Wet Hydrogen Research Articles

Enhanced protonic and oxygen-ionic conductivity in Ga-doped Nd2Ce2O7 electrolytes for intermediate-temperature solid oxide fuel cell

Developing mixed oxygen-ion and proton conductors with high ionic conductivity is crucial for advancing intermediate temperature-solid oxide fuel cell (IT-SOFC). In this study, a novel Nd2-xGaxCe2O7 (NGCO, x = 0, 0.05, 0.075, 0.10 and 0.15) ceramic is synthesized by the citric acid-nitrate sol-gel combustion process. The influence of Ga doping on crystal structure, oxygen vacancy, morphology, proton transport characteristic and electrochemical performance of this materials is systematically investigated. It is found that the NGCO exhibits the fluorite-type structure and belongs to space group Fm3¯m. NGCO shows remarkable chemical stability, resisting harmful effects from CO2, water, and wet hydrogen exposure. Adding a small amount of Ga results in high-density ceramics with enlarged grain size and reduced grain boundary density. Nd1.925Ga0.075Ce2O7 (7.5NGCO) displays outstanding conductivities, exceeding Nd2Ce2O7 (NCO) by 271.4% and 248.6% in dry air and wet hydrogen conditions. Further, an anode-supported structure fuel cell with 7.5NGCO electrolyte is constructed and evaluated. The peak power density (PPD) at 700 °C reaches 702 mW/cm2, a 96% enhancement over the fuel cells with NCO electrolyte. These findings indicate that Ga-doped NCO electrolyte holds promise as a proton-conducting electrolyte suitable for IT-SOFC.

Step-by-step strategy to improve the performance of the (La,Sr)(Ga,Mg)O3-δ electrolyte for symmetrical solid oxide fuel cells

Research on the highly conductive solid electrolyte with the overall composition of (La,Sr) (Ga,Mg)O3-δ (LSGM) has reached a new stage of development in recent years due to the successes in the field of symmetrical electrochemical devices in which LSGM utilizing as a supporting layer. This study shows a “step-by-step” approach to modify the LSGM electrolyte using both individual techniques and their combinations to improve the functional properties of the LSGM. As a result of a multi-step modification, the new electrolyte of composition (La0.8Sr0.2)0.98Ga0.7Fe0.1Mg0.2O3-δ + 0.5 wt% Fe2O3 was obtained. It is shown that the conductivity of new electrolyte is about five times higher than that of the basic La0.8Sr0.2Ga0.8Mg0.2O3-δ oxide at 600 °C. Furthermore, the better thermo-mechanical and chemical compatibility with the iron-based electrode was found. It also shows insignificant resistance degradation in long-term tests in air and satisfactory stability in wet hydrogen. Based on the results of the research it can be concluded that the new electrolyte obtained by step-by-step modification has great prospects for utilization in symmetrical fuel cells.

Boosting electrochemical performance of Ni/YSZ electrode through simultaneous injection of nickel and ceria

Nickel/oxygen ion conducting ceramic composite powders (Ni/YSZ) are commonly used materials for fuel electrodes of solid oxide fuel cells and electrolyzers. One of the ways for increasing the activity of Ni/YSZ is infiltration/impregnation, where a formed porous electrode is impregnated with solutions of active elements, followed by thermolysis. In this study, Ni/YSZ electrodes simultaneously impregnated with nickel and ceria particles in different ratios are investigated. It is shown that the introduction of highly dispersed nickel only slightly increases the activity of the Ni/YSZ electrode and does not affect the pathway of the hydrogen oxidation reaction. If a minor amount of ceria particles is introduced into the electrode, it significantly increases its activity and partially changes the reaction mechanism. The best performance is obtained for the electrode impregnated with an equal volume solution of nickel and cerium nitrates. The polarization resistance of such an electrode in wet hydrogen is about 0.05 and 0.17 Ohm cm2 at 850 and 600 °C, respectively, which is about 10 and 65 times lower compared to initial Ni/YSZ. Long-term tests of more than 1100 h in a wet hydrogen atmosphere at 700 °C showed satisfactory stability of polarization resistance of all investigated electrodes.

Electrochemical behaviour of redox-robust electrode in contact with protonic electrolyte: Case of double-layered Sr2Fe1.5Mo0.5O6-δ - Ce0.8Sm0.2O2-δ composite

Electrochemical devices based on proton-conducting oxides offer a significant potential for implementation in a variety of high-temperature electrochemical applications. It is a well-known fact that electrochemical devices require active electrodes to function optimally. Over the last few years, Sr2Fe1.5Mo0.5O6-δ has received much attention as an effective redox-robust electrode for oxygen conducting electrolytes. This study presents, for the first time, the results of investigations on a double-layered composite electrode based on Sr2Fe1.5Mo0.5O6-δ in contact with a barium-free proton-conducting electrolyte La0.9Sr0.1ScO3-δ. It was found that the investigated electrode exhibits low polarization resistance about 0.15 and 0.22 Ohm cm2 in wet air and wet hydrogen at 600 °C, respectively. In addition, the electrode exhibits acceptable redox stability and CO2 tolerance. Also, the results of electrochemical impedance spectra analysis and a discussion on the parallel pathways of hydrogen oxidation and oxygen reduction reactions and the nature of rate-determining steps are presented in the manuscript. The obtained results show the high prospects for a Sr2Fe1.5Mo0.5O6-δ - based composite electrode for protonic ceramic electrochemical cells.

Effects of firings in hydrogen on the insulation performances of a 95 wt% alumina ceramic

To investigate the effects of point defects on the insulation performances of alumina ceramics, we fire a 95 wt% alumina ceramic in wet hydrogen, dry hydrogen, and supplementary air, to change the concentrations of aluminum vacancy (VAl‴) and oxygen vacancy (VO••). The dielectric breakdown strength (DBS) and flashover voltage (FV) are tested, and the point defects are characterized by XPS and optical reflectance. Firing in wet hydrogen decreases the concentration of VO••, improving DBS but deteriorating FV. Nevertheless, firing in dry hydrogen increases the concentration of VAl‴, improving FV but deteriorating DBS. Supplementary firing in air weakens the effects of firing in dry hydrogen on the point defects and insulation performances. The effects of firings on insulation performances are attributed to the concentrations of electrical carriers that are determined by the point defects, and this is confirmed by the results of electrical resistivity.

Mn Additive Improves Zr Grain Boundary Diffusion for Sintering of a Y-Doped BaZrO3 Proton Conductor.

Yttrium-doped barium zirconate (BZY) has garnered attention as a protonic conductor in intermediate-temperature electrolysis and fuel cells due to its high bulk proton conductivity and excellent chemical stability. However, the performance of BZY can be further enhanced by reducing the concentration and resistance of grain boundaries. In this study, we investigate the impact of manganese (Mn) additives on the sinterability and proton conductivity of Y-doped BaZrO3 (BZY). By employing a combinatorial pulsed laser deposition (PLD) technique, we synthesized BZY thin films with varying Mn concentrations and sintering temperatures. Our results revealed a significant enhancement in sinterability as Mn concentrations increased, leading to larger grain sizes and lower grain boundary concentrations. These improvements can be attributed to the elevated grain boundary diffusion of zirconium (Zr) cations, which enhances material densification. We also observed a reduction in Goldschmidt's tolerance factor with increased Mn substitution, which can improve proton transport. The high proton conduction of BZY with Mn additives in low-temperature and wet hydrogen environments makes it a promising candidate for protonic ceramic electrolysis cells and fuel cells. Our findings not only advance the understanding of Mn additives in BZY materials but also demonstrate a high-throughput combinatorial thin film approach to select additives for other perovskite materials with importance in mass and charge transport applications.

Defect-induced improved structural and electrical properties of Gd-Sr co-doped ceria for solid oxide fuel cell applications

Compositions of Ce1-x-yGdxSryO2-δ (x = 0.1, 0.2, and y = 0.025, 0.05, 0.075) are prepared using the sol-gel auto combustion method. The as-prepared powders are calcined at 500 °C for 2 h, followed by pelletization and sintering at 1450 °C for 4 h. Phase identification, defect distribution, microstructural analysis, and conductivity are examined using X-ray diffraction, Raman spectroscopy, scanning electron microscopy and impedance spectroscopy, respectively. A single crystalline phase is formed, and the lattice parameter variation with dopant concentration exhibits anomalous behavior. All the samples show relative densities higher than 92 %. The partial liquid phase sintering is also observed. In co-doped samples, the doping of 10 % Gd with 2.5 % Sr exhibits the highest conductivity, i.e., 1.20 × 10−2 S cm−1 at 600 °C. The developed materials are used in anode-supported cell testing. It shows a maximum power density of 112.7 mW cm−2 and a current density of 288.7 mA cm−2 at 600 °C with wet hydrogen and air on the anode and cathode side, respectively.

Structural stability and features of electrical and electrochemical behavior under reducing conditions of Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ material for the symmetrical SOFCs

In this study, a performance of the complex oxide composition of Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ was investigated from the viewpoint of its use as a fuel or symmetrical electrode for the electrochemical devices with a LaGaO3-based solid electrolyte. The results show that the above-mentioned oxide can be obtained as a single-phase composition using solid-phase synthesis with a final annealing temperature of 1150 °C. It has been shown that the oxide retains satisfactory stability at 800 °C in an atmosphere of 5 % H2 + Ar, only a minor amount, presumably of Co-Fe alloy, has been detected. The electrical conductivity of the oxide in wet hydrogen exhibits a linear semiconductor-type behavior with a conductivity value of 7 S · cm–1 at 800 °C. The polarization resistance of the Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ electrode in wet hydrogen atmosphere reaches approximately 1.09 Ω · cm2 at 800 °C, which is a relatively high value for the electrodes of electrochemical devices. A significant reduction in resistance down to 0.43 Ω · cm2 is observed for the electrode activated with impregnated ceria. It has been demonstrated that the observed decrease in resistance is due to the expansion of the area of the electrochemical reaction without changing its mechanism. The long-term tests with a duration of about 220 h at 800 °C in a wet hydrogen atmosphere demonstrate satisfactory stability of the electrochemical activity of the Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ electrode, which can be considered as a promising electrode for intermediate temperature electrochemical devices, including those of symmetrical design.

ANALYSIS OF THE CAUSES OF DAMAGE TO A LONG-OPERATED PIPELINE OF WET HYDROGEN SULFIDE-CONTAINING NATURAL GAS

The results of ultrasonic inspection of discontinuities in the metal of the pipe walls, long time operation under high pressure of wet hydrogen sulfide-containing natural gas, and analysis of the data characterizing them are presented. The criteria for selecting characteristic sections of the pipe with defects and sample cutting for fractographic research are substantiated. Based on the results of the analysis of ultrasound inspection and fractographic investigation, the causes and factors determining the process and mechanisms of sulfide cracking of the pipe walls have been established. The pipeline damage was assessed.

Direct carbon dioxide-methane solid oxide fuel cells combined with in-situ exsolution perovskite La0.75Sr0.25Cr0.5Fe0.4Cu0.1O3-δ-based dry reforming catalysts

In response to greenhouse effect and energy crisis, the clean and efficient use of CH4 and CO2 resources has become increasingly attractive. Against this background, solid oxide fuel cells (SOFCs) have become one of the research hotspots due to the possibility of utilizing methane and carbon dioxide for the conversion into syngas (H2 and CO) for efficient direct power generation. In this study, we propose to dope Cu into La0.75Sr0.25Cr0.5Fe0.5O3-δ to enhance the catalytic activity for direct carbon dioxide-methane dry reforming reactions. In wet hydrogen conditions, Fe nanoparticles can effectively exsolve from La0.75Sr0.25Cr0.5Fe0.4Cu0.1O3-δ (LSCFC), which is beneficial for the dry reforming reaction of methane. With the LSCFC-Ce0.9Gd0.1O2-δ (LSCFC-GDC) composite reforming layer, the anode-supported single cells exhibited remarkable electrochemical performance. When fueled with both H2 and CH4–CO2, the maximum power densities achieved 608.3 and 497.1 mW cm−2 at 800 °C, with corresponding polarization resistance values of 0.35 and 1.11 Ω cm2, respectively. Furthermore, the single cells with LSCFC-GDC reforming layer showed excellent carbon tolerance, maintaining stable performance for 120 h using 50%CH4–50%CO2. Our results demonstrate the use of dry reforming catalysts in SOFCs is effective in both enhancing CH4–CO2 reforming efficiency and maintaining carbon tolerance.

Novel BaO-decorated carbon-tolerant Ni-YSZ anode fabricated by an efficient phase inversion-impregnation approach

In this study, an efficient phase inversion-impregnation approach is developed for fabricating BaO-decorated Ni-8 mol% yttria-stabilized zirconia (YSZ) anode-supported tubular solid oxide fuel cells (SOFCs) toward anti-coking. This technique involves a simple phase-inversion process, along with the saturated barium nitrate solution as coagulation bath. Experimental results show that BaO nanoislands with particle size of less than 100 nm have been successfully and uniformly introduced inside the Ni-YSZ anode. The corresponding peak power densities are determined to be 0.30 W cm−2 and 0.22 W cm−2 at 800 °C in wet hydrogen and methane fuel, respectively. The long-term stability in methane fuel with the BaO-decorated anode is significantly improved with respect to the pristine one. Density functional theory (DFT) calculations suggest that the loading of BaO nanoislands can efficiently capture and dissociate the H2O molecules to generate OH, which subsequently serves as effective carbon elimination medium. The OH diffusion from BaO to BaO/Ni interface coupling with the formation of COH is the key step involved in the carbon elimination mechanism. The as-proposed phase inversion-impregnation approach exhibits advantage in time and cost savings compared to traditional impregnation methods, providing a new route for fabricating anti-coking SOFC anodes.

Deep decarburization of molybdenum and tungsten powders by wet hydrogen

The control of residual carbon content is an urgent problem to be solved for the preparations of molybdenum and tungsten powders by method of carbothermic reduction of their oxides. In this paper, finer Mo (W) powder with a low residual carbon content was prepared by a two-step reduction process consisting of carbothermal pre-reduction of MoO3 (WO3) at 1050 °C and following deep hydrogen reduction. During the deep hydrogen reduction process, with the increases of hydrogen reduction temperature and dew point, the residual carbon contents of the finally prepared Mo and W powders gradually decreased, while the particle sizes of Mo and W powders gradually increased. The lowest residual carbon and oxygen contents of Mo and W powders obtained after hydrogen reduction at 1100 °C with the hydrogen dew point of 41 °C were 0.007 wt% (carbon content) and 0.104 wt% (oxygen content), as well as 0.010 wt% and 0.086 wt%, respectively. In addition, the mean particle sizes of them were 1032 nm and 998 nm under this condition, respectively.

Stainless Steel in Municipal Sewage-How to Recognize Favorable Corrosion Conditions.

While chromium-nickel steel is known to be extremely resistant to corrosion, the occurrence of certain factors can unfortunately initiate an uncontrolled corrosion process. This paper presents samples made of 304 stainless steel containing delta ferrite that have been exposed to wastewater for 18 months. Samples placed above the surface of the wastewater (A-series) were intensively corroded. Samples half-submerged in the wastewater and periodically fully submerged at higher effluent flows through the screenings and grit separator (B-series) only suffered minor mechanical erosion. No significant changes in the tested surface were observed on samples fully submerged in wastewater (C-series). The results indicated that the observed pitting corrosion of samples placed above the surface of the wastewater was a consequence of the presence of bacteria in a wet hydrogen sulfide environment. The fluorescence in situ hybridization method showed that either the sludge taken from the wastewater, or from the surface of samples submerged in wastewater exhibited increased amounts of bacteria from the δ-proteobacteria class, indicating the presence of microorganisms involved in the reduction of sulfur or sulfate compounds. A new approach to microbiological evaluation by determining classes of bacteria may be a promising tool for evaluating wastewater in terms of aggressiveness and recognizing favorable corrosive conditions.

Predicting sulfide stress cracking in a sour environment: A phase-field finite element study

Sulfide stress cracking (SSC) is a leading cause of failure in sour service environments, where the presence of wet hydrogen sulfide (H2S) causes hydrogen embrittlement and significantly influences the performance and lifespan of casing and tubing pipes. This work presents a numerical investigation on predicting the onset and growth of SSC in a sour environment using a coupled deformation–diffusion phase-field finite element framework, which incorporates the role of sub-surface hydrogen concentration due to H2S exposure and mechanical loading effects on the crack growth response. The numerical results agree with the experimental data from the notched slow strain rate testing performed on high-strength low alloy steel (HSLA) in a sour environment at room temperature. Recently, the oil and gas industry has been heading towards unconventional gas well applications that expose crucial parts of a well construction, such as production casings, to high internal pressures and a sour environment. To simulate such conditions, a numerical study is conducted that examines the onset and growth of SSC in pre-notched pressurized pipes subjected to H2S exposure. The geometry and boundary conditions used for the pre-notched pipes adhere to the API 579 standard for fitness for a service assessment of equipment containing identified flaws or damage. The findings of this comprehensive numerical investigation provide valuable insights into the effectiveness of a coupled phase-field approach for SSC and demonstrate its potential as an engineering tool for structural integrity assessments that consider environmental effects.

Performance enhancement of multi-gas compatible dual-channel interconnector for planar solid oxide fuel cells

This study designed a novel interconnector, known as the dual-channel interconnector (DCI), for the anode-supported planar solid oxide fuel cell (SOFC). The DCI have two independent flow channels and allow multiple gases to enter SOFC simultaneously without interference. The DCI has half the height of a conventional interconnector. The electrochemical reaction of carbon monoxide and hydrogen as well as the methane steam reforming reaction, water gas shift reaction and dry reforming reaction of methane were coupled in the mathematical models. Results show that the peak power densities of the DCI-SOFC increased by 21.7% and 11.3% compared to the SCI–SOFC for wet hydrogen and 30% reformed methane when both channels are utilized together. The DCI-SOFC exhibits similar electrical performance in any single-channel operation, accompanied by a 30% decrease in peak power density. The DCI-SOFC can significantly reduce the activation overpotential and concentration overpotential, while slightly increase the contact overpotential. The DCI eliminates the oxygen-free zone under the ribs and enhances the mass transfer inside the electrodes. The temperature inside of the DCI-SOFCs are strongly correlated with the gas composition and the flow direction. Overall, the DCI for SOFC is a promising design.

Structural and electronic properties of Ce‐doped Ti4O7 based on experiments and first‐principles calculations

AbstractA series of Ti4O7 powders with different Ce‐cation doping concentrations were successfully prepared through a new strategy combining the wet chemical method and hydrogen thermal reduction. It is shown that Ce, entering the lattice of Ti4O7 during the reduction process, only occurs in the form of Ce3+, and the solubility of Ce is equal to 8.93 at.%. Furthermore, the electrical conductivity of Ce‐doped Ti4O7 powders was tested for the first time and theoretically explained by the first‐principles calculations. It was revealed that Ce provides a negative effect on the electrical conductivity of Ti4O7 powders, which is due to the decrease in the number of electronic states near the Fermi energy level caused by the introduction of Ce.

A strategy for CO2 capture and utilization towards methanol production at industrial scale: An integrated highly efficient process based on multi-criteria assessment

CO2 capture and utilization are an effective solution to the problem of CO2 emissions, and a combination of ammonia-based CO2 capture and its use for methanol production is a highly feasible strategy. However, the uses of conventional technologies have resulted in a high demand for energy, with limited use of hydrogen. To address these problems, an innovative strategy is proposed and demonstrated in this study that enhances the conventional design, i.e., to use ammonia-based CO2 capture with double tower absorption and solvent split, along with wet hydrogen for methanol production at industrial scale. The process is further improved through a multi-criteria assessment that considered the CO2 capture rate, NH3 loss rate, CO2 conversion rate, and energy saving factors, in which the latter is based on two components, namely the reboiler duty and the condenser duty. Moreover, an exergy analysis method is used to optimize the improved process, and a highly efficient integrated process is finally established. It has been found that the use of a double-tower absorption process ensures high rates of CO2 capture and low rates of NH3 loss. Additionally, adjusting the molar ratio of H2 to CO2 leads to an impressive 8% increase in the CO2 conversion rate, reaching 25%. In terms of energy savings, the average reboiler duty was reduced from 13.39 to 11.85 MJ/kgCO2, i.e., by 11.50%; while the condenser duty was reduced by 11.36%; both contributed to the overall energy savings. In the I-ACCMP process, the total exergy loss is 437.24 kW, of which the exergy loss of the heat exchangers accounts for 16%, and the desorption tower (DES) accounts for 48%. After optimization, the exergy loss of the heat exchangers decreases from 70.02 kW to 40.45 kW, the exergy loss of the DES decreases from 209.29 kW to 180.91 kW, and the reboiler duty is reduced from 10.60 MJ/kgCO2 to 7.71 MJ/kgCO2. The total exergy loss decreases from 437.24 kW to 372.68 kW, which is a reduction by 14.8%.

Enhanced oxygen reduction reaction activity and electrochemical performance of A-site deficient (La0.6Sr0.4)1-xFe0.8Ni0.2O3−δ cathode for solid oxide fuel cells

In this work, (La0.6Sr0.4)0.9Fe0.8Ni0.2O3-δ (LSFN90), a stable, highly ORR-active and cost-efficient perovskite oxide, is developed as cathode materials for solid oxide fuel cell (SOFC). The introduction of A-site deficiency results in the crystal expansion of the cubic perovskite phase and an increase in oxygen vacancy concentration at operating temperature. The LSFN90 cathode displays good oxygen reduction reaction activity and low polarization resistance values. The A-site deficiency facilitates the diffusion of oxygen ions in the electrode and accelerates the surface oxygen exchange reaction. LSFN90 is used as cathode materials for SOFC to prepare anode-supported single cells, achieving maximum power densities of 1.51, 1.27, 0.95 and 0.63 W cm−2 under wet hydrogen (3%H2O–97%H2) atmosphere at 850, 800, 750 and 700 °C, respectively. The introduction of A-site deficiency can greatly enhance the oxygen reduction reaction activity and electrochemical performance of the cathode, demonstrating that LSFN90 has significant potential as a cathode material for practical applications in solid oxide fuel cells.

Surface regulating of copper-iron nanoparticles bimetallic exsolution for enhanced performance and durability of double perovskite anode in solid oxide fuel cells

The metallic exsolved ceramic anode for Solid oxide fuel cells (SOFCs) has garnered immense attention owing to its abundant active sites and high catalytic efficacy. However, the performance and durability of nanoparticle decorated ceramic anodes are still hindered by the morphology and size of exsolved nanoparticles, but there are few studies on the specific dissolution rules and conditions. Here, the Cu element is doped into high-performance Sr1.9Fe1.5Mo0.5O6-δ materials to study the exsolution law of nanoparticles and the change of nanomorphology in the reduced state. Sr1.9Fe1.5Mo0.4Cu0.1O6-δ (SFMC0.1), used as an anode for solid oxide fuel cells, can evolve into high-performance composite phases composed of perovskite, Ruddlesden-Popper phase, and copper-iron bimetallic nanoparticles under the condition of 800 °C wet hydrogen. At the same time, the reduction treatment containing water vapor will make the Fe nanoparticles exhibit rare whisker-like nanoparticles, and copper will be wrapped on the iron nanoparticles to form a core–shell structure, which effectively inhibits the high-temperature agglomeration of Fe nanoparticles. When used as an anode in an electrolyte-supported SOFC, it exhibits commendable performance and good durability at 800 °C with a maximum power density increasing from 0.63 to 1.2 W cm−2 (H2 fuel) over reduction time due to the influence of phase transition and exsolution morphology. Therefore, the reduction in H2O environment and the low temperature is an effective method to control the whisker-like Fe nanoparticles to improve the catalytic performance, and the doping of Cu can ensure the formation of Cu-coated core–shell structure to inhibit the agglomeration of nanoparticles.

Effect of degraded environmental conditions on the service behavior of a X65 pipeline steel not designed for hydrogen transport

With the international drive to deploy green energies and decarbonized intermediates in the place of fossil fuel sources, a large number of developed countries are actively preparing for a future where hydrogen plays a strategic role as an energy storage medium. Producing and using hydrogen requires the rapid expansion of a dedicated, economically viable industrial sector. Nevertheless, questions on how to safely store, transport and distribute hydrogen remain an important priority today. In countries with existing natural gas transport grids, the possibility to retrofit these networks to store and transport hydrogen-natural gas blends is being studied.A key challenge is to evaluate how pressurized H2 would interact with steel structures with regards structural embrittlement of the latter, with a view to exploiting existing transport infrastructures for storage and transport applications. In this work, we evaluate the H2-performance of a non-hydrogen service ×65 pipeline steel. The cracking susceptibility of this steel grade has been evaluated at 100 bar H2 using slow strain rate testing, Constant strain testing and fracture toughness measurements. Accompanying hydrogen permeation tests under pressure provide diffusion data and elucidate the discussion. Exposures were carried out in dry or wet H2 and with or without H2S contamination at levels representative of biogas. The results underline that the impact of dry or wet hydrogen on this grade are moderate. The presence of traces of H2S together with humidity could risk seriously degrading the mechanical performance of the ×65 steel grade.