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With the increasing amount of renewable energy produced, many governments and industries are pushing for the installation of battery energy storage system (BESS) solutions. Thermal batteries are systems that store heat made from various energy sources, and can be used to produce electricity upon demand. These systems are easily scalable and can be installed in cities, homes and remote locations. Thermochemical energy storage (TCES) uses the enthalpy of a chemical reaction to store and release heat through endothermic and exothermic processes, respectively. CaCO3 has been identified as an ideal TCES material as it is cheap and abundant, but maximising long-term cyclability is key to ensure battery longevity. This article investigates the addition of CaSiO3, CaTiO3 and CaZrO3 to CaCO3 in a 1 : 1 ratio to ascertain the reaction properties and cyclic capacity over time. Cycling longevity and thermodynamic properties were determined using simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC–TGA) along with the Sieverts technique, and their reaction pathway studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The low cost of the CaCO3–CaSiO3 material of $1.8 USD per kW hth suggests that if a suitable particle refinement agent were to be employed to ensure cycling longevity this material would be an excellent TCES material. Despite the CO2 cycling capacity of the CaCO3–CaZrO3 system only reducing by 16 wt% over 100 cycles, the cost of ZrO2 brings the materials cost to $30.9 USD per kW hth, making this material currently unsuitable for application. The CaCO3–CaTiO3 system showed only a 17% drop in total CO2 uptake over 100 cycles, although the cost was $11.1 USD per kW hth. [ABSTRACT FROM AUTHOR]

Alternatives to fossil fuels are necessary to reduce greenhouse gas emissions, and energy storage is crucial to transition to renewable energy. Thermochemical energy storage is one option to store energy for 24/7 utilisation, and as such, the reversible carbonation of the Ca : Mg : Fe oxide system was investigated to determine its feasibility as a thermochemical energy storage material. The Ca : Mg : Fe (1 : 1 : 1) sample synthesised from co-crystallisation of metal acetates retained reversible CO2 sorption at 90% over 100 cycles, thus the associated physical properties were thoroughly investigated. Powder X-ray diffraction analyses indicated the formation of dicalcium ferrite and magnesioferrite, respectively in the decarbonated and carbonated states, which suggested a synergistic effect enhancing the reversible sorption of CO2 in the 2CaO·Fe2O3·MgO intermediate system involved in the reaction mechanism. The thermodynamics of the reactions were determined using pressure-composition-isotherm measurements, resulting in calculated enthalpies and entropies of ΔHabs = −146 ± 5 kJ mol−1 and ΔSabs = −141 ± 5 J mol−1 K−1, and ΔHdes = 178 ± 4 kJ mol−1 and ΔSdes = 167 ± 4 J mol−1 K−1 for CO2 absorption and desorption, respectively. The application of the Kissinger method determined an activation energy of 203 ± 14 kJ mol−1 for the decarbonation reaction. The maximum energy storage density of the system was evaluated to be 468 kJ kg−1 with an operating temperature of ≈750 °C. Overall, the Ca–Mg–Fe system can integrate thermochemical batteries and is promising to promote thermochemical energy storage for backing up power production using renewables. [ABSTRACT FROM AUTHOR]

Metal hydroborates and their derivatives have been receiving attention as potential solid-state ion conductors for battery applications owing to their impressive electrochemical and mechanical characteristics. However, to date only a fraction of these compounds has been investigated as solid-state electrolytes. Here, MB12H11NH3 (M = Li and Na) hydroborates are synthesized and investigated as electrolyte materials for all-solid-state batteries. The room temperature #945;-NaB12H11NH3 was structurally solved in P212121 (a = 7.1972(3) Å, b = 9.9225(4) Å, and c = 14.5556(5) Å). It shows a polymorphic structural transition near 140 °C to cubic Fm3m. LiB12H11NH3 and NaB12H11NH3 exhibit cationic conductivities of σ(Li+) = 3.0 × 10-4 S cm-1 and σ(Na+) = 1.2 × 10-4 S cm-1 at 200 °C. Hydration is found to improve ionic conductivity of the hydroborates. It is presumed that modest ionic conductivities could be due to a lack of significant reorientational dynamics in the crystal structure resulting from the presence of the bulky -NH3 group in the anion. [ABSTRACT FROM AUTHOR]

Research into the use of sodium tetraalkoxyborate salts for different chemical applications including synthetic catalysis, hydrogen storage, or battery applications has been investigated, however, understanding of the structural, thermal and electrochemical properties of these salts has been lacking since the 1950s and 1960s. A review of the synthesis, as well as a thorough characterization using 1H NMR, 11B NMR, 13C{1H} NMR, FTIR, XRD, in situ XRD, DSC-TGA, RGA-MS, TPPA, and EIS has newly identified polymorphic phase changes for Na[B(OMe)4], K[B(OMe)4], Li[B(OMe)4], Na[B(OEt)4], Na[B(OBu)4], and Na[B(OiBu)4]. The crystal structure of K[B(OMe)4] was also solved in I41/a (a = 22.337(2) Å, c = 7.648(3) Å, V = 3815.6(4) Å3, ρ = 1.128(1) g cm−3). Ionic conductivity of the different salts was analyzed, however it was found that the compounds with longer alkyl chains had no measurable ionic conductivity compared to the shorter chained samples, Na[B(OMe)4] and K[B(OMe)4] with 9.6 × 10−8 S cm−1 and 1.6 × 10−7 S cm−1, at 114 °C respectively. [ABSTRACT FROM AUTHOR]

Metal substituted dodecaborate anions can be coupled with alkali metal cations to have great potential as solid-state ion conductors for battery applications. A tin atom can replace a B–H unit within an unsubstituted dodecaborate cage to produce a stable, polar divalent anion. The chemical and structural change in forming a stannaborate results in a modified crystal structure of respective group 1 metal salts, and as a result, improves the material's ion conductivity. Li2B11H11Sn shows high ion conductivity of ∼8 mS cm−1 at 130 °C, similar to the state-of-the-art LiCB11H12 at these temperatures, however, obtaining high ion conductivity at room temperature is not possible with pristine alkali metal stannaborates. [ABSTRACT FROM AUTHOR]

This document provides an overview of the development of hydrogen as a clean energy solution and the challenges of hydrogen storage. It explores the use of metal hydrides as a potential solution for hydrogen storage and investigates various hydrogen-rich materials for different applications. The document covers topics such as hydrogen release and uptake, electrolytes, physical properties, and metallic alloys. It also discusses the use of metallic hydrides for hydrogen purification and compression. The document acknowledges the contributors and sponsors of the International Symposium on Metal-Hydrogen Systems and invites readers to explore the contributed articles in the special edition for more information. [Extracted from the article]

Renewable energy requires cost effective and reliable storage to compete with fossil fuels. This study introduces a new reactive carbonate composite (RCC) where Fe2O3 is used to thermodynamically destabilise BaCO3 and reduce its decomposition temperature from 1400 °C to 850 °C, which is more suitable for thermal energy storage applications. Fe2O3 is consumed on heating to form BaFe12O19, which is a stable Fe source for promoting reversible CO2 reactions. Two reversible reaction steps were observed that corresponded to, first, the reaction between β-BaCO3 and BaFe12O19, and second, between γ-BaCO3 and BaFe12O19. The thermodynamic parameters were determined to be ΔH = 199 ± 6 kJ mol−1 of CO2, ΔS = 180 ± 6 J K−1 mol−1 of CO2 and ΔH = 212 ± 6 kJ mol−1 of CO2, ΔS = 185 ± 7 J K−1 mol−1 of CO2, respectively, for the two reactions. Due to the low-cost and high gravimetric and volumetric energy density, the RCC is demonstrated to be a promising candidate for next generation thermal energy storage. [ABSTRACT FROM AUTHOR]

Li-ion batteries have held the dominant position in battery research for the last 30+ years. However, due to inadequate resources and the cost of necessary elements (e.g., lithium ore) in addition to safety issues concerning the components and construction, it has become more important to look at alternative technologies. Multivalent metal batteries with solid-state electrolytes are a potential option for future battery applications. The synthesis and characterisation of divalent hydrated closo-monocarborane salts – Mg[CB11H12]2·xH2O, Ca[CB11H12]2·xH2O, and Zn[CB11H12]2·xH2O – have shown potential as solid-state electrolytes. The coordination of a solvent (e.g. H2O) to the cation in these complexes shows a significant improvement in ionic conductivity, i.e. for Zn[CB11H12]2·xH2O dried at 100 °C (10−3 S cm−1 at 170 °C) and dried at 150 °C (10−5 S cm−1 at 170 °C). Solvent choice also proved important with the ionic conductivity of Mg[CB11H12]2·3en (en = ethylenediamine) being higher than that of Mg[CB11H12]2·3.1H2O (2.6 × 10−5 S cm−1 and 1.7 × 10−8 S cm−1 at 100 °C, respectively), however, the oxidative stability was lower (<1 V (Mg2+/Mg) and 1.9 V (Mg2+/Mg), respectively). Thermal characterisation of the divalent closo-monocarborane salts showed melting and desolvation, prior to high temperature decomposition. [ABSTRACT FROM AUTHOR]

Solid-state sodium batteries have attracted great attention owing to their improved safety, high energy density, large abundance and low cost of sodium compared to the current Li-ion batteries. Sodium-boranes have been studied as potential solid-state electrolytes and the search for new materials is necessary for future battery applications. Here, a facile and cost-effective solution-based synthesis of Na2B11H13 and Na11(B11H14)3(B11H13)4 is demonstrated. Na2B11H13 presents an ionic conductivity in the order of 10−7 S cm−1 at 30 °C, but undergoes an order–disorder phase transition and reaches 10−3 S cm−1 at 100 °C, close to that of liquids and the solid-state electrolyte Na-β-Al2O3. The formation of a mixed-anion solid-solution, Na11(B11H14)3(B11H13)4, partially stabilises the high temperature structural polymorph observed for Na2B11H13 at room temperature and it exhibits Na+ conductivity higher than its constituents (4.7 × 10−5 S cm−1 at 30 °C). Na2B11H13 and Na11(B11H14)3(B11H13)4 exhibit an oxidative stability limit of 2.1 V vs. Na+/Na. [ABSTRACT FROM AUTHOR]

Stable power generation from renewable energy requires the development of new materials that can be used for energy storage. A new reactive carbonate composite (RCC) based on SrCO3 is proposed as a material with high energy density for thermochemical energy storage. SrCO3–SrSiO3 can promote the thermodynamic destabilisation of SrCO3, making its operating temperature (700 °C) more suitable for concentrated solar thermal power applications. Utilising a eutectic mixture of salts as a catalyst, the reversible carbonation reaction achieves cycle stability of ∼80% of efficiency over multiple cycles. The high volumetric (1878 MJ m−3) and gravimetric energy density (500 kJ kg−1) of the RCC allows a compact thermal battery to be developed. Additionally, the low cost of SrCO3 makes the RCC a highly competitive alternative energy storage material in terms of cost and efficiency when compared to existing molten salt based energy storage technology. [ABSTRACT FROM AUTHOR]

Metal boron–hydrogen compounds are considered as promising solid electrolyte candidates for the development of all-solid-state batteries (ASSB), owing to the high ionic conductivity exhibited by closo- and nido-boranes. In this study, an optimised low cost preparation method of MB11H14·(H2O)n, (M = Li and Na) and KB11H14 is proposed and analysed. The formation of the B11H14− salt is pH-dependent, and H3O+ competes with small ionic radii cations, such as Li+ and Na+, to produce a hydronium salt of B11H14−, which forms B11H13OH− upon heating. The use of diethyl ether to extract B11H14− salt from the aqueous medium during synthesis is an important step to avoid hydrolysis of the compound upon drying. The proposed method of synthesis results in LiB11H14 and NaB11H14 coordinated with water, whereas KB11H14 is anhydrous. Hydrated LiB11H14·(H2O)n and NaB11H14·(H2O)n exhibit exceptional ionic conductivities at 25 °C, 1.8 × 10−4 S cm−1 and 1.1 × 10−3 S cm−1, respectively, which represent some of the highest solid-state Li+ and Na+ conductivities at room temperature. The salts also exhibit oxidative stability of 2.1 V vs. Li+/Li and 2.6 V vs. Na+/Na, respectively. KB11H14 undergoes a reversible polymorphic structural transition to a metastable phase before decomposing. All synthesised nido-boranes decompose at temperatures greater than 200 °C. [ABSTRACT FROM AUTHOR]

CaH2 has 20 times the energy density of molten salts and was patented in 2010 as a potential solar thermal energy storage material. Unfortunately, its high operating temperature (>1000 °C) and corrosivity at that temperature make it challenging to use as a thermal energy storage (TES) material in concentrating solar power (CSP) plants. To overcome these practical limitations, here we propose the thermodynamic destabilization of CaH2 with Zn metal. It is a unique approach that reduces the decomposition temperature of pure CaH2 (1100 °C at 1 bar of H2 pressure) to 597 °C at 1 bar of H2 pressure. Its new decomposition temperature is closer to the required target temperature range for TES materials used in proposed third-generation high-temperature CSP plants. A three-step dehydrogenation reaction between CaH2 and Zn (1 : 3 molar ratio) was identified from mass spectrometry, temperature-programmed desorption and in situ X-ray diffraction studies. Three reaction products, CaZn13, CaZn11 and CaZn5, were confirmed from in situ X-ray diffraction studies at 190 °C, 390 °C and 590 °C, respectively. The experimental enthalpy and entropy of the second hydrogen release reaction were determined by pressure composition isotherm measurements, conducted between 565 and 614 °C, as ΔHdes = 131 ± 4 kJ mol−1 H2 and ΔSdes = 151 ± 4 J K−1 mol−1 H2. Hydrogen cycling studies of CaZn11 at 580 °C showed sufficient cycling capacity with no significant sintering occurring during heating, as confirmed by scanning electron microscopy, demonstrating its great potential as a TES material for CSP applications. Finally, a cost comparison study of known destabilized CaH2 systems was carried out to assess the commercial potential. [ABSTRACT FROM AUTHOR]

This study introduces a new concept of reactive carbonate composites (RCCs) for thermochemical energy storage, where a BaCO3–BaSiO3 mixture offers a successful thermodynamic destabilisation of BaCO3 with moderate cyclic stability ∼60%, close to the theoretical maximum when considering unreactive impurities. This research presents an alternative to molten salt based energy storage technology that operates at higher temperature (850 °C) and hence maintains a higher Carnot efficiency at a competitive price level, enabling the development of a thermal energy storage system more favourable than state-of-the-art technology. Finally, the addition of catalytic quantities of CaCO3 to the RCC significantly improves the reaction kinetics (one order of magnitude) through the formation of intermediate Ba2−xCaxSiO4 compounds, which are hypothesised to facilitate Ba2+ and O2− mobility through induced crystal defects. [ABSTRACT FROM AUTHOR]

Energy storage is one of the key challenges in our society to enable a transition to renewable energy sources. The endothermic decomposition of limestone into lime and CO2 is one of the most cost-effective energy storage systems but it significantly degrades on repeated energy cycling (to below 10% capacity). This study presents the first CaCO3 system operating under physical conditions that mimic a real-life 'thermal battery' over an extended cycling life. These important results demonstrate that a thermal energy storage device based on CaCO3 will be suitable for a range of applications, e.g. concentrated solar power plants, wind farms, photovoltaics, and excess grid energy. The operating temperature of 900 °C ensures a higher Carnot efficiency than state-of-the-art technologies at a fraction of the material cost. The capacity degradation of pure CaCO3 as a function of calcination/carbonation cycling is overcome by the addition of either ZrO2 (40 wt%) or Al2O3 (20 wt%), which results in 500 energy storage cycles at over 80% capacity. The additives result in the formation of ternary compounds, e.g. CaZrO3 and Ca5Al6O14, which restrict sintering and allow for the transmission of Ca2+ and O2− ions to reaction sites. [ABSTRACT FROM AUTHOR]

The thermal conductivity, thermal diffusivity and heat capacity of materials are all vital properties in the determination of the efficiency of a thermal system. However, the thermal transport properties of heat storage materials are not consistent across previous studies, and are strongly dependent on the sample composition and measurement method. A comprehensive analysis of thermal transport properties using a consistent preparation and measurement method is lacking. This study aims to provide the foundation for a detailed insight into thermochemical heat storage material properties with consistent measurement methods. The thermal transport properties of pelletised metal hydrides, carbonates and oxides were measured using the transient plane source method to provide the thermal conductivity, thermal diffusivity and heat capacity. This information is valuable in the development of energy storage and chemical processing systems that are highly dependent on the thermal conductivity of materials. [ABSTRACT FROM AUTHOR]

Altering the decomposition pathway of potassium alanate, KAlH4, with aluminium sulfide, Al2S3, presents a new opportunity to release all of the hydrogen, increase the volumetric hydrogen capacity and avoid complications associated with the formation of KH and molten K. Decomposition of 6KAlH4–Al2S3 during heating under dynamic vacuum began at 185 °C, 65 °C lower than for pure KAlH4, and released 71% of the theoretical hydrogen content below 300 °C via several unknown compounds. The major hydrogen release event, centred at 276 °C, was associated with two new compounds indexed with monoclinic (a = 10.505, b = 7.492, c = 11.772 Å, β = 122.88°) and hexagonal (a = 10.079, c = 7.429 Å) unit cells, respectively. Unlike the 6NaAlH4–Al2S3 system, the 6KAlH4–Al2S3 system did not have M3AlH6 (M = alkali metal) as one of the intermediate decomposition products nor were the final products M2S and Al observed. Decomposition performed under hydrogen pressure initially followed a similar reaction pathway to that observed during heating under vacuum but resulted in partial melting of the sample between 300 and 350 °C. The measured enthalpy of hydrogen absorption (ΔHabs) was in the range −44.5 to −51.1 kJ mol−1 H2, which is favourable for moderate temperature hydrogen applications. Although, the hydrogen capacity decreases during consecutive H2 release and uptake cycles, the presence of excess amounts of aluminium allow for further optimisation of hydrogen storage properties. [ABSTRACT FROM AUTHOR]

Solvated lithium closo-dodecaborate, Li2B12H12 with tetrahydrofuran and acetonitrile, show unexpected melting below 150 °C. This feature has been explored to melt-infiltrate Li2B12H12 in a nanoporous SiO2 scaffold. The ionic conductivity of Li2B12H12·xACN reaches 0.08 mS cm−1 in the liquid state at 150 °C making them suitable as battery electrolytes. [ABSTRACT FROM AUTHOR]

Hydrogen and ammonia have attracted attention as potential energy vectors due to their abundance and minimal environmental impact when used as a fuel source. To be a commercially viable alternative to fossil fuels, gaseous fuel sources must adhere to a wide range of standards specifying hydrogen delivery temperature, gravimetric capacity and cost. In this article, an ammonium chloride–metal hydride reaction cycle that enables the solid thermal decomposition products to be recycled using industrial processes is proposed. A range of metal hydrides and metal amides were reacted with ammonium chloride to determine the reaction pathways, products and overall feasibility of the cycle. The NH4Cl–MH (MH = metal hydride) and NH4Cl–MNH2 (MNH2 = metal amide) mixtures were heated to temperatures of up to 500 °C. The resulting products were experimentally characterised using temperature program desorption residual gas analysis, simultaneous differential scanning calorimetry and thermogravimetric analysis and in situ powder X-ray diffraction. Similar analysis was undertaken to determine the effect of catalyst addition to the starting materials. A maximum yield of 41 wt% of hydrogen and ammonia gas mixtures were released from the NH4Cl–MH materials at a maximum yield of 41 wt%. This exceptional gravimetric capacity allows for volumetric gas densities (363–657 kg m−3) that are much higher than pure NH3, H2 or metal hydride materials. Overall, this reaction cycle allows carbon-neutral regeneration of the starting materials, making it a potential sustainable energy option. [ABSTRACT FROM AUTHOR]

The thermal energy storage properties of dolomite, CaMg(CO3)2, from three sources (commercial, mined, and synthetic) are investigated as a potential solid–gas thermochemical energy store for concentrating solar thermal power (CSP) plants. The reversible carbon dioxide release/absorption cycle can be used to store and release large quantities of thermal energy that can be harnessed near 550 °C. To enable carbon dioxide absorption, a novel molten salt eutectic NaCl : MgCl2 mixture was added to the dolomite, which proved effective. Curiously, the mined (unrefined) sample proved to have the best calcination/carbonation properties with a stable cyclic stability of ∼50 mol% CO2 over 10 cycles. A morphological investigation by scanning electron microscopy reveals the mined sample contains impurities (e.g. quartz) that prevent detrimental agglomeration of dolomite and its reaction products (CaCO3 and MgO). High levels of porosity in the mined dolomite also provide short gas–solid reaction pathways during carbonation. A commercial dolomite source contained too many impurities, resulting in the formation of high levels of Ca2SiO4 that acted as a Ca-sink, lowering CO2 capacity. Finally, a high purity synthetic dolomite sample displayed high levels of agglomeration and phase segregation, lowering reversible CO2 capacity, which was attributed to a lack of impurities that restrict agglomeration. [ABSTRACT FROM AUTHOR]

Complex transition metal hydrides have been identified as being materials for multi-functional applications holding potential as thermal energy storage materials, hydrogen storage materials and optical sensors. Na2Mg2NiH6 (2Na+·2Mg2+·2H−·[NiH4]4−) is one such material. In this study, the decomposition pathway and thermodynamics have been explored for the first time, revealing that at 225 °C, hydrogen desorption commences with two major decomposition steps, with maximum H2 desorption rates at 278 and 350 °C as measured by differential scanning calorimetry. The first step of decomposition results in the formation of Mg2NiHx (x ＜ 0.3) and NaH, before these compounds decompose into Mg2Ni and Na, respectively. PCI analysis of Na2Mg2NiH6 has determined the thermodynamics of decomposition for the first step to have a ΔHdes and ΔSdes of 83 kJ mol−1 H2 and 140 J K−1 mol−1 H2, respectively. Hydrogen cycling of the first step has been achieved for 10 cycles without any significant reduction in hydrogen capacity, with complete hydrogen desorption within 20 min at 395 °C. Despite the relatively high cost of Ni, the ability to effectively store hydrogen reversibly at operational temperatures of 318–568 °C should allow this material to be considered as a thermal energy storage material. [ABSTRACT FROM AUTHOR]

Magnesium hydride (MgH2) is a hydrogen storage material that operates at temperatures above 300 °C. Unfortunately, magnesium sintering occurs above 420 °C, inhibiting its application as a thermal energy storage material. In this study, the substitution of fluorine for hydrogen in MgH2 to form a range of Mg(HxF1−x)2 (x = 1, 0.95, 0.85, 0.70, 0.50, 0) composites has been utilised to thermodynamically stabilise the material, so it can be used as a thermochemical energy storage material that can replace molten salts in concentrating solar thermal plants. These materials have been studied by in situ synchrotron X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, temperature-programmed-desorption mass spectrometry and Pressure–Composition–Isothermal (PCI) analysis. Thermal analysis has determined that the thermal stability of Mg–H–F solid solutions increases proportionally with fluorine content, with Mg(H0.85F0.15)2 having a maximum rate of H2 desorption at 434 °C, with a practical hydrogen capacity of 4.6 ± 0.2 wt% H2 (theoretical 5.4 wt% H2). An extremely stable Mg(H0.43F0.57)2 phase is formed upon the decomposition of each Mg–H–F composition of which the remaining H2 is not released until above 505 °C. PCI measurements of Mg(H0.85F0.15)2 have determined the enthalpy (ΔHdes) to be 73.6 ± 0.2 kJ mol−1 H2 and entropy (ΔSdes) to be 131.2 ± 0.2 J K−1 mol−1 H2, which is slightly lower than MgH2 with ΔHdes of 74.06 kJ mol−1 H2 and ΔSdes = 133.4 J K−1 mol−1 H2. Cycling studies of Mg(H0.85F0.15)2 over six absorption/desorption cycles between 425 and 480 °C show an increased usable cycling temperature of ∼80 °C compared to bulk MgH2, increasing the thermal operating temperatures for technological applications. [ABSTRACT FROM AUTHOR]

A simple and cost-effective method for the synthesis of a porous Al scaffold has been optimised using only NaAlH and TiCl. The starting materials were compacted into a pellet and sintered under dynamic vacuum to remove the Na and H. The sintering conditions, such as vacuum level, temperature, and time, were the key factors that influenced both the extraction of Na and H from the pellet and the overall porosity. Quantitative phase analysis by X-ray diffraction revealed that after the sintering process, the as-prepared porous Al scaffold consisted primarily of Al. Morphological observations conducted by scanning electron microscopy showed that the scaffold exhibited an open network of pores with a small number of mesopores and no formation of micropores. The specific surface area of the scaffold was determined to be 7.9 ± 0.1 and 6.0 ± 0.5 m/g by the Brunauer-Emmet-Teller method and from small-angle X-ray scattering measurements, respectively. The total porosity of the Al scaffold was 44.6%. [ABSTRACT FROM AUTHOR]

Hydrogen has a very diverse chemistry and reacts with most other elements to form compounds, which have fascinating structures, compositions and properties. Complex metal hydrides are a rapidly expanding class of materials, approaching multi-functionality, in particular within the energy storage field. This review illustrates that complex metal hydrides may store hydrogen in the solid state, act as novel battery materials, both as electrolytes and electrode materials, or store solar heat in a more efficient manner as compared to traditional heat storage materials. Furthermore, it is highlighted how complex metal hydrides may act in an integrated setup with a fuel cell. This review focuses on the unique properties of light element complex metal hydrides mainly based on boron, nitrogen and aluminum, e.g., metal borohydrides and metal alanates. Our hope is that this review can provide new inspiration to solve the great challenge of our time: efficient conversion and large-scale storage of renewable energy. [ABSTRACT FROM AUTHOR]

The construction of peak intensity, profile and displacement aberration functions based on the geometry of a powder diffraction measurement allows for physically realistic corrections to be applied in Rietveld modelling through a fundamental parameters approach. Parallel-beam corrections for asymmetric reflection and Debye-Scherrer geometry are summarized, and corrections for thin-plate transmission are derived and validated. Geometrically correct implementations of preferred orientation models are also summarized. [ABSTRACT FROM AUTHOR]

Nanoconfinement of 2LiBH4-NaAlH4 into a mesoporous carbon aerogel scaffold with a pore size, BET surface area and total pore volume of Dmax = 30 nm, SBET = 689 m²/g and Vtot = 1.21 mL/g, respectively is investigated. Nanoconfinement of 2LiBH4-NaAlH4 facilitates a reduction in the temperature of the hydrogen release by 132 °C, compared to that of bulk 2LiBH4-NaAlH4 and the onset of hydrogen release is below 100 °C. The reversible hydrogen storage capacity is also significantly improved for the nanoconfined sample, maintaining 83% of the initial hydrogen content after three cycles compared to 47% for that of the bulk sample. During nanoconfinement, LiBH4 and NaAlH4 reacts to form LiAlH4 and NaBH4 and the final dehydrogenation products, obtained at 481 °C are LiH, LiAl, AlB2 and Al. After rehydrogenation of the nanoconfined sample at T = 400 °C and p(H2) = 126 bar, amorphous NaBH4 is recovered along with unreacted LiH, AlB2 and Al and suggests that NaBH4 is the main compound that can reversibly release and uptake hydrogen. [ABSTRACT FROM AUTHOR]

Designing safe, compact and high capacity hydrogen storage systems is the key step towards introducing a pollutant free hydrogen technology into a broad field of applications. Due to the chemical bonds of hydrogen–metal atoms, metal hydrides provide high energy density in safe hydrogen storage media. Reactive hydride composites (RHCs) are a promising class of high capacity solid state hydrogen storage systems. Ca(BH4)2 + MgH2 with a hydrogen content of 8.4 wt% is one of the most promising members of the RHCs. However, its relatively high desorption temperature of ∼350 °C is a major drawback to meeting the requirements for practical application. In this work, by using NbF5 as an additive, the dehydrogenation temperature of this RHC was significantly decreased. To elucidate the role of NbF5 in enhancing the desorption properties of the Ca(BH4)2 + MgH2 (Ca-RHC), a comprehensive investigation was carried out via manometric measurements, mass spectrometry, Differential Scanning Calorimetry (DSC), in situ Synchrotron Radiation-Powder X-ray Diffraction (SR-PXD), X-ray Absorption Spectroscopy (XAS), Anomalous Small-Angle X-ray Scattering (ASAXS), Scanning and Transmission Electron Microscopy (SEM, TEM) and Nuclear Magnetic Resonance (NMR) techniques. [ABSTRACT FROM AUTHOR]

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed. [ABSTRACT FROM AUTHOR]

Rare earth metal borohydrides have been proposed as materials for solid-state hydrogen storage because of their reasonably low temperature of decomposition. New synthesis methods, which provide halidefree yttrium and gadolinium borohydride, are presented using dimethyl sulfide and new solvates as intermediates. The solvates M(BH4)3S(CH3)2 (M = Y or Gd) are transformed to α-Y(BH4)3 or Gd(BH4)3 at ~140 °C as verified by thermal analysis. The monoclinic structure of Y(BH4)3S(CH3)2, space group P21/c, a = 5.52621(8), b = 22.3255(3), c = 8.0626(1) Å and β = 100.408(1)°, is solved from synchrotron radiation powder X-ray diffraction data and consists of buckled layers of slightly distorted octahedrons of yttrium atoms coordinated to five borohydride groups and one dimethyl sulfide group. Significant hydrogen loss is observed from Y(BH4)3 below 300°C and rehydrogenation at 300°C and p(H2) = 1550 bar does not result in the reformation of Y(BH4)3, but instead yields YH3. Moreover, composites systems Y(BH4)3-LiBH4 1:1 and Y(BH4)3-LiCl 1:1 prepared from as-synthesised Y(BH4)3 are shown to melt at 190 and 220°C, respectively. [ABSTRACT FROM AUTHOR]

A series of monometallic borohydrides and borohydride eutectic mixtures have been investigated during thermal ramping by mass spectroscopy, differential scanning calorimetry, and photography. Mixtures of LiBH4–NaBH4, LiBH4–KBH4, LiBH4–Mg(BH4)2, LiBH4–Ca(BH4)2, LiBH4–Mn(BH4)2, NaBH4–KBH4, and LiBH4–NaBH4–KBH4 all displayed melting behaviour below that of the monometallic phases (up to 167 °C lower). Generally, each system behaves differently with respect to their physical behaviour upon melting. The molten phases can exhibit colour changes, bubbling and in some cases frothing, or even liquid–solid phase transitions during hydrogen release. Remarkably, the eutectic melt can also allow for hydrogen release at temperatures lower than that of the individual components. Some systems display decomposition of the borohydride in the solid-state before melting and certain hydrogen release events have also been linked to the adverse reaction of samples with impurities, usually within the starting reagents, and these may also be coupled with bubbling or frothing of the ionic melt. [ABSTRACT FROM AUTHOR]

Aluminium sulphide (Al2S3) is predicted to effectively destabilise sodium aluminium hydride (NaAlH4) in a single-step endothermic hydrogen release reaction. The experimental results show unexpectedly complex desorption processes and a range of new sulphur containing hydrogen storage materials have been observed. The NaAlH4–Al2S3 system releases a total of 4.9 wt% of H2 that begins below 100 °C without the need for a catalyst. Characterisation via temperature programmed desorption, in situ synchrotron powder X-ray diffraction, ex situ x-ray diffraction, ex situ Fourier transform infrared spectroscopy and hydrogen sorption measurements reveal complex decomposition processes that involve multiple new sulphur-containing hydride compounds. The system shows partial H2 reversibility, without the need for a catalyst, with a stable H2 capacity of ∼1.6 wt% over 15 cycles in the temperature range of 200 °C to 300 °C. This absorption capacity is limited by the need for high H2 pressures (＞280 bar) to drive the absorption process at the high temperatures required for reasonable absorption kinetics. The large number of new phases discovered in this system suggests that destabilisation of complex hydrides with metal sulphides is a novel but unexplored research avenue for hydrogen storage materials. [ABSTRACT FROM AUTHOR]

The thermal decomposition of anhydrous Pa3̅ Li2B12H12 was studied in situ by high resolution synchrotron X-ray diffraction. A first-order phase transition can be observed at 355 °C where the unit cell volume expands by ca. 8.7%. The expanded β-Li2B12H12 polymorph simultaneously decomposes to a hydrogen poor γ-Li2B12H12−x phase. Expansion of the unit cell across the discontinuity is consistent with reorientational motion of B12H122− anions, and the presence of a frustrated Li+ lattice indicating Li ion conduction. [ABSTRACT FROM AUTHOR]

Increased reliance on solar energy conversion technologies will necessarily constitute a major plank of any forward global energy supply strategy. It is possible that solar photovoltaic (PV) technology and concentrating solar thermal (CST) power technology will play roughly equal, but complementary roles by 2050. The ability to increase reliance on CST power technology during this period, however, will be constrained by a number of factors: the large plant sizes dictated by economies of scale, the high associated transmission infrastructure investment cost, and the limitations of current thermal energy storage technologies. Thus, solar technology's main midterm role is seen to be as hybrid solar thermal power plant. The development of low-cost, high-temperature, high-energy density thermal energy storage systems is needed to enable CST plants to be dispatchable and accelerate the deployment of this technology. Thermochemical storage has the best potential to achieve these energy storage requirements and a brief overview of thermochemical energy storage options for CST plants points to high-temperature metal-hydride thermochemical heat energy storage systems. Hydrogen storage systems offer the highest energy storage capacity per volume and are therefore the most likely candidates for achieving the goal of fully dispatchable CST plants. A number of high-temperature metal-hydride thermochemical solar energy storage systems have been proposed and a small number of these systems are currently being investigated and developed. A key component of this work is matching the thermochemical metal-hydride system with a suitable “low-temperature” hydrogen storage material to produce systems that are self-regulating. A summary of the development status of these systems suggests that, despite the technical challenges associated with high-temperature thermochemical energy storage systems, their potential advantages are now seeing development occurring. Although in the early stages, their commercialisation could be fast tracked. [ABSTRACT FROM PUBLISHER]

The article focuses on a study on metal hydrides revived for next-generation solutions to renewable energy storage. It states that metal hydrides could be the next generation of heat storage materials to help reduce the cost of thermal energy storage at solar power plants. It cites a state-of-the-art 110 MW plant in Nevada called the Crescent Dunes Solar Energy Plant which is one of the concentrating solar power (CSP) plant with thermal storage.