Gravimetric Storage Density Research Articles

Experimental and Theoretical Study of the Performance of Li-Oxygen Batteries with Multiwall Carbon Nanotube Cathodes

Although Li-oxygen batteries with organic electrolyte have a theoretical energy density of 3505 kWh/kg (which is comparable to the energy density of gasoline), in practice only a fraction of this energy density has been demonstrated. Despite this gap, Li-oxygen batteries remain to have a great potential to replace the current energy storage devices in applications requiring light power sources such as portable electronic devices, unmanned aerial vehicles, and renewable energy storage. There is great interest in seeing if Li-oxygen batteries, which have the potential to have a far higher gravimetric energy storage density than any other battery chemistry, can be developed to power electric vehicles (EVs) and allow for driving ranges that are comparable to those of gasoline-powered cars [1]. In this presentation we make a combined experimental and theoretical investigation of the performance of the Li-oxygen batteries for different cathode structures, assembling technique (that can induce different concentrations of seeds available for precipitation and growth in the cathode) and discharge conditions. The theoretical model is based on the traditional drift-diffusion approach, coupled with a simple model that describes the precipitation and growth of lithium peroxide on the carbon nanotubes. The model also predicts that it is optimum to use variable porosity cathodes (with higher porosity on the oxygen side and lower porosity on the separator side) in order to maximize the energy density of these cells, a fact which is also demonstrated using our experimental data. More details about the mathematical approach and a comparison with the experimental data will be presented at the conference.[1] N. Imanishi and O. Yamamoto, “Perspectives and challenges of rechargeable lithium–air batteries,” Mater. Today Adv., vol. 4, p. 100031, Dec. 2019, doi: 10.1016/j.mtadv.2019.100031.

(Invited) Study on the Effect of Additive in High Nickel NMC – Graphite Libs for HF- Scavenging and Stabilization of Cei Layer

Lithium ion batteries have been marked by steady progress over the past few decades owing to their high volumetric and gravimetric energy storage densities. The advent of LIBs resulted in the consistent shift of automotive industry towards hybrid EV's and BEV's. The Nissan Leaf, introduced in December 2010, became the first modern all-electric, zero tailpipe emission five door family hatchback to be produced for the mass market from a major manufacturer. Nissan has made constant efforts in improving the existing LIBs.With the advent of new high nickel cathode materials there has been an improvement in the energy density of LIBs and the ability to internalize the material supply chain. However, these cathode materials induce additional challenges due to instability of cathode electrolyte interface and dissolution of transition metals in the systems.[1-4]In the current work, electrolyte additive has been explored for stabilizing the cathode surface by stabilizing the cathode electrolyte interface in NMC811 and Graphite system in carbonate electrolyte system. The cycling data was analyzed with different capacity vs voltage and/current to identify the effect of additive and cycling degradation on the reaction kinetics and potentials. A methodology involving Distribution of Relaxation time (DRT) analysis, equivalent circuit design and electrochemical impedance fitting was developed to identify the different electrochemical components of the cell and their contribution towards the increase in internal resistance. The analysis was conducted during formation cycles and at different checkpoints for long cycling scenarios. The contribution of cathode and anode resistances were deconvoluted for the mixed impedance signal. Furthermore, XPS and TEM analysis were used to verify different features of the cathode and anode wherever applicable and feasible, to study the effect of the additive. Cui, Z., & Manthiram, A. (2023). Thermal Stability and Outgassing Behaviors of High‐nickel Cathodes in Lithium‐ion Batteries. Angewandte Chemie International Edition, 62(43), e202307243.Yu Wu, Xiang Liu, Li Wang, Xuning Feng, Dongsheng Ren, Yan Li, Xinyu Rui, Yan Wang, Xuebing Han, Gui-Liang Xu, Hewu Wang, Languang Lu, Xiangming He, Khalil Amine, Minggao Ouyang, Development of cathode-electrolyte-interphase for safer lithium batteries, Energy Storage Materials, Volume 37, 2021, Pages 77-86, ISSN 2405-8297.Hou, J., Lu, L., Wang, L. et al. Thermal runaway of Lithium-ion batteries employing LiN(SO2F)2-based concentrated electrolytes. Nat Commun 11, 5100 (2020).Yu Wang, Xuning Feng, Yong Peng, Fukui Zhang, Dongsheng Ren, Xiang Liu, Languang Lu, Yoshiaki Nitta, Li Wang, Minggao Ouyang, Reductive gas manipulation at early self-heating stage enables controllable battery thermal failure, Joule, Volume 6, Issue 12, 2022, Pages 2810-2820,ISSN 2542-4351.

Multi scale systematisation of damage and failure modes of high-pressure hydrogen composite vessels in aviation, Part 1: Methodology

In the development of composite Compressed Gaseous Hydrogen (CGH2) storage vessels the multitude of design, material and manufacturing parameters introduce uncertainties. In addition with complex interacting failure modes such as delamination, matrix and fibre failure high safety margins are needed.The aim of this paper is to enable the decrease of safety margins by developing a fundamental methodology to systematise superimposed loads and their propagation across length scales and load domains to enable the reliability assessment and development of CGH2 vessels in aircraft with high reliability and maximum gravimetric storage density. Therefore, the objectives are to analyse existing development strategies, to derive requirements for a new development approach and to define its underlying logic and procedure. This results in a methodology to systematise potentially occurring load cases, corresponding stresses and resulting failure modes of CGH2 vessels in aircraft along the length scales from the aircraft super-system to the material level.

Experimental study on absorption and desorption behavior of a novel metal hydride reactor for stationary hydrogen storage applications

Metal hydrides have captured significant attention for hydrogen storage because of their high energy density and safety. However, the performance of these systems is largely influenced by the design of the storage reactor. In this perspective, a novel compact, lightweight, and effective multi tube MH reactor was designed, fabricated, and experimentally tested. The absorption and desorption behavior of the newly developed Ti0.9Zr0.1Mn1.46V0.45Fe0.09 alloy using the proposed MH reactor for hydrogen storage applications was analysed. At 30 bar supply pressure, the MH reactor absorbed 164.3 g (1.58 wt.%) of hydrogen in 894 s and delivered specific energy at an average rate of 94.7 W/kgMH. Further, the reactor released 153.6 g (1.48 wt.%) of hydrogen in 2246 s, when the desorption temperature was set at 50 °C. Moreover, the parametric study revealed that by raising the supply pressure from 10 bar to 20 bar and 30 bar, the stored capacity was improved by 11 % and 18.9 %, respectively, whereas the absorption time was drastically reduced by 43 % and 61.5 %, respectively. Furthermore, the fabricated reactor achieved gravimetric and volumetric storage densities of 0.75 % and 20.6 kg/m3 of H2. Also, the MH reactor achieved a maximum hydrogen storage efficiency of 82.3 %. Finally, the comparative results indicated that the MH reactor studied in this work demonstrated a faster hydrogen release rate compared to other medium to large capacity MH reactors reported in the literature.

Improving the charging performance of latent heat thermal energy storage systems using triply periodic minimal surface (TPMS) structures

The utilization of latent heat thermal energy storage (LHTES) using phase change materials (PCM) has attracted considerable attention due to their high energy density and thermal regulation. However, the inferior thermal conductivity of PCM has hindered their widespread implementation, triply periodic minimal surface (TPMS) structures could considerably ameliorate the energy storage utilization. TPMS structures offer escalated surface area and pore interconnectivity, which can enhance the apparent thermal conductivity and improve the performance of LHTES systems. This study focuses on investigating the performance and storage capabilities of three unique TPMS structures, namely Gyroid, IWP, and Primitive, at different relative densities and charging temperatures. The computational model is developed, verified, and validated with the relevant experiment results. A comparative analysis of the temperature distribution and liquid fraction evolution in TPMS LHTES units is carried out and compared to pure PCM LHTES. At a charging temperature of 80 °C, compared to the complete melting time of 7206 s for the pure PCM LHTES, the results demonstrate that the G10, IWP10, and P10-PCM LHTES achieve complete melting at 344 s, 276 s, and 368 s, respectively. This affirms the superiority of IWP structures in improving the melting rates due to their escalated surface areas and tortuous paths. The use of TPMS structures improves the total heat storage, heat storage rate, and volumetric heat storage density, while reducing the gravimetric heat storage density, compared to the pure PCM LHTES. The G10-PCM LHTES attains total heat storage, heat storage rate, volumetric, and gravimetric heat storage density of 2120 J, 6.16 W, 63.6 kWh/m3, and 227 kJ/kg, compared to 1910 J, 0.27 W, 57.3 kWh/m3, and 250 kJ/kg for pure PCM LHTES, respectively. Moreover, increasing the relative density of TPMS structures adversely reduces the total heat storage, heat storage rate, and volumetric heat storage density, and significantly increases the heat storage rates. As the charging temperature increases, the complete melting time is reduced and the charging performance indicators are improved, for the pure PCM and TPMS-PCM LHTES units.

Photoresponsive conductive polymer network based on azobenzene bridging crosslinked polycarbazole for boosting solar thermal storage

Azobenzene is one of the most extensively researched multifunctional chromophores and azobenzene including materials has a wide variety of applications due to their photoisomerization behavior. In this study, electroactive and light-harvesting carbazole and photoresponsive azobenzene units have been combined with a special macromolecular design. In this design the azo groups can be effectively isomerized in solid state, and free-standing films can be obtained by the electrochemical method. Thermal characterizations of both monomer and polymer have been performed and isomerization kinetics and solar-thermal properties have been investigated. The half-life at 60 °C and the gravimetric energy storage density of polymer was calculated as 103 min and 179.9 j g−1, respectively. Cross-linked polycarbazole structure causes dramatically increased solar thermal storage and half-life compared to respective monomer and brought unexpected mechanical and solvatochromic properties.

Strategic integration of metamaterials properties and topology optimization of gyroid metal hydride reactor for high-density hydrogen storage

Metal hydride (MH) is considered to be one of the potential materials for storing hydrogen. It has a substantial limitation to wide use in the mobility sector, which is its low gravimetric hydrogen storage density. A novel canister design utilizing the optimization of gyroid structure for MH-based hydrogen storage is proposed to enhance reactor strength and capacity, increasing the favor of using it outside stationary applications. Topology optimization (TO) of the reactor increases the capacity by 49 % while maintaining the capability of this reactor to sustain 5000 N of bending case. On top of that, changing the metamaterial properties of the gyroid results in a larger chamber size for storing a larger amount of MH by the maximum amount of 30 %. However, increasing the chamber size comes with a cost of a lower charging rate and a considerable area of non-reacted hydride at the same charging time compared to the non-modified structure. By evaluating the MH bed that consists of lanthanum nickel (LaNi5), the topologically optimized reactor design is varied with different chamber offsets of 0, 2, and 4 mm. The results show that using a 2 mm offset in this study case can increase hydrogen storage capacity by 22 % while maintaining the same charging time of less than 4500 s. The combination of both proposed methods can increase the overall MH bed chamber by 66.22 % compared to previous initial research that acts as proof of concept.

Heat transfer optimization for MH reactor using combined taguchi design and data-driven optimization method

Adding the heat transfer enhancement components into the MH reactor can improve the hydrogen absorption/desorption rate, but the vital indicators as the gravimetric and volumetric hydrogen storage density decrease at the same time, which is hardly considered in the published researches. In this study, a comprehensive hydrogen storage performance (CHSP) indicator for the MH reactor has been proposed considering the above contradiction, which can be applied to evaluate the comprehensive performance of the MH reactor and compare the reactor performances with different heat transfer configurations. Then, with the constraint of the CHSP, the heat transfer structure of the classical finned-tube MH reactor is optimized using a novel sieving optimization strategy which combines the Taguchi design and the data-driven optimization (ANN model + GA) to increase the optimization efficiency and the reliability of optimization solutions. The optimized results indicate that the optimal structural parameters of the finned-tube MH reactor are the diameter of heat exchange tube d of 5.13 mm, the fin thickness h of 0.28 mm, the fin radius r of 21.73 mm and the fin number N of 11, and the optimal CHSP is 0.547 mg/s.

Theoretical prediction of perovskite ARH3 (A = K, Li, Rb; R[dbnd]Ca, Sr) hydride materials for hydrogen storage applications: A DFT investigation

Hydrogen (H2) storage has attracted the greatest attention in the contemporary day because of the shortage of fuel. The water splitting is considered less cost-effective and lead-free energy production by the photocatalytic process to produce hydrogen as a fuel for vehicles, petroleum refining, Pharmaceuticals, and glass purification. Perovskite materials play a vital role in H2 storage and production applications. The density functional theory (DFT) using the CASTEP code is used to study the various structural, electrical, optical, mechanical, and hydrogen (H2) capacity properties of ARH3 (A = K, Li, Rb; RSr, Ca) compounds. The compounds under investigations are optimized in the cubic structure; for ARH3 (A = K, Li, Rb; RSr, Ca), the optimized lattice constants are 3.924, 4.302, 4.559, 4.817, 4.647, and 4.884 Å, respectively. Since these hydrides are thermally stable, their formation energy is exhibited negative values. ARH3 may find usage in H2 storage applications due to its high gravimetric H2 storage densities (6.042 and 3.678 wt% for LiCaH3 and KCaH3, respectively). Furthermore, band gaps of 2.71, 2.38, 3.27, 2.73, 1.85, and 2.83 eV for ARH3 (A = K, Li, Rb; RCa, Sr) respectively, confirm the semiconductor behavior. These substances satisfy born stability criteria due to its mechanical parameters which derived from elastic constant values such as Pugh's ratio and modulus. Additionally, Pugh's ratio and Cauchy pressure demonstrate that, in contrast to other compounds, the KCaH3 compound has a ductile character (0.29). According to our analyses, studied compounds are observed a potential candidate for hydrogen storage devices.

Hydrogen storage on MgO supported TiMgn (n = 2–6) clusters: A first principle investigation

The current study explores the potential of MgO-supported finite-sized TiMgn (n = 2–6) nanoclusters as hydrogen storage materials, employing density functional theory with a spin-polarized generalized gradient approximation (GGA). These systems' structural stability and electronic characteristics reveal that supported clusters offer superior hydrogen storage capabilities compared to their unassisted counterparts. Various parameters, including cluster-adsorption energy (Eads), hydrogen-adsorption energy in supported clusters (Eads-H), HOMO-LUMO gap, vertical ionization potential (VIP), vertical electron affinity (VEA), chemical potential (μ), and chemical hardness (ɳ) are computed. Substrate support notably enhances the thermodynamic stability and chemical reactivity of the TiMg5 cluster when contrasted with the bare TiMg5 cluster. Furthermore, a remarkable increase in the gravimetric hydrogen storage density, from 1.63 wt% for bare Mg5 clusters to 3.45 wt% for bare TiMg5 clusters, reaching 5.62 wt% in the supported TiMg5 cluster system is observed. These findings indicate the substrate-supported TiMg5 cluster as a promising candidate for hydrogen storage applications.

Sc-Modified C3N4 Nanotubes for High-Capacity Hydrogen Storage: A Theoretical Prediction.

Utilizing hydrogen as a viable substitute for fossil fuels requires the exploration of hydrogen storage materials with high capacity, high quality, and effective reversibility at room temperature. In this study, the stability and capacity for hydrogen storage in the Sc-modified C3N4 nanotube are thoroughly examined through the application of density functional theory (DFT). Our finding indicates that a strong coupling between the Sc-3d orbitals and N-2p orbitals stabilizes the Sc-modified C3N4 nanotube at a high temperature (500 K), and the high migration barrier (5.10 eV) between adjacent Sc atoms prevents the creation of metal clusters. Particularly, it has been found that each Sc-modified C3N4 nanotube is capable of adsorbing up to nine H2 molecules, and the gravimetric hydrogen storage density is calculated to be 7.29 wt%. It reveals an average adsorption energy of -0.20 eV, with an estimated average desorption temperature of 258 K. This shows that a Sc-modified C3N4 nanotube can store hydrogen at low temperatures and harness it at room temperature, which will reduce energy consumption and protect the system from high desorption temperatures. Moreover, charge donation and reverse transfer from the Sc-3d orbital to the H-1s orbital suggest the presence of the Kubas effect between the Sc-modified C3N4 nanotube and H2 molecules. We draw the conclusion that a Sc-modified C3N4 nanotube exhibits exceptional potential as a stable and efficient hydrogen storage substrate.

Experimental study on charging and discharging characteristics of copper finned metal hydride reactor for stationary hydrogen storage applications

With the shift in power generation methods from conventional to renewable, the need for energy storage has increased, and hydrogen as a carrier has great potential. The storage of hydrogen is one of the main obstacles to the effective deployment of the hydrogen economy. Since metal hydride offers a higher energy density than conventional methods, it can potentially be used to store and deliver hydrogen. Also, the metal hydride hydrogen storage system is the primary element of the energy storage system that connects hydrogen production and consumption. Therefore, the present study is focused on the development and testing of a metal hydride reactor. In the present experimental study, 9 kg of La0.7Ce0.1Ca0.3Ni5 is loaded in a single tube copper finned reactor attached to an external jacket, and the charging and discharging characteristics related to hydrogen storage are analysed along with variations in its thermal performance under various operating conditions. Also, the effect of HTF temperature on the hydrogen release performance of the copper finned reactor is studied under constant discharge pressure and constant discharge flow rate. Further, a comparison has been made between the copper and aluminium finned reactors. This fabricated copper finned reactor attained volumetric and gravimetric storage densities of 21.78 kg per m3 of H2 and 0.77%, respectively. The results indicated that La0.7Ce0.1Ca0.3Ni5 filled within the copper finned reactor stores 1.45 wt.% (130.7 g) of hydrogen in 680 s, corresponding to 25 bar feed gas pressure. At the HTF temperature of 60 °C, the copper-finned reactor discharged 1.42 wt.% (127.3 g) of hydrogen in 1450 s, showing the release of 98% of the stored mass of hydrogen. Further, the developed copper finned MH reactor could supply hydrogen at a constant rate of 13 lpm with a capability of 90% discharge even at a discharge temperature of 30 °C. Beside this, the comparative results showed that adding copper fins showed a considerable improvement over aluminium fins during discharging compared to the charging process. The copper-finned reactor consumed 20.9% and 23.6% less time to release 1 wt.% of hydrogen than the aluminium-finned reactor at discharge temperatures of 40 °C and 50 °C, respectively.

Silica dopant effect on the performance of calcium carbonate/calcium oxide based thermal energy storage system

The CaCO3 is being studied for its application in thermal energy storage. However, it has drawbacks of slow reaction rate during calcination and incomplete reversible carbonation which limit its use. In this paper, SiO2 has been studied as a dopant for CaCO3 to improve its cyclic performance. The CaCO3 samples were loaded with different concentrations of SiO2 and its effect on the thermal energy density of CaCO3 was determined. Afterwards, the effect of the dopant on the heat storage process of the synthesized composite along with kinetics of decarbonation reaction was investigated. Cyclic tests were performed to determine the reusability of the material. It was found that the addition of dopant helped to increase the rate of decarbonation reaction, thereby making the heat storage process more efficient as compared to pure CaCO3. The activation energy values are 255.9 kJ/mol, 280.1 kJ/mol, 244.9 kJ/mol, and 234.8 kJ/mol for 5%, 15%, 30%, and 0% doped SiO2 samples, respectively. Furthermore, thermal energy storage density increases when the amount of dopant decreases in the samples such as the 30% and 5% doped samples have gravimetric energy storage densities of 339.85 J/g and 759.24 J/g, respectively. It was observed that the large quantities (15% and 30%) of dopant had introduced a new phase of Ca3SiO5 during CaCO3 decomposition.

Metal(Pt, Pd)-Perovskite Oxide(Ba0.5Sr0.5Co0.8Fe0.2O3-δ) Hybrid Material As a Bifunctional Electrocatalyst for Lithium-Air Battery

The rapid depletion of fossil fuel resources and growing concerns over climate change have made the development of next-generation batteries a top priority. Among these, Li-O2 batteries have attracted significant interest due to their potential for much higher gravimetric energy storage density compared to other chemical batteries. However, efficient and cost-effective catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are critical for the efficient functioning of these batteries.In recent years, complex perovskite oxides, such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), have been identified as promising candidates for bifunctional catalysts due to their defective structures and excellent oxygen mobility. However, while BSCF exhibits high OER activity, its ORR performance is poor. To address this issue, researchers have turned to metal-oxide composite catalysts, where nanosized metals are deposited on the surface of perovskite oxides, to increase activity and stability towards ORR due to the synergistic effect between metal and oxide support.In this study, we report the development of bifunctional electrocatalysts with highly electrocatalytic activity for ORR and OER. We used a simple wet-chemical processing technique to deposit metal catalysts with superior ORR activity on perovskite oxide-based catalysts with high OER activity. The direct deposition method is an effective way to create a good distribution of metal catalysts, intimate contact between metal catalysts and BSCF perovskite oxide, which may contribute to the creation of a synergistic effect between them. Our results showed that the metal catalysts deposited on perovskite oxides of Pd@BSCF and Pt@BSCF exhibited better ORR activity than others and higher OER activity than the perovskite oxides alone, resulting in much-enhanced bifunctionality through a synergistic effect between the metal catalysts and perovskite oxides.We further investigated the enhanced bifunctional electrocatalytic activity of the metal catalysts deposited perovskite oxides for Li-O2 batteries. The assembled Li-O2 batteries with Pd@BSCF cathode demonstrated lower discharge/charge overpotential (0.8 V at the cutoff capacity of 500 mAh gcat -1) and improved cycling stability (over 70 cycles), indicating the effectiveness of our approach in enhancing the bifunctional activities of ORR and OER for application in electrochemical energy storage and conversion systems. The encouraging results obtained from this study might have been attributed to two mechanisms, namely, the synergistic effect of electronic transfer and RDS/spillover. Our study suggests that the deposition of metal catalysts on the surface of perovskite oxides (Pd@BSCF and Pt@BSCF) is an effective approach to enhance bifunctional activities of ORR and OER, making it a promising strategy for the development of next-generation batteries. Figure 1

Hydrogen Storage Using Metal-Organic Frameworks (MOFs): A Computational Fluid Dynamic Study

The existing obstacles toward the usage of fossil fuels as the prime mover of the cars have improved the commercialization of the fuel cells and batteries to replace the internal combustion engines (ICEs). Although the required infrastructure is already established for the ICE cars, the low number of hydrogen refueling stations, low range of batteries, high charging time of the batteries, and the size/weight of the hydrogen tanks are the main concerns toward the transition from ICE cars to environmentally friendly alternatives.Fuel cells can be directly used in the vehicles as the prime mover (mobility applications), or they can be considered as the energy provider of the electric vehicle charging stations (stationary applications). Although the hydrogen storage is not being considered as an obstacle for the stationary applications, the required weight and size of the hydrogen tanks is a barrier to facilitate the usage of hydrogen in the automotive sector. Based on the given standards [1], it is possible to pressurize hydrogen up to 700 bars, hence reducing the size of the hydrogen tanks. This solution has been already used in the development of the Toyota Mirai, which has 114kW/155hp power and 500km range with the fuel consumption of 0.76 kg H2/100km [2]. Similarly, Honda Clarity could reach the range of 650km with 5kg of hydrogen tank capacity at the rated power of 130kW/ 176hp [3]. Although pressurizing the hydrogen is a feasible solution, it will demand further costs and safety procedures to reach the 700 bars. In other words, the best solution would be reaching the same driving range without pressurizing the hydrogen.In this regard, Metal-Organic Framework (MOF) can be used to increase the hydrogen adsorption in the hydrogen tank due to higher gravimetric storage density. Among different types of MOFs, the MOF-5 has shown promising results to increase the hydrogen storage up to wt. 10% absolute at 70 bar and 77K. It is believed that the low thermal conductivity of the MOF-5 can reduce the performance of the system when rapid gas uptake and release is required [4]. Although there have been studies to evaluate the overall possibilities of using MOF-5 to improve the adsorption of hydrogen in the hydrogen tanks, there is not a comprehensive study to simulate and characterize the changes in the hydrogen adsorption once the hydrogen tanks are filled with different types of MOFs.The goal of this study is to use the computational fluid dynamic methodologies to model a hydrogen tank filled with MOFs and to analyze the hydrogen adsorption by the changes in the time. This study can a step toward improving the design of the hydrogen tanks, which will facilitate the hydrogen storage at low pressures close to the ambient temperatures. This study can be also a good start to find the right type of MOF to be used in the hydrogen tanks to have the highest possible hydrogen adsorption. The developed model is based on mass, momentum, and energy conservation equations of the adsorbent-adsorbate system composed of gaseous and adsorbed hydrogen, adsorbent bed and tank wall. It is noteworthy to mention that the adsorption process is based on the modified Dubinin-Astakov (D-A) adsorption isotherm model. Keywords : Hydrogen Storage; Metal Organic Frameworks; Adsorption; Fuel cells. Figure 1

Enhancing solar thermal storage properties of azobenzenes with conductive polymer: Electropolymerization of carbazole containing photoactive cyanoazobenzene derivative

Solar thermal fuels (STFs) have recently drawn attention as a promising strategy for utilization of solar energy that is a clean and renewable source. Especially solid state solar thermal fuels have high potential to be used in thermal applications. However, up to date, it is seen that the solar thermal storage capacity in the polymeric state is lower than in the corresponding monomers. Herein, for the first time, photoactive azobenzene and electroactive carbazole containing monomer (Cz-AzoCN) was designed and thermal storage properties of the monomer and the corresponding polymer obtained by electropolymerization were investigated. This study showed that polycarbazoles containing azobenzene pendant groups can be an effective thermal storage platform due to their easy functionality, high light absorption and rigid conjugated chain structure resembling the structure of rigid templates decorated with closely packed photochromic units. Additionally, electropolymerization is an easy and rapid method for polymer synthesis, producing polymer in the form of film that is ready for irradiation. The gravimetric energy storage density of p(Cz-AzoCN) was calculated as 145.12 j g−1 which was 128 % higher than that of monomer. This is due to boosted light harvesting of conjugated polycarbazole backbone as an organic photosensitizer that providing effective solar thermal storage.

Modeling of the structural, optoelectronic, thermodynamic, dynamical stability, and the hydrogen storage density of CsSnX3 (X ​= ​O, S, Se and Te) perovskites

Based on density functional theory (DFT) approach, investigations on the structural, thermodynamic, electronic, optoelectronic, phonon, mechanical, and the hydrogen gravimetric storage density of CsSnX3 (X ​= ​O, S, Se and Te) perovskite systems is presented herein. While results of the computed lattice constant values for the investigated perovskite systems increased with an increase in the size of the anion X (X ​= ​O, S, Se, Te), the electronic bandgap values of 1.42, 1.02, 0.64, and 0.40 ​eV is obtained for CsSnO3, CsSnS3, CsSnSe3, and CsSnTe3 respectively. Among the studied systems, CsSnO3 and CsSnS3 are found to be dynamically stable, with CsSnO3 material being the most stable among the studied compounds owing to its frequencies in the real state of the phonon dispersion curve. To study the hydrogen storage properties of the materials in this present study: CsSnO3, CsSnS3, CsSnSe3, and CsSnTe3 the crystal structures have been modified by replacing the heteroatoms (O, S, Se, and Te) with hydrogens which is given as: CsSnO_H4, CsSnS_H4, CsSnSe_H4 and CsSnTe_H4. The gravimetric density (GD) suggests a strong agreement with the calculated band structure and decreases as the amount of band gap becomes enormous, where the CsSnO reveals a highest capacity of 0.74 which decrease as we go from O–Te for two atomic hydrogens. The CsSnTe shows the lowest gravimetric density of 0.526. Also, the formation energies obtained for CsSnO3_H4 estimated to be −31.599 ​kJ ​mol−1 ​has the highest energy however, these was observed to decrease as we go from oxygen to S ​> ​Se ​> ​Te. Moreover, the desorption temperature which is necessary for physical application reveals that the investigated materials are in line with the required range of desorption temperature for practical applications 289 ​K ​°K proposed by US-DOE, which implies that there are no barriers for hydrogen desorption from CsSnX3_H4 compounds. Therefore, it can be deduced that CsSnX3_H4 is a reversible hydrogen storage material. However, CsSnO3_H4 the best desorption temperature, this means that the presence of O atom in the perovskite improves the adsorption energy of interaction between the crystal lattice and the hydrogen molecules and decrease in the order of S ​> ​Se ​> ​Te respectively.

Tuning the isomer composition is a key to overcome the performance limits of commercial benzyltoluene as liquid organic hydrogen carrier

This work is the outcome of a three-year journey to develop a technically feasible way to overcome the limits of the benzyltoluene (H0-BT) and perhydro benzyltoluene (H12-BT) pair, recognized as an attractive liquid organic hydrogen carrier (LOHC) system. In the first attempt to synthesize and evaluate three H0-BT regioisomers, the para isomer showed faster H2 storage and release rates than the ortho and meta counterparts. This was attributed to its favorable adsorption capacity and strength on the catalyst surface. The subsequent evaluation of binary and ternary H0-/H12-BT isomeric mixtures, prepared by physical mixing the synthesized isomers, suggested that abundant amounts of para isomer in the mixture were needs to maximize the LOHC performance. Thus, a H0-BT mixture with 72 % para isomer was successfully synthesized using the zeolite H-Beta under optimized conditions, resulting in a faster kinetics of both H2 storage and release than commercial Marlotherm LH. Cycling tests on this mixture indicated that the formation of methylfluorene as a dehydrogenation byproduct was detrimental to the hydrogenation reaction. By reducing the formation of methylfluorene to a level of 3 % using a sulfur-decorated Pt/Al2O3 catalyst, a gravimetric H2 storage density of 6 wt% could be maintained for 10 cycles. Finally, a cost analysis confirmed that the isomeric composition of H0-BT in the mixture should be tuned to increase the para isomer content, while the raw materials for H0-BT synthesis are cheap. The step-by-step approach reported herein will pave the way for the development of novel aromatic LOHC systems in the near future.

Development of over 3000 cycles durable macro-encapsulated aluminum with cavity by a sacrificial layer method for high temperature latent heat storage

The high-temperature metallic phase change materials (PCMs) are attracting great attentions as alternatives to sensible heat storage materials in thermal energy storage (TES) systems. However, the high corrosivity, easy leakage and oxidation phenomena of metallic PCMs have limited their applications. This work reports a facile and novel sacrificial layer method with the purpose to create macro-encapsulating aluminum (Al) PCM by alumina (Al2O3) shell characterized by a ‘buffer’ inner cavity. The inner cavity could offer buffer space to accommodate the huge thermal volume expansion of Al core PCM during heating and melting, thereby preventing the breakage of the capsules and ensuring the long-term stability. A series of Al balls with diameters of 4–25 mm were firstly coated with paraffin sacrificial layer then by Al2O3 dough shell, which was finally conducted by the two-step heat treatment, in which a low-temperature stage aimed at removing the paraffin layer while the high-temperature stage aimed at the capsule sintering formation. The final macrocapsules with diameters of 6.5–31.5 mm were obtained, in which the capsules with Al core balls larger than 15 mm showed superior gravimetric and volumetric heat storage density because of their high core–shell ratio. For example, the 25 mm@0.75 mm@2.5 mm macrocapsules could present high heat storage density of 348 kJ/kg and 902 J/cm3 at the temperature range of 600–700 °C. The macrocapsules also showed a long-time thermal cycling stability, since that no damage or leakage was observed over 3000 times of melting and solidification under air atmosphere, indicating that they can be used over 8 years without any degradation of thermophysical properties. This demonstrates the potential application of the Al2O3 encapsulated Al macrocapsules with inner cavity in high-temperature TES systems.

Photoliquefiable Azobenzene Surfactants toward Solar Thermal Fuels that Upgrade Photon Energy Storage via Molecular Design.

Photoresponsive phase change materials (PPCMs) are capable of storing photon and heat energy simultaneously and releasing the stored energy as heat in a controllable way. While, the azobenzene-based PPCMs exhibit a contradiction between gravimetric energy storage density and photoinduced phase change. Here, a type of azobenzene surfactants with balance between molecular free volume and intermolecular interaction is designed in molecular level, which can address the coharvest of photon energy and low-grade heat energy at room temperature. Such PPCMs gain the total gravimetric energy density up to 131.18 J g-1 by charging solid sample and 160.50 J g-1 by charging solution. Notably, the molar isomerization enthalpy upgrades by a factor of up to 2.4 compared to azobenzene. The working mechanism is explained by the computational studies. All the stored energy can release out as heat under Vis light, causing a fast surface temperature rise. This study demonstrates a new molecular designing strategy for developing azobenzene-based PPCMs with high gravimetric energy density by improving the photon energy storage.