Hydrogen Loading Research Articles

Structure and Composition Modification of Ultrasmall Palladium Nanoparticles upon Hydrogenation from First Principles

Palladium-based materials exhibit a high affinity for hydrogen, making them ideal candidates for hydrogen storage or hydrogen sensing applications owing to the existence of a hydride phase. From the theoretical point of view, a bulk or slab is often used to model such systems but lacks the flexibility to adapt its lattice parameter to an increased load of hydrogen. Using density functional theory, we follow the change in the structure and composition of small palladium nanoparticles upon hydrogenation. We show that a cuboctahedral nanoparticle with hydrogen in the core and on the surface is a relevant model under experimental conditions. CO and NO are then adsorbed on this nanoparticle to highlight the crucial importance of hydrogen loading when considering palladium nanomaterials for-wider sensing applications.

Effects of composition and morphology on the hydrogen storage properties of transition metal hydrides: Insights from PtPd nanoclusters

Transition metal hydride nanoparticles are promising hydrogen storage materials as they store and release hydrogen at near-ambient conditions. Their storage capacities can be modulated by adjusting their size, shape, morphology, and composition. It is however unclear why these factors influence hydrogen storage properties. Here, we present a first-principles study on six 55-atom PtPd nanoclusters to elucidate the effects of nanoparticle morphology and composition on the hydrogen storage characteristics of small nanoclusters. We employ the cluster expansion methodology to analyze how the spatial distribution and energetics of hydrogen adsorption and absorption evolve as a function of hydrogen loading. Our results reveal that at near-ambient pressures and above, hydrogen is actively stored in both the surface—top sites on Pt, and bridge sites on Pd—and the subsurface. The hydrogen storage capacity is controlled by the binding strength of hydrogen, itself influenced by two factors: i) the interaction energy between hydrogen atoms, which dictates how binding strength varies with increasing loading; and ii) the intrinsic binding affinity of a metal cluster for hydrogen, which dictates the magnitude of the nearly-uniform offsets in binding strength across all hydrogen loadings. Bimetallic clusters with alloyed shells and core-shell morphologies modulate these factors by tuning the distribution of hydrogen binding strengths on the surface and subsurface respectively. We shed light on the factors that affect hydrogen storage in clusters and provide insights for the rational design of metal clusters with maximal hydrogen storage capacities.

Effect of sub-surface hydrogen on intrinsic crack tip plasticity in aluminium

ABSTRACTThe effects of sub-surface hydrogen and mixed mode loading on dislocation emission in aluminium are studied using a combination of techniques including crack simulations with an empirical interatomic potential, generalised stacking fault energy (GSF) calculations, with empirical interactions and Density Functional Theory, and the model by Rice which links the critical stress intensity factor to the unstable stacking energy. The crack orientation is and the loading is composed of a moderate traction along and a shear along , such that Shockley partials are emitted along the crack plane. The role of the relaxations around the H atoms and of the concentration of H in the glide plane, in the GSF calculation, is revealed by comparing Rice's model to the results of brute force simulations. The enhanced GSF is then calculated ab initio. The conclusion is a large decrease of the critical load to emit a dislocation, due to the displacement transverse to the glide direction. The effect of sub-surface hydrogen is negligible with respect to the mechanical one.

Application of Membrane Reactor and PEMFC‐based Micro‐CHP System in Off‐grid Applications

AbstractThe performance of an innovative m‐CHP, rated at 5 kWel, is assessed at full and partial load. The system is powered by a polymer electrolyte membrane fuel cell (PEMFC), and hydrogen is produced via ethanol reforming in a membrane reactor. The membrane reactor selectivity may decrease with time and the separated hydrogen may contain other gases with penalties on cell voltage and system efficiency. To account for this aspect, the system is simulated at steady‐state conditions by 1D phenomenological models of the membrane reactor and the fuel cells stack, for different hydrogen purities and load fraction. The fuel cell efficiency is affected by the presence, at anode side, of CO and inert gases coming from the membrane reactor and from the cathode side by membrane electrode assembly (MEA) cross‐over, as well as by voltage decay over time.Then the innovative micro‐combined heat and power (m‐CHP) system, coupled with a heat pump, and heat and electricity storage systems, is applied to two off‐grid houses, located in different climatic regions: it allows about 20% of fuel saving per year compared to a conventional m‐CHP based on an internal combustion engine. The fuel saving reduces to 15% in case of low‐purity hydrogen, and 10% in worst conditions with low‐purity hydrogen and degraded cells.

Positron annihilation spectroscopy study of defects in hydrogen loaded Zr-1Nb alloy

The purpose of this work is to implement the positron lifetime and Doppler broadening techniques for the study of hydrogen-induced defects in Zr–1wt% Nb (hereinafter Zr–1Nb) alloy. It was shown that spark cutting is an appropriate instrument to obtain a pair of Zr-1Nb samples with the same hydrogen content for the “sandwich” geometry and does not introduce open-volume defects in them during the cut. The ab-initio calculations were implemented to evaluate the positron annihilation characteristics for expanded crystal lattice, Zr with absorbed hydrogen, Zr-vacancy and Zr-vacancy-hydrogen complexes. The type of defects created in Zr-1Nb alloy loaded with hydrogen from the gas phase up to various hydrogen concentrations was studied. The main types of defects induced by hydrogen loading are vacancy-hydrogen complexes and dislocations. The processes of crystal lattice expansion and hydrogen dissolution in the lattice were studied.

Ethylene glycol as an efficient and reversible liquid-organic hydrogen carrier

Hydrogen has long been regarded as an ideal alternative clean energy vector to overcome the drawbacks of fossil technology. However, the direct utilization of hydrogen is challenging, due to low volumetric energy density of hydrogen gas and potential safety issues. Herein, we report an efficient and reversible liquid to liquid organic hydrogen carrier system based on inexpensive, readily available and renewable ethylene glycol. This hydrogen storage system enables the efficient and reversible loading and discharge of hydrogen using a ruthenium pincer complex, with a theoretical hydrogen storage capacity of 6.5 wt%.

Off-grid solar powered charging station for electric and hydrogen vehicles including fuel cell and hydrogen storage

Abstract This paper designs an off-grid charging station for electric and hydrogen vehicles. Both the electric and hydrogen vehicles are charged at the same time. They appear as two electrical and hydrogen load demand on the charging station and the charging station is powered by solar panels. The output power of solar system is separated into two parts. On part of solar power is used to supply the electrical load demand (to charge the electric vehicles) and rest runs water electrolyzer and it will be converted to the hydrogen. The hydrogen is stored and it supplies the hydrogen load demand (to charge the hydrogen-burning vehicles). The uncertainty of parameters (solar energy, consumed power by electrical vehicles, and consumed power by hydrogen vehicles) is included and modeled. The fuel cell is added to the charging station to deal with such uncertainty. The fuel cell runs on hydrogen and produces electrical energy to supply electrical loading under uncertainties. The diesel generator is also added to the charging station as a supplementary generation. The problem is modeled as stochastic optimization programming and minimizes the investment and operational costs of solar and diesel systems. The introduced planning finds optimal rated powers of solar system and diesel generator, operation pattern for diesel generator and fuel cell, and the stored hydrogen. The results confirm that the cost of changing station is covered by investment cost of solar system (95%), operational cost of diesel generator (4.5%), and investment cost of diesel generator (0.5%). The fuel cell and diesel generator supply the load demand when the solar energy is zero. About 97% of solar energy will be converted to hydrogen and stored. The optimal operation of diesel generator reduces the cost approximately 15%.

Techno-economic assessment and optimization of a hybrid renewable co-supply of electricity, heat and hydrogen system to enhance performance by recovering excess electricity for a large energy consumer

This study attempts to optimize and examine the techno-economic feasibility of off-grid hybrid renewable energy systems (HRES) to satisfy simultaneously electric, heat and hydrogen load of a large energy consumer. An innovative method is adopted so as to recover surplus electricity to generate heat and cut emissions. The system is comprised of solar panels, wind turbine, diesel generator, electrolyzer and boiler to supply 9910 kWh/day of electricity, 14 kg/day of hydrogen and thermal energy in five different major cities in Iran, namely Bandar Abbas, Shiraz, Tabriz, Tehran and Yazd. These figures are computed on average and the thermal load differs according to yearly weather temperature, which are 75, 22, 2000, 5200, 2200 and 1800 kWh/day respectively. To serve this purpose, HOMER Pro software was used and thermal load controller (TLC) (including electric boiler) was added to generate thermal energy by converting excess electricity of renewable energy production. Thus, a decrease in conventional fuel consumption, emissions and cost of energy (COE), as well as an increase in the renewable fraction of HRES without increasing project’s size would be achievable. To meet peak demand and avoid intermittent behavior of HRES, a 1000 kW generator was picked up. Results indicate that recovering extra electricity can enhance renewable fraction by up to 35% and bring down COE and exhausted CO2 by 7.1% and 10.6% respectively, which highlight the necessity of TLC in HRES, chiefly in off-grid systems.

A Reversible Liquid Organic Hydrogen Carrier System Based on Methanol‐Ethylenediamine and Ethylene Urea

AbstractA novel liquid organic hydrogen carrier (LOHC) system, with a high theoretical hydrogen capacity, based on the unpresented hydrogenation of ethylene urea to ethylenediamine and methanol, and its reverse dehydrogenative coupling, was established. For the dehydrogenation only a small amount of solvent is required. This system is rechargeable, as the H2‐rich compounds could be regenerated by hydrogenation of the resulting dehydrogenation mixture. Both directions for hydrogen loading and unloading were achieved using the same catalyst, under relatively mild conditions. Mechanistic studies reveal the likely pathway for H2‐lean compounds formation.

A Reversible Liquid Organic Hydrogen Carrier System Based on Methanol-Ethylenediamine and Ethylene Urea.

A novel liquid organic hydrogen carrier (LOHC) system, with a high theoretical hydrogen capacity, based on the unpresented hydrogenation of ethylene urea to ethylenediamine and methanol, and its reverse dehydrogenative coupling, was established. For the dehydrogenation only a small amount of solvent is required. This system is rechargeable, as the H2 -rich compounds could be regenerated by hydrogenation of the resulting dehydrogenation mixture. Both directions for hydrogen loading and unloading were achieved using the same catalyst, under relatively mild conditions. Mechanistic studies reveal the likely pathway for H2 -lean compounds formation.

Quantification of Temperature Dependence of Hydrogen Embrittlement in Pipeline Steel.

The effects of temperature on bulk hydrogen concentration and diffusion have been tested with the Devanathan–-Stachurski method. Thus, a model based on hydrogen potential, diffusivity, loading frequency, and hydrostatic stress distribution around crack tips was applied in order to quantify the temperature’s effect. The theoretical model was verified experimentally and confirmed a temperature threshold of 320 K to maximize the crack growth. The model suggests a nanoscale embrittlement mechanism, which is generated by hydrogen atom delivery to the crack tip under fatigue loading, and rationalized the ΔK dependence of traditional models. Hence, this work could be applied to optimize operations that will prolong the life of the pipeline.

Prediction of the Hydrogen-Induced Damage to Ultra-High Strength Steel Concepts

The hydrogen-induced damage behavior of ultra-high strength steels (UHSS) has been predicted by a combination of experimental and numerical investigations. Firstly, the resistance against hydrogen-induced failure was examined by slow strain rate tests (SSRT) using various sample geometries and hydrogen contents. Secondly, the hydrogen distribution and loading conditions during the tensile test were calculated by means of the finite element method (FEM). Finally, a combination of various damage models was applied and validated by further SSRT. The main result of this study is a failure prediction model, which considers local stress and strain conditions, as well as hydrogen content.

Effect of hydriding induced defects on the small-scale plasticity mechanisms in nanocrystalline palladium thin films

Nanoindentation tests performed on nanocrystalline palladium films subjected to hydriding/dehydriding cycles demonstrate a significant softening when compared to the as-received material. The origin of this softening is unraveled by combining in situ TEM nanomechanical testing with automated crystal orientation mapping in TEM and high resolution TEM. The softening is attributed to the presence of a high density of stacking faults and of Shockley partial dislocations after hydrogen loading. The hydrogen induced defects affect the elementary plasticity mechanisms and the mechanical response by acting as preferential sites for twinning/detwinning during deformation. These results are analyzed and compared to previous experimental and simulation works in the literature. This study provides new insights into the effect of hydrogen on the atomistic deformation and cracking mechanisms as well as on the mechanical properties of nanocrystalline thin films and membranes.

Hydrogen adsorption in pyridine bridged porphyrin-covalent organic framework

Covalent organic frameworks (COFs), a class of carbon-based polymeric materials have the potential to be used as hydrogen adsorbent. Three dimensional (3D) COFs, due to their low density and high surface area, although have higher hydrogen adsorption, they have less stability than two dimensional (2D) COFs. Here we studied porphyrin group containing 2D COF, namely H2,P-COF for hydrogen storage using density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations and the results were compared with the most common 2D COFs, COF-1 and COF-5. Cylindrical shaped 2D COFs where isolated unit blocks are stacked in multiple layers due to van der Waals interactions between individual layers, increase the effective surface area for hydrogen storage. A further modification has been done by bridging the inter-layer gap by pyridine molecules. Insertion of pyridine increases the separation distance of layers of 2D COFs as well as the free volume. Feasibility of the structure formation and stability of all the structures were checked using DFT study. To ensure the structural stability of bridged COFs after hydrogen loading, alternating layers of COF were bridged. Single, bi, tri and tetra -pyridine molecules were chemically bonded with the existing carbon ring present in between two C2O2B rings to form pyridine bridged H2,P-COFs. Our GCMC results show a significant increase in storage capacity which is mainly due to an increase in the free volume of the material. The highest capacity of ∼ 5.1 wt% and 20 g H2/L at 298 K and 100 bar, above the gravimetric DOE goal, has been found at room temperature for tetra-pyridine doped porphyrin COF structure.

Hydrogen-affected fatigue crack propagation at various loading frequencies and gaseous hydrogen pressures in commercially pure iron

Hydrogen-Affected Fatigue Crack Growth (HAFCG) in commercially pure iron has been characterized in terms of hydrogen gas pressure, loading frequency and stress intensity factor range ΔK. A higher hydrogen gas pressure decreases the critical value of ΔK triggering the HAFCG enhancement, and a lower loading frequency increases the HAFCG enhancement. Intergranular FCG in the non-accelerated regime is likely caused by the hydrogen-induced microvoid coalescence along the grain boundary, while a brittle cyclic cleavage fracture in the accelerated regime can be explained in terms of crack tip sharpening and hydrogen-enhanced decohesion process.

Attainable Volumetric Targets for Adsorption-Based Hydrogen Storage in Porous Crystals: Molecular Simulation and Machine Learning

Hydrogen fuel is attractive to power vehicles without emitting carbon, but onboard storage of sufficiently densified hydrogen at moderate pressure remains a significant challenge. Adsorption-based storage in porous crystals such as metal–organic frameworks and covalent organic frameworks is attractive to reduce the storage pressure. It is, however, unclear to what extent volumetric storage targets can be met under constraints of adsorbent design and choice of operating conditions. To help elucidate attainable values for volumetric storage metrics upon the potential introduction of strong hydrogen-binding sites, we “computationally synthesized” a library of porous crystals and performed 18 000+ grand canonical Monte Carlo simulations to calculate hydrogen loadings at multiple T, P conditions. The studied frameworks are based on 17 pore topologies and feature alchemical catecholate sites: sites whose interaction with hydrogen was artificially and systematically modified within the range of density functiona...

Process performance and microbial community structure in thermophilic trickling biofilter reactors for biogas upgrading

This study evaluated the process performance and determined the microbial community structure of two lab-scale thermophilic trickling biofilter reactors used for biological methanation of hydrogen and carbon-dioxide for a total period of 94 days. Stable and robust operation was achieved by means of a single-pass gas flow. The quality of the output gas (>97%) was comparable to the methane purity achieved by commercial biogas upgrading systems fulfilling the specifications to be used as substitute to natural gas. The reactors' methane productivity reached >1.7 LCH4/(LR·d) at hydrogen loading rate of 7.2 LH2/(LR·d). The spatial distribution of the microbial consortia localized in the liquid media and biofilm enabled us to gain a deeper understanding on how the microbiome is structured inside the trickling biofilter. Sequencing results revealed a significant predominance of Methanothermobacter sp. in the biofilm. Unknown members of the class Clostridia were highly abundant in biofilm and liquid media, while acetate utilising bacteria predominated in liquid samples.

Magneto-ionic control of magnetism using a solid-state proton pump.

Voltage-gated ion transport as a means of manipulating magnetism electrically could enable ultralow-power memory, logic and sensor technologies. Earlier work made use of electric-field-driven O2- displacement to modulate magnetism in thin films by controlling interfacial or bulk oxidation states. However, elevated temperatures are required and chemical and structural changes lead to irreversibility and device degradation. Here we show reversible and non-destructive toggling of magnetic anisotropy at room temperature using a small gate voltage through H+ pumping in all-solid-state heterostructures. We achieve 90° magnetization switching by H+ insertion at a Co/GdOx interface, with no degradation in magnetic properties after >2,000 cycles. We then demonstrate reversible anisotropy gating by hydrogen loading in Pd/Co/Pd heterostructures, making metal-metal interfaces susceptible to voltage control. The hydrogen storage metals Pd and Pt are high spin-orbit coupling materials commonly used to generate perpendicular magnetic anisotropy, Dzyaloshinskii-Moriya interaction, and spin-orbit torques in ferromagnet/heavy-metal heterostructures. Thus, our work provides a platform for voltage-controlled spin-orbitronics.

Effects of alloying elements (Al, Mn, Ru) on desorption plateau pressures of vanadium hydrides: An experimental and first-principles study

Vanadium-based alloys are promising for the reversible and compact storage of renewable hydrogen. To improve the hydrogen desorption plateau pressure of vanadium hydrides, V–3A binary alloys of V97Al3, V97Mn3, and V97Ru3 were prepared by vacuum arc melting. Hydrogen absorption and desorption properties of the newly prepared V–3A alloys were studied, and compared to vanadium hydrides, by pressure-composition-temperature measurements and first-principles calculations. Among the studied materials, V–3Ru showed the highest hydrogen desorption plateau pressures between T = 373 and 433 K. During hydrogen loading, V–3Ru also reached the highest hydrogen to metal ratio between the alloys. Meanwhile, V–3Ru was also the alloy with the highest hardness. Findings of hydrogen absorption and desorption measurements were supported with DFT calculations of hydride formation energies. The calculated DOS, ELF and atomic charges were used to study the effects of alloying on the electronic properties of hydrides. The bonding interactions in vanadium dihydrides were influenced the most through Al alloying, whereas V–3Mn and V–3Ru hydrides showed comparable electronic properties.

Limitations of the kinematic approximation in neutron reflectivity measurements for the analysis of bilayers

The limitations of a phenomenological fitting approach compared to simulations of the optical model including reflection and refraction at all interfaces are demonstrated using the example of hydrogen loading in ultra-thin vanadium layers. Fe/V superlattices are loaded with deuterium and the lattice expansion and deuterium concentration are extracted from neutron reflectivity data. A noticeable difference is found between the extraction of concentrations and bilayer thicknesses directly from the superlattice peaks and fits of the density profile using the Parratt formalism. The results underline the importance of carefully considering the limitations of phenomenological approaches, in order to obtain robust results. The limitations of the kinematic approximation for the analysis are discussed in detail.