Volumetric Storage Research Articles

Novel Wide-Working-Temperature NaNO3-KNO3-Na2SO4 Molten Salt for Solar Thermal Energy Storage.

A novel ternary eutectic salt, NaNO3-KNO3-Na2SO4 (TMS), was designed and prepared for thermal energy storage (TES) to address the issues of the narrow temperature range and low specific heat of solar salt molten salt. The thermo-physical properties of TMS-2, such as melting point, decomposition temperature, fusion enthalpy, density, viscosity, specific heat capacity and volumetric thermal energy storage capacity (ETES), were determined. Furthermore, a comparison of the thermo-physical properties between commercial solar salt and TMS-2 was carried out. TMS-2 had a melting point 6.5 °C lower and a decomposition temperature 38.93 °C higher than those of solar salt. The use temperature range of TMS molten salt was 45.43 °C larger than that of solar salt, which had been widened about 13.17%. Within the testing temperature range, the average specific heat capacity of TMS-2 (1.69 J·K-1·g-1) was 9.03% higher than that of solar salt (1.55 J·K-1·g-1). TMS-2 also showed higher density, slightly higher viscosity and higher ETES. XRD, FTIR and Raman spectra SEM showed that the composition and structure of the synthesized new molten salt were different, which explained the specific heat capacity increasing. Molecular dynamic (MD) simulation was performed to explore the different macroscopic properties of solar salt and TMS at the molecular level. The MD simulation results suggested that cation-cation and cation-anion interactions became weaker as the temperature increased and the randomness of molecular motion increased, which revealed that the interaction between the cation cluster and anion cluster became loose. The stronger interaction between Na-SO4 cation-anion clusters indicated that TMS-2 molten salt had a higher specific heat capacity than solar salt. The result of the thermal stability analysis indicated that the weight losses of solar salt and TMS-2 at 550 °C were only 27% and 53%, respectively. Both the simulation and experimental study indicated that TMS-2 is a promising candidate fluid for solar power generation systems.

Unstable Metal Hydrides for Possible On-Board Hydrogen Storage

Hydrogen storage in general is an indispensable prerequisite for the introduction of a hydrogen energy-based infrastructure. In this respect, high-pressure metal hydride (MH) tank systems appear to be one of the most promising hydrogen storage techniques for automotive applications using proton exchange membrane (PEM) fuel cells. These systems bear the potential of achieving a beneficial compromise concerning the comparably large volumetric storage density, wide working temperature range, comparably low liberation of heat, and increased safety. The debatable term “unstable metal hydride” is used in the literature in reference to metal hydrides with high dissociation pressure at a comparably low temperature. Such compounds may help to improve the merits of high-pressure MH tank systems. Consequently, in the last few years, some materials for possible on-board applications in such tank systems have been developed. This review summarizes the state-of-the-art developments of these metal hydrides, mainly including intermetallic compounds and complex hydrides, and offers some guidelines for future developments. Since typical laboratory hydrogen uptake measurements are limited to 200 bar, a possible threshold for defining unstable hydrides could be a value of their equilibrium pressure of peq > 200 bar for T < 100 °C. However, these values would mark a technological future target and most current materials, and those reported in this review, do not fulfill these requirements and need to be seen as current stages of development toward the intended target. For each of the aforementioned categories in this review, special care is taken to not only cover the pioneering and classic research but also to portray the current status and latest advances. For intermetallic compounds, key aspects focus on the influence of partial substitution on the absorption/desorption plateau pressure, hydrogen storage capacity and hysteresis properties. For complex hydrides, the preparation procedures, thermodynamics and theoretical calculation are presented. In addition, challenges, perspectives, and development tendencies in this field are also discussed.

Preparation and properties of activated carbon-based Na3PO4 composites for low-temperature thermochemical heat storage

With the advantages of low heat storage temperature, high heat storage density, and a low price, Na3PO4 has been proposed as a thermochemical heat storage candidate material for use in solar low-temperature heat storage engineering applications. However, the application of pure Na3PO4 is limited due to its propensity for agglomeration. In this study, activated carbon-based Na3PO4 (R-AC@Na3PO4) composites with mass fractions of 30 %, 50 %, and 80 % were synthesized by melt impregnation method using activated carbon as the porous matrix. The morphology and structure of the composites were characterized, and their heat storage performances were investigated. The hydration experiments were carried out in a constant temperature and humidity chamber and dehydration experiments were carried out in thermogravimetric analysis and differential scanning calorimetry simultaneously. The results showed that at 30 °C, 60 % relative humidity, the hydration equilibrium time for the composites were only 30 %–40 % of the pure material. Meanwhile, at a mass fraction of 80 %, material's volumetric heat storage can reach 1793 J·cm−3 without agglomeration, and the performance was stable after 20 cyclic tests. This study provides a reference for the research and development of low-temperature thermochemical heat storage materials and offers more possibilities for R-AC@Na3PO4 composites in future engineering applications.

Estimating catchment‐scale sediment storage in a large River Basin, Colorado River, USA

Estimating <scp>catchment‐scale</scp> sediment storage in a large River Basin, Colorado River, <scp>USA</scp>

Study on the impact of hydrogen storage temperature on iron-based thermochemical hydrogen storage technology

Thermochemical hydrogen storage technology based on iron-based materials has received significant attention owing to its low cost, safety features, and high volumetric hydrogen storage density. However, no consensus has been established on the optimal temperature range for hydrogen storage. This study investigated the impact of hydrogen storage temperature on hydrogen consumption capacity, hydrogen release capacity, and hydrogen storage energy consumption. The hydrogen storage temperature was optimized with the objectives of low energy consumption and high hydrogen storage density. The experiments were conducted using thermogravimetric analyzer and gram-scale packed-bed reactor setups, accompanied by thermodynamic and kinetic calculations. The research indicated that at 550 °C, the optimal hydrogen storage temperature, the lowest relative energy demand was 32.30 %, with the hydrogen consumption capacity reaching the theoretical maximum value of 4.8 %, and the hydrogen release capacity reaching 4.04 %. Furthermore, achieving the theoretical maximum value of hydrogen consumption capacity became exceedingly difficult when the hydrogen storage temperature exceeded 570 °C. Microstructural characterization and kinetic calculations revealed that this phenomenon was attributed to the formation of a dense iron layer on the particle surface, which impeded the solid-state diffusion of oxygen atoms. The formation of the intermediate phase wüstite was identified as the cause of the formation of the dense iron layer. Overall, this study provided theoretical support for iron-based thermochemical hydrogen storage processes and offered a perspective into the reaction behavior of the reduction of magnetite with hydrogen.

Comparative analysis of single and paired metal hydrides based thermal energy storage system

This study aims to determine which thermal energy storage (TES) system is most suited for a concentrated solar power (CSP) plant. The question is which the best TES system, whether utilizing a single metal hydride or employing dual metal hydrides with or without reaction heat recovery via phase change material (PCM). The authors noted that no studies have been conducted to address this question thus far. Consequently, the primary aim of this paper is to compare three different TES systems in order to ascertain the viability, efficacy, and performance of the appropriate TES system. The examined TES systems included: (i) TES system 1, based on a single metal hydride tank coupled to a hydrogen tank through an H2 compressor; (ii) TES system 2, based on paired metal hydride tanks without recovering reaction heat; and (iii) TES system 3, based on paired metal hydride tanks incorporating a PCM for reaction heat recovery. To simulate and evaluate the performance of the three TES systems under various operating conditions, a mathematical model and computer program were created and successfully verified. By examining into their thermodynamic performance and practical viability, this study attempts to provide the strengths and limitations of each system. A comparison of the three TES systems' performance indicators indicates that the TES system 1 has the potential to provide a specific power output of 500.8 W/kg of alloy, which is 50.1 % and 76.4 % greater than the TES systems 2 and 3, respectively. With a volumetric storage capacity of 755 MJ/m3, the TES system 2 outperforms the other two TES systems by around 40 %. The TES system 3 can operate with 85.9 % energy storage efficiency. This efficiency is 30.3 % higher than that of the TES system 1 and 10.2 % higher than that of the system 2. Ultimately, the decision to choose either a TES system based on a single metal hydride or one involving paired metal hydrides is hinges on the specific requirements, limitations, and priorities of the TES system under consideration.

Insights into hydrogen and methane storage capacities: Grand canonical Monte Carlo simulations of SIGSUA.

In the pursuit of sustainable energy solutions, the development of materials with efficient hydrogen and methane storage capacities is imperative, particularly for advancing hydrogen-powered vehicles. Metal-organic frameworks (MOFs) have emerged as promising candidates to meet the stringent targets set by the Department of Energy for both hydrogen and methane storage. This study employs Grand Canonical Monte Carlo simulations to investigate the usable hydrogen and methane gravimetric and volumetric storage capacities of the recently synthesized SIGSUA. A comparative analysis encompasses the selected MOFs with similar metal compositions, those with comparable density and average pore radius, and classical benchmarks, such as IRMOF-15 and IRMOF-20, all evaluated at room temperature and moderate pressures ranging from 25 to 35 MPa. The results reveal that SIGSUA demonstrates noteworthy gravimetric and volumetric storage capacities for both hydrogen and methane, rivaling or surpassing those of the selected MOFs for analysis. These findings underscore the potential of SIGSUA in advancing clean energy storage technologies.

Fine-tuned MOF-74 type variants with open metal sites for high volumetric hydrogen storage at near-ambient temperature

Adsorbent-based hydrogen storage systems offer a potential solution to current challenges in hydrogen storage, particularly those requiring high pressures or cryogenic temperatures. Specifically, the use of metal–organic frameworks (MOFs) featuring open metal sites that strongly adsorb hydrogen represents a promising strategy for near-ambient-temperature hydrogen storage. This study investigates the hydrogen storage properties of M2(dondc) (M = Mg2+, Co2+, and Ni2+), an extended version of MOF-74. Among this series, Ni2(dondc) exhibits the second-highest volumetric hydrogen capacity of 10.74 g L−1 at 298 K under pressure swing adsorption conditions (100 to 5 bar) at ambient temperatures. The superior hydrogen storage performance of Ni2(dondc) is attributed to its highly polarizable Ni open metal sites and a significant heat of adsorption of 12.2 kJ mol−1. These findings are corroborated by temperature-programmed desorption spectroscopy and van der Waals-corrected density functional theory calculations. In addition to its exceptional hydrogen capacity, Ni2(dondc) exhibits robust structural stability and long-term durability, positioning it as a promising candidate for near-ambient-temperature hydrogen storage applications.

Application and Analysis of Liquid Organic Hydrogen Carrier (LOHC) Technology in Practical Projects

In contemporary times, the utilization of liquid organic hydrogen carriers (LOHCs) has gained prominence due to their high volumetric storage density and material properties closely resembling conventional fuels. Numerous countries are incorporating LOHCs in hydrogen demonstration initiatives, encompassing applications such as hydrogen refueling stations, hydrogen-powered ships, and trains. This paper conducts a comprehensive review of seventeen LOHC projects, spanning Germany, Europe, and other nations, presenting detailed project specifications. This review includes information on project consortiums, funding sources, covered supply chains, transport modalities, and employed technologies. Through a global evaluation of LOHC projects, this review underscores the promising and competitive nature of LOHCs as a viable option for the large-scale and long-distance storage and transportation of hydrogen. The future development of this field is discussed at in the last section.

Effective hydrogen storage in Na2(Be/Mg)H4 hydrides: Perspective from density functional theory

The utilization of hydrogen energy has garnered significant attention as a viable and environmentally friendly energy alternative. However, there exist some technological challenges pertaining to the storage of hydrogen. In this context, the present study utilizes first-principles calculations to examine the physical characteristics of Na2(Be/Mg)H4 hydrides to better understand their potential for use in hydrogen storage applications. The structure stability of Na2BeH4 and Na2MgH4 hydrides is assessed by formation enthalpy and phonon dispersion calculations. Elastic constants have been utilized to determine the elastic and mechanical stabilities of the studied hydrides. Both hydrides satisfy the established Born stability criteria, suggesting that both Na2BeH4 and Na2MgH4 are mechanically stable compounds. The assessment of electronic properties reveals that Na2BeH4 and Na2MgH4 have semiconducting characteristics with direct and indirect band gaps of 2.22 and 3.10 eV, respectively. Furthermore, various optical characteristics have been evaluated and compared. The computed values of gravimetric and volumetric hydrogen storage capacities for Na2BeH4 (Na2MgH4) hydrides are 6.78 (5.38) wt% and 85.11 (62.78) gH2l−1, respectively, fulfilling the standard set by US-DOE for 2025. This study suggests that both Na2BeH4 and Na2MgH4 hydrides have the potential to be an incredibly efficient choice for solid-state hydrogen storage.

A novel flat coil tube heat exchanger for metal hydride hydrogen storage reactors

Metal hydride (MH) based hydrogen storage is one of the potential methods for achieving higher volumetric storage densities. However, its poor thermal conductivity limits heat transfer during exothermic hydriding and endothermic dehydriding processes. Hence, heat transfer augmentation is essential in MH reactors to speed up the charging and discharging of hydrogen. The present study proposes a novel flat coil tube heat exchanger with a spiral fin for heat transfer augmentation. It offered superior performance than conventional single and double helical tube heat exchangers, taking 35.3 and 16.7% less time for 90% storage time. Further, optimization of design parameters (pitch and fin thickness) is carried out considering several key parameters such as weight ratio (WR), gravimetric exergy output rate (GEOR), and energy efficiency (EE). A pitch of 30 mm with a fin thickness of 0.25 mm is optimum according to a novel performance index. The influence of the operating parameters (H2 supply pressure and heat transfer fluid inlet temperature) on the absorption performance is investigated for the optimized design. Finally, a single desorption case is presented at 1 bar and 333 K to gain insights about desorption behavior.

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.

A Computational Investigation of Lithium‐Based Metal Hydrides for Advanced Solid‐State Hydrogen Storage

AbstractHydrogen storage is a crucial step in commercializing hydrogen‐based energy production. Solid‐state hydrogen storage has gained much attention from researchers and needs extensive research. In the present study, we investigate the structural, mechanical, and optoelectronic properties of lithium‐based LiAH3 (A=Mn, Fe, Co) metal hydrides to elucidate their potential for solid‐state hydrogen storage. First, we evaluate the structure stability of LiAH3 hydrides using formation enthalpies calculations. Then, the mechanical stability is determined by elastic stiffness constants, which reveal that LiAH3 hydrides are stable mechanically as they meet the Born stability requirements. Electronic band structure calculations manifest that all LiAH3 hydrides possess a metallic character. Several optical properties have been discussed in detail. The gravimetric hydrogen storage capacities of LiMnH3, LiFeH3 and LiCoH3 hydrides are 4.65, 4.60 and 4.39 wt%, respectively, achieving the target of US‐DOE for rechargeable equipment. Additionally, we have determined the volumetric hydrogen storage capacities (Cv) for all LiAH3 hydrides. It is worth mentioning that the highest Cv values have been obtained to be 180.80, 188.18 and 177.25gH2l−1 for LiMnH3, LiFeH3 and LiCoH3 hydrides, respectively, which have achieved the US‐DOE target set for 2025. Our investigation predicts the applicability of lithium‐based hydrides as promising solid‐state hydrogen storage materials.

Small-pore hydridic frameworks store densely packed hydrogen

Nanoporous materials have attracted great attention for gas storage, but achieving high volumetric storage capacity remains a challenge. Here, by using neutron powder diffraction, volumetric gas adsorption, inelastic neutron scattering and first-principles calculations, we investigate a magnesium borohydride framework that has small pores and a partially negatively charged non-flat interior for hydrogen and nitrogen uptake. Hydrogen and nitrogen occupy distinctly different adsorption sites in the pores, with very different limiting capacities of 2.33 H2 and 0.66 N2 per Mg(BH4)2. Molecular hydrogen is packed extremely densely, with about twice the density of liquid hydrogen (144 g H2 per litre of pore volume). We found a penta-dihydrogen cluster where H2 molecules in one position have rotational freedom, whereas H2 molecules in another position have a well-defined orientation and a directional interaction with the framework. This study reveals that densely packed hydrogen can be stabilized in small-pore materials at ambient pressures.

High-entropy Ti-Zr-Hf-Ni-Cu alloys as solid-solid phase change materials for high-temperature thermal energy storage

High-performance high-temperature solid-solid phase change materials (SS-PCMs) are urgently demanded for thermal energy storage and thermal management at elevated temperatures in the rapidly developing energy and information industries. Here, we report a novel class of Ti-Zr-Hf-Ni-Cu high-entropy alloys showing high thermal-energy-storage performance at elevated temperatures, which are a robust candidate for high-temperature SS-PCMs. Notably, the figure-of-merit values of these Ti-Zr-Hf-Ni-Cu SS-PCMs are an order of magnitude higher than that of traditional SS-PCMs, due to their much higher thermal conductivity and satisfactory volumetric energy storage capacity as compared to traditional SS-PCMs. Furthermore, the phase transition temperatures of these SS-PCMs can be easily and precisely tuned by composition change, in a wide high-temperature range of 300–470 °C. These high figure-of-merit SS-PCMs with high thermal conductivity have extremely promising prospects for advanced thermal energy storage and compact high-power-density electronic cooling applications. This work opens a new field for exploring high-entropy alloys as solid-solid thermal-energy-storage phase change materials.

Effects of selenium incorporation on the performance of polythiophene based organic electrochemical transistors

This study highlights that an appropriate selenium content should be evaluated to balance the trade-off between charge transfer and volumetric capacitance, paving the way for the optimal product of electronic mobility and volumetric charge storage.

Optimal Energy Storage System Selection: A Decision Support Framework

This study enhances the domain of optimum energy storage system selection by offering a complete decision support framework that incorporates technical, economic, and environmental factors. The technical investigation examines energy and power density measurements, which demonstrate the exceptional volumetric energy storage capacities of lithium-ion batteries at 250 Wh/L. This highlights their appropriateness for applications that prioritize compactness. Lead-acid batteries are a cost-effective option that have a lower energy density of 80 Wh/L. This makes them particularly advantageous in situations where volume limitations are not as important. Flow batteries and supercapacitors are positioned in the middle, with flow batteries offering a well-balanced profile of energy and power density, while supercapacitors excel in applications that need fast charging and discharging. An in-depth evaluation of the startup costs and ongoing expenditures is conducted to thoroughly assess the economic feasibility of adopting an energy storage system. Although lithium-ion batteries have a higher upfront cost of $100,000, they demonstrate a well-balanced economic profile by offering a significant 66% decrease in operating expenditures compared to lead-acid batteries. Lead-acid batteries, which have an initial price tag of $60,000, demonstrate cost-effectiveness but result in higher ongoing costs. Flow batteries and supercapacitors are positioned as premium alternatives, with respective beginning prices of $150,000 and $200,000. Environmental sustainability is a fundamental factor that is assessed via life cycle analysis. Lithiumion batteries, while very efficient, give rise to problems over resource depletion and environmental damage linked to mining activities. Lead-acid batteries, due to their recyclability, provide a more ecologically sound alternative. Flow batteries, which use readily available and environmentally safe components, are very compatible with objectives aimed at promoting sustainability. Supercapacitors, which often use ecologically friendly materials, have potential in reducing negative environmental impacts. MultiCriteria Decision Analysis (MCDA) is used to integrate technical, economic, and environmental assessments. Lithium-ion batteries are considered the most favorable choice due to their exceptional technical performance and economic viability. Lead-acid batteries have a strong market position due to their cost-efficiency and ecofriendliness. Flow batteries and supercapacitors, while they have distinct benefits, are only suitable for certain applications. The stability of the framework is shown by sensitivity analysis, which identifies energy density and beginning costs as crucial factors. Engaging stakeholders helps confirm the framework’s usefulness, ensuring that it can be practically used and remains relevant in guiding well-informed choices in the ever-changing field of energy storage technologies. This study provides vital insights into the discussion on sustainable and efficient energy solutions, presenting a clear plan for decision-makers to navigate the intricacies of selecting energy storage systems.

Nanoconfined carbonization enabling high-density porous carbon for jointly superior gravimetric and volumetric zinc-ion storage

Jointly exceptional gravimetric and volumetric capacitances in porous carbons were achieved through nanoconfined carbonization. Critical roles of 1.2–5.5 nm pores for zinc-ion storage and pores above 5.5 nm for rapid ion diffusion were revealed.

Ultra-high surface area ionic-liquid-derived carbons that meet both gravimetric and volumetric methane storage targets

Activation of N-rich and O-poor carbonised matter from ionic liquids yields ultraporous carbon (4000 m2 g−1 and 3.3 cm3 g−1) with high packing density that translates to methane uptake of up to 0.53 g g−1 and 289 cm3 (STP) cm−3 at 25 °C and 100 bar.

Polymer coating assisted shaping of metal–organic framework particles into pellets with enhanced methane uptake

Compacting well-defined HKUST-1@polyimide core–shell particles instead of pristine HKUST-1 can result in more densely packed pellets with less structural damage, thus leading to enhanced volumetric methane storage.