High Hydrogen Content Research Articles

Hydrogen Release from Ammonia: Size and Support Effects in Heterogeneous Transition Metal Catalysis

Ammonia can serve as a promising renewable energy carrier based on its high hydrogen content and energy density as well as its full‐fledged transportation infrastructure. Renewable hydrogen can be converted in ammonia synthesis, stored and/or transported bound in ammonia and released on demand by ammonia decomposition. The most active catalysts for this reaction are Ru‐based due to its optimal nitrogen binding energy compared to other transition metals. However, the development of alternative non‐noble transition metal catalysts such as Fe, Ni or Co is attractive. For supported metal catalysts, size and support effects play important roles in many catalytic reactions resulting in a change of geometric and/or electronic properties. In this review, we first discuss existing studies of size and support effects on Ru, Fe, Ni, Co catalysts in ammonia decomposition from an experimental and theoretical viewpoint. Afterwards, we compare the available catalytic data in the form of TOFH2 and reaction rate for each metal catalyst supported on different supports and as a function of particle size, attempting to identify an optimum particle size and a trend for the different supports. Finally, we discuss the challenges and perspectives of future research on the size and support effect in ammonia decomposition.

Photothermally-activated suspended aerogel triggers a biphasic interface reaction for high-efficiency and additive-free hydrogen generation.

The need for a sustainable hydrogen supply has sparked significant efforts to develop effective liquid hydrogen carriers with high hydrogen content that can be safely stored and undergo controlled hydrogen release. However, a major challenge lies in the ultralow hydrogen evolution rate caused by the direct dehydrogenation of liquid hydrogen carriers. Conventionally, accelerant additives are employed to improve the dehydrogenation rate, but this strategy inevitably sacrifices the hydrogen storage density. Therefore, achieving high-efficiency hydrogen release and high storage density remains a daunting task. Herein, we develop an innovative photothermally-activated suspended biphasic reaction strategy, which absorbs solar radiation and re-radiates infrared photons to induce photothermal evaporation and in situ dehydrogenation of liquid hydrogen carriers, fundamentally circumventing the employment of additives. Furthermore, by leveraging this phase transition-induced biphasic reaction design, the strategy improves the required reaction temperature and drastically lowers hydrogen transport resistance. Therefore, an impressive hydrogen evolution rate of 386 mmol g-1 h-1 is achieved from pure formic acid with an ultrahigh hydrogen storage density of 53 g L-1, representing a threefold improvement in rate compared to state-of-the-art strategies. Our approach introduces a fresh perspective for the dehydrogenation of liquid hydrogen carriers, encompassing formic acid, hydrazine hydrate, and so on, and concurrently guarantees exceptional hydrogen release capabilities and excellent hydrogen storage density.

Harnessing Ruthenium and Copper Catalysts for Formate Dehydrogenase Reactions.

Formic acid (HCOOH) is a promising source of hydrogen energy that can be used to produce hydrogen in a more economical and ecological way. Formic acid is a simple carboxylic acid with a high hydrogen concentration and is generally stable, making it useful as a hydrogen transporter. Catalytic dehydrogenation is usually used to extract hydrogen from formic acid; this process releases hydrogen gas and yields carbon dioxide as a byproduct. Comparing this technology to conventional hydrogen generation methods, there are several benefits, such as the utilization of the formic acid handling infrastructure already in place and the possibility of a simpler integration into different energy systems. Notwithstanding, several obstacles persist, including enhancing the effectiveness of the dehydrogenation procedure and reducing the ecological consequences of the correlated carbon dioxide discharges. Catalysts, reaction conditions, and carbon collection and utilization methodologies are all being researched further. The development of Ru and Cu-based catalysts for the catalytic breakdown of HCOOH into CO2 and H2 is the main topic of this account. Herein, the focus is on the kinetic studies of HCOOH dehydrogenation, encompassing mechanistic investigations that consider intermediate studies and DFT calculations.

Low frequency quartz tuning fork as hydrogen sensor

The use of hydrogen as a sustainable energy source is pushing the development of innovative sensing strategies for the monitoring of H2 concentration during its production processes and transportation. In this work, we propose a custom quartz tuning fork (QTF) as sensor for the detection of high concentrations of hydrogen in air. The selectivity derives directly from values of molar mass and the viscosity of hydrogen molecules, significantly different from those of the other main constituents of air. Exciting the fundamental flexural mode of a commercially available 12.4 kHz-QTF, we demonstrated the linear dependence of its resonance frequency and quality factor on the H2 concentration, passing through their relationship with molar mass and the viscosity of the H2-air mixture. Monitoring the shift of the resonance frequency of the QTF, the H2-component in air can be estimated with a precision level of 0.74% and accuracy error of 1.82%. The same parameters resulted 0.40% and 4.29%, respectively, when Q values are evaluated. Finally, a beat-frequency approach was proposed to speed up the acquisition in few seconds, monitoring both resonance parameters of the QTF.

FeCo Alloy-Decorated Proton-Conducting Perovskite Oxide as an Efficient and Low-Cost Ammonia Decomposition Catalyst

Ammonia is known as an alternative hydrogen supplier because of its high hydrogen content and convenient storage and transport. Hydrogen production from ammonia decomposition also provides a source of hydrogen for fuel cells. While catalysts composed of ruthenium metal atop various support materials have proven to be effective for ammonia decomposition, non-precious-metal-based catalysts are attracting more attention due to desires to reduce costs. We prepared a series of Fe, Co, Ni, Mn, and Cu monometallic catalysts and their alloys as catalysts over proton-conducting ceramics via the impregnation method as precious-metal-free ammonia decomposition catalysts. While Co and Ni showed superior performance compared to Fe, Mn, and Cu on a BaZr0.1Ce0.7Y0.1Yb0.1O3−б (BZCYYb) support as an ammonia decomposition catalyst, the cost of Fe is much lower than that of other metals. Alloying Fe with Co can significantly increase the conversion and stability and lower the overall cost of materials. The measured ammonia decomposition rate of FeCo/BZCYYb reached 100% at 600 °C, and the ammonia decomposition rate was almost unchanged during the long-term test of 200 h, which reveals its good catalytic activity for ammonia decomposition and thermal stability. When the metallic catalyst remained unchanged, BZCYYb also exhibited better performance compared to other commonly used oxide supports. Finally, when ammonia cracked using our alloy catalyst was fed to solid oxide fuel cells (SOFCs), the peak power densities were very close to that achieved with a simulated fully cracked gas stream, i.e., 75% H2 + 25% N2, thus proving the effectiveness of this new type of ammonia decomposition catalyst.

Electrochemical Ammonia Synthesis at Intermediate Temperatures Using Solid-State Phosphate Electrolyte

As we aim to realize a carbon-neutral sustainable society and a CO2-free society, methods of converting renewable energy into hydrogen and then further into a hydrogen carrier with high energy density are attracting much attention. Among various energy carrier materials, ammonia is regarded as a promising candidate, which has a high hydrogen content and is easy to transport and store. Currently, ammonia is industrially produced by the Haber-Bosch process under high-temperature and high-pressure conditions, which is energy intensive and has a large environmental impact. Therefore, in this study, we focused on electrolytic synthesis under mild conditions. Due to the operating temperature constraints of the electrolyte, ammonia electrosynthesis is mainly classified into three temperature ranges: low temperature range below 100℃, high temperature range above 500℃, and medium temperature range from 100℃ to 500℃. Since ammonia synthesis from hydrogen and nitrogen is exothermic, synthesis at a low temperature is thermodynamically advantageous, but the disadvantage is that the reaction rate is limited because N2 molecules are difficult to active at low temperatures. On the other hand, although NH3 synthesis proceeds at a high reaction rate in the high temperature range, decomposition of ammonia in the reverse reaction is also likely to occur, leading to low equilibrium conversion of N2. Based on these considerations, we target NH3 synthesis in the intermediate temperature range, which is expected to have both the advantages of the low-temperature and high-temperature types, namely thermodynamic and kinetic advantages. In addition, ammonia synthesis was performed using a solid-state phosphate electrolyte that exhibits high proton conductivity and stability in the intermediate temperature range, and research focus was posed on cathode catalysts to raise the ammonia production rate and faradaic efficiency simultaneously. In this study, we have investigated Fe, which has a high dissociation activity for nitrogen molecules, and the first candidate for the cathode catalyst was a composite catalyst of Fe and yttrium-doped barium zirconate (BZY), that had shown the yield rate and faradaic efficiency at 220℃ and ambient pressure. [1] First, ammonia electrosynthesis was performed using Fe/BZY-Ru as cathode catalyst, in which RuO2 was added to Fe/BZY to maintain the reduced state of Fe. The highest NH3 yield rate of 2.7x10-10 mol (s cm2)-1 was achieved at -1.5 V (vs. open-circuit voltage (OCV)) and the highest faradaic efficiency of 0.3% was achieved at -0.5 V (vs. OCV). This low faradaic efficiency was thought to be derived from H2 generation as a side reaction of NH3 generation, so we started electrosynthesis using Fe/BZY without RuO2 as a cathode catalyst. As a result, the faradaic efficiency of 4.8％ was achieved at -1.5 V (vs. OCV) with the NH3 yield rate of 2.1x10-10 mol (s cm2)-1. [1] Y. Yuan, S. Tada, R. Kikuchi, Mater. Adv., 2, 793 (2021).

Control of hydrogen concentrations by microbial sulfate reduction in two contrasting anoxic coastal sediments.

Molecular hydrogen is produced by the fermentation of organic matter and consumed by organisms including hydrogenotrophic methanogens and sulfate reducers in anoxic marine sediment. The thermodynamic feasibility of these metabolisms depends strongly on organic matter reactivity and hydrogen concentrations; low organic matter reactivity and high hydrogen concentrations can inhibit fermentation so when organic matter is poor, fermenters might form syntrophies with methanogens and/or sulfate reducers who alleviate thermodynamic stress by keeping hydrogen concentrations low and tightly controlled. However, it is unclear how these metabolisms effect porewater hydrogen concentrations in natural marine sediments of different organic matter reactivities. We measured aqueous concentrations of hydrogen, sulfate, methane, dissolved inorganic carbon, and sulfide with high-depth-resolution and 16S rRNA gene assays in sediment cores with low carbon reactivity in White Oak River (WOR) estuary, North Carolina, and those with high carbon reactivity in Cape Lookout Bight (CLB), North Carolina. We calculated the Gibbs energies of sulfate reduction and hydrogenotrophic methanogenesis. Hydrogen concentrations were significantly higher in the sulfate reduction zone at CLB than WOR (mean: 0.716 vs. 0.437 nM H2) with highly contrasting hydrogen profiles. At WOR, hydrogen was extremely low and invariant (range: 0.41-0.52 nM H2) in the upper 15 cm. Deeper than 15 cm, hydrogen became more variable (range: 0.312-2.56 nM H2) and increased until methane production began at ~30 cm. At CLB, hydrogen was highly variable in the upper 15 cm (range: 0.08-2.18 nM H2). Ratios of inorganic carbon production to sulfate consumption show AOM drives sulfate reduction in WOR while degradation of organics drive sulfate reduction in CLB. We conclude more reactive organic matter increases hydrogen concentrations and their variability in anoxic marine sediments. In our AOM-dominated site, WOR, sulfate reducers have tight control on hydrogen via consortia with fermenters which leads to the lower observed variance due to interspecies hydrogen transfer. After sulfate depletion, hydrogen accumulates and becomes variable, supporting methanogenesis. This suggests that CLB's more reactive organic matter allows fermentation to occur without tight metabolic coupling of fermenters to sulfate reducers, resulting in high and variable porewater hydrogen concentrations that prevent AOM from occurring through reverse hydrogenotrophic methanogenesis.

Targeting Full-Hydrogen Operation on Industrial-Scale Gas Turbines: Impact of Unconventional Fuels on Turbine Module Performance and Aeromechanics

Abstract With the trend to full decarbonization, a full hydrogen economy development is a key industrial objective. Gas turbines, currently one of the cleanest fossil fuel-based power generation solutions, provide reliable and on-demand power. The introduction of hydrogen into the fuel mix of existing gas turbines represents a solution with great potential to provide low-carbon or even carbon-free energy. High-hydrogen content fuels, however, challenge the efficient operation of the gas turbine expander, as crucial aspects such as increased flow rate, different gas properties and temperature operating range may affect performance and structural integrity. To evaluate the impact of this conversion, a numerical investigation of five cases with increasing percentages of hydrogen in the fuel was carried out for an industrial four stages gas turbine module. The variation of turbine inlet temperature distribution from combustion chamber was considered, to assess the impact of the unconventional fuel on the well-known aeromechanical behavior of the last stage blades. Variations in capacity, efficiency, power and potential limits due to aeroelasticity were evaluated, identifying the most relevant differences with respect to the full methane case. All these analyses confirm the possibility to employ high-hydrogen fuel operation in a current gas turbine without the need of a further redesign, while maintaining acceptable performance levels.

The role of hydrogen in the synthesis of High-entropy alloys and their hydrides

The aim of this work is to present the new technique processes of formation of stable hydrides of High-entropy alloys (HEAs) with high hydrogen content. The essence of the proposed method is the sequential use of self-propagating high-temperature synthesis (SHS) method for producing the metal hydrides, followed by the formation of alloys in the hydride cycle (HC) method. Preliminary, the hydrides of three compositions of metal mixtures were synthesized in SHS: 0.2TiH2+0.2ZrH2+0.2HfH2+0.2VH2+0.2NbH2, 0.3TiH2+0.15ZrH2+0.15HfH2+0.2VH2+0.2NbH2 and 0.3TiH2+0.1ZrH2+0.1HfH2+0.2VH2+0.2NbH2+0.1MgH2. From the synthesized mixtures of metal hydrides, the HEAs were produced in HC. The resultant hard alloys Ti0.2Zr0.2Hf0.2V0.2Nb0.2, Ti0.3Zr0.15Hf0.15V0.2Nb0.2 and Ti0.3Zr0.15Hf0.15V0.2Nb0.2Mg0.1 without crushing combusted in Н2 at РH2 = 5–30 atm. in SHS mode. As a result, the hydrides of HEAs (Ti0.2Zr0.2Hf0.2V0.2Nb0.2)Н2.05, (Ti0.3Zr0.15Hf0.15V0.2Nb0.2)H2.05 and (Ti0.3Zr0.1Hf0.1V0.2Nb0.2 Mg0.1)H182 were synthesized with H2 content between 2.17 and 2.42 wt% and H/Me = 1.82–2.05. The repeating the hydrogenation-dehydrogenation processes for 1–3 times confirmed the exceptional cyclic stability of hydrides and the reversible high hydrogen storage capacity of the alloys. The regularities and the mechanism of formation of HEAs and their hydrides were elucidated. The applicability of combination of SHS and HC methods for synthesis of solid solutions of BCC structure HEAs and of their hydrogen-rich hydrides was demonstrated. The remarkable advantages of the developed efficient, low-energy consuming, waste-free and safe method for the synthesis of HEAs and their hydrides can be of commercial interest and attractive to industry, given the current needs for the development of renewable energy, in particular, the solid hydrogen storage facilities.

Experimental and theoretical study on high hydrogen storage performance of Mg(NH2)2-2LiH composite system driven by nano CeO2 oxygen vacancies

The magnesium based metal hydrogen storage composite system Mg(NH2)2-2LiH has a theoretical hydrogen storage capacity of 5.6 wt.% and is a promising hydrogen storage material for vehicles. However, its application is limited due to serious thermodynamic and kinetic barriers. Introducing efficient catalysts is an effective method to improve the hydrogen storage performance of Mg(NH2)2-2LiH. This article investigates for the first time the use of nano rare earth oxide CeO2 (∼44.5 nm) as an efficient modifier, achieving comprehensive regulation of the hydrogen storage performance of Mg(NH2)2-2LiH composite system through oxygen vacancy driven catalysis. The modification mechanism of nano CeO2 is also systematically studied using density functional theory (DFT) calculations and experimental results. Research has shown that the comprehensive hydrogen storage performance of the Mg(NH2)2-2LiH-5 wt.% CeO2 composite system is optimal, with high hydrogen absorption and desorption kinetics and reversible performance. The initial hydrogen absorption and desorption temperatures of the composite system were significantly reduced from 110/130°C to 65/80°C, and the release of by-product ammonia was significantly inhibited. Under the conditions of 170°C/50 min and 180°C/100 min, 4.37 wt.% of hydrogen can be rapidly absorbed and released. After 10 cycles of hydrogen release, the hydrogen cycle retention rate increased from 85% to nearly 100%. Further mechanistic studies have shown that the nano CeO2−x generated in situ during hydrogen evolution can effectively weaken the Mg–N and N–H bonds of Mg(NH2)2, exhibiting good catalytic effects. Meanwhile, oxygen vacancies provide a fast pathway for the diffusion of hydrogen atoms in the composite system. In addition, nano CeO2−x can effectively inhibit the polycrystalline transformation of the hydrogen evolving product Li2MgN2H2 in the system at high temperatures, reducing the difficulty of re-hydrogenation of the system. This study provides an innovative perspective for the efficient modification of magnesium based metal hydrogen storage composite materials using rare earth based catalysts, and also provides a reference for regulating the comprehensive hydrogen storage performance of hydrogen storage materials using rare earth catalysts with oxygen vacancies.

Boosting light olefin production from pyrolysis of low-density polyethylene: A two-stage catalytic process

The increasing production of waste plastics poses significant environmental and health risks. Low-density polyethylene (LDPE), a major component of plastic waste, is a high-quality feedstock for pyrolysis due to its high carbon and hydrogen content. Traditional pyrolysis methods, such as thermal cracking and one-step catalytic pyrolysis, have limitations in yield and selectivity of valuable products like light olefins. This study introduces a two-stage catalytic pyrolysis (TSCP) process aimed at enhancing the production of light olefins from LDPE. In the first stage, LDPE undergoes pyrolysis with MCM-41 catalyst, yielding a substantial number of liquid products and a minor portion of light olefins. The second stage utilizes Mg-ZSM-5 catalyst to further crack the high-temperature volatile matter into light olefins. The optimal conditions identified were 450 °C in the first stage and 500 °C in the second stage, achieving a maximum light olefin yield of 45.80 wt% and a low reaction temperature, decreasing the energy consumption. Additionally, the MCM-41 catalyst demonstrates excellent regeneration performance, with only a slight decrease in liquid yield after nine cycles. The Mg-ZSM-5 catalyst maintains high stability, with light olefin yield remaining at 83.60 % of the initial yield after 48 h of operation.

Smart reforming for hydrogen production via machine learning

The integration of diesel autothermal reforming and solid oxide fuel cells holds a key position in hydrogen-electricity co-generation, where optimization of the reforming process is essential for generating high hydrogen content for fuel cells while maintaining thermal neutrality. Aspen Plus, despite its common usage, suffers from the inability to reflect the interaction effects between parameters, which machine learning can enhance it. In this study, twelve machine learning models have been developed using data from thermodynamic calculations and then screened with Extreme Gradient Boosting for analysis, prediction, and optimization of hydrogen production. Machine learning provides detailed explanations of the impacts of individual and multiple factors, demonstrating powerful optimization capabilities through predictive evaluation and fit with experimental data. This method highlights the potential of integrating machine learning with Aspen technology for optimizing chemical processes.

Atomistic modeling of hydrogen embrittlement at grain boundaries of Mg

Magnesium is a competitive candidate material for engineering lightweight structures and biomedical degradable scaffolds. However, it often suffers unpredictably sudden failure in atmospheric and physiological environments. The prevailing viewpoints have indicated that the failure is closely related to hydrogen. So far, the relevant hydrogen-induced damage mechanisms are still of significant controversy. Building an Mg-H atomic system and conducting molecular dynamics (MD) simulations, this study quantitatively investigates the possibility of hydrogen segregation at grain boundaries (GBs) and reveals the trend of critical energy release rate (CERR) for fracture at the matrix and GBs with increasing hydrogen concentration of single-crystal and polycrystalline systems. The results show that hydrogen tends to segregate at GBs due to GB energy providing more trapping sites. The CERRs for cracking both at the matrix crystal planes and GBs significantly decrease with increasing hydrogen concentration owing to metallic bond weakening, and GBs become more brittle than crystal planes. In the systems without hydrogen, there is a higher tensile strain at fracture, the growth of the free surface is usually accompanied by dislocation emission, and the cracks can even propagate along the migrated GBs with a higher misorientation angle, resulting in an uneven fracture surface with void coalescence features. The tensile stress-strain curves of the systems with high hydrogen concentration exhibit a significant low-stress rapid unloading characteristic. As the hydrogen concentration increases, the dislocation density decreases significantly and the free surface rapidly grows along the hydrogen-distributed crystal planes or GBs, resulting in a smooth fracture surface with cleavage features.

Evaluating the efficacy of multiple concrete compositions in gamma ray and fast neutron shielding

This study comprehensively evaluates the gamma-ray and neutron shielding properties of various concrete types such as Standard Concrete, Hematite Concrete, PC00, HC50, and lead-enriched concretes (e.g., Concrete+50PbO, Concrete+50PbO2, and Concrete+50PbTiO3) using MCNP simulations and Phy-X/PSD code. The results indicate that lead-enriched concretes exhibit superior gamma-ray attenuation capabilities, with Concrete+50PbO2 showing the lowest HVL and TVL (approximately 33 % reduction compared to Standard Concrete), values at 15 MeV. Concrete+50PbO2 also demonstrated a 33 % reduction in TF at 0.662 MeV compared to Standard Concrete. Additionally, Standard Concrete demonstrated the highest fast neutron removal cross section (ΣR) of approximately 0.22 1/cm due to its high hydrogen content. The findings emphasize the critical role of heavy elements like lead in enhancing concrete's shielding performance, making them suitable for nuclear safety applications. It can be concluded that the incorporation of heavy elements into concrete compositions is essential for achieving optimal radiation protection in high-radiation environments.

Hydrogen diffusion mechanisms in the 4130X steel: An integrated study with electrochemical experiments and molecular dynamics simulations

In this work, hydrogen diffusion behavior and mechanisms in the 4130X steel influenced by temperature, locally high concentration, and grain boundary were studied by leveraging both electrochemical hydrogen permeation experiments and molecular dynamics simulations. It was revealed that the hydrogen diffusion coefficient of the 4130X steel was increased with increasing temperature and decreasing locally high hydrogen concentration. The grain boundaries with misorientation below 15° characterized by an electron backscatter diffraction map were identified as hydrogen trapping sites, thus rendering a lower mean square displacement of hydrogen atoms and localized hydrogen diffusion trajectories. Furthermore, at a high hydrogen concentration of 4 at. %, these grain boundaries were saturated by hydrogen atoms, and platelet-like hydrogen clusters were formed within the lattice, which further inhibited the diffusive motion of hydrogen atoms. These findings would deepen our understanding of hydrogen embrittlement mechanisms by establishing the connections between macroscopic permeation behavior and atomic-scale hydrogen diffusion in structural materials.

Influence of in-situ hydrogenation on photoelectrical properties of amorphous and nanocrystalline GeSn deposited by magnetron sputtering

This study investigates the fabrication of short-wavelength infrared (SWIR) photosensitive amorphous and nanocrystalline Ge1-xSnx:H thin films by magnetron sputtering from separate Ge and Sn targets using different Ar:H mixing ratios as working gas. Amorphous Ge1-xSnx:H films have been obtained on both c-Si and fused quartz substrates at ambient temperature, while dynamic nanocrystallization occurs in-situ when the substrate temperature during deposition is raised to 200 °C. Fourier-transform infrared spectroscopy has shown the hydrogen incorporation by detecting an absorption line at 1873 cm−1, close to the value corresponding to Ge-H bonding, only in the room temperature amorphous films. Based on that, we infer that the hydrogen concentration is very low in the films deposited at high temperature. The higher concentration of hydrogen in the amorphous samples is associated with an increase of the absorption gap to 0.5 eV compared to 0.3 eV in the 200 °C samples. In-situ (during deposition) and ex-situ (by subsequent rapid thermal annealing) nanocrystallization have been analyzed by high-resolution transmission electron microscopy, X-ray diffraction and micro-Raman spectroscopy. SWIR spectral photosensitivity up to 2.4 µm was found to be more than two orders of magnitude improved in hydrogenated amorphous films with high hydrogen content, compared to the nanocrystalline ones that are weakly hydrogenated. These findings demonstrate the potential of hydrogenation to enhance the photoelectric properties of GeSn sputtering films for optoelectronic SWIR infrared applications.

The regulation of dislocation and precipitated phase improving hydrogen embrittlement resistance of pipeline steel in high pressure hydrogen environment

In this study, the hydrogen embrittlement behavior of quenched pipeline steel tempered at 550 °C to 650 °C in a high-pressure hydrogen environment was analyzed. Hydrogen permeation tests and microstructural analyses indicated that the dislocation density of the steel decreases with increasing tempering temperature, while precipitates gradually nucleate and grow. These hydrogen traps interact with hydrogen atoms, resulting in significantly higher diffusible hydrogen content in steel tempered at 550 °C compared to that tempered at 600 °C and 650 °C. Fatigue crack growth (FCG) test results show that steel tempered at 600 °C and 650 °C exhibits significantly better hydrogen embrittlement resistance than steel tempered at 550 °C. This is primarily due to the combined effect of the high hydrogen concentration, high dislocation density and low nano carbide content in the steel tempered at 550 °C, which inhibits dislocation slip and emission, leading to high crack tip stress and rapid crack propagation. In contrast, the low dislocation density and and dispersed nano carbides in steel tempered at 600 °C and 650 °C facilitate some dislocation slip and emission, result in crack tip stress relaxation and reduced crack propagation rate. Properly controlling the initial dislocation density and increasing the density of irreversible hydrogen traps can enhance the strength of materials while improving their resistance to hydrogen embrittlement.

Burner and Flame Transfer Matrices of Jet-Stabilized Flames: Influence of Jet Velocity and Fuel Properties

Abstract To achieve the decarbonization of electrical power generation, gas turbines need to be upgraded to combust high-hydrogen content fuels reliably. One of the main challenges in this upgrade is the burner design. A promising burner concept for a high-hydrogen fuel mixture are jet burners, which are highly flashback resistant thanks to their high bulk velocity. Due to its nonacoustically compact extension and the presence of hydrogen in the fuel mixture, new challenges arise in assessing the (thermo)acoustic response of this burner design. A burner transfer matrix (BTM) and the flame transfer function (FTF) or transfer matrix (FTM) are typically measured with the multimicrophone method (MMM) to assess the performance of new burner types in relation to thermoacoustic stability. With the switch toward hydrogen, the fuel/air mixture is significantly altered in its properties regarding the speed of sound and density, which are of fundamental importance for acoustic waves propagation and their reconstruction via the MMM, as highlighted in recent work. In this work, we extend this discussion by studying the influence of the gas composition within the burner when measuring BTMs, and its indirect effect on the assessment of FTFs. Experimentally, we achieve this by adapting the preheating temperature during the measurement of the BTM with a nonreactive mixture in order to match the speed of sound of the hydrogen–air mixture required to flow in the burner under reactive conditions. Additionally, we present an analytical model for the jet burner transfer matrix, which is validated against the experimental data. Since the BTM is fundamental for the assessment of the FTM and FTF, the propagation of the error of changing fuel mixtures in the burner is evaluated. The influence of the variation in reactant composition of the BTM on the FTM assessment is noticeable, particularly in the gain of the FTFs. Furthermore, the influence of the total mass flow and, thus, the bulk flow velocity on the FTF is analyzed.

Simulated hydrogen diffusion in diamond grain boundaries

To evaluate hydrogen diffusion within diamond, a series of molecular dynamics simulations have been carried out in which diffusion coefficients and activation energies were determined. Diamond grown via chemical vapour deposition (CVD) contains a high hydrogen concentration within grain boundaries, because of this, common tilt grain boundaries were recreated from transmission electron microscopy images taken from literature. Diffusion coefficients of hydrogen placed within the grain boundary were estimated and compared to the bulk diffusion. Unlike many crystalline structures, some grain boundaries presented limited diffusion when compared to the bulk. Diffusion characteristics of grain boundaries are thought to be a result of channelling effects combined with the formation of sp3C-H bonds with sp2 carbon present within some grain boundaries - increasing and decreasing diffusion rates respectively. Potential wells were observed across some but not all the grain boundaries resulting in hydrogen trapping and anisotropic diffusion.

Ni-Doped SFM Double-Perovskite Electrocatalyst for High-Performance Symmetrical Direct-Ammonia-Fed Solid Oxide Fuel Cells.

Ammonia has emerged as a promising fuel for solid oxide fuel cells (SOFCs) owing to its high energy density, high hydrogen content, and carbon-free nature. Herein, the electrocatalytic potential of a novel Ni-doped SFM double-perovskite (Sr1.9Fe0.4Ni0.1Mo0.5O6-δ) is studied, for the first time, as an alternative anode material for symmetrical direct-ammonia SOFCs. Scanning and transmission electron microscopy characterization has revealed the exsolution of Ni-Fe nanoparticles (NPs) from the parent Sr2Fe1.5Mo0.5O6 under anode conditions, and X-ray diffraction has identified the FeNi3 phase after exposure to ammonia at 800 °C. The active-exsolved NPs contribute to achieving a maximal ammonia conversion rate of 97.9% within the cell's operating temperatures (550-800 °C). Utilizing 3D-printed symmetrical cells with SFNM-GDC electrodes, the study demonstrates comparable polarization resistances and peak power densities of 430 and 416 mW cm-2 for H2 and NH3 fuels, respectively, with long-term stability and a negligible voltage loss of 0.48% per 100 h during ammonia-fed extended galvanostatic operation. Finally, the ammonia consumption mechanism is elucidated as a multistep process involving ammonia decomposition, followed by hydrogen oxidation. This study provides a promising avenue for improving the performance and stability of ammonia-based SOFCs for potential applications in clean energy conversion technologies.