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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.

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.

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.

© 2020 The Authors Globally, the accelerating use of renewable energy sources, enabled by increased efficiencies and reduced costs, and driven by the need to mitigate the effects of climate change, has significantly increased research in the areas of renewable energy production, storage, distribution and end-use. Central to this discussion is the use of hydrogen, as a clean, efficient energy vector for energy storage. This review, by experts of Task 32, “Hydrogen-based Energy Storage” of the International Energy Agency, Hydrogen TCP, reports on the development over the last 6 years of hydrogen storage materials, methods and techniques, including electrochemical and thermal storage systems. An overview is given on the background to the various methods, the current state of development and the future prospects. The following areas are covered; porous materials, liquid hydrogen carriers, complex hydrides, intermetallic hydrides, electrochemical storage of energy, thermal energy storage, hydrogen energy systems and an outlook is presented for future prospects and research on hydrogen-based energy storage.

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.