Hydrogen Permeation Research Articles

Silver‐Based Supportless Membrane Electrode Assemblies for Electrochemical CO2 Reduction

ABSTRACTMost commonly, electrochemical CO2 reduction is performed in a three‐compartment setup employing gas diffusion electrodes (GDEs) to decrease mass transport limitations of the gaseous reactant CO2 to the reaction interface. However recently, there has been a rising number of investigations on suitable membrane electrode assemblies (MEAs) to overcome ohmic potential losses caused by the electrolyte gaps in the systems. While the significant majority of MEAs exhibited in literature is based on catalyst‐coated gas diffusion layers, this work presents an approach that does not require a likewise support. On the basis of a catalyst suspension similar to mixtures already employed for GDE production on industrial level, a method to directly transfer the resulting catalyst layers to the membrane is developed. The Faradaic efficiency of carbon monoxide, i.e. target product formation of GDEs manufactured according to a similar procedure, can be matched or even exceeded for individual modifications of the exchange MEAs. Simultaneously, the cell potentials can be remarkably decreased in this setup. By gradual adaptation of the fabrication procedure, the influence of important manufacturing parameters is unraveled, also discussing the effect of hydrogen permeation through the membrane.

Microstructures of Directionally Solidified Nb15Ti55Fe30 Alloy and Its Hydrogen Permeation Properties in the Presence of H2S

Currently, the main limitations of Pd-coated Nb-TiFe dual-phase alloys include insufficient hydrogen permeability, susceptibility to hydrogen embrittlement (HE), and poor tolerance of H2S poisoning. To address these issues, this study proposes a series of improvements. First, a novel Nb15Ti55Fe30 alloy composed of a well-aligned Nb-TiFe eutectic was successfully prepared using directional solidification (DS) technology. After deposition with a Pd catalytic layer, this alloy exhibits high hydrogen permeability of 3.71 × 10−8 mol H2 m−1 s−1 Pa−1/2 at 673 K, which is 1.4 times greater than that of the as-cast counterpart. Second, to improve the H2S corrosion resistance, a new Pd88Au12 catalytic layer was deposited on the surface using a multi-target magnetic control sputtering system. Upon testing in a 100 ppm H2/H2S mixture, this membrane exhibited better resistance to bulk sulfidation and a higher permeance recovery (ca. 58%) compared to pure Pd-coated membrane. This improvement is primarily due to the lower adsorption energies of the former with H2S, which hinders the formation of bulk Pd4S. Finally, the composition region of the Pd-Au catalytic membrane with high comprehensive performance was determined for the first time, revealing that optimal performance occurs at around 12–18 at.% Au. This finding explains how this composition maintains a balance between high H2 permeability and excellent sulfur resistance. The significance of this study lies in its practical solutions for simultaneously improving hydrogen permeability and resistance to H2S poisoning in Nb-based composite membranes.

Matrimid®/LaNi5 mixed matrix membranes for selective hydrogen separation from industrial waste gas streams

This study reports the synthesis, characterization, and evaluation of Matrimid®/LaNi5 mixed matrix membranes for selective hydrogen separation from industrial waste gas streams. Through a combination of experimental investigation and modelling, hydrogen absorption in LaNi5 intermetallic compounds and its impact on separation performance were explored. It was observed that the composite membranes exhibit significant enhancement in hydrogen permeation compared to pristine Matrimid® membranes. The results showed that Matrimid®/LaNi5 membranes deliver 5 times higher H2 permeability (107 Barrer) and higher selectivity (H2/CO2: 14.5, H2/N2: 83.5, H2/CH4: 78.5 and H2/CO: 84.5). Furthermore, hydrogen permeation flux modelling in Matrimid®/LaNi5 elucidated the contribution of each transport mechanism with high regression coefficients (> 0.92) and within ± 15% error. Moreover, the results demonstrate the capability of Matrimid®/LaNi5 membranes to surpass Robeson upper bound for H2/CO2 while it is almost reached for H2/N2 and H2/CH4 separations, highlighting the potential of these new membranes for industrial-scale applications.

The impact of helium on plasma-driven hydrogen permeation and implications for direct internal recycling in the fusion fuel cycle

Abstract Metal foil pumps (MFPs) are the leading technology for direct internal recycling (DIR) of hydrogen isotopes from the plasma exhaust in future fusion plants. MFPs rely on the concept of superpermeation, where superthermal H atoms directly absorb into the metal foil, rapidly diffuse, and desorb downstream. To date, studies of superpermeation have predominantly employed either pure hydrogen or in some cases trace levels of impurities. The plasma exhaust is expected to contain just ~1% helium, but in DIR the source gas would be enriched in helium as hydrogen isotopes are extracted. In this work, we explore the impact of helium on hydrogen superpermeation at low temperature (75-200 ºC) using Pd-based foils. To first order, the flux scaled linearly with the hydrogen mole fraction. Stable permeation was observed until the helium fraction reached ~80%, where the flux began to decline slowly with time. In addition, short term (1-5 minute) exposure to pure helium plasma significantly attenuated subsequent hydrogen plasma permeation, and the degree was more dramatic at elevated temperature. This attenuation was correlated with He retention in the foils, which was detected by time-of-flight secondary ion mass spectrometry at low levels (< 0.1 at. %) and limited to the near surface (< 10 nm). Similar trends were observed among all alloys (Pd, PdAg, PdCu), and the foils were restored to full performance with an Ar+ sputter clean. The potential for helium plasma exposure to impact MFP performance under these conditions has not been previously reported, and these findings have significant implications to the design and implementation of practical DIR systems.

Accelerated stress corrosion cracking of X80 pipeline steel under the combined effects of sulfate-reducing bacteria and hydrostatic pressure

The microbially mediated metal stress corrosion cracking (SCC) mechanisms in deep-sea environments remain unclear, hindering the safe use of deep-sea equipment materials. Hydrostatic pressure facilitated microbiologically influenced corrosion resulting in the pitting depth increase. The stress concentration at the pit bottom induced anodic dissolution (AD), leading to ductile fracture. Hydrostatic pressure and iron sulfides both enhanced the hydrogen evolution reaction (HER). The sulfides produced by SRB metabolism inhibit hydrogen atom recombination, leading to a higher hydrogen permeation current and inducing hydrogen embrittlement (HE) fracture. The combined effect of AD and HE increases the SCC susceptibility of deep-sea pipeline steel.

Study on the effect of hydrogen cycle pressure relief time on the hydrogen permeability and mechanical properties of polyamide liner materials for type IV hydrogen storage cylinders of HFCVs

Plastic liners for type IV hydrogen storage cylinders of hydrogen fuel cell vehicles (HFCVs) experience varying pressure loads, deteriorating both hydrogen permeability and mechanical properties and impacting cylinder safety. This study performs hydrogen cycle tests on polyamide 6 (PA6) and polyamide 11 (PA11) samples (temperature: 288 K; pressure relief times: 6, 60, 3600 s; upper/lower pressure limits: 70/1 MPa). After 50 hydrogen cycles with 60 and 3600 s relief times, PA6 and PA11 exhibit changes in hydrogen permeability coefficients within 2%. However, with a 6 s relief time, the coefficients significantly decrease (>10%). After 6 s cycles, PA6 exhibits tiny holes, while PA11 exhibits clustered pieces of holes. Cracks appear in both materials' internal structures after 60 s cycles. Despite minimal tensile strength changes (within 5%), the nominal strain at tensile fracture of both materials changes significantly under different times. These findings can help determine optimal pressure relief times for hydrogen cycle tests on plastic liners.

Unravelling the role of calcareous deposits on hydrogen uptake: The duality in the calcite behavior

The permeation of hydrogen in carbon steel immersed in deaerated NaCl and artificial seawater solutions under various cathodic polarization is investigated using the Devanathan and Stachurski method combined with in-situ electrochemical impedance spectroscopy (EIS). The results indicate calcite's dual role in hydrogen uptake: it promotes uptake for bare samples and lower cathodic currents, but inhibits it for preformed deposits and higher cathodic currents. Deposits are characterized through in-situ EIS and scanning electron microscopy, providing further insights into the specific morphology of calcite. These findings are correlated with hydrogen permeation results, elucidating a mechanism for the dual behavior of calcite.

Alloying element Ag modifies the behavior of H and defects in Pd alloys

Although alloying can significantly increase the hydrogen permeability of palladium (Pd) and solve the problem of hydrogen embrittlement in service, the intrinsic mechanism has not been revealed. Here, we report intuitive differences in the nucleation, growth and distribution of dislocation loops in Pd and PdAg alloys by in-situ hydrogen irradiation in TEM. The results reveal that alloying element Ag not only modifies the behavior of H, but also induces defects to change from the original long-range one-dimensional (1D) diffusion to short-range three-dimensional (3D) diffusion, which significantly delays the aggregation and growth of dislocation loops and reduces the total irradiation damage and H retention. A new strategy to improve hydrogen embrittlement resistance is proposed, i.e., constructing dense dislocation loop bands (or other sinks that can efficiently trap H) in front of grain boundaries to prevent H from diffusing into the grain boundaries.

Surface modification to mitigate gaseous hydrogen effects in a 1800 MPa martensitic steel

A 0.8 % carbon steel was heat treated in air, resulting in an ultimate tensile strength of 1800 MPa and a highly ductile, dense and adhering decarburized ferritic layer, approximately 50 µm thick. The chemical composition and mechanical properties of this ferritic layer were thoroughly examined. Tensile testing and fractography revealed that the decarburized ferritic layer serves as a barrier, protecting the ultra-high strength martensitic steel from gaseous hydrogen-assisted fracture. This outcome implies that, in terms of preventing hydrogen-assisted fractures, the low hydrogen permeability of a protective surface layer is less critical compared to adjusted mechanical properties of the bulk material and surface layer.

Surface properties of PdAu and PdNi alloys under dynamic conditions: NAP-XPS study

Electroless-deposited PdAu and PdNi alloy samples were analyzed using near-ambient X-ray photoelectron Spectroscopy (NAP-XPS) under H2, CO, and CO2-containing streams. Gold enrichment in the near-surface region was evidenced in the PdAu sample under all the analyzed conditions, while palladium increment to the surface was observed in the PdNi alloy. The appearance of a new contribution on the Pd 3d core-level region evidenced the formation of PdHx species on the surface. Competitive CO adsorption and the formation of CHx species at the surface led to the partial blocking of hydrogen adsorption sites, thereby decreasing the PdHx formation. Methane production was detected under CO/H2 and CO2/H2 mixtures in both PdAu and PdNi alloy samples. Our findings demonstrate that both competitive adsorption and the formation of CHx or carbide species on the surface of PdAu and PdNi alloys can negatively influence hydrogen permeation through Pd-based membranes.

Zeolite‐Based “Particle Board” Membranes for Rapid and Selective Hydrogen Permeation

AbstractZeolites, with their well‐defined pore sizes and outstanding stability, are regarded as the quintessential material for precise molecular separation tasks. However, the leap from easily produced zeolite powders to synthesizing free‐standing zeolite membranes, which can fully leverage their ordered porosity, presents substantial technical hurdles. Addressing this challenge, this study introduces polymers of intrinsic microporosity (PIM‐1) as adhesives through a wrapping‐compression method for the facile fabrication of high‐performance and free‐standing zeolite (FAU) “particle board” membranes. The 3D tomogram reconstruction from the focused ion beam‐scanning electron microscope images reveals the “particle board” membranes exhibit hierarchical porous structures. The non‐interconnecting macropores between zeolite particles facilitate the rapid H2 permeation, and the zeolites’ ordered micropores sieve the gas molecules. The optimized FAU@PIM‐1 free‐standing membrane with hierarchically pore structures demonstrated hydrogen permeance (2240 GPU) alongside H2/CH4 selectivity (31.68) for mixed gas and maintained this performance level under pressure ranges from 1.2 to 4.0 bar and over protracted operational periods (up to 3200 h). Meanwhile, EMT and MFI‐type zeolites have also been successfully applied to validate the versatility of this method, demonstrating its widespread potential for the fabrication of various free‐standing zeolite membranes.

Cryogenic Impact on Carbon Fiber-Reinforced Epoxy Composites for Hydrogen Storage Vessels

Carbon fiber-reinforced epoxy (CF/EP) composites are attractive materials for hydrogen storage tanks due to their high strength-to-weight ratio and outstanding chemical resistance. However, cryogenic temperatures (CTs) have a substantial impact on the tensile strength and interfacial bonding of CF/EP materials, producing problems for their long-term performance and safety in hydrogen storage tank applications. This review paper investigates how low temperatures affect the tensile strength, modulus, and fracture toughness of CF/EP materials, as well as the essential interfacial interactions between carbon fibers (CFs) and the epoxy matrix (EP) in cryogenic environments. Material toughening techniques have evolved significantly, including the incorporation of nano-fillers, hybrid fibers, and enhanced resin formulations, to improve the durability and performance of CF/EP materials in cryogenic conditions. This review also assesses the hydrogen barrier properties of various composites, emphasizing the importance of reducing hydrogen permeability in order to retain material integrity. This review concludes by highlighting the importance of optimizing CF/EP composite design and fabrication for long-term performance and safety in hydrogen storage systems. It examines the prospects for using CF/EP composites in hydrogen storage tanks, as well as future research directions.

Effect of texture, grain boundary constitution, and molybdenum partitioning on corrosion and hydrogen permeation behavior of pulse electrodeposited Ni-Mo coatings

Microstructural evolution, electrochemical corrosion and hydrogen permeation in pulse electrodeposited Ni-Mo coatings (2, 4, 8, and 11wt% Mo) were investigated. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements revealed improved corrosion resistance at an optimum Mo content. The corrosion current density icorr and polarization resistance Rp values obtained were 13.8 μA/cm2 and 1745 Ωcm2 respectively for pure Ni coating while the icorr and Rp values obtained were 1.7 μA/cm2 and 5406 Ωcm2 respectively for Ni-4wt% Mo coating. Further, increase in the Mo content beyond 4 wt% increased the corrosion rate. Nevertheless, corrosion resistance of Ni-Mo coatings was found to be higher than the pure Ni coating. Ni-Mo coatings contained relatively Mo-enriched clusters in a solid solution matrix. The highest corrosion resistance of Ni-4wt% Mo coating was due to lower energy (001) and (111) textures, lower energy grain boundary constitution, and low coating strain. In Ni-4wt% Mo coating, Mo-enriched Ni-Mo nanoclusters inhibited hydrogen passage by providing a torturous path. In contrast, a high fraction of high-angle grain boundaries (compared to pure Ni coating) facilitated hydrogen permeation leading to a similar extent of hydrogen permeation through pure Ni and Ni-4wt% Mo coatings.

An empirical model of the kinetics of hydrogen-induced cracking in pipeline steel, using statistical distribution models and considering microstructural characteristics and hydrogen diffusion parameters

This study proposes an empirical model to predict the kinetics of hydrogen-induced cracking (HIC) growth rate in pipeline steels based on experimentally measured hydrogen diffusion parameters and spatial distribution of microstructural features previously identified to have a role on HIC kinetics. In the experimental work, the HIC was induced by electrochemical cathodic charging and the crack growth was monitored by ultrasonic inspection. Optical and scanning electron microscopy were used to determine the spatial distribution parameters of non-metallic inclusions, and the ferrite grain and second phase characteristics. The hydrogen microprint technique used to visualize hydrogen diffusion path in the microstructure and the hydrogen diffusion parameters were determined by hydrogen permeation tests. Results show that NMI shape affects HIC nucleation sites, using student's t-distribution, while ferrite grain characteristics affect HIC growth rates, with X70–2 and X56 steel plates recorded highest HIC growth rate. The Log-Normal distribution model, supported by statistical analysis, effectively predicts HIC growth rates compared with Weibull and Gamma distribution models.

Dual functionality of cathode microporous layers: Reducing hydrogen permeation and enhancing performance in proton exchange membrane water electrolyzers

Hydrogen permeation and cell performance are critical factors for the safe and efficient operation of proton exchange membrane (PEM) water electrolysis. In this study, the effects of a cathode microporous layer (MPL) on water transport, hydrogen permeation, and cell performance in a proton exchange membrane water electrolyzer (PEMWE) were investigated. Results reveal that adding an MPL between the catalyst layer (CL) and the porous transport layer (PTL) at the cathode reduces interfacial contact resistance by approximately 60 % under 400 N cm−2, leading to superior performance. The wettability of the MPL plays a crucial role in water transport and hydrogen permeation in PEMWEs. The hydrophobic MPL-P-CB4, which uses polytetrafluoroethylene (PTFE) as a binder with a carbon black (CB) loading of 4 mgCB cm−2, enhances the crossover of water and hydrogen from the cathode to the anode through back diffusion, exceeding the technical safety criterion of 2 vol% H2 in the anode product gas (50 % lower explosion limit) at 2.0 A cm−2. However, the hydrophilic MPL with Nafion ionomers as binders (MPL-N-CB4) facilitates efficient removal of water and hydrogen from the cathode CL to the cathode flow field via capillary pressure, resulting in only 0.2 vol% H2 in O2 at 2.0 A cm−2. Consequently, a hydrophilic MPL is optimal for achieving superior performance and low-hydrogen-crossover in a PEMWE cathode. This study provides valuable insights for designing the PTL/CL interface in next-generation PEMWE cathodes.

The role of hydrogen gas in SRB-induced degradation of X80 pipeline steel in hydrogen-blending environments

The pipeline transportation of hydrogen poses higher challenges to the safety of pipes. In this study, the corrosion mechanisms of SRB in X80 pipeline steel under H₂ conditions were investigated. Thermodynamic analysis revealed that the introduction of hydrogen enhances SRB metabolic activity, facilitating the reduction of sulfate to sulfide and promoting hydrogen embrittlement. Additionally, hydrogen permeation tests confirmed that SRB significantly increase hydrogen diffusion in steel, accelerating corrosion. The enhanced hydrogen permeation under biotic conditions was linked to increased hydrogen uptake and sulfide formation, which further destabilized the steel microstructure. This study provides critical insights into the interplay between microbial activity, hydrogen permeation, and corrosion, offering a deeper understanding of the factors influencing hydrogen-assisted corrosion in steel pipelines. The findings contribute to the optimization of material performance and risk assessment in hydrogen-blended environments.

Formation of hydrogen resistant oxides of titanium alloy in water corrosion environment

The structure changes and hydrogen permeation behavior of Titanium alloy TA17 in simulated water environment of small modular reactor (SMR) at 320°C for 8000h was investigated. We found a corrosion layer consist of TiO2 and FeTiO3 with a good hydrogen permeation resistance. The structure and hydrogen permeation resistance change with the increase of corrosion period. At the first corrosion period of 3000h, FeTiO3 grows rapidly with an exponential parameter of 0.663 fitted by parabolic law. As the initial TiO2 layer destroyed, the deuterium permeation flux increases. After the thickness of FeTiO3 reaches a limit at corrosion time of 4000h, there exists a dynamic balance between the growth and the dissolution of FeTiO3, result in a small fluctuant deuterium permeation flux at corrosion periods of 5000－8000h. The deuterium permeation flux of the corrosion layer can be two orders of magnitude lower to that of Titanium alloy TA17 substrate. The formation process of corrosion layer and its effect on hydrogen permeation resistance are discussed in detail.

Preparation and electrochemical performance of alkaline earth metal-doped Nd2Ce2O7 proton conductor hydrogen separation membranes

Nd2Ce2O7 is a rare earth oxide with a fluorite structure and exhibits proton conductivity. Alkaline earth metals (Mg, Ca, Sr, Ba) doped Nd2Ce2O7 powders were synthesized using the citrate sol-gel method. The doped samples retain the fluorite structure, and enhanced oxygen vacancy concentration. Notably, Nd1.85Mg0.15Ce2O7-δ exhibited the highest oxygen vacancy concentration, reaching an electrical conductivity of 2.91 × 10−2 S cm−1 in a humid atmosphere of 20%H2 and 80%N2 at 900 °C. Hydrogen separation membranes were fabricated using alkaline earth metal-doped Nd2Ce2O7 as the proton-conducting phase and Pt as the electron-conducting phase. The results indicated that Pt-Nd1.85Mg0.15Ce2O7-δ had the optimal hydrogen permeation flux, reaching 8.35 × 10−9 mol cm−2•s−1 at 900 °C. It demonstrated short-term stability in environments containing CO2 and H2O, and an increase in temperature and hydrogen partial pressure on the feed side enhanced hydrogen permeation, highlighting its potential as a hydrogen separation membrane material.

Evaluating membranes for hydrogen storage and utilization in next-generation aviation systems

This study aims to provide a comprehensive evaluation of membrane technologies for hydrogen-related processes in aviation, specifically focusing on hydrogen production, hydrogen separation, and fuel cells. As aviation seeks to transition to cleaner energy solutions, the selection of appropriate membranes is critical for ensuring efficiency and sustainability. The research utilizes the Analytic Hierarchy Process (AHP) to systematically assess membrane alternatives based on key criteria: economic factors, environmental impact, technical performance, and technological maturity. By conducting pairwise comparisons and detailed matrix calculations, this study establishes the relative importance of sub-criteria and ranks membrane types for each hydrogen-related application. The analysis identifies Nonporous Dense Films as the most effective membrane for hydrogen production, due to their balance of cost and technical performance. For hydrogen separation, Ceramic and Metal Membranes are determined to be the optimal choice, offering superior durability, hydrogen permeability, and thermal stability. In fuel cell applications, Electrically Charged Membranes are found to be the most suitable for Proton Exchange Membrane Fuel Cells (PEMFCs), while Ceramic and Metal Membranes excel in Solid Oxide Fuel Cells (SOFCs). The outcomes of this study not only highlight the most suitable membranes for different aviation hydrogen processes but also offer a strategic framework for decision-makers. By identifying the key factors driving membrane selection, this research contributes to advancing hydrogen adoption in aviation, facilitating the development of efficient, low-emission technologies for the future of sustainable air travel.

Effectiveness-MTU modeling approach for hydrogen separation with dense metallic membranes

As hydrogen gains interest as energy vector, so it happens for its purification techniques. In particular, dense metallic membranes are a promising technology for many high-temperature applications. Modeling of hydrogen permeation is a fundamental support to their commercial development. Permeation through metallic membranes, in particular Pd-alloys, is regulated by a generalized form of the Richarson’s equation, where driving force for permeation is due to the difference in hydrogen partial pressure at the membrane surfaces. From the flux expression it is possible to develop a model for a mass exchanger, in analogy with the mathematical description of heat exchangers. For the latter, a well-known method, called , is used to simplify heat transfer problem. The same approach applies to mass exchangers, where the method had already been transferred to reverse osmosis. In this article, method is applied to ideal mass exchangers for hydrogen separation. Effectiveness showed to be influenced by inlet hydrogen fraction, exponent of partial pressures and pressure ratio. Moreover, a procedure to include concentration polarization losses is presented. A rule-of-thumb approach is proposed for an estimation of hydrogen recovery, validated to reproduced an experimental result with less that 7% relative error. shows to be a fundamental support to membrane module design.