Concentration dependence of hydrogen diffusion in α-iron from atomistic perspectives

Evaluation of hydrogen diffusion in structural materials is essential to predict the leakage and embrittlement of hydrogen storage applications. In this work, we investigate the atomic-scale diffusion of interstitial hydrogen (H) in α-iron (Fe) over a temperature range from 350 to 900 K with different H concentrations (0.01–5%), employing classical molecular dynamics (MD) simulations. The self-diffusivity of H atoms increases with increasing temperature and decreasing concentration. With low concentrations, the calculated diffusion properties agree well with prior experiments. However, with a higher concentration (≥1%), the H diffusivity at low temperatures deviates from a high-temperature Arrhenius behavior. Through the energetic and structural analysis, we suggest that this deviation is attributed to a reduced mobility due to increased energy barrier by other H interstitials. This work contributes to the effective design of H storage applications by identifying temperature and concentration effects on permeability and addressing possible microstructural transformation.     

Atom probe tomography observation of hydrogen in high-Mn steel and silver charged via an electrolytic route

We investigate an electrolytic route for hydrogen charging of metals and its detection in Atom Probe Tomography (APT) experiments. We charge an austenitic Fe-30Mn-8Al-1.2C (wt.%) weight reduced high-Mn steel and subsequently demonstrate the detectability of deuterium in an APT experiment. The experiment is repeated with a deposited Ag film upon an APT tip of a high-Mn steel. It is shown that a detectable deuterium signal can be seen in the high-Mn steel, and a D:H ratio of 0.84 can be reached in Ag films. Additionally, it was found that the predicted time constraint on detectability of D in APT was found to be lower than predicted by bulk diffusion for the high-Mn steel.     

Fast computational framework for optimal life management of lithium ion batteries

The determination of optimal charging profiles over cycle life of a lithium ion battery is a challenging problem that is extremely important for commercial applications. It is a difficult problem to solve owing to the complex degradation processes occurring inside the battery. Further, modeling of a realistic battery operation, let alone the degradation mechanisms, results in computationally expensive mathematical models. In the present study, a framework is developed towards addressing this problem by (1) developing a method to formulate extremely fast and accurate algebraic models that capture essential features such as charging time and aging characteristics described by battery models and (2) utilizing these algebraic models in an optimization framework involving genetic algorithms for determining the optimal charging profiles over the cycle life of the battery. The utility of the present framework in determining the optimal charging solutions is illustrated with various real‐life usage scenarios such as fast charging and extension of cycle life. The proposed solution can be utilized onboard for generating the optimal charging profiles over cycle life of the battery.     

The effect of quench cracks and retained austenite on the hydrogen trapping capacity of high carbon martensitic steels

Hypereutectoid martensitic steels possess excellent hardness levels which make them attractive materials for specific industrial applications. However, they can contain cracks and/or retained austenite after quenching which show a particular interaction with hydrogen (H). Hence, this work evaluates the interaction between H and a martensitic Fe-1.1C alloy by combining a wide variety of (H) characterization techniques with a systematic approach for specially designed H charged and heat treated samples. A detailed analysis of the microstructure for every condition serves as the basis for the interpretation. The results show that the presence of H leads to additional cracking and branching or growth of pre-existing quench cracks. Moreover, it is shown that when the temperature exceeds the retained austenite decomposition temperature while the austenitic grains contain H, additional cracking occurs which increases the amount of reversible H trapping sites thus raising the HE susceptibility.     

A novel multiobjective charging optimization method of power lithium‐ion batteries based on charging time and temperature rise

Power lithium‐ion batteries have been widely utilized in energy storage system and electric vehicles, because these batteries are characterized by high energy density and power density, long cycle life, and low self‐discharge rate. However, battery charging always takes a long time, and the high current rate inevitably causes great temperature rises, which is the bottleneck for practical applications. This paper presents a multiobjective charging optimization strategy for power lithium‐ion battery multistage charging. The Pareto front is obtained using multiobjective particle swarm optimization (MOPSO) method, and the optimal solution is selected using technique for order of preference by similarity to ideal solution (TOPSIS) method. This strategy aims to achieve fast charging with a relatively low temperature rise. The MOPSO algorithm searches the potential feasible solutions that satisfy two objectives, and the TOPSIS method determines the optimal solution. The one‐order resistor‐capacitor (RC) equivalent circuit model is utilized to describe the model parameter variation with different current rates and state of charges (SOCs) as well as temperature rises during charging. And battery temperature variations are estimated using thermal model. Then a PSO‐based multiobjective optimization method for power lithium‐ion battery multistage charging is proposed to balance charging speed and temperature rise, and the best charging stage currents are obtained using the TOPSIS method. Finally, the optimal results are experimentally verified with a power lithium‐ion battery, and fast charging is achieved within 1534 s with a 4.1°C temperature rise.     

Geometrical effect in Mg-based metastable nano alloys with BCC structure for hydrogen storage

Mg-based materials are thought to be promising candidates for future hydrogen storage applications due to the low cost, abundant resources and large hydrogen storage capacity. However, they suffer from the challenges of sluggish kinetics and large volume change after hydriding/dehydriding (H/D) process. In order to address the problems, we successfully synthesized the Mg-based Body-Centered Cubic (BCC) metastable nano alloys with much improved kinetics while almost no obvious structure change after H/D process. In this work, the obtained Mg₅₅Co₄₅ metastable alloy with BCC structure can reach a hydrogen storage capacity of 3.24 wt% (hydrogen per metal or H/M = 1.28, H/Mg = 2.33) at −15 °C and this absorption temperature in Mg-based BCC structure is the lowest temperature reported for Mg-based materials to absorb hydrogen. Importantly, the BCC structure is maintained without obvious metal lattice change after H/D process. Nevertheless, the potential uptake of about 20 wt% theoretical hydrogen capacity (H/M = 9) for this unique BCC structure cannot be reached up to now. Herein, we discuss the mechanism from the geometrical effect aspect to figure out the difference between the experimental hydrogen storage capacity (H/M = 1.28) and the theoretical one (H/M = 9).     

Nanostructured materials for solar energy conversion

This review article deals with the motivation for using nanostructured materials in the field of solar energy conversion. We discuss briefly some recent fundamental observations on supported nanoclusters and optical properties of embedded metallic nanoclusters in a dielectric matrix. An overview on current research and existing applications in this field is given. Nanocomposite thin films developed for the application as optically selective absorber coatings in thermal solar collectors are described in some more detail. These coatings are based on transition metal containing amorphous hydrogenated carbon films (a-C:H/TM) or on transition metal containing silicon–carbon films (a-Si:C:H/TM) produced by a combined PVD/PECVD process.     

Recent developments in high eficiency photovoltaic cells

Enormous progress has been made in recent years on a number of photovoltaic materials and devices in terms of conversion efficiencies. Efficiencies in the range of 18%–24% have been achieved in traditional silicon-based devices fabricated from both multicrystalline and single-crystal materials. Ultrahigh-efficiency (>30%) photovoltaic (PV) cells have been fabricated from gallium arsenide (GaAs) and its ternary alloys like gallium indium phosphide (GaInP₂). The high-efficiency GaAs-based solar cells are being produced on a commercial scale, particularly for space applications. Major advances in efficiency have also been made on various thin-film solar cells based on amorphous silicon (aSi:H), copper gallium indium diselenide (CIGS), and cadmium telluride materials. This paper gives a brief overview of the recent progress in PV cell efficiencies based on these materials and devices.     

组合相变材料储热系统的储热速率研究

建立了组合式柱内封装相变材料熔化－固化循环相变储热系统的物理模型,用有限差分法进行了数值模拟求解。结果表明,与采用单一相变材料的传统储热系统相比,在给定相变材料组合方式和传热流体进口温度条件下,传热流体流量存在最佳值;选用三种石蜡作用相变材料和水作传热流体的模拟计算结果表明,相变速率可提高１５％￣２５％左右。     

Electronic structure and nanoindentation properties of electrochemical hydrogen-charged Zr-based metallic glasses

Zr₅₅Cu₃₀Ni₅Al₁₀ metallic glasses were treated by an electrochemical hydrogen- (H-)charging method. Samples with different H content were obtained by changing the H-charging current density and charging time. X-ray diffraction, nanoindentation, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy, and positron annihilation experiments were used to investigate amorphous structure, nanomechanical properties, electronic structure, and positron annihilation behavior of Zr₅₅Cu₃₀Ni₅Al₁₀ metallic glasses after electrochemical hydrogenation treatment. The results showed that the diffraction angle corresponding to the diffuse scattering peak gradually moved to a low angle with increased H content. At the same time, the hardness and elastic modulus of the MG were significantly increased with increased H-charging content. When the H content was high, the sawtooth rheological phenomenon disappeared in the load displacement curve of the MG during nanoindentation. XPS narrow spectrum analysis showed that the Zr-3d peak in samples shifted to higher binding energies, while the other elements shifted toward lower binding energy, indicating that H addition led to the transfer of valence electrons from Zr-3d to the Zr–H bond state, resulting in hardening. Three lifetime components are observed in the uncharged and charged sample, indicating the presence of three size ranges of open volume sites. After electrochemical hydrogen charging it causes a significant decrease in the size (lifetime) of the three open volume defects, indicating that the hydrogen occupies those sites. With the increase of hydrogen content, the concentration (intensity) of the first two open volume defects gradually decreases, while the third open volume defect gradually enhances, indicating that hydrogen atom mainly occupies the first two open volume defects. Positron annihilation experiments showed that H addition reduced the average annihilation lifetime of positron vacancies in these MGs, but no new defects were produced.     

Nanoporous metal organic framework materials for smart applications

Abstract

This review is concerned with the recent advances in metal organic framework (MOF) materials. We highlight the unique combination of physicochemical and thermomechanical characteristics associated with MOF-type materials and illustrate emergent applications in three challenging technological sectors: energy, environmental remediation and biomedicine. MOFs represent an exciting new class of nanoporous crystalline solids constituting metal ions/clusters and multifunctional organic linkages, which self-assemble at molecular level to generate a plethora of ordered 3D framework materials. The most intriguing feature of a MOF lies in its exceptionally large surface area, far surpassing those of the best activated carbons and zeolites. Next generation multifunctional materials encompassing MOF based thin films, coatings, membranes and nanocomposites have potential for exploitation in an immense array of unconventional applications and smart devices. We pinpoint the key technological challenges and basic scientific questions to be addressed, so as to fulfil the translational potential for bringing MOFs from the laboratory into commercial applications.     

Hydrogen embrittlement susceptibility of tempered 9%Cr-1%Mo steel

The influence of the subsurface hydrogen activity on the hydrogen embrittlement (HE) susceptibility of a tempered 9%Cr-1%Mo ferritic-martensitic steel (T91) has been studied by constant extension rate tests (CERT) performed under cathodic charging during straining at 20 °C. Changes in the hydrogen activity on the surface were obtained by varying the cathodic current density imposed during a tensile test completed to fracture. The broken samples were observed by scanning electron microscopy (SEM). The results show a strong dependence of the extent of the brittle zone with the subsurface hydrogen activity. This effect could be attributed to an enhancement of the apparent diffusion coefficient of hydrogen when increasing H activity. Increasing H activity could enhance both the trapping rate on pre-existing and strain-induced traps and H dragging by moving traps such as dislocations.     

Development of a renewable hydrogen economy: Optimization of existing technologies

There is an increasing need for new and greater sources of energy for future global transportation applications. One recognized possibility for a renewable, clean source of transportation fuels is solar radiation collected and converted into useable forms of electrical and/or chemical (hydrogen) energy. This paper describes methods for utilizing and combining existing technologies into systems that optimize solar energy collection and conversion into useful transportation fuels. Photovoltaic (PV)-electrolysis (solar hydrogen) and PV-battery charging systems described in this paper overcome inefficiencies inherent in past concepts, where DC power from the PV system was first converted to AC current and then used to power electrical devices at the point of generation, or fed back to the grid to reduce electricity costs. These past, non-optimized concepts included efficiency losses in power conversion and unnecessary costs. These drawbacks can be avoided by capitalizing on the unique feature of solar photovoltaic devices that match their maximum power point to the operating point of an electrolyzer or a battery charger without intervening power transformers. This concept is illustrated for two systems designed, built, and tested by General Motors for fueling a fuel cell electric vehicle and charging an automotive propulsion battery. Based on this research, we propose a scenario in which individual home-owners, businesses, or sites at remote locations with no grid electricity, can capture solar energy, store it as hydrogen generated via water electrolysis, or as electrical energy used to charge storage batteries. Such a decentralized energy system provides a home refueling option for drivers who only travel limited distances each day.     

H,OH and COOH functionalized magnesium phthalocyanine as a catalyst for oxygen reduction reaction (ORR) – A DFT study

Platinum is an efficient catalyst for a fuel cell, however of its high cost and rarity on Earth, it becomes necessary to predict an effective, low cost, and abundantly available catalyst. Here, hydrogen (H), hydroxyl (OH) and carboxyl (COOH) group functionalized magnesium phthalocyanine (MgPc) are considered as catalysts to enhance oxygen reduction reaction (ORR) mechanism via direct four-electron reduction reaction. The density functional theory (DFT) based results show that the reactions occur on the top site of the magnesium (Mg) metal center than the edge site of the phthalocyanines (Pcs). From thermochemical parameters, the reactions are highly exothermic, hence feasible. The atoms in molecules (AIM) analysis reveals that the adsorbates stabilize over catalysts through ionic, covalent, hydrogen and weak interactions. The adsorption energy and reversible potential of the intermediates and product on phthalocyanines shows that MgPc(OH)₁₆ is a better catalyst for the ORR process. Conclusively, this study establishes that phthalocyanines are promising materials as a catalyst for ORR which is vital for fuel cell applications.     

Energetic and structural analysis of N2H4BH3 inorganic solid and its modified material for hydrogen storage

Here we have exposed the electronic structure, chemical bonding of the light-weight N₂H₄BH₃ inorganic material for hydrogen storage applications and analyzed its hydrogen removal energetics using state-of-the-art first-principles method. The mechanism for the H-host bond weakening in this kind of solid has also been explored. It is shown that the electronic density of states of N₂H₄BH₃ solid near the Fermi level is mainly contributed by the B p-states, H (B) s-states, and the end N p-states. The calculated smallest hydrogen removal energy of N₂H₄BH₃ solid is 4.16 eV. One Li-modified structure has been obtained through ab initio relaxations and its hydrogen removal energies are found dramatically decreased by as much as 50% compared with those of pristine N₂H₄BH₃ solid. The B–H bond weakening is attributed to the elongation of the bond length; for the N–H bonds, the weakening is found to be due to the destabilization of N–H bonds before hydrogen removal and the stabilization of residual N–H bond after hydrogen removal. The weakening of these bonds is of great significance for the improvement of hydrogen desorption kinetics of the material. We propose this study should help to deepen understanding of properties of N₂H₄BH₃ inorganic solid and its related materials for hydrogen storage applications and guide experimentalists and engineers to develop better candidate materials for the advance of the field.     

Allotrope carbon materials in thermal interface materials and fuel cell applications: A review

The performance of allotrope carbon materials has been explored because of their superior properties in energy system applications. This review provides an understanding of the current work focusing on the applications of selected carbon materials in important energy systems, focus on thermal interface materials (TIMs), and fuel cell applications. This article begins with the introduction of TIMs and fuel cell in general working principle and presents details on carbon materials. The discussion focuses on updates from the latest research work and addresses current challenges and opportunities for research toward TIMs and fuel cell applications. The optimum performance of TIMs was seen when thermal conductivity achieved at a maximum of 3000 W (m K)⁻¹ by using vertically aligned carbon nanotubes (CNTs) and a minimum internal thermal resistance of 0.3 mm² K W⁻¹. Meanwhile for fuel cell, the platinum/CNTs catalyst applied proton exchange membrane fuel cell achieved high power density of 661 mW cm⁻² in the presence of Nafion electrolyte membrane. This review provides insights for scientists about the use of carbon materials, especially in energy system applications.     

Investigations on calculation of heat of formation for multi-element AB5-type hydrogen storage alloy

With development in hydrogen energy research, more and more applications of hydrogen storage materials have been put forward. This requires synthesis of new materials for specific purpose. In context to designing of metal hydride bed, thermodynamic parameter ‘Heat of formation’ (ΔH) for hydrogen storage alloy is very important. Theoretical calculation of ΔH for binary compound or ternary hydride is accomplished by well known ‘Miedema's Rule of Reverse Stability’. Experimentally ΔH may be determined using Van't Hoff Equation. So far, theoretical calculation of ΔH for multi-element alloy is not known. In the present investigation simple phenomenological formulae have been proposed to calculate ΔH for multi-element alloy including AH_m, BH_m, AB_n, AB_nH_2m, AB_n-xC_x, AB_n-xC_xH_2m, AB_n-x-yC_xD_y, AB_n-x-yC_xD_yH_2m and so on. The calculated values of ΔH in present investigation have been compared with the experimental reported value or calculated by any other model reported in literature. An excellent agreement has been observed between the two.     

Metal free hydrogenation reaction on carbon doped boron nitride fullerene: A DFT study on the kinetic issue

By the incorporation of C into (BN)₁₂ fullerene, our theoretical investigation shows that the hydrogenation reaction on carbon doped B₁₁N₁₂C cluster is both thermodynamically favored and kinetically feasible under ambient conditions. Without using the metal catalyst, the C atom can work as an activation center to dissociate H₂ molecule and provide the free H atom for further hydrogenation on the B₁₁N₁₂C fullerene, which saves the materials cost in practical applications for hydrogen storage. Moreover, the material curvature also plays an important role in reducing the activation barrier for the hydrogen dissociation on the BN fullerenes.