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Open AccessArticle

A Brief on Nano-Based Hydrogen Energy Transition

by

Rui F. M. Lobo

Hydrogen 2023, 4(3), 679-693; https://doi.org/10.3390/hydrogen4030043 - 12 Sep 2023

Viewed by 468

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

CuCoMgAlO_x Mixed Oxides as Selective Catalysts for the Hydrogenation of Furan Compounds

by

Elena O. Kobzar

,

Liudmila N. Stepanova

,

Aleksandr A. Nepomniashchii

,

Anastasia V. Vasilevich

,

Tatiana I. Gulyaeva

,

Mikhail V. Trenikhin

and

Aleksandr V. Lavrenov

Hydrogen 2023, 4(3), 644-657; https://doi.org/10.3390/hydrogen4030041 - 08 Sep 2023

Viewed by 300

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

CFD Model of Refuelling through the Entire HRS Equipment: The Start-Up Phase Simulations

by

Vladimir Molkov

,

Hazhir Ebne-Abbasi

and

Dmitriy Makarov

Hydrogen 2023, 4(3), 585-598; https://doi.org/10.3390/hydrogen4030038 - 01 Sep 2023

Viewed by 398

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

Stability of the TiO₂ Nanuclusters Supported on Fe₂O₃-Hematite for Application in Electrocatalytic Water Splitting—An Insight from DFT Simulations

by

Tomasz Dymkowski

,

Wiktor Żuczkowski

,

Wojciech Kołodziejczyk

,

Glake Hill

and

Bartłomiej M. Szyja

Hydrogen 2023, 4(3), 573-584; https://doi.org/10.3390/hydrogen4030037 - 24 Aug 2023

Viewed by 868

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

The Effect of Liquid Hydrogen Tank Size on Self-Pressurization and Constant-Pressure Venting

by

Konstantin I. Matveev

and

Jacob W. Leachman

Hydrogen 2023, 4(3), 444-455; https://doi.org/10.3390/hydrogen4030030 - 19 Jul 2023

Viewed by 641

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

Investigation of Different Load Characteristics, Component Dimensioning, and System Scaling for the Optimized Design of a Hybrid Hydrogen-Based PV Energy System

by

Marius C. Möller

and

Stefan Krauter

Hydrogen 2023, 4(3), 408-433; https://doi.org/10.3390/hydrogen4030028 - 13 Jul 2023

Viewed by 444

Abstract

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 [...] Read more.

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 (

H_{2}

) was produced by using an electrolyser (ELY) with a PV surplus during the summer months and then stored in an

H_{2}

tank. During the winter, due to the lack of PV power, the

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

Gasification of Lower Monohydric Alcohols by Solution Plasma Treatment and Its Reaction Mechanism

by

Takaki Miyamoto

,

Eiji Minami

and

Haruo Kawamoto

Hydrogen 2023, 4(2), 373-388; https://doi.org/10.3390/hydrogen4020026 - 16 Jun 2023

Viewed by 594

Abstract

Solution plasma is a gas-phase discharge in the vapor bubbles in a solution and has the potential to efficiently produce H₂ by decomposing aqueous alcohols. However, the mechanism of alcohol decomposition in solution plasma remains unclear. In this study, lower monohydric alcohols [...] Read more.

Solution plasma is a gas-phase discharge in the vapor bubbles in a solution and has the potential to efficiently produce H₂ by decomposing aqueous alcohols. However, the mechanism of alcohol decomposition in solution plasma remains unclear. In this study, lower monohydric alcohols (methanol and ethanol, as well as 1- and 2-propanol) were treated in solution plasma, and in this paper, the gasification mechanism is discussed. The gases produced from these alcohols were mainly H₂ and CO, with small ratios of C₁–C₃ hydrocarbons. Thus, the O/C ratio in the product gas was close to 1 for all alcohols, and most of the C atoms in the alcohols were bonded to O atoms. This excess of O atoms could have only come from water, suggesting a strong contribution of OH radicals from water for gasification. However, the C₁–C₃ hydrocarbons were produced solely by the decomposition of the alcohol. For both decomposition routes, possible reaction pathways are proposed that are consistent with the experimental facts such as the composition of the product gas and the intermediates detected. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

LCA Analysis Decarbonisation Potential of Aluminium Primary Production by Applying Hydrogen and CCUS Technologies

by

,

,

and

Hydrogen 2023, 4(2), 338-356; https://doi.org/10.3390/hydrogen4020024 - 20 May 2023

Cited by 1 | Viewed by 1209

Abstract

The energy intensity and high emissions of extractive industries bring a major need for decarbonisation actions. In 2021, extraction and primary processing of metals and minerals were responsible for 4.5 Gt of equivalent CO₂. The aluminium industry specifically accounted for total [...] Read more.

The energy intensity and high emissions of extractive industries bring a major need for decarbonisation actions. In 2021, extraction and primary processing of metals and minerals were responsible for 4.5 Gt of equivalent CO₂. The aluminium industry specifically accounted for total emissions of 1.1 Gt CO₂ eq. per year. Reaching the European milestone of zero emissions by 2050, requires a 3% annual reduction. To achieve this, the industry has searched for innovative solutions, considering the treatment of emitted CO₂ with techniques such as Carbon Capture Utilisation and Storage (CCUS), or the prevention of CO₂ formation on the first place by utilising alternative fuels such as hydrogen (H₂). This study aims to comprehensively compare the overall environmental performance of different strategies for addressing not only greenhouse gas (GHG) emission reduction potential, but also emissions to air in general, as well as freshwater and terrestrial ecotoxicity, which are commonly overlooked. Specifically, a Life Cycle Assessment (LCA) is conducted, analysing four scenarios for primary Al production, utilising (1) a combination of fossil fuels, specifically Natural Gas (NG), Light Fuel Oil (LFO) and Heavy Fuel Oil (HFO) (conventional approach); (2) carbon capture and geological storage; (3) Carbon Capture and Utilisation (CCU) for methanol (MeOH) production and (4) green H₂, replacing NG. The results show that green H₂ replacing NG is the most environmentally beneficial option, accounting for a 10.76% reduction in Global Warming Potential (GWP) and 1.26% in Photochemical Ozone Formation (POF), while all other impact categories were lower compared to CCUS. The results offer a comprehensive overview to support decision-makers in comparing the overall environmental impact and the emission reduction potential of the different solutions. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessCommunication

Nuclear Motion Is Classical: Spectra of Hydrogen Chloride and Ammonia

by

Irmgard Frank

Hydrogen 2023, 4(2), 287-294; https://doi.org/10.3390/hydrogen4020020 - 15 May 2023

Viewed by 642

Abstract

The concept of classical nuclear motion is extremely successful in describing motion at the atomic scale. In describing chemical reactions, it is even far more convincing than the picture obtained by using the Schrödinger equation for time development. However, this theory must be [...] Read more.

The concept of classical nuclear motion is extremely successful in describing motion at the atomic scale. In describing chemical reactions, it is even far more convincing than the picture obtained by using the Schrödinger equation for time development. However, this theory must be subject to critical tests. In particular, it must be checked if vibrational and rotational spectra are obtained correctly. Particularly critical are the spectra of small molecules containing the light hydrogen atom, since they have a distinctive rotational structure. The present study presents computations of the spectra of ammonia and hydrogen chloride using ab initio molecular dynamics, that is, by describing nuclear motion classically. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

Evaluation of Hydrogen Blend Stability in Low-Pressure Gas Distribution

by

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,

,

and

Hydrogen 2023, 4(2), 210-225; https://doi.org/10.3390/hydrogen4020015 - 14 Apr 2023

Viewed by 1692

Abstract

Natural gas distribution companies are developing ambitious plans to decarbonize the services that they provide in an affordable manner and are accelerating plans for the strategic integration of renewable natural gas and the blending of green hydrogen produced by electrolysis, powered with renewable [...] Read more.

Natural gas distribution companies are developing ambitious plans to decarbonize the services that they provide in an affordable manner and are accelerating plans for the strategic integration of renewable natural gas and the blending of green hydrogen produced by electrolysis, powered with renewable electricity being developed from large new commitments by states such as New York and Massachusetts. The demonstration and deployment of hydrogen blending have been proposed broadly at 20% of hydrogen by volume. The safe distribution of hydrogen blends in existing networks requires hydrogen blends to exhibit similar behavior as current supplies, which are also mixtures of several hydrocarbons and inert gases. There has been limited research on the properties of blended hydrogen in low-pressure natural gas distribution systems. Current natural gas mixtures are known to be sufficiently stable in terms of a lack of chemical reaction between constituents and to remain homogeneous through compression and distribution. Homogeneous mixtures are required, both to ensure safe operation of customer-owned equipment and for safety operations, such as leak detection. To evaluate the stability of mixtures of hydrogen and natural gas, National Grid experimentally tested a simulated distribution natural gas pipeline with blends containing hydrogen at up to 50% by volume. The pipeline was outfitted with ports to extract samples from the top and bottom of the pipe at intervals of 20 feet. Samples were analyzed for composition, and the effectiveness of odorant was also evaluated. The new results conclusively demonstrate that hydrogen gas mixtures do not significantly separate or react under typical distribution pipeline conditions and gas velocity profiles. In addition, the odorant retained its integrity in the blended gas during the experiments and demonstrated that it remains an effective method of leak detection. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

Distributional Trends in the Generation and End-Use Sector of Low-Carbon Hydrogen Plants

by

Nick James

and

Max Menzies

Hydrogen 2023, 4(1), 174-189; https://doi.org/10.3390/hydrogen4010012 - 02 Mar 2023

Cited by 3 | Viewed by 1197

Abstract

This paper uses established and recently introduced methods from the applied mathematics and statistics literature to study trends in the end-use sector and the capacity of low-carbon hydrogen projects in recent and upcoming decades. First, we examine distributions in plants over time for [...] Read more.

This paper uses established and recently introduced methods from the applied mathematics and statistics literature to study trends in the end-use sector and the capacity of low-carbon hydrogen projects in recent and upcoming decades. First, we examine distributions in plants over time for various end-use sectors and classify them according to metric discrepancy, observing clear similarity across all industry sectors. Next, we compare the distribution of usage sectors between different continents and examine the changes in sector distribution over time. Finally, we judiciously apply several regression models to analyse the association between various predictors and the capacity of global hydrogen projects. Across our experiments, we see a welcome exponential growth in the capacity of zero-carbon hydrogen plants and significant growth of new and planned hydrogen plants in the 2020’s across every sector. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

Multi-Model Assessment for Secondary Smelting Decarbonisation: The Role of Hydrogen in the Clean Energy Transition

by

Antonis Peppas

,

Sotiris Kottaridis

,

Chrysa Politi

,

Panagiotis M. Angelopoulos

and

Maria Taxiarchou

Hydrogen 2023, 4(1), 103-119; https://doi.org/10.3390/hydrogen4010007 - 27 Jan 2023

Viewed by 1370

Abstract

Extensive decarbonisation efforts result in major changes in energy demand for the extractive industry. In 2021, the extraction and primary processing of metals and minerals accounted for 4.5 Gt of CO₂ eq. per year. The aluminium industry was responsible for 1.1 Gt [...] Read more.

Extensive decarbonisation efforts result in major changes in energy demand for the extractive industry. In 2021, the extraction and primary processing of metals and minerals accounted for 4.5 Gt of CO₂ eq. per year. The aluminium industry was responsible for 1.1 Gt CO₂ eq. direct and indirect emissions. To reach the European milestone of zero emissions by 2050, a reduction of 3% annually is essential. To this end, the industry needs to take a turn towards less impactful production practices, coupling secondary production with green energy sources. The present work aims to comprehensively compare the lifecycle energy consumption and environmental performance of a secondary aluminium smelter employing alternative thermal and electricity sources. In this frame, a comparative analysis of the environmental impact of different thermal energy sources, namely natural gas, light fuel oil, liquified petroleum gas, hydrogen and electricity, for a secondary aluminium smelter is presented. The results show that H₂ produced by renewables (green H₂) is the most environmentally beneficial option, accounting for −84.156 kg CO₂ eq. By producing thermal energy as well as electricity on site, H₂ technologies also serve as a decentralized power station for green energy production. These technologies account for a reduction of 118% compared to conventionally used natural gas. The results offer a comprehensive overview to aid decision-makers in comparing environmental impacts caused by different energy sources. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

The Boundary between Two Modes of Gas Evolution: Oscillatory (H₂ and O₂) and Conventional Redox (O₂ Only), in the Hydrocarbon/H₂O₂/Cu(II)/CH₃CN System

by

Igor Yu. Shchapin

and

Andrey I. Nekhaev

Hydrogen 2023, 4(1), 74-102; https://doi.org/10.3390/hydrogen4010006 - 16 Jan 2023

Viewed by 1415

Abstract

During the oxidation of hydrocarbons using hydrogen peroxide solutions, the evolution of gaseous oxygen is a side and undesirable process, in which the consumption of the oxidizer is not associated with the formation of target products. Therefore, no attention is paid to the [...] Read more.

During the oxidation of hydrocarbons using hydrogen peroxide solutions, the evolution of gaseous oxygen is a side and undesirable process, in which the consumption of the oxidizer is not associated with the formation of target products. Therefore, no attention is paid to the systematic study of the chemical composition of the gas and the mechanisms of its formation. Filling this gap, the authors discovered a number of new, previously unidentified, interesting facts concerning both gas evolution and the oxidation of hydrocarbons. In a 33% H₂O₂/Cu₂Cl₄·2DMG/CH₃CN system, where DMG is dimethylglyoxime (Butane-2,3-dione dioxime), and is at 50 °C, evidence of significant evolution of gaseous hydrogen, along with the evolution of gaseous oxygen was found. In the authors’ opinion, which requires additional verification, the ratio of gaseous hydrogen and oxygen in the discussed catalytic system can reach up to 1:1. The conditions in which only gaseous oxygen is formed are selected. Using a number of oxidizable hydrocarbons with the first adiabatic ionization potentials (AIPs) of a wide range of values, it was found that the first stage of such a process of evolving only gaseous oxygen was the single electron transfer from hydrogen peroxide molecules to trinuclear copper clusters with the formation, respectively, of hydrogen peroxide radical cations H₂O₂^•+ and radical anions Cu₃Cl₅^•− (AIP = 5 eV). When the conditions for the implementation of such a single electron transfer mechanism are exhausted, the channel of decomposition of hydrogen peroxide molecules into gaseous hydrogen and oxygen is switched on, which is accompanied by the transition of the system to an oscillatory mode of gas evolution. In some cases, the formation of additional amounts of gaseous products is provided by the catalytically activated decomposition of water molecules into hydrogen and oxygen after the complete consumption of hydrogen peroxide molecules in the reaction of gaseous oxygen evolution. The adiabatic electron affinity of various forms of copper molecules involved in chemical processes is calculated by the density functional theory method. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

µ-CT Investigation of Hydrogen-Induced Cracks and Segregation Effects in Austenitic Stainless Steel

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Hydrogen 2023, 4(1), 60-73; https://doi.org/10.3390/hydrogen4010005 - 13 Jan 2023

Viewed by 4801

Abstract

Hydrogen can drastically degrade the mechanical properties of a variety of metallic materials. The so-called hydrogen environment embrittlement of austenitic CrNi-type steels is usually accompanied by the formation of secondary surface cracks, which can be investigated in order to assess the embrittlement process. [...] Read more.

Hydrogen can drastically degrade the mechanical properties of a variety of metallic materials. The so-called hydrogen environment embrittlement of austenitic CrNi-type steels is usually accompanied by the formation of secondary surface cracks, which can be investigated in order to assess the embrittlement process. The occurrence of hydrogen-induced cracks is often related to element segregation effects that locally impact the austenite stability. Since there is as yet a lack of investigation methods that can visualize both structures three-dimensionally, the present study investigates the imageability of hydrogen-induced cracks and element segregation structures in austenitic CrNi-steel via micro-computed tomography (CT). In order to improve the X-ray visibility of segregation structures, modified versions of the reference steel, X2CrNi18-9, that contain W and Si are designed and investigated. The investigations demonstrated that small differences in the X-ray attenuation, caused by the W or Si modifications, can be detected via CT, although segregation structures could not be imaged due to their small size scale and image noise. Hydrogen-induced cracks were characterized successfully; however, the detection of the smaller cracks is limited by the resolution capability. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessArticle

Comprehensive Thermodynamic Study of Alkyl-Cyclohexanes as Liquid Organic Hydrogen Carriers Motifs

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and

Hydrogen 2023, 4(1), 42-59; https://doi.org/10.3390/hydrogen4010004 - 10 Jan 2023

Cited by 2 | Viewed by 1000

Abstract

Alkyl-cyclohexanes can be considered as suitable model compounds to understand the thermochemistry of aromatic compounds and their hydrogenated counterparts discussed as Liquid Organic Hydrogen Carrier systems. Thermochemical measurements on these hydrogen-rich compounds are thwarted by complications due to the 99.9 % purity limitation [...] Read more.

Alkyl-cyclohexanes can be considered as suitable model compounds to understand the thermochemistry of aromatic compounds and their hydrogenated counterparts discussed as Liquid Organic Hydrogen Carrier systems. Thermochemical measurements on these hydrogen-rich compounds are thwarted by complications due to the 99.9 % purity limitation and sample size specific to these methods. However, the data on vaporisation and formation enthalpies are necessary to optimize the hydrogenation/dehydrogenation processes. In this work, various empirical and theoretical methods are described to reliably assess the gas phase enthalpies of formation and vaporization enthalpies of alkyl-substituted cyclohexanes. The empirical and quantum-chemical methods have been validated against reliable literature data and provide reasonable estimates with an accuracy comparable to that of the experimental data. The liquid phase enthalpies of formation of differently shaped alkyl-cyclohexanes were derived and used to estimate the energetics of their dehydrogenation reactions. The influence of alkyl substituents on the reaction enthalpy is discussed. The vapour pressures of typical hydrogen-rich compounds at technically relevant temperatures were calculated and compared to vapour pressures of biodiesel fuels measured in this work using the static method. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Review

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Open AccessReview

Cu-Based Z-Schemes Family Photocatalysts for Solar H₂ Production

by

Rossella Greco

,

Romain Botella

and

Javier Fernández-Catalá

Hydrogen 2023, 4(3), 620-643; https://doi.org/10.3390/hydrogen4030040 - 06 Sep 2023

Viewed by 305

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessReview

Material Challenges and Hydrogen Embrittlement Assessment for Hydrogen Utilisation in Industrial Scale

by

Alexander Ilyushechkin

,

Liezl Schoeman

,

Lachlan Carter

and

San Shwe Hla

Hydrogen 2023, 4(3), 599-619; https://doi.org/10.3390/hydrogen4030039 - 01 Sep 2023

Viewed by 609

Abstract

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. [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessReview

Effect of Ti-Based Additives on the Hydrogen Storage Properties of MgH₂: A Review

by

Mukesh Jangir

,

Indra Prabh Jain

and

Daniele Mirabile Gattia

Hydrogen 2023, 4(3), 523-541; https://doi.org/10.3390/hydrogen4030034 - 05 Aug 2023

Viewed by 571

Abstract

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. [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Open AccessReview

Tailoring Ceria-Based Nanocatalysts for Enhanced Performance in Steam Reforming Processes: Exploring Fundamentals and Morphological Modulations

by

Samuel da Silva Eduardo

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Jhonatam Pinheiro Mendonça

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Pedro Nothaft Romano

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João Monnerat Araújo Ribeiro de Almeida

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Giovanna Machado

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Marco Aurélio Suller Garcia

Hydrogen 2023, 4(3), 493-522; https://doi.org/10.3390/hydrogen4030033 - 31 Jul 2023

Viewed by 443

Abstract

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 [...] Read more.

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

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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Preventing Hydrogen Embrittlement: The Role of Barrier Coatings for the Hydrogen Economy

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,

,

and

Hydrogen 2023, 4(2), 307-322; https://doi.org/10.3390/hydrogen4020022 - 17 May 2023

Viewed by 1988

Abstract

Hydrogen barrier coatings are protective layers consisting of materials with a low intrinsic hydrogen diffusivity and solubility, showing the potential to delay, reduce or hinder hydrogen permeation. Hydrogen barrier coatings are expected to enable steels, which are susceptible to hydrogen embrittlement, specifically cost-effective [...] Read more.

Hydrogen barrier coatings are protective layers consisting of materials with a low intrinsic hydrogen diffusivity and solubility, showing the potential to delay, reduce or hinder hydrogen permeation. Hydrogen barrier coatings are expected to enable steels, which are susceptible to hydrogen embrittlement, specifically cost-effective low alloy-steels or light-weight high-strength steels, for applications in a hydrogen economy. Predominantly, ceramic coating materials have been investigated for this purpose, including oxides, nitrides and carbides. In this review, the state of the art with respect to hydrogen permeation is discussed for a variety of coatings. Al₂O₃, TiAlN and TiC appear to be the most promising candidates from a large pool of ceramic materials. Coating methods are compared with respect to their ability to produce layers with suitable quality and their potential for scaling up for industrial use. Different setups for the characterisation of hydrogen permeability are discussed, using both gaseous hydrogen and hydrogen originating from an electrochemical reaction. Finally, possible pathways for improvement and optimisation of hydrogen barrier coatings are outlined. Full article

(This article belongs to the Special Issue Feature Papers in Hydrogen (Volume 2))

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