Synthetic strategies for the enhancement of Mg(OH)2 thermochemical performances as heat storage material

Abstract This work deals with the study of influence of multi walled carbon nanotubes (CNTs) characteristics on thermochemical performance of hybrid materials based on Mg(OH) 2 (M) as heat storage medium. Two different functionalized CNTs samples are investigated, separated curly tubes (SN) and bundles of straight nanotubes (BN). Hybrids were synthesized by reverse deposition precipitation method and their structure was characterized by X-ray analysis and scanning electron microscopy. The heat storage performance was studied through a thermogravimetric apparatus, simulating heat storage/release cycles. It is demonstrated that separated CNTs owning mainly carboxylic groups increase the interaction with precipitated magnesium hydroxide, improving the reacted fraction during dehydration/hydration cycle. In terms of dehydration/hydration conversion the samples' rank is SN-M>Mg(OH) 2 >BN-M. SN-M exhibits higher heat storage/output capacity (~1250 kJ/kg Mg(OH)2 , ~350 MJ/m 3 )

Influence of the Cobalt Phase on the Highly Efficient Growth of MWNTs

In this work, the influence of the cobalt phase on the growth of carbon nanotubes by the catalytic chemical vapour deposition of CH4 with catalysts containing Co, Mo and Mg is investigated. To this end, the catalytic behaviour of physically mixed CoO/MgO+MgMoO4 and CoMoO4+MgMoO4 is studied. The results obtained show that CoMoO4+MgMoO4 allows for the attainment of the highest CNT yield (2407 wt % against 1296 wt %). Its higher activity is ascribed to the greater formation of active sites that, in light of current assessments, are constituted by metallic cobalt adjacent to Mo2C, and the huge exfoliation of the catalyst, which contributes towards enhancing their exposure

Chapter Six - Thermochemical heat storage at high temperature

Implementation of cost-effective thermal energy storage systems is one of the signature advantages of concentrating solar power (CSP) plants. Currently these components are based on sensible heat storage in molten salts, but those compounds start to decompose below 600 °C. Accordingly, more stable storage media are required for future more efficient CSP plants, which are expected to operate at temperatures exceeding 1000 °C. This has prompted an active investigation on materials and reactors for thermochemical storage because, those systems can achieve higher energy densities than sensible heat media and they able to operate under harsher conditions. Alkaline-earth carbonates and redox oxides are the most relevant types of materials currently under development. Carbonates, such those based in Ca or natural mineral like dolomites, have been used for CO2 capture and they present relatively high energy densities. In the case of oxides, one important advantage is that they can use atmospheric air. Besides, these materials present a great variety of compositions that can be adapted to different operation conditions. Stoichiometric oxides such Co3O4 and Mn2O3 show promising thermodynamic properties. More recently nonstoichiometric oxides, particularly perovskites with general formula ABO3, are gaining interest because their good reversibility and quick response in a broad interval of conditions. Reactor design for thermochemical storage depends on whether the configuration is intended for direct or indirect solar heating, and it must be adapted to the specific solid-gas reaction, enabling an efficient heat exchange. The latest developments in materials and reactors for thermochemical energy storage are reviewed in detail in this chapter.Peer reviewe

Morphological Observation of LiCl Deliquescence in PDMS-Based Composite Foams

The LiCl-based heat storage system exhibits a high-energy density, making it an attractive and one of the most investigated candidates for low-temperature heat storage applications. Nevertheless, lithium chloride, due to its hygroscopic nature, incurs the phenomenon of deliquescence, which causes some operational challenges, such as agglomeration, corrosion, and swelling problems during hydration/dehydration cycles. Here, we propose a composite material based on silicone vapor-permeable foam filled with the salt hydrate, hereafter named LiCl-PDMS, aiming at confining the salt in a matrix to prevent deliquescence-related issues but without inhibiting the vapour flow. In particular, the structural and morphological modification during hydration/dehydration cycles is investigated on the composite foam, which is prepared with a salt content of 40 wt.%. A characterization protocol coupling temperature scanned X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM) analysis is established. The operando conditions of the dehydration/hydration cycle were reproduced while structural and morphological characterizations were performed, allowing for the evaluation of the interaction between the salt and the water vapor environment in the confined silicon matrix. The material energy density was also measured with a customized coupled thermogravimetric/differential scanning calorimetric analysis (TG/DSC). The results show an effective embedding of the material, which limits the salt solution release when overhydrated. Additionally, the flexibility of the matrix allows for the volume shrinkage/expansion of the salt caused by the cyclic dehydration/hydration reactions without any damages to the foam structure. The LiCl-PDMS foam has an energy density of 1854 kJ/kg or 323 kWh/m3, thus making it a competitive candidate among other LiCl salt hydrate composites

The favourable thermodynamic properties of Fe-doped CaMnO3for thermochemical heat storage

[EN]The CaMnO oxide can reversibly release oxygen over a relatively wide range of temperatures and oxygen partial pressures (pO) and is thus a promising candidate for thermochemical heat storage in Concentrated Solar Power (CSP) plants. Moreover, it is composed of earth-abundant, inexpensive and non-toxic elements and exhibits a high-energy storage density, which are desirable characteristics for decreasing the deployment costs of the system. However, it undergoes decomposition atpO≤ 0.008 atm and temperature ≥ 1100 °C. Here the possibility of overcoming this limitation and extending the operating temperature range by B-site doping with Fe (CaFeMnO) is explored. Two doping levels are investigated,x= 0.1 and 0.3. The enthalpy of reduction was determined from a measurement of continuous equilibrium non-stoichiometry curves (δ,T) at severalpO, enabling an evaluation of the heat storage capacity with high accuracy over widely ranging oxygen non-stoichiometry. Introduction of 0.1 Fe (CaFeMnO) prevented CaMnO decomposition up to 1200 °C atpO= 0.008 atm, thus widening the operating temperature range and the oxygen reduction extent. The increase in the accessible nonstoichiometry translates into an increase in the heat storage capacity (Q(kJ mol)) from ∼272 kJ kgin CaMnOto ∼344 kJ kgin CaFeMnOWhile even larger changes in oxygen content were accessible in CaFeMnO, the oxidation state changes are accompanied by a lower enthalpy of reduction, resulting in a diminished heat storage capacity of ∼221 kJ kg.This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 746167. Support of the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Award DE-EE0008089.0000, is also acknowledged. We acknowledge the support with the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)

Editorial: Recent Advances in Solar-Driven Thermochemical Fuel Production and Thermal Energy Storage

descripción no proporcionada por scopusAC thanks the support of a fellowship from “la Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/PI20/11760015. JC acknowledge financial support from ACES 2030 (P2018/EMT-4319) from “Comunidad de Madrid” and European Structural Funds

Thermochemical Storage of Middle Temperature Wasted Heat by Functionalized C/Mg(OH)2 Hybrid Materials

For the thermochemical performance implementation of Mg(OH)2 as a heat storage medium, several hybrid materials have been investigated. For this study, high-performance hybrid materials have been developed by exploiting the authors’ previous findings. Expanded graphite (EG)/carbon nanotubes (CNTs)-Mg(OH)2 hybrid materials have been prepared through Mg(OH)2 deposition-precipitation over functionalized, i.e., oxidized, or un-functionalized EG or CNTs. The heat storage performances of the carbon-based hybrid materials have been investigated through a laboratory-scale experimental simulation of the heat storage/release cycles, carried out by a thermogravimetric apparatus. This study offers a critical evaluation of the thermochemical performances of developed materials through their comparison in terms of heat storage and output capacities per mass and volume unit. It was demonstrated that both EG and CNTs improves the thermochemical performances of the storage medium in terms of reaction rate and conversion with respect to pure Mg(OH)2. With functionalized EG/CNTs-Mg(OH)2, (i) the potential heat storage and output capacities per mass unit of Mg(OH)2 have been completely exploited; and (ii) higher heat storage and output capacities per volume unit were obtained. That means, for technological applications, as smaller volume at equal stored/released heat

Tuning Mg(OH)₂ Structural, Physical, and Morphological Characteristics for Its Optimal Behavior in a Thermochemical Heat-Storage Application

Thermochemical materials (TCM) are among the most promising systems to store high energy density for long-term energy storage. To be eligible as candidates, the materials have to fit many criteria such as complete reversibility of the reaction and cycling stability, high availability of the material at low cost, environmentally friendliness, and non-toxicity. Among the most promising TCM, the Mg(OH)2/MgO system appears worthy of attention for its properties in line with those required. In the last few decades, research focused its attention on the optimization of attractive hydroxide performance to achieve a better thermochemical response, however, often negatively affecting its energy density per unit of volume and therefore compromising its applicability on an industrial scale. In this study, pure Mg(OH)2 was developed using different synthesis procedures. Reverse deposition precipitation and deposition precipitation methods were used to obtain the investigated samples. By adding a cationic surfactant (cetyl trimethylammonium bromide), deposition precipitation Mg(OH)2 (CTAB-DP-MH) or changing the precipitating precursor (N-DP-MH), the structural, physical and morphological characteristics were tuned, and the results were compared with a commercial Mg(OH)2 sample. We identified a correlation between the TCM properties and the thermochemical behavior. In such a context, it was demonstrated that both CTAB-DP-MH and N-DP-MH improved the thermochemical performances of the storage medium concerning conversion (64 wt.% and 74 wt.% respectively) and stored and released heat (887 and 1041 kJ/kgMg(OH)2). In particular, using the innovative technique not yet investigated for thermal energy storage (TES) materials, with NaOH as precipitating precursor, N-DP-MH reached the highest stored and released heat capacity per volume unit, ~684 MJ/m3

Fe-doped CaMnO3 for Thermochemical Heat Storage Application

[EN] CaMnO3 oxide can be considered a promising candidate for high temperature thermochemical heat storage, since it is able to release oxygen in a wide temperature range (800-1000 °C) at different oxygen partial pressures (pO2) suitable for Concentrated Solar Power (CSP) plants. Moreover, it is composed of earth abundant, inexpensive, non-toxic elements. However, it undergoes decomposition at pO2<0.01 atm and at temperature above 1100 °C. In order to overcome this limitation and to extent the operating temperature range, in this study B-site doping with Fe was used as approach for preventing decomposition. The reaction enthalpy was measured through equilibrium non-stoichiometry curves so that the heat storage capacity could be evaluated. It was demonstrated that Fe-doping prevented CaMnO3 decomposition up to 1200 °C at pO2=0.008 thus widening the operating temperature range and the oxygen reduction extent. In addition, the heat storage capacity (ΔH (kJ/molABO3)) of Fe-CaMnO3 (∼324 kJ/kgABO3) is remarkably higher than that of the un-doped CaMnO3 (∼250 kJ/kgABO3This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement N° 74616. Support of the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Award DE-EE0008089.0000, is also acknowledged.Peer reviewe

Carbon Nanotubes-Filled Siloxane Composite Foams for Oil Recovery Application: Compression Properties

This paper studies the correlation between oil recovery usability and mechanical behavior under compression loads of an innovative oil recovery material. The examined composites are silicone foams filled with carbon nanotubes (CNT). Here, the reutilization of oil recovery processes of the newly developed composite foams is evaluated. In this regard, static and cyclic compressive tests are carried out. Samples filled with pristine and functionalized CNT are tested to evaluate the influence of the filler&rsquo;s characteristics on the composite foam&rsquo;s mechanical behavior. The results show that the presence of CNT (CNT-0) increases the elastic modulus (0.030 MPa) and collapse stress (0.010 MPa) of the siloxane matrix. On the contrary, as the CNT functionalization degree increases, a worsening of the composite&rsquo;s mechanical performance is observed. CNT-0 foam evidences, also, the optimal mechanical stability to cyclic compressive loads, maintaining high stress values until 30 cycles. Furthermore, a correlation between the absorption capacity, elastic modulus, and cyclability is reported, highlighting a simplified approach to tailor the high absorption durability performance of filled CNT silicone foams. The promising results confirm the possible reuse of these new composite foams as absorbent materials for oil spill recovery applications