High-pressure Hydrogen Research Articles

Characterization of High-Pressure Hydrogen Leakages

Abstract Reduction of gas turbine (GT) carbon emissions relies on a strategy for fueling the engines with pure or blended hydrogen. The major technical challenges to solve are (i) the adjustments to the engine and in particular the combustion chamber and (ii) a series of issues to solve to guarantee safe operations. In fact, compared to natural gas, hydrogen fueling implies higher risks of explosion in case of leak in the turbine enclosure and a more careful design of the ventilation system. Thus, a deeper comprehension of hydrogen leak scenarios is needed to adjust the safe design strategy of the enclosure. To this aim, a series of numerical investigations was carried out to understand how different methane–hydrogen blends (from pure methane to pure hydrogen) behave when leaking from a pipeline with fuel pressure that span from 1.5 to 4.5 MPa. The different fuel blends' leaks in form of underexpanded jets were studied under different cross-flow ventilation conditions, with ventilation velocity spanning from 0 m/s to 5 m/s. When compared to pure methane, the outcome is a three times longer penetration distance for pure hydrogen axisymmetric flammable clouds, whereas in cross-flow conditions a more complex three-dimensional behavior was found, potentially opening a safety-related concerns discussed in the paper.

Design and optimization of high-density cryogenic supercritical hydrogen storage systems integrating with dual mixed refrigerant cycles

To address the low density of high-pressure gaseous hydrogen and evaporation issues associated with liquid hydrogen storage, cryogenic supercritical hydrogen storage method is presented in this paper. Based on a dual parallel mixed refrigerant cycle (DPMR) and a dual cascade mixed refrigerant cycle (DCMR), the density of supercritical hydrogen product is 70.74 kg/m3, closely approaching liquid hydrogen. The processes are simulated in Aspen HYSYS, optimized by genetic algorithm for lower specific energy consumption (SEC). Thermodynamic analysis is conducted to compare with hydrogen liquefaction processes, demonstrating the feasibility and superiority of proposed process. The results show that the DPMR process has an SEC of 6.422 kWh/kgH2 and exergy efficiency of 52.66%, while DCMR is 6.872 kWh/kgH2 and 49.24%. Additionally, the inclusion of ortho-para convertors in DPMR process is investigated to further analyze the impact of heat release for ortho-para conversion. Furthermore, a techno-economic analysis is conducted on three processes, validating the economic feasibility. The study indicates that cryogenic supercritical hydrogen storage system is of great significance to the development of high-density hydrogen storage technology. The DPMR and DCMR presented in this paper can significantly improve the energy efficiency and provide valuable information for the design of high-density hydrogen storage system.

Microgrids for green hydrogen production for fuel cell buses – A techno-economic analysis for Fiji

The study examines the feasibility of producing hydrogen for fuel cell buses in Fiji. The paper focuses on sizing hybrid microgrids comprising solar panels and wind turbines as the primary power source for hydrogen production while considering both off-grid and grid-connected cases. As no fuel cell vehicles exist in Fiji at present, five long-distance buses with daily travel of 380 km are proposed as a pilot scale baseline system, which would operate in the daytime only. Detailed technical and economic modelling was done using the HOMER Pro software with cost inputs derived from literature. A total of three cases for the on-grid and four cases for the off-grid systems are analyzed based on the various combinations of components. HOMER Pro optimized the grid configurations to minimize the Net Present Cost (NPC) values. All seven cases were also modelled with and without the effects of hydrogen gas compressors to emulate the production of low-pressure gas without compression and compressed high-pressure hydrogen required for fuel cell buses. It was found that a grid-connected system with solar and wind hybrid was the most feasible configuration and yielded the lowest NPC of $6 million. The grid-connected case also yielded a Levelized Cost of Electricity (LCOE) of $0.10/kWh and a Levelized Cost of Hydrogen (LCOH) of $9.08/kg with compression to 400 bars. The LCOH stood at $8.73/kg for hydrogen generation without compression. The most feasible off-grid configuration using solar and wind power attained an LCOE of $1.15/kWh while giving a LCOH of $13.00/kg for compressed hydrogen. It was also found that neglecting hydrogen compression load and costs can underestimate the LCOH by as much as 6.92 %. The off-grid best case had no CO2 produced during its operation, leading to a net zero process that offsets 929.9 tons of CO2 compared to the baseline. The grid-connected system does have some emissions but leads to a 93.9 % reduction in CO2 emissions, offsetting 873.3 tons of CO2 compared to the baseline. The study updated the cost inputs to account for inflation, logistics, and hydrogen gas compression, which are not available directly in HOMER Pro software. At the time of writing this paper, no feasibility study existed for hydrogen production in Fiji using renewable energy.

Amplification of Supercontinuum Seed Pulses at ~1078–1355 nm by Cascade Rotational SRS in Compressed Hydrogen

Multiple higher-order Stokes of rotational stimulated Raman scattering (SRS) in compressed hydrogen covered the wavelength range from ~1.1 µm to ~1.4 µm using ~1.2 ps pump pulses from a Yb:YAG laser. In this study, the influence of polarization, energy, and the focusing conditions of the pump pulse, as well as gas pressure, on the conversion efficiency and modification of the spectral envelope of rotational and vibrational SRS was investigated. The use of a supercontinuum seed, as well as circular polarization of pump pulses at high hydrogen pressure, made it possible to significantly reduce the threshold for rotational SRS and suppress vibrational Stokes modes. The cascade excitation of rotational SRS, corresponding to a shift of 587 cm−1, ensured a spectrum spanning four Stokes orders withs a conversion efficiency of 52% and an output energy exceeding 3 mJ. The synthesized spectrum corresponded to ~14 fs transform-limited pulses.

High-Strength PPS-Polymer Composites for Hydrogen High-Pressure Applications

Hydrogen technology can be one key for a transition to sustainable energy necessary to achieve climate targets and limit global warming to 1.5 °C since the beginning of the industrial revolution. Hydrogen as a CO2 neutral energy carrier must replace fossil fuels from the existing natural gas grid and infrastructure to enable an environmentally friendly and circular economy in future societies. Batteries and e-fuels are practicable technologies for short term and quantitatively limited energy provision, with disadvantages including raw material demands and technologically complex transformation cycles. Utilizing advanced power-to-gas concepts, hydrogen will not only be most efficient technology in energy storage, but also allows adaption and reuse of existing energy transportation infrastructure.To provide volatile hydrogen gas in the required flow and energy densities, advanced compression technology needs to be developed inspired by conventional gas compression systems. Reciprocating piston compressors are developed for high-pressure hydrogen applications, providing high pressure levels and flow rates. Compression equipment must be designed for non-lubricated dry-running conditions, as high gas purity standards of hydrogen do not allow for oil-based lubricants to be introduced into the process gas. High-strength carbon fiber reinforced composites are developed as piston and packing ring materials to withstand extreme pressure differences under harsh thermo-mechanically loaded operation conditions.Promising candidates with high strength and wear resistance in the form of PPS-polymers, are developed with PTFE solid lubricants and different carbon fiber fractions to combine high strength, with low friction and wear, improve pressure operation range, and limit down times of hydrogen piston compressors. The current work describes tribological testing of advanced PPS-polymers with 10 to 30 wt.% carbon fibers in a high-velocity tribometer under hydrogen gas atmosphere. Supporting thermo-mechanical tests give new insights in deformation mechanisms of fiber reinforced polymer composites and allow conclusions on their applicability for hydrogen compression.

Hydrogen-related degradation of fracture properties and altered fracture behavior of Cr–Mo steel used in hydrogen stationary vessels

This study comprehensively analyzes the effect of high-pressure hydrogen gas on the elastic-plastic fracture toughness, fatigue crack growth rate (FCGR) properties, and the corresponding fracture behavior of Cr–Mo steel in hydrogen stationary vessels. The fracture toughness value under 99 MPa hydrogen pressure significantly reduced by approximately one-third of the value tested in ambient air while FCGRs tested under hydrogen environments at a specified ΔK exhibited an approximate two-order magnitude increase compared to those observed in ambient air. The hydrogen-assisted fracture mechanism, encompassing crack initiation, propagation, and crack arrested, was meticulously examined. The distinct variations in fracture modes with changes in the ΔK range can be attributed to the synergistic interaction of HELP and HEDE mechanisms. Leak before break (LBB) behavior was not satisfied for the hydrogen vessel due to a significant reduction in the fracture toughness of materials when exposed to 99 MPa H2.

Amine-Functionalized SBA-15 Mesoporous Silica-Anchored Ni Nanocatalyst for CO2 Hydrogenation Reaction

Abstract: In this study, we successfully synthesized amine-functionalized SBA-15 mesoporous silicasupported Nickel nanoparticles (Ni NPs) and investigated their potential for CO2 transition to formic acid via high-pressure hydrogenation reaction. The metal-support interface between the Ni NPs and the amine-functionalized SBA-15 mesoporous silica was examined using various techniques, including BET, TEM, and XPS analyses. Our findings reveal a robust metal-support interaction between the NiNPs and the mesoporous silica substrate, highlighting the suitability of the catalyst for the CO2 conversion reaction. Additionally, the catalyst CAT$Ni-1 exhibited good catalytic activity over CAT$Ni-2 and CAT$Ni-3, and we were able to recycle them up to five runs with no significant reduction in catalytic activity. These results suggest that the synthesized Ni NP catalysts have the potential for large-scale CO2 conversion, contributing to the development of sustainable technologies for reducing greenhouse gas emissions.

Modelling the conjugate heat transfer during the fast-filling of high-pressure hydrogen vessels for vehicular transport

Compressed gas in cylinders is currently the preferred solution for storing hydrogen on board vehicles. Fast-filling combined with high storage pressures is required to meet competitive targets of long driving ranges and short refuelling times. Experiments and CFD models have shown that the fast-filling leads to significant rise in temperature within the hydrogen cylinder, which can lead to its structural failure. Thus, controlling the rise in temperature is vital during the refuelling process. This paper describes the implementation of a universal thermodynamic model that determines the gas and structural temperature during the fast-filling of hydrogen cylinders. It includes the computation of conjugate heat transfer from the gas to the cylinder structure. The thermodynamic model requires negligible computational time without compromising accuracy and can used to implement different fast-filling scenarios on a laptop or personal computer. The flexibility and robustness of the model is shown as it is capable of modelling the fast-filling of cylinders while varying different key parameters such as fill time, structural material, cylinder volume, final pressure, filling rate, initial temperatures and pressures.

Nickel-Catalyzed Chemo- and Enantioselective Hydrogenation and Deuteration of α,β-Unsaturated Ketimines Using Alcohols: Synthesis of Deuterated Chiral Allylic Amines.

A nickel-catalyzed chemoselective asymmetric transfer hydrogenation of α,β-unsaturated ketimines using ethanol as a hydrogen donor under mild conditions that avoid using high-pressure hydrogen gas was developed. With this catalyst, C1-selective deuterated chiral allylic amines were efficiently synthesized using only stoichiometric 2-propanol-d8. Mechanism studies demonstrated the formation of a nickel hydride intermediate.

Effect of Hydrogen Pressure and Punch Velocity on the Hydrogen Embrittlement Susceptibility of Pipeline Steels Using Small Punch Tests under Gaseous Hydrogen Environments at Room Temperature

The in situ small punch (SP) test method is a simple screening technology developed to assess the hydrogen embrittlement (HE) characteristics of structural steels. This method can easily adjust the influencing parameters such as test temperature, gas pressure, and punch velocity depending on the hydrogen service environment. With increased hydrogen consumption, using pipelines for mass hydrogen transportation is being considered. This study evaluated the HE susceptibility of API-X52 and API-X70 steels, considering the hydrogen usage environment. The study investigated the effects of hydrogen pressure and punch velocity on the HE behaviors of each pipe steel at room temperature using the SP energy and relative reduction in thickness (RRT) to determine their effect on HE susceptibility quantitatively. The study found that hydrogen pressure produced a different HE effect; the lower the hydrogen pressure, the more HE was relieved. Particularly, when the punch velocity was high, such as 1 mm/min, the HE effect was significantly relaxed. However, when the punch velocity was below 0.01 mm/min, HE occurred even at low hydrogen pressure conditions, meaning hydrogen diffusion within the specimen during the SP testing reached a critical hydrogen concentration to create a brittle fracture. Both pipeline steels showed similar HE behaviors under a wide range of H2 pressures and punch velocities, showing an inverse S-curve for quantitative factors of SP energy and RRT against the H2 pressure at 1.0 mm/min punch velocity. The study classified the observed HE behaviors into four types based on quantitative and qualitative aspects. These findings confirm that the in situ SP test is a useful screening technique, and the factor RRT can be effectively applied to the HE screening of pipeline steels in low and high-pressure hydrogen environments.

Changes in the Optical Properties of Rubber Exposed to High-Pressure Hydrogen Using Pulsed Terahertz Waves.

In this study, we investigated how high-temperature, high-pressure hydrogen affects the optical properties of three kinds of sealing rubber (chloroprene rubber, ethylene propylene diene monomer, and acrylonitrile butadiene rubber) using pulsed terahertz waves. The optical properties of the rubber samples were analyzed before and after exposure to hydrogen (80 °C and 200 bar) for 72 h. The results showed that the terahertz waves had a shorter time delay and a lower signal intensity for all rubber types. The exposure response intensity, refractive index, and absorption rate also changed in the frequency domain. Raman and Fourier transform infrared spectroscopy were used for comparison, and a few peak shifts were observed. However, the Raman spectra had low signal quality, and the laser damaged the specimen. The study demonstrates that terahertz waves can be used as a non-contact non-destructive testing technique to evaluate the changes in sealing rubbers after hydrogen exposure.

Effect of polypropylene pyrolyzate as the solvent on hydrodeoxygenation of palm oil using Ni-Cu/ZrO2 catalyst

Green diesel is a biofuel that can be used directly in diesel engines and can be synthesized by hydrodeoxygenation (HDO) reaction of triglyceride (TG). Generally, this reaction requires a high hydrogen pressure (40–150 bar) and a high composition of organic solvent to facilitate a higher hydrogen solubility in the liquid phase. In many cases, long carbon-chain alkanes, mostly n-dodecane, have been used as solvents. The present work aims to investigate the potential of hydrogenated and non-hydrogenated polypropylene (PP) pyrolyzate as solvents in an effort to utilize plastic wastes in HDO reaction of palm oil. The reaction was carried out using bimetallic catalyst Ni-Cu/ZrO2 in a reactor with a hydrogen gas self-inducing impeller to facilitate a higher load-up hydrogen gas in the liquid phase. The effect of reaction time in HDO involving two solvents, i.e., PP pyrolyzate and hydrogenated PP pyrolyzate, was elucidated in this work. The results showed that hydrogenated PP pyrolyzate facilitates a higher deoxygenation activity than PP pyrolyzate. In addition, the synthesized bimetallic catalyst promoted the decarbonylation/decarboxylation route over the hydrodeoxygenation route at reaction temperatures of 280–350 °C. The conversion of TG increased from 51 % to 93 % by increasing the reaction temperature from 280 °C to 350 °C, with the corresponding highest yield of green diesel was 82 %. Therefore, the hydrogenated PP pyrolyzate can substitute the usual long carbon-chain alkanes.

Experimental investigation on the deformation and damage of steel ribbon wound vessel for hydrogen storage under external impact and blast loading

Steel ribbon wound vessel is a preferred type for stationary storage of high-pressure hydrogen in refueling stations. However, it is under the threat of fragment impact and blast loads caused by accidental explosions of hydrogen or other vessels. For the first time, the fragment-simulating projectile (FSP) impact tests with impact kinetic energy range from 1.8 × 103 J–4.9 × 103 J and external blast loading tests with TNT equivalent range from 157 g–4 kg of industrial-grade 50 MPa steel ribbon wound vessel were carried out. The damage of vessel under FSP impact loading was studied. The effect of concentrated and distributed blast loads on the deformation and damage of gas-filled vessel was analyzed, and the explosion resistance of vessel under near-field blast loading was explored. It is revealed that: 1) the steel ribbon wound vessels generally have good resistances to external blast and impact loads, 2) the primary damage characteristics of vessel under contact/near-field blast loading was localized depression deformation, accompanied by steel ribbons warping as the shock wave impulse increases, 3) the saddle fails earlier than the vessel under the near-field blast loading. Further, the failure modes of vessel under extreme blast loads were revealed. Results can provide reference for the safe design and validation of dynamic damage/failure analysis models of steel ribbon wound vessels.

Numerical simulation and performance analysis of solar hydrogen production using anion exchange membrane electrolyzer and blending with natural gas

Hydrogen production using solar energy and blending in a natural gas pipeline is a cost-effective alternative to hydrogen storage and transmission that leads to lower CO2 emissions caused by the energy infrastructure. In this paper, energy, exergy, and Exergoeconomic analyses of a solar hydrogen production system and its blending with natural gas in a city gate station of Isfahan city are performed in three days with minimum, average, and maximum solar irradiations. The system includes photovoltaic arrays, anion exchange membrane electrolyzer cells (AEMECs), a hydrogen compressor, and a system blending. The AEMEC is used due to its less expensive catalysts, non-acidic electrolyte, and high efficiency at high pressures. A three-dimensional numerical model is developed to determine the AEMEC’s polarization curve, accurately. The results show that with increasing solar irradiation and decreasing ambient temperature, the maximum power of the PV increases and the energy and exergy efficiency of the PV decreases. By increasing the injection of hydrogen into natural gas from 1% to 10% vol., the lower heating value of the fuel and the Wobbe Index decrease by 6% and 1.55%, respectively. By injection of 10% vol. hydrogen gas into natural gas compared to the case of using natural gas without hydrogen, the exergy cost of natural gas blended with hydrogen increases by 5.9%. Considering the environmental benefits of using hydrogen in combination with natural gas, including the reduction of greenhouse gases, and the fact that blending hydrogen up to 10% vol. with natural gas does not require any change in urban gas supply facilities, this process is feasible. In the case of using high-pressure AEMEC and removing the compressor to produce hydrogen at high pressure, the exergy cost of high-pressure hydrogen reduces by 29.3%.

Techno-Economic Analysis of a Physisorption-Based Hydrogen Storage System

Abstract Alternative long-term storage of energy is becoming increasingly important due to climate change. Hydrogen-based storage technologies have long been considered promising alternatives to batteries. However, the different forms of hydrogen storage have various disadvantages and are still comparatively expensive. As an alternative, this paper deals with a new concept for hydrogen storage, the Cryogenic Flux Capacitor (CFC). It is intended as an intermediate between high-pressure and liquid storage to exploit the advantages and reduce the disadvantages. This paper ranks the CFC technology against the others. For this purpose, it investigates the economic viability and the specific application as a grid-connected system. A complete system from hydrogen production and storage to conversion into electrical energy is considered. In detail, the costs for storage and storage time are compared, and the size scaling of a CFC-based system as a grid-connected system is examined. The Levelized Costs of Energy (LCOE) are calculated and compared as a benchmark. It turns out that a CFC-based storage system also requires a tremendous amount of energy in the form of liquid nitrogen and the associated operational costs for cooling down the hydrogen. Nevertheless, the overall operating costs are between high-pressure and liquid hydrogen storage. Most surprising is the LCOE, which, at 0.192 $/kWh–0.234 $/kWh, is well within the range of the other storage technologies. As a grid-connected storage system, CFC technology can be used as a small- to a medium-scale energy storage system, e.g., to serve smaller neighborhoods.

Thermo-mechanical properties and internal architecture of PI composites for high-pressure hydrogen applications

The efficient transport of Hydrogen is pivotal to the wide scale adaption of energy produced from renewable sources. Reciprocating piston compressors with high strength non-lubricated sealing solutions for piston and rod packing rings will be a key technology to fulfill gas purity and high-pressure gradients demands set by hydrogen applications. Polyimide polymer matrix composites have seen use in tribological applications and promise high mechanical strength and temperature resistance. The presented work describes carbon fiber reinforced Polyimide blends in comparison, characterized by complementary advanced methods to investigate their properties and potential for reciprocating compressor applications. Thermo-mechanical and tribological testing was supported by microstructure analysis utilizing synchrotron tomography and electron microscopy, pinpointing the necessity of dry lubricating additives such as PTFE. New insights in micromechanical deformation behavior of fiber reinforced polymers are given and promising fiber-reinforced polyimide compositions suitable for high-pressure hydrogen compression applications were identified.

A highly dispersed amorphous iridium nanoclusters electrocatalyst synthesized at a quasi-room temperature for efficient oxygen evolution reaction

The water-splitting by proton-exchange-membrane (PEM) electrolyser is a highly appealing technology for hydrogen (H2) production. However, oxygen evolution reaction (OER) at anode of PEM electrolyser requires expensive and scarce iridium (Ir) catalysts to overcome its sluggish kinetics. Therefore, minimizing the amount of Ir used in OER electrocatalysts is critical for commercial application of PEM electrolyser. Herein, we report a flexible one-pot pathway to prepare carbon supported amorphous Ir nanoclusters (NCs) with low-Ir-loading (5.1 wt% Ir) via high-pressure hydrogen (1 MPa) reducing Ir(IV) precursors at a quasi-room temperature (50℃). The obtained amorphous Ir NCs catalyst shows a high performance for OER in an acidic electrolyte with a overpotential of 290 mV and Tafel slope of 55 mV/dec, superior to those of crystalline Ir nanoparticles (NPs) and commercial Ir catalysts (340 mV; 77 mV/dec). We find that the high OER activity is related to amorphous IrOx formed on the Ir NCs surface. When Ir NCs was used as the anodic catalyst, the current density of the electrolyzer reached 30 mA cm−2 only requiring a cell voltage of 1.56 V. This work demonstrates that Ir NCs catalyst exhibits a promising application in practical overall water splitting for H2 production.

Numerical investigation on the influence of geometrical parameters on the temperature distribution in marine hydrogen storage tanks during filling

This paper established a two-dimensional axisymmetric model with a marine high-pressure hydrogen storage tank as the research object. Using numerical simulation, the effects of different aspect ratios, inlet diameters, and inlet pipe lengths on the temperature rise of the hydrogen storage tank during the filling process were studied. As the L/D ratio of the hydrogen storage tank increases, the momentum of the hydrogen gas reaching the bottom of the tank gradually decreases, making it easier to form localized high-temperature regions. For a hydrogen storage tank with an L/D of 6.0, the difference between the maximum and average temperature at the end of filling was 155.85 K. In contrast, the temperature difference of the tank with an L/D of 3.6 was only 32.81 K. In addition, the inlet pipe delivers the hydrogen deep into the tank and reduces the obstructing effect of the existing hydrogen in the tank on the newly filled hydrogen. For smaller L/D hydrogen storage tanks, the inlet pipe may backfire and create a high-temperature zone at the shoulder of the tank. In contrast, for larger L/D hydrogen storage tanks, a suitable length of inlet pipe can deliver the hydrogen deep into the tank. This will enhance the gas flow inside the tank, facilitating heat exchange and avoiding the formation of localized high-temperature areas at the bottom of the tank. However, excessively long inlet pipes can also lead to high-temperature areas on the shoulders. At a specific charge mass flow rate, the lower the inlet diameter, the higher the hydrogen flow rate. The larger flow rate helped promote uniform hydrogen mixing in the tank and made it challenging to form localized high-temperature regions.

Numerical simulation study on the leakage and diffusion characteristics of high-pressure hydrogen gas in different spatial scenes

This paper presents a computational fluid dynamics (CFD) model for simulating high-pressure hydrogen leakage and diffusion. The model incorporates heat exchange during hydrogen leakage diffusion and the real gas equation of state in high-pressure conditions. The CFD model can provide superior predictions of pressure, temperature, hydrogen density, and mass flow rate within the hydrogen storage cylinder changes during high-pressure hydrogen leakage compared to existing models. Moreover, the model validated by experimental data enables simulation of the spatiotemporal evolution law of hydrogen concentration and the change of the combustible region in space following a high-pressure hydrogen storage cylinder leak in various spatial scenarios. It can also determine the safe distance after the hydrogen leakage and simulate the impact of the hydrogen leakage on the surrounding environment in terms of temperature, pressure and other physical factors. Furthermore, the model is applicable for simulating the leakage and diffusion behavior of high-pressure hydrogen in various leakage conditions. This capability helps researchers understand the characteristics of high-pressure hydrogen leakage and diffusion, and further study the phenomenological evolution law of hydrogen safety accidents, so as to formulate emergency response strategies.

Hydrogen Embrittlement Characteristics of Tempered Martensitic Steels under Electrochemical and High-Pressure Hydrogen Environments

The effect of hydrogen charging methods on the hydrogen embrittlement characteristics of tempered martensitic steels were discussed in terms of hydrogen diffusion behavior. Two tempered martensitic steels with different Si content were fabricated by quenching and tempering. The steel with high Si content had a lower cementite fraction because the addition of Si changed the morphology of cementite from a long film-like shape to a short-rod shape by suppressing the precipitation and growth of the cementite. To evaluate the hydrogen embrittlement resistance of the two tempered martensitic steels with different Si content, slow strain-rate tensile testing was employed after introducing hydrogen using three types of hydrogen charging methods (ex-situ electrochemical hydrogen charging, in-situ electrochemical hydrogen charging, and in-situ high-pressure gaseous hydrogen environment). For the hydrogen pre-charged tensile specimens using the ex-situ electrochemical charging method, the steel with high Si content had a better hydrogen embrittlement resistance, with a higher relative reduction in area. On the other hand, there was no significant difference in the relative notch tensile strength of the two tempered martensitic steels with different Si content, regardless of the hydrogen charging methods. In addition, the ex-situ hydrogen charging method exhibited higher relative notch tensile strength compared to the in-situ hydrogen charging method due to the release of hydrogen during the tensile test, after exsitu hydrogen charging. This implies that hydrogen embrittlement resistance can be differently estimated depending on the kind of hydrogen charging methods.