSI onto mesoporous carbon electrodes are tested for their hydrogen evolution reaction capabilities. The use of these intrinsically conducting polymers is seen as a way of stepping away from expensive and rare metallic catalysts. Co‐polymerisation of polypyrrole and polyaniline in a 1 : 10 ratio in EMIM‐TFSI was found to be doped with the TFSI− anion and be much more active to the hydrogen evolution reaction when compared to pure polymers. Tafel analysis of the composite gave a value of 144 mV/dec indicating that the Volmer step is the rate limiting step. However, stability tests showed an improvement in the composite's overpoential performance for the hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

The traditional 70 MPa liquid hydrogen (LH 2) refueling stations (HRSs) require LH 2 pumps with high outlet pressures, leading to high initial investment, energy consumption, and difficulty in developing an LH 2 pump meeting requirements. Existing LH 2 HRSs using thermal compression eliminate the need for pressurization equipment but result in significant waste due to low-pressure hydrogen venting. Therefore, we have pioneered a novel pump-thermal synergistic pressurization process for an efficient LH 2 HRS system. The process utilizes a 45 MPa LH 2 pump and an electric heating method, allowing easily controllable heat input. This study constructs a thermodynamic model for this system that includes the dynamic operational processes of all core components. Based on the established model, the outlet parameters of the LH 2 pump, characteristic parameters of the pressure vessel, the refueling process, and the operation of the entire system are investigated. By dynamic simulation of the whole HRS system with pump and thermal compression, it is found that the specific energy consumption for hydrogen refueling is reduced to 0.55 kWh/kg, with the pump consuming 0.2 kWh/kg while thermal compression consuming 0.35 kWh/kg. After optimizing control strategies, the cycle venting of the pressure vessel and the residual hydrogen gas after re-heating and pressurization account for only 11.6%, and further utilization through the pump pressurization cycle can achieve high utilization with no residuals. This system effectively reduces the initial investment and energy consumption for LH 2 HRSs. It simplifies the structure, facilitating the retrofit of existing stations and promoting the construction and application of HRSs. [Display omitted] • An advanced hydrogen refueling station with pump and thermal compression is proposed. • A simulation model is developed for HRS with pump and thermal compression. • Thermodynamic analysis of HRS with pump and thermal compression is conducted. [ABSTRACT FROM AUTHOR]

A series of Pt/CeO 2 compounds with hollow spheres (Pt/CeO 2 –S), wires (Pt/CeO 2 –W), and particle (Pt/CeO 2 –P) morphologies were prepared and further used for catalytic liquid organic hydrogen carrier (LOHC) dehydrogenation. The exposure and distribution of different crystal faces affected the nucleation process of crystals and then formed different microscopic morphologies. Compared with Pt/CeO 2 –W and Pt/CeO 2 –P, Pt/CeO 2 –S showed hollow spherical structures with significantly higher oxygen vacancy concentrations and specific surface areas. These structural differences not only affected platinum (Pt) dispersion, but also affected the activity and stability of the catalyst, thus promoting methylcyclohexane (MCH) conversion. The fixed bed reaction showed that Pt/CeO 2 –S had excellent catalytic activity, with the MCH conversion rate at 97.7 % and hydrogen release rate of 350.50 mmol/g (Pt) /min, and it still maintained stable activity after 72 h. Under the same conditions, the MCH conversion rates for Pt/CeO 2 –W and Pt/CeO 2 –P were only 77.23 % and 32.02 %, respectively. Therefore, through the growth pattern and morphology controls of catalyst supports, this was an effective means for improving the dehydrogenation performance of LOHC. • The growth mechanism of CeO 2 hollow spheres, wires, and particles. • High catalytic activity of Pt/CeO 2 hollow spheres. • Liquid organic hydrogen carrier dehydrogenation. [ABSTRACT FROM AUTHOR]

Liquid hydrogen represents a potential candidate for a climate neutral fuel for shipping. The utilization of this fuel necessitates the implementation of safe and reliable bunkering operations. This paper employs a quantitative risk assessment to compare the safety of bunkering liquid hydrogen with the safety of bunkering LNG. Initially, a frequency analysis is conducted using an event tree. It can be demonstrated, that the occurrence of the hazardous events, pool fire, flash fire and explosion, is more frequent with liquid hydrogen than with LNG. In the second step, the consequence analysis determines necessary safety distances for the hazardous events under consideration. For the events of pool fire and explosion, LNG-bunkering requires higher safety distances. Liquid hydrogen-bunkering requires higher distances for flash fire event. Since the safety distances for flash fire events are largest, they define the distances for the system. However, the consequences of flash fire events are subject to greater uncertainties and require further investigation. Overall, hazardous events occur more often with liquid hydrogen-bunkering, but LNG-bunkering requires in two out of three cases larger safety distances. • A quantitative risk assessment of liquid hydrogen and LNG bunkering is performed. • Leaks will occur more frequently when bunkering liquid hydrogen. • LNG-bunkering requires larger safety distances in two out of three cases. • Flash fire events drive the safety distances of bunkering systems. • However, the consequences of flash fire events still need to be investigated further. [ABSTRACT FROM AUTHOR]

In this study, an automatic control technology for liquid-hydrogen zero boil-off was developed to improve the long-term storage capability of small-scale liquefaction systems. An innovative system capable of monitoring both the pressure within the heat pipe and the pressure within the LH 2 vessel was developed. This innovative approach ensures continuous efficiency and reduces downtime, significantly improving the overall performance of the hydrogen liquefaction process. The optimal conditions for automatic control were obtained through a cycle test in ON/OFF mode. In addition, experimental investigations were conducted sequentially to investigate the effect of the water level of liquid hydrogen such as 1st section, 2nd section and 3rd section of LH 2. As a result, these experiments successfully demonstrated zero boil-off of liquid hydrogen for long-term storage in the vessel, corresponding to a constant value in the liquid level meter in each section. The velocity of stabilization from the temperature and pressure perspectives in the vessel increased, and the entire cryocooler cycle time was significantly influenced by the amount of liquid hydrogen produced. • An automatic control technology for liquid-hydrogen zero boil-off was developed. • The pressure data on the liquid hydrogen vessel and heat exchanger were determined. • The effect of the water level of liquid hydrogen was investigated. • Experiments demonstrated zero boil-off of liquid hydrogen for long-term storage. • The entire cryocooler cycle time was influenced by the amount of liquid hydrogen. [ABSTRACT FROM AUTHOR]

Hydrogen is regarded as the premier energy source for future sustainability and renewability. However, its distinct physicochemical properties render it prone to explosions in the event of a leak. Therefore, there is a need for more comprehensive research dealing with hydrogen leakage, explosion scenarios, and risk assessment. This paper provides an overview of the current hydrogen policies adopted in China. It reviews the processes of hydrogen refueling station construction and the thermophysical mechanisms of liquid hydrogen leakage. In this regard, the effects of various factors, including leakage rate, leakage time, leakage hole size, wind direction and speed, and building location, on the hydrogen leakage rate are analyzed and evaluated. Additionally, the impacts of different factors on hydrogen explosion overpressure are reported, including hydrogen concentration, wind speed, obstacles, and ignition position, in addition to the current applications of quantitative risk assessment methods in hydrogen refueling stations. Finally, the limitations of current research on liquid hydrogen leakage and explosion accidents are highlighted, along with the shortcomings of current risk assessment methods for liquid hydrogen refueling stations. [ABSTRACT FROM AUTHOR]

The growing interest in hydrogen (H2) has motivated process engineers and industrialists to investigate the potential of liquid hydrogen (LH2) storage. LH2 is an essential component in the H2 supply chain. Many researchers have studied LH2 storage from the perspective of tank structure, boil-off losses, insulation schemes, and storage conditions. A few review studies have also been published considering LH2 storage; however, most are simply collections of previous articles. None of these review articles have critically evaluated the research articles. In this review study, recent reports, conceptual studies, and patents have been included and critically discussed. Further, challenges and recommendations have been listed based on the literature review. Our results suggest that the multi-layer insulation scheme and integrated refrigeration system can effectively reduce boil-off losses. However, boil-off losses from storage tanks during transportation are the least discussed and must be addressed. The cost of an LH2 storage tank is high, but it can be reduced with advancements in materials and the utilization of latest technologies. The present challenges and future directions for LH2 storage include minimizing and utilizing boil-off losses, improving insulation schemes, and ensuring cost-effective large-scale LH2 storage. This review study can be fundamental for process engineers and new academic researchers to design energy-efficient and cost-effective LH2 storage systems. [ABSTRACT FROM AUTHOR]

In order to ensure operational efficiency and safety, the flow dynamics of the ortho-para hydrogen converter in a liquid hydrogen system was studied. The precise selection of filtration accuracy stands as a critical factor in maintaining system stability and reliability. Unforeseen pressure drops within the filter layer hinted at microchannel blockages. Electron microscopy inspection and test result analysis suggested adhesion of catalyst particles to microfiltration channel surfaces within the filter layer. Experimental data and fluid dynamics analyses were utilized to reconstruct actual effective microchannel apertures under diverse temperature and fluid settings, unveiling a gradual narrowing mechanism of microchannels in colder temperatures. Enhanced magnetism exhibited by catalyst and filter materials at lower temperatures emerged as a major driver behind magnetic adhesion, significantly contributing to microchannel constriction. Besides magnetic forces, fluid-solid interface tensions influenced the flow dynamics within liquid hydrogen microchannels, leading to heightened particle adhesion and consequent dimensional reductions in surface channels. Successful adjustments in filtration accuracy substantially alleviated the ortho-para converter's resistance from over 100 kPa–22 kPa. This research bears profound implications for the widespread application of liquid hydrogen systems. • Catalyst resistance is crucial to the operability and reliability of liquid hydrogen systems. • Catalyst dust adhesion blockages lead to variable flow resistance. • Adhesion mechanisms consisted of liquid-solid tension, magnetic and electrostatic forces. • Observed cryogenically enhanced magnetism effects were for 316L stainless steel and catalyst. • Actual filtration precision exceeds nominal values, recommended precision 5–25 μm for catalyst. [ABSTRACT FROM AUTHOR]

Dodecahydro-N-ethylcarbazole (H 12 -NEC) is an ideal liquid organic hydrogen carrier (LOHC). In this paper, Fe/MCM-41 is synthesized using electrostatic adsorption with MCM-41 as the support. Fe@Pd core-shell nanoparticles (NPs) are successfully prepared through galvanic replacement, facilitated by ultrasonication, using Fe NPs as a template and reducing agent. The resulting Fe 6 @Pd 1 NPs, with an average particle size of 1.9 nm, are uniformly dispersed on MCM-41, exhibiting significant electronic interactions between the metals. At 180 °C, Fe 6 @Pd 1 /M41 catalyzes the dehydrogenation of H 12 -NEC, achieving a hydrogen release of 4.84 wt% after 1 h and complete dehydrogenation after 6 h. DFT calculations demonstrate that coordination and strain effects modulate the d-band center of Pd, optimizing the adsorption strength for intermediates and thereby enhancing the catalytic performance. Even after 7 cycles, Fe 6 @Pd 1 /M41 maintains a hydrogen release of 5.08 wt%. This work provides a valuable reference for the development of high-performance LOHC dehydrogenation catalysts. Synopsis sentence:H 12 -NEC hydrogen storage technology has the advantages of safety and stability, which is beneficial for improving the hydrogen economy. In the process of preparing nanocatalysts by the electric replacement method, there is no need to add any stabilizer or reducing agent, and it is necessary to use compound green chemistry. [Display omitted] • Fe@Pd core-shell NPs loaded on MCM-41 for fast catalytic H12-NEC dehydrogenation. • Electron and strain effects in Fe@Pd are vital for improved catalytic performance. • The introduction of Fe shifts the D-band of Pd and boosts its catalytic properties. [ABSTRACT FROM AUTHOR]

Hydrogen emerges as a promising energy carrier in achieving carbon neutrality, especially in countries such as South Korea and Japan, where renewable energy resources are scarce. Consequently, economically importing hydrogen from overseas is paramount to a stable supply. However, previous studies have often oversimplified the estimation of hydrogen import costs with optimistic assumptions, raising doubts about their reliability. This study comprehensively assesses costs incurred from green hydrogen production to liquefaction and transportation. The cost analysis includes detailed design considerations for hydrogen liquefaction and re-conditioning plants, alongside thermodynamic simulations to estimate the boil-off gas rate of liquid hydrogen during transport. Focusing on a case study of importing liquefied green hydrogen from Australia to South Korea, our findings reveal that the levelized cost of hydrogen is approximately 30.2 USD/kgH 2 as of 2023. Projections suggest a decrease to around 18.3 USD/kgH 2 by 2050, assuming technological advancements, significantly exceeding values reported in the existing literature. Sensitivity analysis highlights the renewable electricity price in Australia and the boil-off rate during shipping as key factors that significantly influence the levelized cost of hydrogen. • Costs for producing and transporting liquified green hydrogen are rigorously analyzed. • Detailed process design and thermodynamic simulation are conducted for realistic analysis. • A case of importing hydrogen from Australia to South Korea is studied. • LCOH for 2023 and 2050 are 30.2 and 18.3 USD/kgH 2 , which exceed literature values. [ABSTRACT FROM AUTHOR]

This study simulates the self-pressurization of liquefied hydrogen using a three-element lumped model. We analyze the effects of liquid filling ratio, heat flux distribution, interface heat transfer parameters, and tank shape on pressure build-up, which can vary due to ship transportation conditions. Key findings are: lower liquid levels correlate with faster pressure build-up; the sensitivity of pressure build-up to changes in the heat flux ratio between vapor and liquid is higher during laden voyages compared to ballast voyages; The effect of heat absorption by vapor on pressure build-up is greater than that of BOG caused by heat transfer; and horizontal tanks exhibit the longest holding time. These findings enhance the understanding and prediction of pressure dynamics in liquid hydrogen transportation, aiding the design and optimization of systems for safe and efficient operation. A comprehensive study on pressure build-up in a large liquid hydrogen tank considering voyage condition, heat transfer and shape of a tank. [Display omitted] • We investigated the behaviors of large-scale liquid hydrogen tank. • The lower liquid level has a longer holding time. • Laden voyages are more sensitive to the external heat leakage flux. • The heat absorption of vapor is the main factors in pressure build-up. • The horizontal tank has the longest holding time. [ABSTRACT FROM AUTHOR]

The catalytic conversion of ortho-hydrogen (o-H2) to para-hydrogen (p-H2) serves as a crucial step in the storage of liquid hydrogen. A variety of iron-cobalt bimetallic catalysts (FCO) were synthesized using a precipitation method, incorporating diverse levels of Co doping into Fe-based catalysts. The effects of Co doping on the crystal structure, porosity, and magnetism of FCO catalysts were studied by XRD, N2 physical adsorption, FTIR, XPS, and VSM analyses. The efficiency of ortho-para hydrogen conversion over FCO at 77 K was evaluated. It was found that the catalyst's lag coefficient was significantly improved by Co doping, leading to an increase of magnetic moment. The catalyst of FCO-5 with a Fe/(Fe + Co) molar ratio of 0.5 exhibited the highest activity in ortho-para hydrogen conversion. The corresponding conversion rate, outlet p-H2 content, and the reaction rate constant were 99.2%, 49.7% and 291.7 mol·L−1·s−1, respectively, under a gas hourly space velocity of 5400 h−1. [ABSTRACT FROM AUTHOR]

Ionic liquid compressors are suitable for high-pressure hydrogen refuelling stations. The initial liquid piston height is a critical parameter in designing ionic liquid compressors. Sufficient initial liquid column height can effectively prevent hydrogen leakage and exposure of the solid piston. However, there is a lack of basis for selecting the initial ionic liquid column height in the compression cylinder. The gas-liquid interface in the multi-stage compression is investigated by an experimentally verified numerical simulation model. The results show that in the low-pressure stage of the ionic liquid compressor, the initial liquid piston height can equal to the piston stroke, but in the high-pressure stage, the solid piston could be exposed to the hydrogen, so it is necessary to increase the initial liquid piston height. By analyzing the fluctuation characteristics in the cylinder, it is found that there is a minimum initial liquid piston height in each stage to ensure effective sealing. The minimum liquid piston height for the first to the fifth stage is 52 mm, 40 mm, 44 mm, 51 mm, and 54 mm, respectively. • The compression cylinders of a five-stage ionic liquid compressor were designed. • A numerical method was established and verified by experiment data. • The characteristics of the gas-liquid interface were analyzed. • The minimum initial ionic liquid height in each stage was recommended. [ABSTRACT FROM AUTHOR]

Cryo-adsorptive hydrogen storage exhibits high hydrogen storage density and low storage pressure, rendering it highly promising. Among various adsorption materials, covalent organic frameworks (COFs) stand out as promising materials for cryo-adsorptive hydrogen storage. However, current research has problems of low research pressure and limited hydrogen storage density, which hinder the widespread application of cryo-adsorptive hydrogen storage. In this work, the gravimetric and volumetric hydrogen storage densities of different cryo-adsorptive hydrogen storage tanks are simulated and predicted in the pressure range of 0.1–55 MPa at 77 K. Nine kinds of COFs are selected as adsorbents for cryo-adsorptive hydrogen storage. The modified Dubinin-Astakhov (D-A) model is used to simulate the hydrogen adsorption isotherms. The relevant model parameters of COFs are nonlinearly fitted and then validated for reliability. The results indicate that under specific conditions, 3D COFs can achieve hydrogen storage density comparable to liquid hydrogen at relatively lower pressures, exhibiting excellent cryo-adsorptive hydrogen storage performance with promising application prospects. • CcH 2 combined with adsorption can reach higher density with lower pressure. • COFs adsorption performance simulation in a wide pressure range at 77 K. • COF-108 plays a negative role when exceeds the specific pressure (19 MPa at 77 K). • COFs can significantly improve the density of CcH 2 in a wide range. [ABSTRACT FROM AUTHOR]

Maritime propulsion is recognized as a hard-to-abate sector and its decarbonization will therefore require transversal efforts, including the introduction of alternative fuels to reduce CO 2 emissions. Both ammonia and hydrogen could provide clean power; however, forecasts hint that ammonia will be especially useful for longer routes, while hydrogen suffers from low volumetric energy density. This paper evaluates the feasibility of a cargo ship with a SOFC powertrain equipped with LOHC-based hydrogen storage and compares the sizing and heat management requirements of four LOHC systems, namely N-ethylcarbazole (NEC), dibenzyltoluene (DBT), methylcyclohexane (MCH), decaline (DEC), with an ammonia-based one. The size of the 8.4 MW SOFC system is similar for the five carriers as expected. The dynamic performance of the LOHC system shows that the hydrogen flow rate can be effectively controlled by acting on the LOHC flow rate, reactor temperature, and pressure. However, LOHC systems are heavier (by a factor of 1.6 to 2.1) and larger (by 1.6 to 2.3 times) than ammonia systems. The decalin system results in the lowest mass and volume, while NEC is the heavier, and MCH is the least dense of the evaluated LOHCs. Similarly, the utilization of SOFC waste heat to cover dehydrogenation heat ranges from 45.6 % (NEC) to 27.9 % (ammonia). Overall, even considering the lower reaction temperature, LOHCs do not appear to be competitive with ammonia as hydrogen storage systems in the maritime sector. • Liquid organic hydrogen carrier (LOHC) systems discussed for maritime applications. • Different LOHC systems are sized, and the heat demand is evaluated. • Control strategies are devised to meet instantaneous hydrogen demand. • The dynamic response of LOHC-based systems is more than satisfactory. • Comparison with ammonia is unfavorable in terms of mass, volume and heat demand. [ABSTRACT FROM AUTHOR]

Hydrogen liquefaction is one of the main methods for hydrogen energy applications, and obtaining a high para-hydrogen concentration is an indispensable part of the storage and transportation of liquid hydrogen. Therefore, the preparation and research of catalysts to accelerate ortho-para hydrogen conversion (OP conversion) is an important method to solve the problem of liquid hydrogen storage and transportation. In this paper, we demonstrate the catalytic effect of metal-organic frameworks (MOFs) on OP conversion at 77 K. The crystal structure, morphology and magnetization of the catalyst were discussed by using XRD, BET, FTIR, VSM and other characterization techniques. Among them, Ni-BTC (Ni-based MOF material synthesized from H 3 BTC and Ni2+) has the highest catalytic activity, and the conversion efficiency reaches the highest value of 91.4% when the GHSV (Gas Hourly Space Velocity) is 12000 h−1, which opens a new way for the design and synthesis of catalytic materials for OP conversion. [Display omitted] • The catalytic performance of M-BTC for ortho-para hydrogen conversion was studied. • The structure of M-BTC can be adjusted by changing different metal bases. • M-BTC exhibits the best catalytic performance when Ni is the metal center. • Ni-BTC has the highest conversion efficiency of 91.4% when the GHSV is 12000 h-1. [ABSTRACT FROM AUTHOR]

Hydrogen energy has made significant progress as one of the technological pathways that can facilitate the green transformation of various sectors, including the chemical industry, steel production, transportation, and power generation. However, areas with high demand for hydrogen are typically located thousands of kilometers away from large-scale production facilities. Hydrogen transported from the most cost-competitive large production sites to areas that lack hydrogen resources requires converting gaseous hydrogen into a high-density liquid. Thus, global market trade is important for hydrogen carriers in long-distance and large-scale transportation. In this study, liquefied hydrogen (LH2) and ammonia (NH3), which are hydrogen-based energy carriers, are analyzed and compared in terms of economic costs, energy efficiency, and carbon dioxide (CO2) emissions. It has been demonstrated that the LH2 supply chain is more energy-efficient and has higher CO2 emissions compared to the NH3 supply chain. Furthermore, this study shows that the levelized cost of hydrogen transportation (LCoHT) delivered from Australia to Ningbo, China, is lower for NH3 (19.95 yuan/kg-H2) compared to LH2 (22.83 yuan/kg-H2). Meanwhile, the LCoHT for the two supply chains is in a similar range (27.82 yuan/kg-H2 and 21.53 yuan/kg-H2 for LH2 and NH3, respectively) from Norway to Ningbo, China. The impacts of important parameters on the LCoHT, energy efficiency, and CO2 emissions of the LH2/NH3 supply chain are also considered through a sensitivity analysis. [ABSTRACT FROM AUTHOR]

Aromatic esters such as phenyl acetates are of interest as promising liquid organic hydrogen carriers (LOHCs) due to the presence of double bonds. However, the key factor for the development of green hydrogen fuel is the production of LOHCs from renewable sources. Since the synthesis and isolation of such esters is a complex task, understanding the relationship between the chemical structures of aromatic esters and their thermodynamic properties is of great importance for their further practical use as LOHCs. Obtaining reliable thermodynamic and thermochemical properties of phenyl and benzyl phenyl acetates formed the basis of this work. Vapour pressures, enthalpies of vaporisation, and enthalpies of formation were systematically studied. An approach based on the structure–property correlation was used to confirm these quantities. Additionally, the high-level quantum-chemical method G4 was used to estimate the enthalpy of formation in the gas phase. The final stage was the assessment of the energetics of chemical reactions based on aromatic esters and their partially and fully hydrogenated analogues. [ABSTRACT FROM AUTHOR]