Hydrogen

In this work, geochemical modelling using PhreeqC was carried out to evaluate the effects of geochemical reactions on the performance of underground hydrogen storage (UHS). Equilibrium, exchange, and mineral reactions were considered in the model. Moreover, reaction kinetics were considered to evaluate the geochemical effect on underground hydrogen storage over an extended period of 30 years. The developed model was first validated against experimental data adopted from the published literature by comparing the modelling and literature values of H₂ and CO₂ solubility in water at varying conditions. Furthermore, the effects of pressure, temperature, salinity, and CO₂% on the H₂ and CO₂ inventory and rock properties in a typical sandstone reservoir were evaluated over 30 years. Results show that H₂ loss over 30 years is negligible (maximum 2%) through the studied range of conditions. The relative loss of CO₂ is much more pronounced compared to H₂ gas, with losses of up to 72%. Therefore, the role of CO₂ as a cushion gas will be affected by the CO₂ gas losses as time passes. Hence, remedial CO₂ gas injections should be considered to maintain the reservoir pressure throughout the injection and withdrawal processes. Moreover, the relative volume of CO₂ increases with the increase in temperature and decrease in pressure. Furthermore, the reservoir rock properties, porosity, and permeability, are affected by the underground hydrogen storage process and, more specifically, by the presence of CO₂ gas. CO₂ dissolves carbonate minerals inside the reservoir rock, causing an increase in the rock’s porosity and permeability. Consequently, the rock’s gas storage capacity and flow properties are enhanced. Full article

Hydrogen barrier coatings are protective layers consisting of materials with a low intrinsic hydrogen diffusivity and solubility, showing the potential to delay, reduce or hinder hydrogen permeation. Hydrogen barrier coatings are expected to enable steels, which are susceptible to hydrogen embrittlement, specifically cost-effective low alloy-steels or light-weight high-strength steels, for applications in a hydrogen economy. Predominantly, ceramic coating materials have been investigated for this purpose, including oxides, nitrides and carbides. In this review, the state of the art with respect to hydrogen permeation is discussed for a variety of coatings. Al₂O₃, TiAlN and TiC appear to be the most promising candidates from a large pool of ceramic materials. Coating methods are compared with respect to their ability to produce layers with suitable quality and their potential for scaling up for industrial use. Different setups for the characterisation of hydrogen permeability are discussed, using both gaseous hydrogen and hydrogen originating from an electrochemical reaction. Finally, possible pathways for improvement and optimisation of hydrogen barrier coatings are outlined. Full article

Hydrogen is not only an important industrial chemical but also an energy carrier with increasing demand. However, the current production techniques are based on technologies that result in massive CO₂ emissions. In contrast, the pyrolysis of alkanes in a liquid metal bubble column reactor does not lead to direct CO₂ emissions. In order to transfer this technology from lab-scale to industrial applications, it has to be scaled up and the influences of the most common constituent of natural gas on the pyrolysis process have to be determined. For this study, the liquid metal bubble column technology developed at the KIT was scaled up by a factor of 3.75, referred to as the reactor volume. In this article, the experimental setup containing the reactor is described in detail. In addition, new methods for the evaluation of experimental data will be presented. The reactor, as well as the experimental results from pure methane pyrolysis (PM), will be compared to the previous generation of reactors in terms of methane conversion. It could be proven that scaling up the reactor volume did not result in a decrease in methane conversion. For part II of this publication, methane-ethane (MEM) gas mixtures and high calorific natural gas (nGH) were pyrolyzed, and the results were discussed on the basis of the present part I. Full article

The concept of classical nuclear motion is extremely successful in describing motion at the atomic scale. In describing chemical reactions, it is even far more convincing than the picture obtained by using the Schrödinger equation for time development. However, this theory must be subject to critical tests. In particular, it must be checked if vibrational and rotational spectra are obtained correctly. Particularly critical are the spectra of small molecules containing the light hydrogen atom, since they have a distinctive rotational structure. The present study presents computations of the spectra of ammonia and hydrogen chloride using ab initio molecular dynamics, that is, by describing nuclear motion classically. Full article

Cottonseed oil (CSO) is well known as one of the commercial cooking oils. However, CSO still needs to compete with other edible oils available in the market due to its small production scale and high processing cost, which makes it a potential candidate as a feedstock for biodiesel production. To date, transesterification is the most widely applied technique in the conversion of vegetable oil to biodiesel, with glycerol produced as a by-product. Large-scale biodiesel production also implies that more glycerol will be produced, which can be further utilized to synthesize hydrogen via the steam reforming route. Therefore here, an integrated biodiesel and hydrogen production from CSO was simulated using Aspen Hysys v11. Simulation results showed that the produced biodiesel has good characteristics compared to standard biodiesel. An optimum steam-to-glycerol ratio for hydrogen production was found to be 4.5, with higher reaction temperatures up to 750 °C resulting in higher hydrogen yield and selectivity. In addition, a simple economic analysis of this study showed that the integrated process is economically viable. Full article

The design of a 10 cm² (3.4 cm by 3.4 cm) and a 100 cm² (10 cm by 10 cm) anion exchange membrane (AEM) water electrolyser cell for hydrogen production are described. The AEM cells are based on a zero-gap configuration where the AEM is sandwiched between the anode and cathode so as to minimise voltage drop between the electrodes. Nonprecious nickel-based metal alloy and metal oxide catalysts were employed. Various experiments were carried out to understand the effects of operating parameters such as current densities, electrolyte concentrations, and testing regimes on the performance of both 10 cm² and 100 cm² AEM electrolyser cells. Increasing electrolyte concentration was seen to result in reductions in overpotentials which were proportional to current applied, whilst the use of catalysts improved performance consistently over the range of current densities tested. Extended galvanostatic and intermittent tests were demonstrated on both 10 cm² and 100 cm² cells, with higher voltage efficiencies achieved with the use of electrocatalysts. Stability tests in the 100 cm² AEM electrolyser cell assembled with catalyst-coated electrodes demonstrated that the cell voltages remained stable at 2.03 V and 2.17 V during 72 h operation in 4 M KOH and 1 M KOH electrolyte, respectively, at a current density of 0.3 A cm⁻² at 323 K. The inclusion of cycling load tests in testing protocols is emphasized for rational evaluation of cell performance as this was observed to speed up the rate of degradation mechanisms such as membrane degradation. Full article

Selected results of investigations focused on the changes to some mechanical properties of palladium and several palladium-based alloys caused by exposure to hydrogen have been collected and presented. The findings indicate that the mechanical properties of pure palladium are highly susceptible to alteration upon exposure to hydrogen. In the cases of alloying palladium with silver and copper, the alloys, as compared to palladium, appear to resist changes to mechanical properties. In the case of alloying palladium with manganese, the interesting order–disorder phenomenon plays an important role on the effects of hydrogen exposure on their mechanical properties. Full article

Here, the authors report the results of their study on the key characteristics of microscale periodic Ni-Mg-Ni-Mg film structures as metal-hydride hydrogen accumulators, namely, the microstructure, phase state, operation temperatures and rate of the sorption/desorption processes, complete and reversible mass content of hydrogen, and enthalpy of metal hydrides’ phase-formation. The study has shown that hydride-formation films can be saturated with up to 7.0–7.5 wt.% of hydrogen at pressures up to 30 atm and temperatures of 200–250 °C, with a reversible amount of stored hydrogen up to 3.4 wt.% during its desorption at a pressure of 1 atm and temperatures of 250–300 °C with the phase-formation enthalpy in the range of 19.8–46.7 kJ/mol H₂ depending on the nickel content (the thickness of the nickel layer). Structural and constructive schemes are proposed for film metal-hydride hydrogen accumulators for various applications of the hydrogen power industry. Full article

Natural gas distribution companies are developing ambitious plans to decarbonize the services that they provide in an affordable manner and are accelerating plans for the strategic integration of renewable natural gas and the blending of green hydrogen produced by electrolysis, powered with renewable electricity being developed from large new commitments by states such as New York and Massachusetts. The demonstration and deployment of hydrogen blending have been proposed broadly at 20% of hydrogen by volume. The safe distribution of hydrogen blends in existing networks requires hydrogen blends to exhibit similar behavior as current supplies, which are also mixtures of several hydrocarbons and inert gases. There has been limited research on the properties of blended hydrogen in low-pressure natural gas distribution systems. Current natural gas mixtures are known to be sufficiently stable in terms of a lack of chemical reaction between constituents and to remain homogeneous through compression and distribution. Homogeneous mixtures are required, both to ensure safe operation of customer-owned equipment and for safety operations, such as leak detection. To evaluate the stability of mixtures of hydrogen and natural gas, National Grid experimentally tested a simulated distribution natural gas pipeline with blends containing hydrogen at up to 50% by volume. The pipeline was outfitted with ports to extract samples from the top and bottom of the pipe at intervals of 20 feet. Samples were analyzed for composition, and the effectiveness of odorant was also evaluated. The new results conclusively demonstrate that hydrogen gas mixtures do not significantly separate or react under typical distribution pipeline conditions and gas velocity profiles. In addition, the odorant retained its integrity in the blended gas during the experiments and demonstrated that it remains an effective method of leak detection. Full article

Photoreforming biomass-derived waste such as glycerol into hydrogen fuel is a renewable hydrogen generation technology that has the potential to become important due to unavoidable CO₂ production during methane steam reforming. Despite tremendous efforts, the challenge of developing highly active photocatalysts at a low cost still remains elusive. Here, we developed a novel photocatalyst with a hybrid support comprising reduced graphene oxide (rGO) and TiO₂ nanorods (TNR). rGO in the hybrid support not only performed as an excellent scavenger of electrons from the semiconductor conduction band due to its suitable electrochemical potential, but also acted as an electron transport highway to the metal co-catalyst, which otherwise is not possible by simply increasing metal loading due to the shadowing effect. A series of hybrid supports with different TNR and rGO ratios were prepared by the deposition method. Pd nanoparticles were deposited over hybrid support through the chemical reduction method. Pd/rGO-TNRs photocatalyst containing 4 wt.% rGO contents in the support and 1 wt.% nominal Pd loading demonstrated hydrogen production activity ~41 mmols h⁻¹g⁻¹, which is 4 and 40 times greater than benchmark Au/TiO₂ and pristine P25. The findings of this works provide a new strategy in optimizing charge extraction from TiO₂, which otherwise has remained impossible due to a fixed tradeoff between metal loading and the detrimental shadowing effect. Full article

This paper uses established and recently introduced methods from the applied mathematics and statistics literature to study trends in the end-use sector and the capacity of low-carbon hydrogen projects in recent and upcoming decades. First, we examine distributions in plants over time for various end-use sectors and classify them according to metric discrepancy, observing clear similarity across all industry sectors. Next, we compare the distribution of usage sectors between different continents and examine the changes in sector distribution over time. Finally, we judiciously apply several regression models to analyse the association between various predictors and the capacity of global hydrogen projects. Across our experiments, we see a welcome exponential growth in the capacity of zero-carbon hydrogen plants and significant growth of new and planned hydrogen plants in the 2020’s across every sector. Full article

New Pt-Co catalysts of hydrogen purification from CO impurities for fuel cells were fabricated via the deposition of monodispersed 1.7 nm Pt nanoparticles using laser electrodispersion on Co-modified ZSM-5 prepared by the Co(CH₃COO)₂ impregnation. The structure of prepared Pt-Co zeolites was studied by low-temperature N₂ sorption, TEM, EDX, and XPS methods. The comparative analysis of samples with different Pt (0.01–0.05 wt.%) and Co (2.5–4.5 wt.%) contents on zeolites with the ratio of Si/Al = 15, 28, and 40 was performed in the CO-PROX reaction in H₂-rich mixture (1%CO + 1%O₂ + 49%H₂ + 49%He). The synergistic catalytic action of Pt and Co on zeolite surface makes it possible to completely remove CO from a mixture with hydrogen in a wide temperature range from 50 to 150 °C; the high efficiency of designed composites with low Pt loading is maintained for a long time. The enhancement of PROX performance originates from the formation of new active sites for the CO oxidation at the Pt-Co interfaces within zeolite channels and at the surface. In terms of their activity, stability, and selectivity, such composites are significantly superior to known supported Pt-Co catalysts. Full article

With the accelerating development of liquid-hydrogen storage facilities, the problem of boil-off hydrogen losses becomes very important. A promising method to reduce these losses is to utilize the endothermic para-orthohydrogen conversion of vented hydrogen, which can effectively decrease heat loads on a hydrogen tank. To model such a process, a hybrid computational model has been developed, based on the application of computational fluid dynamics for an ullage space, where knowledge of thermal stratification is important, and reduced-order models for other system elements. The simulation results for a spheroidal tank in selected conditions indicated a 10–25% reduction of boil-off losses due to cooling produced by vented hydrogen undergoing para-ortho-conversion. Full article

The sulfur dioxide (SO₂) compound is a primary environmental pollutant worldwide, whereas elemental sulfur (S) is a global commodity possessing a variety of industrial as well as commercial functions. The chemical relationship between poisonous SO₂ and commercially viable elemental S has motivated this investigation using the Density Functional Theory calculation of the relative transition state barriers for the two-step dehydro-sulfurization oxidation–reduction reaction. Additionally, doubly-charged nanoscale platelet molybdenum disulfide (MoS₂), armchair (6,6) carbon nanotube, 28-atom graphene nanoflake (GR-28), and fullerene C-60 are utilized as catalysts. The optimal heterogeneous and homogeneous catalysis pathways of the two-step oxidation–reduction from SO₂ to elemental S are further inspired by the biomimicry of the honeybee species’ multi-step bio-catalysis of pollen conversion to organic honey. Potential applications include environmental depollution, the mining of elemental sulfur, and the functionalization of novel technologies such as the recently patented aerial and amphibious Lynchpin^TM drones. Full article

Molecular cobaloxime-based heterogeneous systems have attracted great interest during the last decades in light-driven hydrogen production. Here, we present a novel cobaloxime-tethered periodic mesoporous organosilica (PMO) hybrid (Im-EtPMO-Co) prepared through the immobilization of a molecular cobaloxime complex on the imidazole groups present in ethylene-bridged PMO. The successful assembly of a molecular cobaloxime catalyst via cobalt-imidazole axial ligation has been evidenced by several techniques, such as ¹³C NMR, Raman spectroscopy, ICP-MS, and XPS. The catalytic performance of Im-EtPMO-Co catalyst was essayed on the hydrogen evolution reaction (HER) under visible light in presence of a photosensitizer (Eosin Y) and an electron donor (TEOA). It showed an excellent hydrogen production of 95 mmol hydrogen at 2.5 h, which corresponded to a TON of 138. These results reflect an improved photocatalytic activity with respect to its homogenous counterpart [Co(dmgH)₂(Im)Cl] as well as a previous cobaloxime-PMO system with pyridine axial ligation to the cobaloxime complex. Full article

Extensive decarbonisation efforts result in major changes in energy demand for the extractive industry. In 2021, the extraction and primary processing of metals and minerals accounted for 4.5 Gt of CO₂ eq. per year. The aluminium industry was responsible for 1.1 Gt CO₂ eq. direct and indirect emissions. To reach the European milestone of zero emissions by 2050, a reduction of 3% annually is essential. To this end, the industry needs to take a turn towards less impactful production practices, coupling secondary production with green energy sources. The present work aims to comprehensively compare the lifecycle energy consumption and environmental performance of a secondary aluminium smelter employing alternative thermal and electricity sources. In this frame, a comparative analysis of the environmental impact of different thermal energy sources, namely natural gas, light fuel oil, liquified petroleum gas, hydrogen and electricity, for a secondary aluminium smelter is presented. The results show that H₂ produced by renewables (green H₂) is the most environmentally beneficial option, accounting for −84.156 kg CO₂ eq. By producing thermal energy as well as electricity on site, H₂ technologies also serve as a decentralized power station for green energy production. These technologies account for a reduction of 118% compared to conventionally used natural gas. The results offer a comprehensive overview to aid decision-makers in comparing environmental impacts caused by different energy sources. Full article

During the oxidation of hydrocarbons using hydrogen peroxide solutions, the evolution of gaseous oxygen is a side and undesirable process, in which the consumption of the oxidizer is not associated with the formation of target products. Therefore, no attention is paid to the systematic study of the chemical composition of the gas and the mechanisms of its formation. Filling this gap, the authors discovered a number of new, previously unidentified, interesting facts concerning both gas evolution and the oxidation of hydrocarbons. In a 33% H₂O₂/Cu₂Cl₄·2DMG/CH₃CN system, where DMG is dimethylglyoxime (Butane-2,3-dione dioxime), and is at 50 °C, evidence of significant evolution of gaseous hydrogen, along with the evolution of gaseous oxygen was found. In the authors’ opinion, which requires additional verification, the ratio of gaseous hydrogen and oxygen in the discussed catalytic system can reach up to 1:1. The conditions in which only gaseous oxygen is formed are selected. Using a number of oxidizable hydrocarbons with the first adiabatic ionization potentials (AIPs) of a wide range of values, it was found that the first stage of such a process of evolving only gaseous oxygen was the single electron transfer from hydrogen peroxide molecules to trinuclear copper clusters with the formation, respectively, of hydrogen peroxide radical cations H₂O₂^•+ and radical anions Cu₃Cl₅^•− (AIP = 5 eV). When the conditions for the implementation of such a single electron transfer mechanism are exhausted, the channel of decomposition of hydrogen peroxide molecules into gaseous hydrogen and oxygen is switched on, which is accompanied by the transition of the system to an oscillatory mode of gas evolution. In some cases, the formation of additional amounts of gaseous products is provided by the catalytically activated decomposition of water molecules into hydrogen and oxygen after the complete consumption of hydrogen peroxide molecules in the reaction of gaseous oxygen evolution. The adiabatic electron affinity of various forms of copper molecules involved in chemical processes is calculated by the density functional theory method. Full article

Hydrogen can drastically degrade the mechanical properties of a variety of metallic materials. The so-called hydrogen environment embrittlement of austenitic CrNi-type steels is usually accompanied by the formation of secondary surface cracks, which can be investigated in order to assess the embrittlement process. The occurrence of hydrogen-induced cracks is often related to element segregation effects that locally impact the austenite stability. Since there is as yet a lack of investigation methods that can visualize both structures three-dimensionally, the present study investigates the imageability of hydrogen-induced cracks and element segregation structures in austenitic CrNi-steel via micro-computed tomography (CT). In order to improve the X-ray visibility of segregation structures, modified versions of the reference steel, X2CrNi18-9, that contain W and Si are designed and investigated. The investigations demonstrated that small differences in the X-ray attenuation, caused by the W or Si modifications, can be detected via CT, although segregation structures could not be imaged due to their small size scale and image noise. Hydrogen-induced cracks were characterized successfully; however, the detection of the smaller cracks is limited by the resolution capability. Full article