A2B7 compounds (A = rare earth or Mg, B = transition metal) are widely studied as active materials for negative electrode in Ni-MH batteries. By playing on the substitution rate of both A and B elements, it is possible to prepare various compositions. This strategy will help to improve the properties, for example get a higher reversible hydrogen capacity and a well-adapted hydrogen sorption pressure. Indeed, A can be almost all light rare earths (La to Gd), yttrium and alkaline earth metals (Mg or Ca), whereas B can contain various late transition metals (Mn to Ni). To understand the effects of composition on the physicochemical properties of La2Ni7-based compound, various pseudo-binary systems have been investigated: Gd2 xLaxNi7 (x = 0, 0.6, 1, 1.5), Sm2-xLaxNi7 (x = 0, 0.5, 1, 1.5), Y2-xLaxNi7 (x = 0, 0.4, 0.5, 0.6, 0.8, 1, 1.5, 1.75) and A0.5La1.1Mg0.4Ni7 (A = Sm, Gd and Y). To determine their crystallographic properties, X-ray diffraction analysis was performed followed by Rietveld refinement. Thermodynamic properties regarding reversible hydrogen sorption were investigated at room temperature. Quaternary compounds present drastically improved sorption properties in the frame of practical energy storage applications with reversible capacity equivalent to 400 mAh/g for the compound La1.1Sm0.5Mg0.4Ni7.
Typical ferroelectrics possess a large spontaneous polarization Ps but simultaneously a large remnant polarization Pr as well, resulting in an inferior energy storage density.A mechanism that can reduce the Pr while maintain the Ps is demanded to enhance the energy storage property of ferroelectrics.In the present study, it is shown that after acceptor doping and aging treatment, the domain switching in ferroelectrics becomes reversible, giving rise to a pinched double hysteresis loop. The pinched loop with a large Ps and a small Pr thus results in an enhanced energy storage density. The physi…
Despite high interest in compact and safe storage of hydrogen in the solid-state hydride form, the design of alloys that can reversibly and quickly store hydrogen at room temperature under pressures close to atmospheric pressure is a long-lasting challenge. In this study, first-principles calculations are combined with experiments to develop high-entropy alloys (HEAs) for room-temperature hydrogen storage. TixZr2-xCrMnFeNi (x = 0.4-1.6) alloys with the Laves phase structure and low hydrogen binding energies of -0.1 to -0.15 eV are designed and synthesized. The HEAs reversibly store hydrogen in…
By applying density functional theory (DFT) and ab-initio molecular dynamics (AIMD) simulations, we predict the ultrahigh hydrogen storage capacity of K and Ca decorated single-layer biphenylene sheet (BPS). We have kept various alkali and alkali earth metals, including Na, Be, Mg, K, Ca, at different sites of BPS and found that K and Ca atoms prefer to bind individually on the BPS instead of forming clusters. It was found that 2x2x1 supercell of biphenylene sheet can adsorb eight K, or eight Ca atoms, and each K or Ca atom can adsorb 5 H$_2$, leading to 11.90 % or 11.63 % of hydrogen uptake, …
The identification and use of reversible Martensitic transformations, typically described as shape memory transformations, as a new class of solid-solid phase change material is experimentally demonstrated here for the first time. To prove this claim, time-domain thermoreflectance, frequency-domain thermoreflectance, and differential scanning calorimetry studies were conducted on commercial NiTi alloys to quantify thermal conductivity and latent heat. Additional Joule-heating experiments demonstrate successful temperature leveling during transient heating and cooling in a simulated environment…
Dispersion corrected density functional theory ($ω$B97X-D DFT) method is used to study the molecular hydrogen adsorption in $Ni_nMg_m$ $(1\geq n\geq 3,1\geq m\geq9)$ clusters. All these clusters can effectively adsorb multiple $H_2$ in the preferred binding energy (BE) range between physisorption and chemisorption, i.e., $0.1 eV\geq BE \geq0.8 $eV. $H_2$ adsorption on $Ni_kMg_k$ (Ni:Mg=1:1), $Ni_kMg_{2k}$ (Ni:Mg=1:2) and $Ni_kMg_{3k}$ (Ni:Mg=1:3) (k=1-3) clusters shows fascinating behaviours in terms of Ni:Mg alloying ratio and cluster size. In each Ni:Mg ratio, the number of adsorbed $H_2$ in…
We have investigated the hydrogen storage capabilities of scandium decorated holey graphyne, a recently synthesized carbon allotrope, by applying density functional theory and molecular dynamics simulations. We have observed that one unit cell of holey graphyne can adsorb 6 Sc atoms, and each Sc atom can adsorb up to 5 H$_2$ molecules with an average binding energy and average desorption temperature of -0.36 eV/H$_2$ and 464 K, respectively. The gravimetric weight percentage of hydrogen is 9.80 %, which is considerably higher than the Department of Energy, United-States requirements of 6.5 %. …
Using first-principles density functional theory simulations, we have observed that the scandium decorated C$_{24}$ fullerene can adsorb up to six hydrogen molecules with an average adsorption energy of -0.35 eV per H$_2$ and average desorption temperature of 451 K. The gravimetric wt % of hydrogen for the scandium decorated C$_{24}$ fullerene system is 13.02%, which is sufficiently higher than the Department of Energy, United States demand. Electronic structure, orbital interactions, and charge transfer mechanisms are explained using the density of states, spatial charge density difference pl…
A Spintronic Battery with Reversible Modulation of Spin Polarization through Li Charge/Discharge: A First Principles Computational Modelling Case Study for an Antiperovskite System
Hydrogen is an efficient energy carrier that can be produced from renewable sources, enabling the transition towards CO2-free energy. Hydrogen can be stored for a long period in the solid-state, with suitable alloys. Ti-rich TiFe0.90 compound exhibits a mild activation process for the first hydrogenation, and Ti(Fe,Mn)0.90 substituted alloys can lead to the fine tuning of equilibrium pressure as a function of the final application. In this study, the crystal structure of TiFe(0.90-x)Mnx alloys (x = 0, 0.05 and 0.10) and their deuterides has been determined by in-situ neutron diffraction, while…
Hydrogen Storage on Transition-Metal-Decorated Nitrogen-Modified Carbon Nanoribbons
University of New England（新英格兰大学）；Karpagam Academy of Higher Education（卡尔帕甘高等教育学院）；Bhabha Atomic Research Centre（巴哈原子研究中心）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；University of Canberra（堪培拉大学）；The University of Queensland（昆士兰大学）
Electric Field Enhanced Hydrogen Storage on BN Sheet
使用密度泛函理论，我们表明，施加的电场通过极化氢分子以及基板，大大提高了BN片的储氢性能。在0.05 a. u.的电场存在下单个H2分子的吸附能。是0.48 eV，而在其不存在时为0.07 eV。当吸附一层H2分子时，每个H2分子的结合能从无场情况下的0.03 eV增加到存在0.045 a. u的电场时的0.14 eV/H2。7.5wt%的相应重量密度与DOE为2010年设定的6wt%系统目标一致。一旦去除所施加的电场，存储的H2分子可以容易地释放，从而使存储可逆。
AB5 compounds (A = rare earth, B = transition metal) have been widely studied as anodes for Ni-MH applications. However, they have reached their technical limitations and the search for new promising materials with high capacity is foreseen. ABy compounds (2 < y < 5) are good candidates. They are made by stacking [AB5] and [A2B4] units along the c crystallographic axis. The latter unit allows a large increase in capacity, while the [AB5] unit provides good cycling stability. Consequently, the AB3.8 composition (i.e. A5B19 with three [AB5] for one [A2B4]) is expected to exhibit better cycling s…
By employing the state-of-the-art density functional theory, we report the hydrogen storage capability of yttrium decorated C$_{24}$ fullerene. Single Y atom attached on C$_{24}$ fullerene can reversibly adsorb a maximum number of 6 H$_2$ molecules with average adsorption energy -0.37 eV and average desorption temperature 477 K, suitable for fuel cell applications. The gravimetric weight content of hydrogen is 8.84 %, which exceeds the target value of 6.5 wt % H by the department of energy (DoE) of the United States. Y atom is strongly bonded to C$_{24}$ fullerene with a binding energy of -3.4…
Sorbent materials are a promising alternative to advance hydrogen storage technologies. The general disadvantage is the relatively weak solid-gas interaction and adsorption energy, providing low gravimetric and volumetric capacities and extreme operational conditions. Here we propose Au-doped carbon nanotubes (CNTs) as an efficient alternative for reversible hydrogen capture at high temperatures. This work investigates the properties of several modified CNTs using density functional theory. We analyze the binding and formation energies of the uniformed Au-doped CNTs and assess their adsorption…
Intermetallic compounds are key materials for energy transition as they form reversible hydrides that can be used for solid state hydrogen storage or as anodes in batteries. ABy compounds (A = Rare Earth (RE); B = transition metal; 2 < y < 5) are good candidates to fulfill the required properties for practical applications. They can be described as stacking of AB5 and AB2 sub-units along the c crystallographic axis. The latter sub-unit brings a larger capacity, while the former one provides a better cycling stability. However, ABy binaries do not show good enough properties for applications. U…
Reversible Superdense Ordering of Tetragonal Lithium in a Layered Material
Cornell University（康奈尔大学）；Princeton University（普林斯顿大学）；Indian Institute of Technology Guwahati（印度理工学院古瓦哈提分校）；University of Wisconsin-Platteville（普拉特维尔威斯康星大学）；Yale University（耶鲁大学）
Monolayer transition metal dichalcogenides (TMDs) are direct gap semiconductors emerging promising applications in diverse optoelectronic devices. To improve performance, recent investigations have been systematically focused on the tuning of their optical properties. However, an all-optical approach with the reversible feature is still a challenge. Here we demonstrate the tunability of the photoluminescence (PL) properties of monolayer WS2 via laser irradiation. The modulation of PL intensity, as well as the conversion between neutral exciton and charged trion have been readily and reversibly…
MXene transition-metal carbides and nitrides are of growing interest for energy storage applications. These compounds are especially promising for use as pseudocapacitive electrodes due to their ability to convert energy electrochemically at fast rates. Using voltage-dependent cluster expansion models, we predict the charge storage performance of MXene pseudocapacitors for a range of electrode compositions. $M_3C_2O_2$ electrodes based on group-VI transition metals have up to 80% larger areal energy densities than prototypical titanium-based ( e.g. $Ti_3C_2O_2$) MXene electrodes. We attribute …
Machine learning via artificial neural networks coupled with density functional theory and experiments for thermodynamic optimization of high-entropy alloys for hydrogen storage at room temperature
WPI, International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University（九州大学）；Department of Automotive Science, Graduate School of Integrated Frontier Sciences, Kyushu University（九州大学）；Institute for Materials Science, University of Stuttgart（斯图加特大学）
With the rapid development of economy, the consumption of fossil fuels, and the increasing environment pollution, there is in urgent need of seeking clean and renewable energy sources, as well as highly efficient and low-cost energy storage technologies. Concerning electrochemically active materials, transition metal oxides (TMOs) are regarded as the most promising candidates for the next generation SCs and have been widely reported. Therefore, in this review, we mainly pay attention to TMOs with excellent electrochemical performance. This review is divided into four parts: (a) the background …
How surface chemistry influences reactions occurring thereupon has been a long-standing question of broad scientific and technological interest for centuries. Recently, it has re-emerged as a critical question in a subdiscipline of chemistry - electrochemistry at heterointerphases, where the answers have implications for both how, and in what forms, humanity stores the rising quantities of renewable electric power generated from solar and wind installations world-wide. Here we consider the relation between the surface chemistry at such interphases and the reversibility of electrochemical trans…
Magnesium and its alloys are the most investigated materials for solid-state hydrogen storage in the form of metal hydrides, but there are still unresolved problems with the kinetics and thermodynamics of hydrogenation and dehydrogenation of this group of materials. Severe plastic deformation (SPD) methods, such as equal-channel angular pressing (ECAP), high-pressure torsion (HPT), intensive rolling and fast forging, have been widely used to enhance the activation, air resistance, and hydrogenation/dehydrogenation kinetics of Mg-based hydrogen storage materials by introducing ultrafine/nanosca…
Pristine graphene is not suitable for hydrogen storage at ambient conditions since it binds the hydrogen molecules only by van der Waals interactions. However, the adsorption energy of the hydrogen molecules can be improved by doping or decorating metal atoms on the graphene monolayer. The doping and decoration processes are challenging due to the oxygen interference in hydrogen adsorption and the clustering issue of metal atoms. To improve the hydrogen adsorption energy in pristine graphene, we have explored the hydrogen storage capabilities of graphene monolayer in the presence of compressiv…
Carbon Layer Orientation and Closed-Pore Construction Achieving Ultra-Low Specific Surface Area Hard Carbon for High-Performance Na-ion Storage
School of Materials Science and Engineering, Guilin University of Electronic Technology（桂林电子科技大学材料科学与工程学院）；Siyuan Laboratory, Guangdong Provincial Engineering Technology Research Center of Vacuum Coating Technologies and New Materials, Guangdong Provincial Key Laboratory of Nanophotonic Manipulation, Department of Physics, College of Physics & Optoelectronic Engineering, Jinan University（暨南大学物理与光电工程学院物理系、广东省纳米光子学调控重点实验室、广东省真空镀膜技术与新材料工程技术研究中心、思源实验室）；Department of Semiconductor Engineering, Hoseo University（韩国好星大学半导体工程系）
