Inexpensive thermochemical energy storage utilising additive enhanced limestone

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 CO2is 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 CaCO3system 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 CaCO3will 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 CaCO3as 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.CaZrO3and Ca5Al6O14, which restrict sintering and allow for the transmission of Ca2+and O2-ions to reaction sites

Thermochemical energy storage properties of a barium based reactive carbonate composite

This study introduces a new concept of reactive carbonate composites (RCCs) for thermochemical energy storage, where a BaCO3-BaSiO3mixture offers a successful thermodynamic destabilisation of BaCO3with 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 CaCO3to the RCC significantly improves the reaction kinetics (one order of magnitude) through the formation of intermediate Ba2−xCaxSiO4compounds, which are hypothesised to facilitate Ba2+and O2−mobility through induced crystal defects

Synergetic effect of multicomponent additives on limestone when assessed as a thermochemical energy storage material

The effect of adding both Al2O3 and ZrO2 to limestone (CaCO3) to enhance the cyclic stability and reaction kinetics of endothermic CO2 desorption and exothermic CO2 absorption is investigated. The formation of CaZrO3 and Ca-Al-O compounds, e.g. CA5Al6O14, is evident, which enables a substantial >80% capacity retention over 50 calcination/carbonation cycles. The additives enable fast reaction kinetics where an 80% energy storage capacity is reached within 20–30 min, which is attributed to the synergetic effect of having both Ca-Zr-O and Ca-Al-O ternary additives present. The inert nature of the formed compounds prevents sintering of the particles, whilst allowing ion migration throughout the crystal structures, catalysing the carbonation reaction

Thermochemical energy storage system development utilising limestone

For renewable energy sources to replace fossil fuels, large scale energy storage is required and thermal batteries have been identified as a commercially viable option. In this study, a 3.2 kg prototype (0.82 kWhth) of the limestone-based CaCO3-Al2O3 (16.7 wt%) thermochemical energy storage system was investigated near 900 °C in three different configurations: (i) CaCO3 was thermally cycled between 850 °C during carbonation and 950 °C during calcination whilst activated carbon was utilised as a CO2 gas storage material. (ii) The CaCO3 temperature was kept constant at 900 °C while utilising the activated carbon gas storage method to drive the thermochemical reaction. (iii) A mechanical gas compressor was used to compress CO2 into volumetric gas bottles to achieve a significant under/overpressure upon calcination/carbonation, i.e. ≤ 0.8 bar and > 5 bar, respectively, compared to the ∼1 bar thermodynamic equilibrium pressure at 900 °C. Scenarios (i) and (iii) showed a 64% energy capacity retention at the end of the 10th cycle. The decrease in capacity was partly assigned to the formation of mayenite, Ca12Al14O33, and thus the absence of the beneficial properties of the expected Ca5Al6O14 while sintering was also observed. The 316L stainless-steel reactor was investigated in regards to corrosion issues after being under CO2 atmosphere above 850 °C for approximately 1400 h, and showed no significant degradation. This study illustrates the potential for industrial scale up of catalysed CaCO3 as a thermal battery and provides a viable alternative to the calcium-looping process

Comment on "bi-functional Li2 B12 H12 for energy storage and conversion applications: Solid-state electrolyte and luminescent down-conversion dye" by J. A. Teprovich Jr, H. Colón-Mercado, A. L. Washington II, P. A. Ward, S. Greenway, D. M. Missimer, H. Hartman, J. Velten, J. H. Christian and R. Zidan,: J. Mater. Chem. A, 2015, 3, 22853

The photoluminescent properties of selected metal closo-boranes have been assessed. Group 3 elements Sc, Y, and La as well as Li, Na, and Eu-based B 10 H 102- and B 12 H 122- compounds displayed photoluminescence in the ultraviolet (emission λ max ≈ 350 nm) that was not visible to the human eye, in contrast to previous reports. We attribute these earlier results to arachno-borane impurities, which are more readily observed due to their longer wavelength emission spectra

Hydrated alkali-B<inf>11</inf>H<inf>14</inf>salts as potential solid-state electrolytes

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 bycloso- andnido-boranes. In this study, an optimised low cost preparation method of MB11H14·(H2O)n, (M = Li and Na) and KB11H14is 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 LiB11H14and NaB11H14coordinated with water, whereas KB11H14is anhydrous. Hydrated LiB11H14·(H2O)nand NaB11H14·(H2O)nexhibit exceptional ionic conductivities at 25 °C, 1.8 × 10−4S cm−1and 1.1 × 10−3S 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 Vvs.Li+/Li and 2.6 Vvs.Na+/Na, respectively. KB11H14undergoes a reversible polymorphic structural transition to a metastable phase before decomposing. All synthesisednido-boranes decompose at temperatures greater than 200 °C

Molten metal closo-borate solvates

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

Hydrogen sorption in TiZrNbHfTa high entropy alloy

© 2018 Elsevier B.V. High Entropy Alloys (HEA), where five or more elements are mixed together in near equiatomic ratios offer promising properties as hydrogen storage materials due to their ability to crystallize in simple cubic structures in the presence of large lattice strain originating from the different sizes of the atoms. In this work, the hydrogen absorption and desorption as well as the cycling properties of the TiZrNbHfTa HEA have been studied by in situ Synchrotron X-Ray diffraction, Pressure-Composition-Isotherm, Thermal Desorption Spectroscopy and Differential Scanning Calorimetry. The alloy crystallizes in a cubic bcc phase and undergoes a two-stage hydrogen absorption reaction to a fcc dihydride phase with an intermediate tetragonal monohydride, very similar to the V-H system. The hydrogen absorption/desorption in TiZrNbHfTa is completely reversible and the activation energy of desorption could be calculated. Furthermore, we have observed an interesting macrostructure following parallel planes after the formation of the dihydride phase, which is retained after desorption