Stability of a hydrogen molecule in a vacancy of palladium hydrides

We report our ab-initio calculations of energy states of equilibrium H–H separation in a vacancy of palladium and palladium hydrides at a variety of H/Pd loading ratios. In a vacancy of pure palladium, the H₂ molecule has a shallow local energy minimum only in the [001] direction at a separation of 0.96 Å and it dissociates into positions near interstitial sites due to its high energy state. Increasing the H/Pd ratio to the beta phase deepens the energy well of the H₂ molecule and results in a shorter H–H separation. At a loading ratio around 1, the H₂ molecule is mostly affected by surrounding hydrogen neighbors and the H–H separation reaches 0.77 Å. The H₂ molecule is then fairly stable and its energy state is comparable to that of nearby interstitial sites. Our calculations suggest that the loading ratio of hydrogen in palladium has a significant effect on the stability of the H₂ molecule in the vacancy.     

Role of S-S interlayer spacing on the hydrogen storage mechanism of MoS2

Hydrogen storage mechanism and hydrogen storage capacity are the great challenges for the development of hydrogen energy technology. Besides the better catalytic properties, it is crucial to search for suitable material that provides enough space to store H₂ molecule. Similar to graphene, MoS₂ with S-S layered structure opens up a new way to improve the hydrogen storage capacity. By using the first-principles calculations, in this work, we investigate the hydrogen diffusion mechanism, hydrogenation process and hydrogen storage capacity of MoS₂ with S-S interlayer. We find that hydrogen prefers to diffuse into S-S interlayer along the interstitial site (path: IT-IT). H₂ molecule is a stable in S-S interlayer because the charge interaction of H-H atoms is stronger than that of H-S atoms. Finally, we predict that MoS₂ with S-S layered-by-layered stacking can effectively improve the hydrogen storage capacity.     

Advancements in hydrogen energy research with the assistance of computational chemistry

Hydrogen and electricity are the leading energy sources for most applications in the near future. With the rapid development of computers and computational chemistry methods, the research in hydrogen production, infrastructure materials, storage, and utilization more than ever benefits from close interactions with computational chemistry. The present review aims at presenting the modern state of hydrogen energy chemical research in all processes of hydrogen economy. Directions of further research efforts are given in the context of chemometrics and computational chemistry advancements. Problems of computational chemistry that hinder rapid progress are given and their possible solutions are outlined. It is expected that new artificial neural network (ANN) algorithms will play a decisive role in the creation of dependable computational chemistry methods and their application for hydrogen infrastructure, production, storage, and consumption.     

Hydrogen adsorption on pristine and platinum decorated graphene quantum dot: A first principle study

In the ever growing demand of future energy resources, hydrogen production reaction has attracted much attention among the scientific community. In this work, we have investigated the hydrogen evolution reaction (HER) activity on an open-shell polyaromatic hydrocarbon (PAH), graphene quantum dot “triangulene” using first principles based density functional theory (DFT) by means of adsorption mechanism and electronic density of states calculations. The free energy calculated from the adsorption energy for graphene quantum dot (GQD) later guides us to foresee the best suitable catalyst among quantum dots. Triangulene provides better HER with hydrogen placed at top site with the adsorption energy as −0.264 eV. Further, we have studied platinum decorated triangulene for hydrogen storage. Three different sites on triangulene were considered for platinum atom adsorption namely top site of carbon (C) atom, hollow site of the hexagon carbon ring near triangulene's unpaired electron and bridge site over C–C bond. It is found that the platinum atom is more stable on the hollow site than top and bridge site. We have calculated the density of states (DOS), highest occupied molecular orbitals (HOMO), lowest unoccupied molecular orbitals (LUMO) and HOMO-LUMO gap of hydrogen molecule adsorbed platinum decorated triangulene. Our results show that the hydrogen molecule (H₂) dissociates instinctively on all three considered sites of platinum decorated triangulene resulting in D-mode. The fundamental understanding of adsorption mechanism along with analyses of electronic properties will be important for further spillover mechanism and synthesis of high-performance GQD for H₂ storage applications.     

Review and comparison of various hydrogen production methods based on costs and life cycle impact assessment indicators

Hydrogen is a clean, renewable secondary energy source. The development of hydrogen energy is a common goal pursued by many countries to combat the current global warming trend. This paper provides an overview of various technologies for hydrogen production from renewable and non-renewable resources, including fossil fuel or biomass-based hydrogen production, microbial hydrogen production, electrolysis and thermolysis of water and thermochemical cycles. The current status of development, recent advances and challenges of different hydrogen production technologies are also reviewed. Finally, we compared different hydrogen production methods in terms of cost and life cycle environmental impact assessment. The current mainstream approach is to obtain hydrogen from natural gas and coal, although their environmental impact is significant. Electrolysis and thermochemical cycle methods coupled with new energy sources show considerable potential for development in terms of economics and environmental friendliness.     

Thermophysical properties of supercritical H2 from Molecular Dynamics simulations

The ability to predict thermophysical properties of molecular hydrogen with high accuracy, especially at high pressures, is crucial to design and to operate processes involving compressed hydrogen. Molecular simulations comprise an adequate tool to investigate both thermodynamic and transport properties of different molecular systems using a single potential energy surface model. Such a potential is called a force field. Here we propose a new single-site force field for pure hydrogen using a Mie potential to describe the intermolecular interactions. The proposed force field yields better predictions of thermodynamic properties when compared to other available force fields that use Lennard-Jones interaction potential. The new force field is also able to predict transport properties with reasonable accuracy.     

Characterization of the energy of hydrogen under pressure in pure metals

In this work we study the total energy of hydrogen under pressure in a metallic medium. We use the effective jellium model to characterize the electronic density, which, based upon the density-functional formalism, determines, in principle, all the physical properties of the system. Although this formalism is not valid for systems under pressure, we will use some approximations obtained from the model of molecular hydrogen in a dense system confined by a penetrable barrier. In this model, the energy of the ground state of the molecular hydrogen ion and its associated pressure are obtained for different barrier heights and nuclear radii. With these results, we recover the system at zero pressure, but with a given initial density, able to treat with the jellium model. This analysis is very useful and quite exact for the treatment of such complex systems as hydrogen under pressure.     

Modeling hydrogen adsorption in the metal organic framework (MOF-5, connector): Zn4O(C8H4O4)3

Density functional theory investigation is performed to understand the underlying mechanism of hydrogen adsorption in the MOF-5 by using for first time the connector structure. The analysis of chemical bonds of the connector's atoms shows a good agreement between experimental and theoretical results. In particular, we show that this material has a desorption temperature of 115 K and an initial hydrogen storage capacity around 1.57 wt% which are close to the experimental values. We consider the coupling-energy mechanism to explore the most stable configurations in multiple adsorption sites namely metallic, carboxylic and cyclic sites. Three orientations which are vertical, horizontal and sloping are taking into account. The results show that the metallic and cyclic sites are more stable for multiple hydrogen molecule storage and the system reaches 4.57 wt% as a gravimetric storage capacity which is located in the interval 4.50–5.20 wt% found experimentally. In addition, the desorption temperature is improved significantly.     

Energy management of a thermally coupled fuel cell system and metal hydride tank

Being produced from renewable energy, hydrogen is one of the most efficient energy carriers of the future. Using metal alloys, hydrogen can be stored and transported at a low cost, in a safe and effective manner. However, most metals react with hydrogen to form a compound called metal hydride (MH). This reaction is an exothermic process, and as a result releases heat. With sufficient heat supply, hydrogen can be released from the as-formed metal hydride. In this work, we propose an integrated power system of a proton exchange membrane fuel cell (PEMFC) together with a hydride tank designed for vehicle use. We investigate different aspects for developing metal hydride tanks and their integration in the PEMFC, using water as the thermal fluid and a FeTi intermetallic compound as the hydrogen storage material. Ground truth simulations show that the annular metal hydride tank meets the hydrogen requirements of the fuel cell, but to the detriment of the operating temperature of the fuel cell (FC).     

Economical assessment of a wind–hydrogen energy system using WindHyGen software

This paper considers the problem of analyzing the economical feasibility of a wind–hydrogen energy storage and transformation system. Energy systems based on certain renewable sources as wind power, have the drawback of random input making them a non-reliable supplier of energy. Regulation of output energy requires the introduction of new equipment with the capacity to store it. We have chosen the hydrogen as an energy storage system due to its versatility. The advantage of these energy storage systems is that the energy can be used (sold) when the demand for energy rises, and needs (prices) therefore are higher. There are two disadvantages: (a) the cost of the new equipment and (b) energy loss due to inefficiencies in the transformation processes. In this research we develop a simulation model to aid in the economic assessment of this type of energy systems, which also integrates an optimization phase to simulate optimal management policies. Finally we analyze a wind–hydrogen farm in order to determine its economical viability compared to current wind farms.     

Recent advances in hydrogen compressors for use in large-scale renewable energy integration

Given global warming, which limits the use of classical energy sources, renewables can provide a solution to the dilemma between environmental protection and sustainable economic growth. In this complex and changing context, green hydrogen can become a promising link between renewable energy sources and end users. However, although hydrogen has a high gravitational energy density, it has a very low volumetric energy density. This challenge requires hydrogen compression at several stages in the supply chain from electrolysis units to conversion, storage, and distribution. Recently, many studies have focused on hydrogen compression technologies. This paper provides an overview of recent advances in large-scale hydrogen compression. First, the role of hydrogen compression in providing clean energy for the future is explored. Then the thermodynamic concept of hydrogen compression is investigated. Gaining a proper understanding of compressor operating conditions in various operations in the large hydrogen industry is the next focus of this paper. Later, the capabilities and limitations of available mechanical compressors for the hydrogen industry, including reciprocation and centrifugal, are summarized. Finally, research gap and recommended new areas in this field are recognized. The presented insightful concepts provide students, experts, researchers, and decision-making working on large-scale hydrogen industry with the state of the art in hydrogen compressors industry.     

Hydrogen adsorption on and diffusion through MoS2 monolayer: First-principles study

We investigate the hydrogen adsorption on and diffusion through the MoS₂ monolayer based on density-functional theory. We show that the hydrogen atom prefers to bond to the S atom at the monolayer, leading to enhanced conductivity. The hydrogen atom can also adsorb at the middle of the hexagon ring by overcoming an energy barrier of 0.57 eV at a strain of 8%. Also, we show that the MoS₂ monolayer is flexible and any mechanical deformation of the monolayer is reversible because the extension of the Mo–S bond is much smaller than the applied strain. The monolayer can block the diffusion of hydrogen molecule from one side to the other due to a high energy barrier (6.56 eV). However, the barrier can be reduced to 1.38 eV at a strain of 30% and even totally removed by creating S vacancies and applying a strain of 15%. The MoS₂ monolayer may find applications in sensors to detect hydrogen, and as mechanical valve to control the concentration of hydrogen gas.     

Ab initio study on hydrogen interaction with calcium decorated silicon carbide nanotube

Ab initio study on the viability of calcium decorated silicon carbide nanotube as a hydrogen storage material was conducted. Calcium strongly adsorbs on silicon carbide nanotube (SiCNT) with a significant binding energy of ?2.83 eV, thus calcium's low cohesive energy and strong binding with SiCNT may prevent Ca to form clusters with other adsorbates. Bader charge analysis also revealed a charge transfer of 1.45e from Ca to SiCNT resulting to calcium's cationic state, which may induce charge polarization to a nearby molecule such as hydrogen. Hydrogen molecule was then allowed to interact with the calcium adatom where it exhibited charge polarization, induced by the electric field from calcium's positive charge. This resulted to a significant binding energy of ?0.22 eV for the first hydrogen molecule. Results reveal that Ca on SiCNT can hold up to 7 hydrogen molecules and can be a promising candidate for a hydrogen storage material.     

Cost and performance sensitivity studies for solar photovoltaic/electrolytic hydrogen systems

In previous work, we have investigated the implications of projected advances in thin film solar cell technology for producing electrolytic hydrogen from photovoltaic (PV) electricity. These studies indicate that if year 2000 cost and efficiency goals for thin film solar cells are achieved, PV hydrogen produced in the Southwestern U.S. could become roughly cost competitive with other synthetic fuels for applications such as automotive transport and residential heating, if efficient energy use is stressed. This suggests that PV hydrogen could potentially play a significant role in future energy supply.However, the estimated production cost of PV hydrogen depends on the cost and performance parameters assumed for the PV hydrogen system. In this paper we investigate the sensitivity of PV hydrogen production costs to changes in the system parameters and identify key conditions for low cost PV hydrogen production.     

Assessment of a theoretical model of turbulent combustion by comparison with a simple experiment

In this study a turbulent combustion model for premixed flames with finite rate chemistry is implemented with a new calculation of the diffusion fluxes and turbulent kinetic energy taking into account the fluctuations of density. After the proposal of closure assumptions related to this phenomenon, the model is integrated and the results compared with a simple experimental study.This experimental study concerns an oblique plane premixed (hydrogenair) flame expanding in a turbulent confined flow. Measurements of mean and turbulent velocity field are made using an LDV technique. For mean temperature and concentration measurements, a thermocouple and an isokinetic sampling probe, respectively, are used.     

Research on optimizing control model of hydrogen fueled engines based on thermodynamics and state space analysis method about nonlinear system

With its obvious advantages, hydrogen is expected to be greatly used as a new energy, which can reduce vehicle emissions effectively and efficiently. Besides, it can be adopted as an alternative fuel for petroleum fuel of internal combustion engine. However, due to its unique physical and chemical characteristics, hydrogen often leads to abnormal combustion and decay of power, which can be effectively dealt with by optimal control. In this paper, thermodynamic analysis methods, like mass transfer and energy transfer, is combined with state space analysis methods of nonlinear control system, so that an optimal control model of nonlinear combustion control system for hydrogen fueled engines can be established. Through illustrating the inner relations between combustion and energy transfer of hydrogen fueled engines and operating parameter, state parameter and performance index, this paper provides theoretical analysis and found experimental research for promoting abnormal combustion and performance index after controlling operating parameters optimally and changing state parameters of the cylinder. Based on nonlinear programming theory and multi-objective genetic algorithm, the methods of establishing the optimal control model and carrying out the optimal value of operating parameters are shown in this paper. What’s more, some new ways are proposed to integrate the optimal control aspects of multi-variate, multiple targets and multiple constraints for hydrogen fueled engines by changing the multi-objective and multi-constraint optimal control into the single-target integrated optimal control.     

Time development of new hydrogen transmission pipeline networks for France

The development of a hydrogen economy will need a transportation infrastructure to deliver hydrogen from production sites to end users. For the specific case of hydrogen, pipelines networks compete with other hydrogen carriers: compressed gas trucks and liquid cryogenic trucks. In this paper, we deal with the determination of the temporal deployment of a new hydrogen transportation infrastructure. Starting from the expected final horizon pipelines network, we propose a backward heuristic approach. The proposed approach is illustrated on a French regional hydrogen transportation network tacking into account two scenarios for hydrogen penetration into the fuel markets. We showed that for the mid term perspective and low market share, the trucks are the most economical options. However, for the long term, the pipeline option is considered as an economical viable option as soon as the hydrogen energy market share for the car fueling market reaches 10%.     

An adaptive chemistry approach to modeling complex kinetics in reacting flows

Existing algorithms use a single chemical kinetic model over the entire domain of a reacting flow simulation. However, it is well known that the chemistry varies significantly in different regions of a flame. For combustion and other reacting flows with very complex chemistry, computing all possible reactions and species everywhere in the computational domain (the full chemistry approach) is very computationally demanding. Here we propose an adaptive chemistry approach that avoids computing species and reactions in regions where they are negligible. In this approach, a set of reduced chemical kinetic models is used in a simulation, each reduced model being used only under reaction conditions where it is faithful to the full model. A procedure to implement adaptive chemistry is presented, and compared with the conventional full chemistry approach. Adaptive chemistry fairly accurately reproduces the full chemistry solutions, while reducing the cost of the computation both in terms of CPU time and in terms of memory requirements. This was demonstrated by simulating a turbulent planar hydrogen/air shear layer flame and two axisymmetric laminar co-flowing partially premixed methane-air flames. The challenges that need to be overcome to make this method more broadly useful are summarized.     

A first-principles study of Li and Na co-decorated T4,4,4-graphyne for hydrogen storage

To obtain high hydrogen storage performance, Li and Na co-decorated T4,4,4-graphyne have been studied by the method of first-principles calculations in this paper. Li and Na atoms are bound on hexagonal ring and acetylenic ring included in T4,4,4-graphyne, with the average adsorption energy of 1.73 and 2.38 eV, respectively. Our calculations show that the maximum gravimetric density of H₂ uptake is 10.46 wt%, and an appropriate adsorption energy is reached. Moreover, by plotting charge density differences, it is found that the induced electric field between Li/Na and T4,4,4-graphyne can enhance the adsorption for hydrogen molecule. Furthermore, this complex is thermodynamic stable at room temperature, which is certificated by molecule dynamics simulation. Our results demonstrate that Li and Na co-decorated T4,4,4-graphyne is an alternative material for hydrogen storage.