Thermochemical Energy Storage Material Research Articles

Development of Co3-xNixO4 materials for thermochemical energy storage at lower red-ox temperature

Heat storage technologies are subject of great research efforts aimed at improving the energy efficiency of power plants and heat recovery processes. In this context, the development of highly efficient and low-cost materials for thermal energy storage is imperative for a large use of this technology. The storage of thermal energy using reversible thermo-chemical reactions can provide large storage capacities especially at high temperatures. Within this class of materials, the red-ox reactions have particular interest due to the low cost of the materials involved (metal oxides) and the use of air both as reacting gas and heat transfer fluid. Therefore, many efforts are doing to improve the efficiency and reversibility of this type of reactions. In this work the synthesis and thermal performances of a novel mixed metal oxide based on cobalt/nickel metals with spinel structure Co3-xNixO4 is reported. A deep study was carried out in order to find the best synthesis conditions and optimum relative metal content in the structure with the objective of decreasing as much as possible the red-ox temperature. The study allowed to determine the optimum Ni content in the oxide structure in order to minimize the reaction temperature. In particular, a linear relationship of the red-ox temperature as a function of the Ni content was observed, enabling reaching red-ox temperature below 700 °C. These results are very promising and open the perspective of using of these types of materials to a wider field of application.

Experimental and numerical investigations for effective thermal conductivity in packed beds of thermochemical energy storage materials

Abstract Salt hydrates are promising candidates for long-term thermochemical heat storage (TCHS) in the building environment. In such storage systems, the surplus of energy will be exploited in an endothermic reaction to dehydrate the salt hydrates. Once it is demanded, the stored energy will be released through an exothermic reaction by hydrating the salt, which results in an increase in the mass and temperature of salt particles as well as changes in the species of material. In order to construct an improved storage system, it is very important to deeply understand the details of the heat and mass transfer processes in the packed beds of salt hydrates. Poor heat (in the closed systems) and mass transfer (in open systems) can be the bottleneck in this technology. The main objective of this work is to investigate how heat transfer will be affected by applied pressure, particle size, and packing arrangement through calculating/measuring the effective thermal conductivity of the packed beds of salt hydrates. This is achieved by applying and developing a CFD-DEM model and by experimental measurements in a vacuum oven. Comparisons are carried out for the numerical results at low and high ambient pressures with the experimental measurements, which show a very good agreement. The obtained results show the effect of natural convection in the packed bed when the higher vapor pressure is applied.

Composite MWCNT/ MIL-101 (Cr)/CaCl2 as High-Capacity Water Adsorbent for Long-Term Thermal Energy Storage

Mil-101 (Cr) material is considered to be one of the most potential thermochemical energy storage materials in recent years. It has the advantages of a typical S-type water adsorption isotherm. Has low working temperature and large water adsorption amount. However, the adsorption properties of the material need to be improved under low water pressure. To improve the performance, the acidified MWCNTs were added before the hydrothermal reaction of mil-101 (Cr) materials to optimize the micropore structure. After the preparation, the new composite thermochemical energy storage materials were prepared by impregnation with a certain concentration of calcium chloride aqueous solution. The effects of multi-walled carbon nanotubes and calcium chloride on the physical and chemical properties of the materials were discussed. Through X-ray diffraction experiment, scanning electron microscope, microstructure analysis, nitrogen adsorption capacity test, water adsorption capacity test, and other means, the micro characteristics, pore structure, crystal morphology, and chemical composition of the materials were characterized, and the water adsorption performance of the materials was synthesized. The experimental results show that the addition of carbon nanotubes can improve the pore properties of the materials so that the porous organic skeleton can accommodate more calcium chloride particles. The composite materials with calcium chloride can provide excellent hydrophilicity and high water adsorption capacity. Also, the water absorption rate and adsorption-desorption cycle capacity of the material have been significantly improved. The experimental results show that when the mass fraction of calcium chloride reaches 30% when 90 mg acidified MWCNTs are added into every four chromium nitrate crystals, the hydrophilicity and adsorption capacity of the composite can reach a high equilibrium state. At the same time, the experimental yield of the material is high, the product is easy to obtain, the environmental friendliness is also reflected, so it is expected to become the adsorption heat pump thermochemical energy storage material with research potential.

Membrane distillation crystallization of ammonium nitrate solutions to enable sustainable cold storage: Electrical conductivity as an in-situ saturation indicator

A novel refrigeration cycle is proposed using crystallized ammonium nitrate as a thermochemical energy storage material that is recharged with membrane distillation. Cooling is provided when needed by the dissolution of ammonium nitrate in water, an endothermic process that absorbs heat from the surroundings. The dilute solution is then concentrated to recrystallize the ammonium nitrate using membrane distillation, a thermally driven separation process capable of operating at low temperatures and high solution concentrations. Unlike conventional vapor compression refrigeration systems, this process does not rely on refrigerants with high global warming potential and could potentially utilize low-grade heat as the primary energy input rather than electricity. Membrane distillation was found to be capable of crystallizing ammonium nitrate from water at temperatures between 50 and 70 °C. The membranes tested were found to be very resistant to damage by ammonium nitrate crystallization, and performance (water flux, thermal efficiency, and rejection) was maintained even after repeated exposure to crystallization. Additionally, conductivity was found to be a reliable and consistent indicator of concentration and showed potential for use in monitoring and control systems.

Free energy of ( CoxMn1−x)3O4 mixed phases from machine-learning-enhanced ab initio calculations

(CoxMn1-x)3O4 is a promising candidate material for solar thermochemical energy storage. A high-temperature model for this system would provide a valuable tool for evaluating its potential. However, predicting phase diagrams of complex systems with ab initio calculations is challenging due to the varied sources affecting the free energy, and with the prohibitive amount of configurations needed in the configurational entropy calculation. In this work, we compare three different machine learning (ML) approaches for sampling the configuration space of (CoxMn1-x)3O4, including a simpler ML approach, which would be suitable for application in high-throughput studies. We use experimental data for a feature of the phase diagram to assess the accuracy of model predictions. We find that with some methods, data pre-treatment is needed to obtain accurate predictions due to inherently composition-imbalanced training data for a mixed phase. We highlight that the important entropy contributions depend on the physical regimes of the system under investigation and that energy predictions with ML models are more challenging at compositions where there are energetically competing ground state crystal structures. Similar methods to those outlined here can be used to screen other candidate materials for thermochemical energy storage

An Experimental Study of the Decomposition and Carbonation of Magnesium Carbonate for Medium Temperature Thermochemical Energy Storage

To improve the energy efficiency of an industrial process thermochemical energy storage (TCES) can be used to store excess or typically wasted thermal energy for utilisation later. Magnesium carbonate (MgCO3) has a turning temperature of 396 °C, a theoretical potential to store 1387 J/g and is low cost (~GBP 400/1000 kg). Research studies that assess MgCO3 for use as a medium temperature TCES material are lacking, and, given its theoretical potential, research to address this is required. Decomposition (charging) tests and carbonation (discharging) tests at a range of different temperatures and pressures, with selected different gases used during the decomposition tests, were conducted to gain a better understanding of the real potential of MgCO3 for medium temperature TCES. The thermal decomposition (charging) of MgCO3 has been investigated using thermal analysis techniques including simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), TGA with attached residual gas analyser (RGA) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (up to 650 °C). TGA, DSC and RGA data have been used to quantify the thermal decomposition enthalpy from each MgCO3.xH2O thermal decomposition step and separate the enthalpy from CO2 decomposition and H2O decomposition. Thermal analysis experiments were conducted at different temperatures and pressures (up to 40 bar) in a CO2 atmosphere to investigate the carbonation (discharging) and reversibility of the decarbonation–carbonation reactions for MgCO3. Experimental results have shown that MgCO3.xH2O has a three-step thermal decomposition, with a total decomposition enthalpy of ~1050 J/g under a nitrogen atmosphere. After normalisation the decomposition enthalpy due to CO2 loss equates to 1030–1054 J/g. A CO2 atmosphere is shown to change the thermal decomposition (charging) of MgCO3.xH2O, requiring a higher final temperature of ~630 °C to complete the decarbonation. The charging input power of MgCO3.xH2O was shown to vary from 4 to 8136 W/kg with different isothermal temperatures. The carbonation (discharging) of MgO was found to be problematic at pressures up to 40 bar in a pure CO2 atmosphere. The experimental results presented show MgCO3 has some characteristics that make it a candidate for thermochemical energy storage (high energy storage potential) and other characteristics that are problematic for its use (slow discharge) under the experimental test conditions. This study provides a comprehensive foundation for future research assessing the feasibility of using MgCO3 as a medium temperature TCES material. Future research to determine conditions that improve the carbonation (discharging) process of MgO is required.

Medium-temperature thermochemical energy storage with transition metal ammoniates – A systematic material comparison

Materials with high volumetric energy storage capacities are targeted for high-performance thermochemical energy storage systems. The reaction of transition metal salts with ammonia, forming reversibly the corresponding ammonia-coordination compounds, is still an under-investigated area for energy storage purposes, although, from a theoretical perspective this should be a good fit for application in medium-temperature storage solutions between 25 °C and 350 °C.In the present study, the potential of reversible ammoniation of a series of transition metal chlorides and sulphates with gaseous ammonia for suitability as thermochemical energy storage system was investigated. Among the investigated metal chlorides and sulphates, candidates combining high energy storage densities and cycle stabilities were found. For metal chlorides, during the charging / discharging cycles in the presence of ammonia slow degradation and evaporation of the materials was observed. This issue was circumvented by reducing the operating temperature and cycling between different degrees of ammoniation, e.g. in the case of NiCl2 by cycling between [Ni(NH3)2]Cl2 and [Ni(NH3)6]Cl2. In contrast, sulphates are perfectly stable under all investigated conditions. The combination of CuSO4 and NH3 provided the most promising result directing towards applicability, as the high energy storage density of 6.38 GJ m−3 is combined with full reversibility of the storage reaction and no material degradation over cycling. The results of this comparative systematic material evaluation encourage for a future consideration of the so far underrepresented transition metal ammoniates as versatile thermochemical energy storage materials.

CaCo0.05Mn0.95O3-δ: A Promising Perovskite Solid Solution for Solar Thermochemical Energy Storage.

The redox cycle of doped CaMnO3-δ has emerged as an attractive way for cost-effective thermochemical energy storage (TCES) at high temperatures in concentrating solar power. The role of dopants is mainly to improve the thermal stability of CaMnO3-δ at high temperatures and the overall TCES density of the material. Herein, Co-doped CaMnO3-δ (CaCoxMn1-xO3-δ, x = 0-0.5) perovskites have been proposed as a promising candidate for TCES materials for the first time. The phase compositions, redox capacities, TCES densities, reaction rates, and redox chemistry of the samples have been explored via experimental analysis and theoretical calculations. The results demonstrate that CaCo0.05Mn0.95O3-δ showed an enhanced redox capacity (1000 °C at pO2 = 10-5 bar) without decomposition and provided the highest TCES density of ∼571 kJ kg-1 reported so far. The effective Co doping tended to increase the valence states of B-site cations in perovskite and facilitate the diffusion of the lattice oxygen atoms into the surface-active oxygen sites. Furthermore, the high cooling rates deteriorated the microstructure of CaCo0.05Mn0.95O3-δ particles and resulted in incomplete heat release, which is instructive to the design and operation of the TCES systems.

Thermal protection of electronic devices based on thermochemical energy storage

With the widespread use of electronic devices, heat dissipation and thermal protection issues have attracted attention. High temperatures can lead to failure or even burnout of the circuit boards, which are key parts of electronic devices. Most of the current research uses passive thermal protection based on phase change materials. In this study, a thermochemical energy storage material, boric acid, is applied as the thermal protection layer of electronic devices, and a thermal protection system that integrates heat insulation, heat storage, and heat reflection is proposed. The characterization results reveal that the decomposition temperature of boric acid is 112.9 °C, which is close to the thermal protection temperature of the circuit board, and the decomposition enthalpy of boric acid is as high as 1173.7 J/g, indicating that it has a relatively high heat storage capacity. In the experiments performed at 300 °C, the thermal decomposition of boric acid provides a 108.1 °C constant-temperature platform for 1800 s for the circuit board, proving that boric acid can effectively prevent heat input from the external high-temperature environment and extend the thermal protection time. In addition, as the water vapor produced by thermal decomposition evaporates, the boric acid does not release heat like phase change materials during the cooling process, which can prevent secondary heat damage to the circuit board. The performance of the boric acid-based thermal protection system can be further improved by adding heat insulation and heat reflection materials to it.

Characterization of an ettringite-based thermochemical energy storage material in an open-mode reactor

The mismatch between renewable energy supply and demand requires energy storage technologies to work out the dilemma. In the thermal energy field, ettringite-based energy storage seems to be a good solution thanks to its high energy density and low material cost. It can store excess solar energy to meet the heating and domestic hot water demand in buildings. Therefore, the current work experimentally examines the energetic performance of an ettringite-based material made of commercial cements. The TG-DSC analysis shows the energy storage capacity of the investigated material is as high as 282 kWh/m3 original hydrated materials. Besides, the laboratory reactor tests prove the charging temperature is as low as 55–65°C for ettringite. Under operating conditions, the average energy-releasing power during the full period is about 33.3 W/kg while the maximum power is about 915 W/kg original hydrated materials, which are significantly higher than most materials from the literature. The best volumetric energy-releasing density and the corresponding prototype storage density of the fixed-bed obtained are 176 kWh/m3 original hydrated materials and 104 kWh/m3, respectively.

Comparative kinetics study on carbonation of ettringite and meta-ettringite based materials

The use of ettringite-based materials for thermochemical heat energy storage has attracted researchers' attention in recent years since ettringite has advantages like low material cost and high energy storage density (~500 kWh/m3). However, carbonation, which modifies its structure and reduces the capacity of energy storage, is an important hindrance to real applications. To address this issue, the present study focuses on the carbonation kinetics of three ettringite-based and corresponding meta-ettringite-based materials (dehydrated samples) exposed to different relative humidity (RH) and CO2 concentrations. A mixture of 80 wt% pre-blended Calcium Aluminate Cement/20 wt% OPC (C80P20) proved to be the most resistant against CO2. The hydrated and dehydrated C80P20 grains carbonated slowly at 50% RH and 1 vol% CO2, consuming little ettringite after 28 days. At 90% RH, carbonation was accelerated such that all ettringite and meta-ettringite materials were depleted at 11 days with vaterite and aragonite as the main calcium carbonates. The produced CaSO4 hydrates were found as hemihydrate at 70% RH and gypsum at 90% RH. Finally, the thermal energy storage capacity (TESC) of the material was systematically quantified as essentially decreasing with the carbonation degree of ettringite-based materials.

Fe- and Mn-Doped Ca-Based Materials for Thermochemical Energy Storage Systems

In recent years, CaO/CaCO3 has attracted great attention in the field of thermochemical energy storage. However, due to its very low optical absorption, thermochemical energy storage materials made...

Investigation of Ca12Al14O33 Mayenite for hydration/dehydration thermochemical energy storage

Abstract Thermal energy storage using a reversible chemical reaction is a key parameter for increasing the storage capacity especially for medium and high temperature applications. The reversible hydration/dehydration reaction of calcium hydroxide Ca(OH)2 to calcium oxide CaO is among the most investigated system due to its reaction cyclability and interesting operating temperature above 450 °C suitable for high temperature applications. However, the indicated reaction temperature was considered too high for some industrial applications which limit a further development of thermal energy storage technologies using this promising reaction system. In this regard, the material development is a key point to broaden the application of sustainable technologies. In this work, the investigation of Mayenite with general formula Ca12Al14O33 as a thermochemical energy storage material was conducted. Thereby, it was confirmed the possibility of the pair “Ca12Al14O12(OH)42”/Ca12Al14O33 to store and release the heat through chemical reaction thanks to a novel activation process of the pristine Mayenite that is presented for the first time in this work. This study might help to identify new pairs based on materials that have already been classified as inactive for the hydration/dehydration reaction. In addition, it was found that the hydration reaction temperature of “Ca12Al14O12(OH)42”/Ca12Al14O33 pair of 228 °C is much lower compared to that of CaO/Ca(OH).

Background and Strategies for Identification and Design of Materials for Thermochemical Energy Storage and Conversion

Background and Strategies for Identification and Design of Materials for Thermochemical Energy Storage and Conversion

Potential of solid residues from power plants as thermochemical energy storage materials

Due to large amounts of solid residue of oil shales produced every year by thermal processing, new ways of utilizing them are constantly investigated. As the main components of oil shale ash are calcium, magnesium and silica, the material has potential for different areas. In this paper, we investigated the possibility and potential of utilizing Estonian oil shale ash, rich in CaO, for thermochemical energy storage material. The investigated samples included the sources of main ash flow—bottom and electrostatic precipitator ash from two power plants utilizing circulating fluidized bed combustion technology. The ash from the economizer was also analysed as a comparison. The samples were characterized through elemental and chemical analysis and XRF and subjected to thermal analysis in either mixtures or pure environments of N2 and/or CO2.

Experimental Studies on Endothermic Reversible Reaction of Salts for Cooling

Thermal energy storage has a potential future to store renewable energy. Thermochemical energy storage (TCES) is the most promising and possesses more advantages over sensible and latent heat thermal storage systems such as higher energy storage density and ambient temperature storage. The major concern at this time for TCES is to find the material or combination of materials which can be thermally stable, have high energy storage density and be nontoxic. In this paper, Fertilizer based salts as a potential TCES material for cooling applications are studied experimentally. To produce a cooling effect, salts are dissolved in water and a drop in temperature is measured experimentally. Systematic evaluation for the combination of Nitrogen (N), phosphorus (P) and potassium (K) based salts are used to produce the cooling effect. Individuals and 14 various mixtures of NPK salts such as NH4Cl, K2SO4, (NH4)2CO, NH4NO3, KNO3, NaNO3, and NH4H2PO4 have been studied experimentally. The cooling effect in the range of 200-400 kJ per kg of salt is produced when the salt is dissolved in the water. It is observed that an average of 24 °C to 28 °C instant decrease in temperature is noticed when 60-80 g of water is added to the mixture of salt. Among the investigated salt mixture, NPK4 yielded a maximum temperature drop of 30 °C.

Double hydrates salt as sustainable thermochemical energy storage materials: Evaluation of dehydration behavior and structural phase transition reversibility

Currently, thermochemical energy storage (TCES) offers the opportunity to relieve the enormous gap of energy demand and supply in the solar energy field. This method has its specific requirements, such as high energy storage density, good thermal stability, high reaction enthalpy, high heat capacity and switched temperature range of thermochemical storage material (TCM) for low to medium temperature building applications. This paper reports the synthesis of blödite-type structure Na2M(SO4)2·4H2O (M = Zn, Mg) and copper kröhnkite phase Na2Cu(SO4)2·2H2O. Their structural and thermal behavior were also investigated to explore a new temperature range using incorporated salts. An evaluation of potential energy storage density, structural reversibility, thermal cycling stability and storage efficiency of double salts compared to pure hydrates salts as TCM was carried out. The preliminary results show a good structural matching of synthesized double salts confirmed by XRD, FTIR, and Raman spectroscopy, while the transition phase investigation since dehydration process was reported by XRD and Raman spectroscopy. Moreover, Na2Zn(SO4)2·4H2O exhibited a suitable charging range temperature (<105 °C), good cycling stability at the first ten hydration/dehydration cycles with an excellent energy storage density of 4.7 GJ m−3 and an interesting theoretical efficiency up to 77.4%.

Optimization of LiNO3–Mg(OH)2 composites as thermo-chemical energy storage materials

To reduce the emission of greenhouse gases, the substitution of fossil fuel by renewable energy sources is increasingly important. Matching energy supply and demand is however required, even more so if intermittent renewable energy sources are employed. Thermal energy storage then offers significant advantages. Thermo-chemical energy storage systems, using reversible reactions, have a high reaction enthalpy that exceeds the storage capacities of sensible and latent heat modes.Magnesium hydroxide is a candidate TCES material for such a system at temperature around 300 °C, and adaptable when doping Mg(OH)2 with metal salts. Both pure Mg(OH)2 and its composites with 1, 3, 6 and 10 wt% LiNO3 are studied. The present work validates this TCES process and develops reaction rate equations needed for its design. The LiNO3-doping significantly reduces the onset temperature of dehydration. For pure Mg(OH)2, the temperature is 325 °C. It is reduced to 289 °C when 1 wt% LiNO3 is present, and further reduced to 269 °C at a dosage of 10 wt% LiNO3. Whereas the dehydration of pure Mg(OH)2 is slow, with a rate constant k of 1.72 10−5 s−1 at 300 °C, adding increasing amounts of LiNO3 progressively increases the reaction rate constant to ~10−2 s−1 at 300 °C when 10 wt% LiNO3 is present. The kinetic expressions enable to predict the conversion yield and amount of heat stored or released for any desired temperature and selected duration of the heat-induced dehydration. LiNO3- doped Mg(OH)2 have a high potential in TCES applications when the heat source is available at temperatures between 250 and 400 °C, since the equilibrium temperature and the extent of de-hydration Mg(OH)2 can be tuned to the required temperature range by adding different wt% of LiNO3.

Redox thermochemistry of Ca-Mn-based perovskites for oxygen atmosphere control in solar-thermochemical processes

Sustainable energy supply is a crucial issue in times of climate change and receding fossil energy reserves. The emerging field of solar-driven thermochemical H2O and CO2 splitting cycles is a very promising approach to address this challenge. Providing low oxygen partial pressures is crucial in these processes. This issue is tackled by either high vacuum pumping or inert-gas sweeping. Both techniques come with a rather high energy penalty, leading to lower efficiencies of the whole process. Thermochemical oxygen pumping offers great potential to efficiently reduce oxygen partial pressures in these splitting cycles. In this work a material investigation campaign focusing on earth-abundant, cheap and non-toxic perovskites is presented. The experimental results are complemented with an approach to correlate this performance to inherent material properties, and in particular to the tolerance factor. In this framework, Ca-Mn-based perovskite compositions were demonstrated to function effectively as combined thermochemical oxygen-pumping and energy storage materials. Not only an almost two-fold increase of the reduction extent of ceria as a water splitting material was achieved due to the operation of perovskites as oxygen pumping materials, but this increase was rendered three-fold by applying a suitable temperature swing operation strategy. In parallel, the perovskites’ energy storage density can be significantly increased by exploiting specific phase transitions that can be rationally explained via the Goldschmidt tolerance factor. Hence, the work offers a novel approach to reach low oxygen partial pressures with minimal energy penalties and a derived model to evaluate occurring phase transitions and their corresponding heat effects.

Life cycle assessment of thermochemical energy storage integration concepts for a concentrating solar power plant

AbstractThis paper presents an original life cycle assessment (LCA) of a concentrating solar power (CSP) plant with thermochemical energy storage (TCES). The studied CSP plant is a hypothetic solar tower plant with a Rankine power cycle, and the TCES material used is calcium hydroxide. Based on three proposed TCES integration concepts, detailed sizing and the associated emission inventory are performed for four main groups that constitute the CSP plant, including the solar field, the solar tower, the storage system and the power cycle. Various midpoint impact categories are evaluated using the IMPACT 2002+ method embedded in the SimaPro 7.3 software. A sensitivity analysis is performed to identify the most influencing elements of the CSP plant on the environmental impacts. LCA results show that the CSP plant with different TCES integration alternatives has comparable global warming potential (approximately 11 kg CO2.eq/MWh) and energy payback time (approximately 4 months). The additional environmental burden due to the addition of the TCES system is relatively small (about 30%). The use of calcium hydroxide for the TCES has noticeable midpoint impacts on the respiratory inorganics, the terrestrial ecotoxicity and the mineral extraction. Solar field group (heliostat mirrors) is generally the most sensitive and environmental impacting factor of the CSP installation. The Turbine integration concept has the smallest environmental impacts among the three concepts proposed.