Loss Of Hydrogen Research Articles

Phase separation of planetary ices explains nondipolar magnetic fields of Uranus and Neptune

The Voyager spacecraft discovered that the ice giants Uranus and Neptune have nondipolar magnetic fields, defying expectations that a thick interior layer of planetary ices would generate strong dipolar fields. Stanley and Bloxham showed that nondipolar fields emerge if the magnetic field is only generated in a thin outer layer. However, the origin and composition of this dynamo active layer has so far remained elusive. Here, we show with ab initio computer simulations that a mixture of H 2 O, CH 4 , and NH 3 will phase separate under the pressure–temperature condition in the interiors of Uranus and Neptune, forming a H 2 O-dominated fluid in the upper mantle and a CH 4 -NH 3 mixture below. We further demonstrate that with increasing pressure, the CH 4 -NH 3 mixture becomes increasingly hydrogen depleted as it assumes the state of a polymeric C-N-H fluid. Since the amount of hydrogen loss increases with pressure, we propose that the C-N-H fluid forms a stably stratified layer. The magnetic fields are primarily generated in an upper layer that is H 2 O-rich, homogeneous, convective, and electrically conducting. Under these assumptions, we construct ensembles of models for the interiors of Uranus and Neptune with the Concentric MacLaurin Spheroid method. We demonstrate that the phase separation of the solar-type H 2 O-CH 4 -NH 3 mixture leads to models that match the observed gravity field and to layer thicknesses that are compatible with magnetic field measurements.

Gas-phase preparation of silylacetylene (SiH3CCH) through a counterintuitive ethynyl radical (C2H) insertion.

Elementary reaction mechanisms constitute a fundamental infrastructure for chemical processes as a whole. However, while these mechanisms are well understood for second-period elements, involving those of the third period and beyond can introduce unorthodox reactivity. Combining crossed molecular beam experiments with electronic structure calculations and molecular dynamics simulations, we provide compelling evidence on an exotic insertion of an unsaturated sigma doublet radical into a silicon-hydrogen bond as observed in the barrierless gas-phase reaction of the D1-ethynyl radical (C2D) with silane (SiH4). This pathway, which leads to the D1-silylacetylene (SiH3CCD) product via atomic hydrogen loss, challenges the prerequisite and fundamental concept that two reactive electrons and an empty orbital are required for the open shell, unsaturated radical reactant to insert into a single bond.

Methanogenic activity in water-saturated reservoir analogues for underground hydrogen storage: The role of surface area

The activity of methanogenic Archaea in porous formations is influenced by various pore characteristics, including porosity, surface area, and the gas-liquid interfacial area. This study explores the impact of surface area on methanogenic activity using techniques such as MICP, NMR, SEM, and μCT. The cells of Methanothermococcus thermolithotrophicus, ranging from 1 to 2 μm, indicate that pores smaller than this threshold are not accessible for microbial traversal and colonization. Upon normalization of microbial activities based on pore volume and interfacial area, the findings exhibit strong correlations with specific surface areas of accessible pores in the examined rocks, as determined by MICP, NMR, and SEM. These areas ranged from 0.001 to 0.017 m2/g, 0.003–0.024 m2/g, and 0.012–0.02 m2/g, respectively. The normalized activities increase from 0.19 to 0.44 mM/(h·cm3·cm2) with an increase in the specific surface area, varying by method. Furthermore, an empirical model has been established to quantitatively evaluate hydrogen loss during underground hydrogen storage or the efficiency of bio-methanation, incorporating pore volume, specific surface area, and interfacial area.

JWST/NIRISS Reveals the Water-rich “Steam World” Atmosphere of GJ 9827 d

With sizable volatile envelopes but smaller radii than the solar system ice giants, sub-Neptunes have been revealed as one of the most common types of planet in the galaxy. While the spectroscopic characterization of larger sub-Neptunes (2.5–4 R ⊕) has revealed hydrogen-dominated atmospheres, smaller sub-Neptunes (1.6–2.5 R ⊕) could either host thin, rapidly evaporating, hydrogen-rich atmospheres or be stable, metal-rich “water worlds” with high mean molecular weight atmospheres and a fundamentally different formation and evolutionary history. Here, we present the 0.6–2.8 μm JWST/NIRISS/SOSS transmission spectrum of GJ 9827 d, the smallest (1.98 R ⊕) warm (T eq,A=0.3 ∼ 620 K) sub-Neptune where atmospheric absorbers have been detected to date. Our two transit observations with NIRISS/SOSS, combined with the existing HST/WFC3 spectrum, enable us to break the clouds–metallicity degeneracy. We detect water in a highly metal-enriched “steam world” atmosphere (O/H of ∼4 by mass and H2O found to be the background gas with a volume mixing ratio of >31%). We further show that these results are robust to stellar contamination through the transit light source effect. We do not detect escaping metastable He, which, combined with previous nondetections of escaping He and H, supports the steam atmosphere scenario. In water-rich atmospheres, hydrogen loss driven by water photolysis happens predominantly in the ionized form, which eludes observational constraints. We also detect several flares in the NIRISS/SOSS light curves with far-UV energies of the order of 1030 erg, highlighting the active nature of the star. Further atmospheric characterization of GJ 9827 d probing carbon or sulfur species could reveal the origin of its high metal enrichment.

Analysis of the efficiency of reducing hydrogen losses in a pipeline made of various austenitic stainless steels

Analysis of the efficiency of reducing hydrogen losses in a pipeline made of various austenitic stainless steels

Nonadiabatic Photodynamics of Amantadine and 1-Cyanoadamantane Cations.

Cations of diamondoids and derivatives thereof have recently become the subject of experimental, spectroscopic studies due to their potential role in astrochemistry. In particular, their electronic spectra and photoinduced dynamics trigger great interest. Here, we report on computational investigations of two nitrogen-containing derivatives of the adamantane cation (Ada+, ), the amantadine cation (Ama+, ) and the 1-cyanoadamantane cation (Ada-CN+, C10H15CN+). Specifically, we study electronic (vibrationally resolved) spectra and nonadiabatic molecular dynamics (modeled using the surface hopping approach based on semiempirical electronic structure theory) of these radical cations. The internal conversion time constants as well as reactive relaxation outcomes (cage-opening and hydrogen loss) are compared for the two derivatives and also with the case of Ada+.[29] Remarkably, we find a longer ground-state recovery time for Ada-CN+ than for Ama+ (for the same excitation energy window), despite a smaller excitation energy for the former. Thus, a static energy gap law cannot be used to rationalize nonadiabatic dynamics and excited state lifetimes in this case: Dynamics and details of the couplings between several states play a decisive role.

Efficient cooling strategies for liquid hydrogen pipelines: A comparative analysis

Liquid hydrogen (LH2) stands out for its high energy density, efficient transportation, and safe low-pressure storage. However, the challenge lies in achieving rapid cooling of LH2 pipelines while minimizing hydrogen loss. This paper introduces a robust three-dimensional model for simulating the unsteady-state heat transfer and the gas-liquid two-phase flow within LH2 pipelines. Throughout the cooling cycle, the pipe undergoes transitions in flow patterns, including stratified smooth flow, wavy flow, and intermittent flow, in which wavy flow dominates due to the extremely low liquid-to-gas density ratio of hydrogen. A comprehensive comparative analysis is conducted for three cooling modes: constant flow, variable flow, and pulsing flow. Finally, an evaluative framework for distinct pipeline cooling modes has been proposed. A reasonable variable flow cooling mode exhibits certain advantages in both cooling time and liquid hydrogen consumption when compared with the constant flow cooling mode, and the pulse flow cooling method adeptly capitalizes on the performance benefits derived from intermittent flow. Specifically, within the cooling range of 40 K–20 K, it substantially economizes liquid hydrogen consumption (15%–20 %), albeit concomitant with an extended total cooling time (40%–60 %). This study can offer theoretical insights to guide the high-efficiency cooling of liquid hydrogen pipelines.

Systematic Literature Review on Pipeline Transport Losses of Hydrogen, Methane, and Their Mixture, Hythane

The transition to cleaner energy sources necessitates an in-depth understanding of the transport characteristics, losses, and opportunities associated with various gaseous fuels, including hydrogen, methane, and their mixtures, such as hythane. Hydrogen (H2), the most abundant element in the universe, is increasingly recognized as a viable alternative to fossil fuels, primarily due to its potential to reduce carbon footprints as a cleaner energy source. Gradually gaining prominence in the energy market, it is displacing other fuels such as methane. In some transport systems, hydrogen is mixed with methane (CH4) in order to reduce the carbon footprint while using the same existing production equipment. As more and more large methane consumers are implementing this mixture, we would like to see how the research has followed the market trend. An up-to-date research, development, and implementation status review is critical. This study aims to identify the main indicators of H2 and CH4 transport losses in pipes, providing a review of the state of the art in the specific literature. To deliver this, a systematic literature review (SLR) was carried out using preferred reporting items for systematic reviews and meta-analyses (PRISMA) methodology, pinpointing the research trends and results in peer review-published articles over a period of twelve years (2012–2024). Findings: this review identifies and points out, in numbers, the boundaries of the 2012–2024 timeline research.

Hydrogen loss from pyroxene within granulite xenoliths at Damaping, North China craton

The preservation of original water contents within nominally anhydrous minerals is essential for understanding the deep Earth’s water budget. Here we present a comprehensive analysis of mineral chemistry and Fourier transform infrared spectroscopy on 15 lower-crustal granulite xenoliths collected from Damaping in the North China craton. Our analyses reveal that the orthopyroxene grains from two samples exhibit hydrogen-deficient rims, suggestive of hydrogen loss. Drawing upon experimentally determined hydrogen diffusivity in pyroxene, we propose that clinopyroxene, despite the absence of evident hydrogen zoning, may have likewise undergone partial hydrogen depletion. Our findings call into question the conventional belief that hydrogen concentrations in pyroxene are faithful proxies for the original water content in the continental lower crust. We attribute the loss of hydrogen in pyroxene to magmatic outgassing, most likely occurring during the surface flow stage. Such a process could partially explain the relatively lower water contents documented in the granulite xenoliths when compared to those found in the Precambrian granulite terranes from the North China craton. Considering recent studies on mantle xenoliths, it becomes evident that both basalt-hosted mantle and lower-crustal xenoliths may have experienced partial loss of their original water contents within the deep Earth.

Low-grade lignite derived nitrogen doped hierarchical porous carbon for advanced lead-carbon batteries

The addition of carbon materials to the negative electrode would inhibit sulfation and prolong the cycle life of the lead-acid batteries. However, carbon materials contribute to the emergence of hydrogen evolution reaction (HER) and loss of water on the negative electrode. Accordingly, low-grade lignite raw material was one-step pyrolyzed to prepare nitrogen doped porous carbon (LNC) materials, which were further employed as negative additives to mitigate the above issues. The as-prepared LNC delivered large specific surface area (SSA) in the range of 1675.0–2503.3 m2 g−1, micro-mesoporous hierarchical structure, and high nitrogen doping level. Nitrogen doping considerably inhibited the HER and promoted the conversion kinetics between PbSO4/Pb in the negative electrode. Besides, the cycling life of lead-carbon battery containing LNC-1/3 at high-rate partial state of charge reached 9100 cycles, which reflected a 5.5-fold improvement over the blank. The improved performance could be attributed to the large SSA and plentiful functional groups, which offer active sites for the conversion of active substances, construct abundant ion channels, and refine the PbSO4 particles, thereby successfully minimizing irreversible sulfation. The short-route synthesis method provides a feasible approach to the reutilization of low-grade lignite, reflecting the circular economy.

Modeling Photodissociation: Quantum Dynamics Simulations of Methanol.

A comprehensive computational study of the gas-phase photodissociation dynamics of methanol is presented. Using a multiconfigurational active space based method (RASSCF) to obtain multidimensional potential energy surfaces (PESs) on-the-fly, direct quantum dynamics simulations were run using the variational multi-configurational Gaussian method (DD-vMCG). Different initial excitation energies were simulated to investigate the dependence of the branching ratios on the electronic state being populated. A detailed mechanistic explanation is provided for the observed differences with respect to the excitation energy. Population of the lowest lying excited state of methanol leads to rapid hydroxyl hydrogen loss as the main dissociation channel. This is rationalized by the strongly dissociative nature of the PES cut along the O-H stretching coordinate, confirmed by the broad feature in the absorption spectrum. In contrast, more energetic excitations lead mainly to C-O bond breaking. Again, analysis of the diabatic surfaces offers a clear explanation in terms of the nature of the electronic states involved and the coupling between them. The type of calculations presented, as well as the subsequent analysis of the results, should be seen as a general workflow for the modeling of photochemical reactions.

Optimizing Hydride Stability in U-ZrHx Nuclear Fuel: The “Goldilocks Radius”

Nuclear-powered microreactors show great promise for opening new nuclear energy markets due to the flexibility offered by their rapid/streamlined in-factory fabrication, transportability, and self-regulating nature. The economic benefits of any commercialized nuclear reactor, however, rely on the system’s ability to produce large amounts of heat and efficiently convert that heat into electrical power reliably for long periods of time. Uranium-zirconium hydride (U-ZrHx) is currently being considered for compact reactor designs because it is a well-known nuclear fuel system that is self-moderating, but this fuel, which has historically been used for research reactors, has not been optimized for commercial power production. This paper analyzes the hydride stability of standard 304 stainless steel–clad U-ZrHx fuel under commercially relevant conditions. Fuel element design parameters, including physical dimensions, as-fabricated hydrogen content, burnup, peak fuel temperature, temperature gradient, operational fuel cycle duration, and volumetric heat generation rate, are discussed with a focus on hydrogen distribution and phase stability within the fuel element. Hydride stability declines more rapidly as the coolant temperature, burnup, and fuel cycle duration increase. Using a fuel-cladding gap material with heat transfer properties superior to air, such as helium or sodium, is essential to prolonging fuel hydride stability. The fuel’s physical dimensions are also important. At very small fuel diameters, the H/Zr ratio in the fuel meat decreases too rapidly due to the hydrogen content’s dependence on fuel meat volume. Conversely, the fuel meat temperature and temperature gradient exacerbate hydrogen loss at very large fuel diameters. We find that the most important parameter to consider when optimizing the hydride stability of U-ZrHx fuel is the relationship between the fuel meat radius and the power density in the fuel. A simple equation is empirically determined that relates the “Goldilocks radius,” that is, the fuel radius for which the H/Zr ratio is most stable, to the power density in the fuel.

Exergetic efficiency and CO2 intensity of hydrogen supply chain including underground storage

Hydrogen plays a crucial role in the transition to low-carbon energy systems, especially when integrated into energy storage applications. In this study, the concept of exergy-return on exergy-investment (ERoEI) is applied to investigate the exergetic efficiency (defined as the ratio of useful exergy output to invested exergy input) and CO2 equivalent intensity of the hydrogen supply chain, with a specific focus on the underground hydrogen storage process. Our findings reveal that the overall exergetic efficiency of the electricity-to-hydrogen-to-electricity conversion process can reach up to 25 %. Among the hydrogen production methods, green hydrogen, produced via electrolysis powered by renewable energy, exhibits the lowest CO2 equivalent intensity. Blue hydrogen, produced from natural gas with carbon capture, can significantly reduce the carbon footprint of electricity generation, though this advantage comes at the expense of decreased exergetic efficiency. Analysis further indicates that the exergetic efficiency of underground storage components ranges from 72 % to 92 %. A substantial fraction of the exergy is lost during compression and injection of the stored hydrogen. Nevertheless, the subsurface operations contribute a minimal CO2 emission, between 1.46–4.56 grams of equivalent CO2 per megajoule (gr-CO2eq/MJ) when powered by low-carbon energy sources. Furthermore, it is found that hydrogen loss in the reservoir, along with methane and hydrogen leak during surface operations, notably affects the overall efficiency of the storage process.

Influence of Reservoir Salinity, Mineralogy, Temperature, and Pressure on Geochemical Hydrogen Loss in Depleted Carbonates

Summary Underground hydrogen storage (UHS) is a cost-effective and safer system vital for the growth of the hydrogen market and its role as an essential transitional fuel. Presently, depleted hydrocarbon reservoirs (DHR) account for more than 75% of all UHS sites due to their higher prevalence and readiness for use. However, hydrogen (H2) loss primarily due to abiotic interactions poses a significant challenge to the integrity of DHR sites, and while the underlying conditions have been investigated in some studies, the conclusions have been inconsistent, particularly for carbonate reservoirs. In this study, we analyzed the impact of reservoir physical and chemical parameters, (i.e., salinity, mineralogy, temperature, and pressure) on H2-brine-mineral interactions and the extent of H2 loss in carbonate formations. Static batch simulations were performed using PHREEQC and MATLAB® for a 1-year storage cycle period with three different brine and rock samples at 50–130°C and 15–30 MPa. The results showed that the dissociation of H2 and formation of CH4 and H2S increased with increasing temperature, at a two times higher rate compared to pressure. Also, markedly, in various brine compositions and reactive mineralogy, a 20% or less H2 loss could be attained in temperatures <50°C and 115–130°C, with pressure below 17 MPa; meanwhile, the pressure condition 18 MPa and greater (at 50°C) would risk at least 50% loss, with >86% from 19 MPa. Second, H2 loss increased to 80% after about 50 days for all the brines, and pressure and temperature conditions in the mineral sample with the largest composition of reactive minerals (i.e., pyrite, anhydrite, etc.) suggested a 50% loss risk in such mineralogy during the storage cycle period of about 1 month. Lastly, in the mineral sample with >90 wt% calcite and 0–2 wt% reactive minerals composition, H2 molality increased at least fourfold on average across the storage period and reservoir brine/temperature/pressure conditions. This result further indicates that reactive mineralogy has a more significant effect on the stability of hydrogen relative to temperature and pressure in a carbonate UHS formation. In summary, the findings suggest that a minimal reactive mineral composition, 100°C or higher, and 17 MPa or lower constitutes a set of reservoir physical and chemical conditions with the potential for a limited risk of H2 loss (<20%) in carbonate DHR. However, the extension of the present work to the dynamic UHS conditions is necessary to further ascertain these conclusions.

Ion Precipitation Into Io's Poles Driven by a Strong Sub‐Alfvénic Interaction

AbstractJuno performed two close flybys of Io and found enhanced field‐aligned proton fluxes are absorbed by Io. These protons are absorbed at mass input rates comparable to previous estimates for hydrogen losses from Io, hence Jupiter is likely the source of hydrogen at Io. The conditions necessary for this to occur are: (a) formation of Alfvén waves at Io, (b) wave‐particle coupling to energize protons, (c) anti‐planetward transport of ions due to the magnetic mirror force and/or parallel acceleration, and (d) strong sub‐Alfvénic interaction slowing the flow connected to Io's fluxtube allowing for sufficient travel time for energized ions to transit to Io. The derived slowdown of ≤12% the upstream value is linked to filamentation within the Alfvén wing. This mechanism is likely operating at all strongly interacting satellites and provides an avenue to transfer material from a planetary body to its satellites, including exoplanets and brown dwarfs.

Comparative study on hydrogen losses via microbial byproduct in the presence of methane and nitrogen cushion gas

This study comprehensively investigates H2 loss resulting from injecting two gas mixtures: I (60% H2 + 30% CH4 + 5% N2 + 5% CO2) and II (60% H2 + 30% N2 + 5% CH4 + 5% CO2) into an aqueous solution containing 20,000 ppm sodium chloride and 100 ppm acetic acid (a microbial by-product of acetogenesis) within Bandera clay-rich sandstone reservoirs. Conducted at 42 °C and 1350 psi, various analytical techniques, including X-ray diffraction (XRD), Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, porosity and permeability assessments, pH and ion analysis, and gas chromatography, were utilized to assess the relevant properties of rocks, formation water, and gas content before and after 50 days treatment. The results indicate minimal sample reactivity, with dissolution primarily affecting dolomite and albite minerals. On average, porosity increased by 19% in formulation I and 15% in formulation II, while permeability decreased by 4.7% in formulation I and 5.3% in formulation II. In formulation I, H2 fraction decreased by 2.79%, CH4 increased by 7.15%, and CO2 decreased by 9.36%, with N2 remaining constant, whereas in formulation II, H2 only decreased by 1.3%, CH4 increased by 19.22%, and CO2 decreased by 3.58%, with N2 remaining consistent. Overall, the N2 cushion gas condition (i.e., formulation II) slightly outperformed CH4 in minimizing H2 losses. This study thus provides significant insights into potential H2 loss within a microbial-by-product-rich environment for underground hydrogen storage.

Pore scale modeling on microbial hydrogen consumption and mass transfer of multicomponent gas flow in underground hydrogen storage of depleted reservoir

As first effort in literature, this study proposed a mathematical model for microbial hydrogen consumption of underground hydrogen storage in the depleted reservoir, considering phase-change mechanism in growth-decay of bio-film, methanogen reaction, and mass transfer in the multicomponent flow. Effects of the growth-decay mechanisms of methanogens on pore structure, permeability and gas components, were simulated and analyzed in 2D and 3D porous models. The results indicated that: 1) The potential risk of the clogging of the pore space by microbial community was confirmed. 2) The initial volume fraction of microbial saturation (VFm) has a great effect on the growth and decay mechanism of methanogen which adopts the hydrogen as the energy source. 3) The optimized decay coefficient of the biomass could be achieved to decrease the loss of hydrogen and its purity. 4) The reduction rate of porosity and normalized permeability (KN) was believed to be related to decay-growth mechanism of microbials and the pore structure. The model with a lower porosity would lead to a higher saturation of biofilm-water layer (BWL), as well as a higher reduction of the porosity. The required time to reach the maximum BWL was the same, when assuming the growth process of methanogen was homogeneous and isotopic.

A Redox-Reversible Switch of DNA Hydrogen Bonding and Structure.

Modulating molecular structure and function at the nanoscale drives innovation across wide-ranging technologies. Electrical control of the bonding of individual DNA base pairs endows DNA with precise nanoscale structural reconfigurability, benefiting efforts in DNA origami and actuation. Here, alloxazine DNA base surrogates were synthesized and incorporated into DNA duplexes to function as a redox-active switch of hydrogen bonding. Circular dichroism (CD) revealed that 24-mer DNA duplexes containing one or two alloxazines exhibited CD spectra and melting transitions similar to DNA with only canonical bases, indicating that the constructs adopt a B-form conformation. However, duplexes were not formed when four or more alloxazines were incorporated into a 24-mer strand. Thiolated duplexes incorporating alloxazines were self-assembled onto multiplexed gold electrodes and probed electrochemically. Square-wave voltammetry (SWV) revealed a substantial reduction peak centered at -0.272 V vs Ag/AgCl reference. Alternating between alloxazine oxidizing and reducing conditions modulated the SWV peak in a manner consistent with the formation and loss of hydrogen bonding, which disrupts the base pair stacking and redox efficiency of the DNA construct. These alternating signals support the assertion that alloxazine can function as a redox-active switch of hydrogen bonding, useful in controlling DNA and bioinspired assemblies.

Hydrogen Use in a Dual-Fuel Compression Ignition Engine with Alternative Biofuels

Recent progress has been made towards decarbonisation of transport, which accounts for one quarter of global carbon dioxide emissions. For the short to medium term, new European Union (EU) and national energy and climate plans agree on a strategy based on the combination of increasing shares of electric vehicles with the promotion of sustainable fuels, especially if produced from residual feedstock and routes with low or zero net carbon emission. Hydrogen stands out among these fuels for its unique properties. This work analyses the potential of using hydrogen in a dual-fuel, compression ignition (CI) engine running with three diesel-like fuels (conventional fossil diesel, advanced biodiesel (BD) and hydrotreated vegetable oil (HVO)) and different hydrogen energy substitution ratios. The results were confronted with conventional diesel operation, revealing that dual-fuel combustion with hydrogen demands higher exhaust gas recirculation (EGR) rates and more advance combustion, leading to a remarked reduction of NOx emission at the expense of a penalty in energy consumption due mainly to unburnt hydrogen and wall heat losses. Unreacted hydrogen was ameliorated at high load. At low load, the use of BD dual combustion permitted higher hydrogen substitution ratios and higher efficiencies than diesel and HVO.

Comparisons between the high-pressure SPS and routine SPS of dense YH2-x

Spark plasma sintering (SPS) shows great potential in the fabrication of bulk YH2-x. For the first time, the high-pressure SPS (HPSPS) of YH2-x is explored and compared with the routine SPS. It is found that HPSPS remarkably reduces the densification temperature, and thus the thermal dehydrogenation phase transition (δ-YH2-x → α-Y) and the hydrogen loss of YH2-x can be avoided. Nearly fully dense δ-YH1.80 monolith is successfully prepared by HPSPS under 500 MPa at a relatively low temperature of 800 °C. HPSPS is effective in overcoming the thermal dehydrogenation problem during the sintering of YH2-x. Compared with significant grain growth in the routine SPS, the grain growth in the HPSPS is very limited. In terms of thermal properties, the thermal conductivity of HPSPS prepared YH2-x is relatively low below 600 °C, then tends to be closed above 600 °C, compared with routine SPS prepared and directly hydrided YH2-x. The thermal expansion of HPSPS prepared dense YH2-x is basically consistent with that of directly hydrided bulk. This study provides a valuable reference for the sintering of high-quality δ-YH2-x and other metal hydrides monoliths.