Magnesium Manganese Oxide Research Articles

Enhanced photoelectrochemical water splitting and photocatalytic decomposition performance of visible light active MgMnO3 perovskite nanostructure

Clean energy production and environmental remediation are imperative for sustainable future. Specially, exploration of multifunctional catalyst, for production of low-cost and eco-friendly hydrogen (H2) fuel as well as efficient decomposition of emerging pollutants are certainly needed. This study investigates magnesium manganese oxide (MgMnO3), a perovskite oxide, synthesized by simple citrate sol–gel technique, and its structural, morphological, optical, and photoelectrochemical properties were analyzed for the photodegradation of ciprofloxacin (CIP) antibiotic, methylene blue (MB) dye, and photoelectrochemical (PEC) water splitting. The cubic spinel crystal structure of MgMnO3 was confirmed through powder X-ray diffraction (XRD) analysis. FE-SEM images of the MgMnO3 material revealed a cauliflower-like morphology, consisting of an assembly of microspherical grains of varying sizes. UV–Vis spectroscopy exhibited broad absorption in the UV–Visible region, and the Tauc plot estimated a band gap of 1.54 eV. The MgMnO3 catalyst showed 88% and 96% for photodecomposition of CIP (10 mg/L) and MB (10 mg/L), respectively, using 35 mg and 30 mg of catalyst quantity over 90 min. In addition, MgMnO3 photoelectrode showcases superior photoelectrochemical behavior, exhibiting maximal photocurrent density of 13.21 mA cm−2 measured at 1.2 V vs. RHE and achieving a solar-to-hydrogen conversion efficiency of 2.45% compared to MgO and MnO2 photoelectrode. EIS measurements of MgMnO3 show enhanced charge transfer and recombination kinetics. Notably, the MgMnO3 electrode reveals outstanding photoelectrochemical durability, maintaining its stability even after continuous illumination for 9 h. Improved PEC properties could be attributed to wider light absorption, enhanced photo-induced charge-separations, and electron mobility. Thus, present study established an efficient and enduring multifunctional catalyst, catering photocatalytic degradation and PEC H2 generation.

Synthesis, characterization, and hydrogen storage capacity of MgMn2O4 spinel nanostructures

Pure MgMn2O4 spinel nanostructures were synthesized by the sol-gel method using stearic acid as a reducing and complexing agent. Structural characterization performed by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) with energy dispersive spectrometry (EDS) mapping, Diffuse reflectance spectroscopy (DRS), Vibrating sample magnetometer (VSM) and surface area analyses (Brauner–Emmett–Teller). In this work, the hydrogen storage capacity of MgMn2O4 nanostructures was studied by the chronopotentiometry (CP) technique for the first time. The discharge capacity of the Magnesium manganese oxide in 1 mA current and after five cycles achieved 2000 mAh/g. Therefore, MgMn2O4 spinel nanostructures could be suitable materials for energy storage applications.

Experimental Performance of a Nonlinear Control Strategy to Regulate Temperature of a High-Temperature Solar Reactor

Abstract Despite the significant potential of solar thermochemical process technology for storing solar energy as solid-state solar fuel, several challenges have made its industrial application difficult. It is important to note that solar energy has a transient nature that causes instability and reduces process efficiency. Therefore, it is crucial to implement a robust control system to regulate the process temperature and tackle the shortage of incoming solar energy during cloudy weather. In our previous works, different model-based control strategies were developed namely a proportional integral derivative controller (PID) with gain scheduling and adaptive model predictive control (MPC). These methods were tested numerically to regulate the temperature inside a high-temperature tubular solar reactor. In this work, the proposed control strategies were experimentally tested under various operation conditions. The controllers were challenged to track different setpoints (500 °C, 1000 °C, and 1450 °C) with different amounts of gas/particle flowrates. Additionally, the flow controller was tested to regulate the reactor temperature under a cloudy weather scenario. The ultimate goal was to produce 5 kg of reduced solar fuel magnesium manganese oxide (MgMn2O4) successfully, and the controllers were able to track the required process temperature and reject disturbances despite the system's strong nonlinearity. The experimental results showed a maximum error in the temperature setpoint of less than 0.5% (6 °C), and the MPC controller demonstrated superior performance in reducing the control effort and rejecting disturbances.

A reduced-order modeling of a tubular solar reactor for long duration thermochemical energy storage

The storage of solar energy in a solid form, referred to as a “solar fuel”, can be achieved through a process known as endothermic solar thermochemistry. This process transforms the absorbed solar energy into a stable and retrievable form that can be stored for extended periods of time. This paper presents a low–order heat transfer model of a counter–current tubular falling bed reactor designed to produce thermally reduced magnesium manganese oxide pellets for long duration thermochemical energy storage. The energy required for the endothermic reduction was supplied by concentrated solar energy or renewable electricity via indirect heating of the gas and solid reactants flowing in a ceramic tube. The counter-current gas flow enhances the mixing of the solid particles with the heat recuperation zone, allowing the gas and particles to enter and exit the tubular reactor close to room temperature. The reactor was vertically oriented and was heated circumferentially by an adjustable level heat flux along a finite segment of its length. The temperature distribution of the reactor in response to transient changes along the tube was modeled by considering conduction, convection, and radiation heat transfer. Governing equations for the heat transfer model were solved by discretizing the reactor tube into a finite number of control volumes and using an energy balance for the heat exchange between the reactor wall, gas, and particles within the control volume. The energy absorbed during this endothermic reaction was modeled numerically by fitting the data of the chemical conversion rate with the corresponding temperature of particles in the heating zone. The numerical model has been experimentally validated using a reactor prototype made of a 121.92 cm alumina tube heated by a 7 kW electric tube–furnace. The alumina tube receives magnesium manganese oxide pellets of 3.66 ± 0.516 mm in diameter from the top, and a counter–current gas flow from the bottom. The reactor wall temperature was monitored by six thermocouples installed along the reactor tube length. The experimental procedure was numerically simulated, and the temperature variation along the reactor tube was compared with a matrix of experimental runs for a range of particles mass flowrates (0.75–1.25 g/s) and corresponding gas flowrates (36–65 SLPM). The reactor system was heated gradually from room temperature to a steady state temperature of 1673 K, and then cooled down to room temperature. The heating and cooling processes were simulated, and the numerical and experimental results were compared throughout processes. The numerical model showed similar trends to the experimental results, with an error of 0.69 to 7.9 % for the particle inlet and 0.7 to 7.9 % for the gas inlet during steady-state operation. The proposed numerical model can be implemented as a simplified physical model to design a feedback control system to regulate reactor temperature.

Thermodynamic and Structural Effects of Fe Doping in Magnesium Manganese Oxides for Thermochemical Energy Storage

Thermochemical energy storage potentially provides a cost-effective means of directly storing thermal energy that can be converted to electricity to satisfy demand, and MgxMn1–xO4 has been identified as a stable, high-energy density storage material. Here, we investigate the effects of doping small quantities of Fe into the MgMnOx system as a means to increase the reduction extent and storage energy via an increase in entropic contributions and the higher reduction energy of Fe as compared to that of Mn. We find that small additions of Fe (Mg0.5Mn0.4975Fe0.0025)3O4 (Fe = 0.5%) show increased reduction extent, but larger quantities of Fe (Mg0.5Mn0.485Fe0.015)3O4 and (Mg0.5Mn0.475Fe0.025)3O4 (Fe = 3 and 5%) show decreased reduction capability. This finding suggests that small quantities of Fe as a substituent change the thermodynamics of the material increasing the reduction extent through entropic effects, but at larger quantities of Fe, the higher reduction energy of Fe lowers the overall reduction capability. Additionally, the reduction occurs through the formation of intermediate phases which co-occur with the oxidized spinel and reduced halite phases; the presence of Fe significantly narrows the window where the intermediate phase is present, narrowing the T range where most of the reduction occurs. This narrowing thus potentially stabilizes the outlet temperature of a thermochemical energy storage system as compared to undoped (MgxMn1–x)3O4.

Chemical equilibrium of the magnesium manganese oxide redox system for thermochemical energy storage

The magnesium manganese oxide redox system shows great promise for use in grid-scale, long duration thermochemical storage. We measured the equilibrium extent of oxidation, y=yeq, of the MgMnO2+y system, in a series of thermogravimetric relaxation experiments. Temperatures and oxygen partial pressure ranges are 1000–1500 °C and 0.01–0.9 atm respectively. The equilibrium oxygen stoichiometry ranges from MgMnO2.109 at 1500 °C and pO2=0.01 atm to MgMnO2.672 at 1000 °C and pO2=0.9 atm. The equilibrium extent of oxidation, as a function of temperature and oxygen partial pressure, was matched with two semi-heuristic Gibbs-free energy based models that combine theoretical considerations with experimental observations to extract a functional relation between the chemical potential of oxygen and yeq. We obtained enthalpies of reaction of -335.3±31.2 kJ/molO2 and -340.8±18.0 kJ/molO2 respectively. The entropy of reaction is -184.8±20.3 J/molO2/K.

Flexible structural transformation and high oxygen-transfer capacity of mixed inverse spinel magnesium manganese oxides during methane chemical looping combustion

This study aimed at elucidating the active species in spinel crystals composed of Mg and Mn calcined at various temperatures and to determine the relationships among their crystal structure, oxidation state, and oxygen-transport capacity. The particles were obtained as mixed inverse spinel [Mg1.5-xMn2+y]td[MgxMn(3+ or 4+)1.5-y]ohO4 polyhedra, which were strongly distorted owing to the Jahn–Teller effect. Their structural transformation to Mg0.43Mn0.57O occurred via reduction with methane (CH4) and the significant shrinkage of the M–O bonds caused the migration of cationic metals into the inner crystal. This structural transformation created maze-like large spaces (50–75 nm); however, during oxidation, oxygen species re-filled these spaces and the structure completely attained its original mixed inverse spinel [Mg0.73Mn2+0.27]td[Mg0.77Mn(3+,4+)1.23]ohO4 polyhedral shape. The oxygen-transfer capacity of MMO-1100, calcined at 1100 °C, was improved by 8.10% in the CH4-CO2/air redox system, and the abundance ratio of [(Mn3+) + (Mn4+)]oh/(Mn2+)td, corresponding to the oxygen-transferring redox species, was 4.5. Upon 1000 cyclic voltammetry cycles, the current density related to the oxygen-transfer capacity of the MMO-1100 particles was unchanged, suggesting that the oxygen-transfer capacity remained stable even after the 1000th redox cycle.

Porous Spinel Magnesium Manganese Oxide/Multiwalled Carbon Nanotubes Composite Synthesized by Electrochemical Conversion as High-Performance Cathode for Aqueous Magnesium Ion Battery

Aqueous magnesium ion batteries (AMIBs) have attracted great interest due to the low manufacture cost and eco-friendliness, but the lack of suitable cathodes with good electrochemical performance obstructs their development. Here, a composite of spinel magnesium manganese oxide (MgMn2O4) and multiwalled carbon nanotubes (MWCNTs) with a porous structure is synthesized by electrochemical conversion method and used as the cathode for the AMIB, which improves the inherent low conductivity for MgMn2O4 and enhanced its specific capacity. The electrochemical conversion method helps preserve the surface integrity and structure stability of the electrode, and the MWCNTs network provides the pathway of Mg ion migration among the MgMn2O4 particles. The obtained MgMn2O4/MWCNTs displays a discharge capacity of 322.3 mAh g−1 at 50 mA g−1, and the capacity retention is 81.8% after 2000 iterations at 1000 mA g−1. Further, the MgMn2O4/MWCNTs//VO2 system is assembled, which displays a capacity retention rate of near 100%. The electrochemical mechanism of Mg ion insertion/extraction is investigated though the ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. This paper extends synthesis method of the high performance cathode material for AIMB system.

A continuum model for heat and mass transfer in moving-bed reactors for thermochemical energy storage

In this work, a continuum heat and mass transfer model coupling transport phenomena and high-temperature thermochemical reactions is developed for stationary packed-bed and counter-flow moving-bed reactors. After presenting the general modeling framework, we focus on the 2D axisymmetric version of the model for which validation is conducted with experimental results for a packed-bed reactor in the literature for manganese-iron oxide reduction/oxidation and an in-house counter-flow moving-bed reactor for magnesium-manganese oxide reduction up to 1450 °C. Transient simulation results including the local distributions of gas/solid temperatures, oxygen concentration and the extent of reaction, as well as the various energy flow components and energy conversion efficiencies are reported. The results based on the 2D axisymmetric model are also compared with those obtained from a previous 1D model. The comparison shows that capturing the radial variation is critical in reactor modeling and the 2D results demonstrate improved agreement with experiments. Specifically, large temperature variations along the radial direction are observed especially in the reaction zone; this non-uniform radial temperature distribution has a significant effect on the chemical reaction extent due to its strong dependence on temperature; and the overall oxygen concentration at the reactor exit and the predicted system efficiency are slightly lower in the 2D model compared to the 1D model. The present heat and mass transfer model can provide valuable insights into reactor design, scale-up, and operating conditions selection to maximize system energy storage efficiency.

Effect of doping nickel/cobalt ions on the structural and photocatalytic efficiency of magnesium manganese oxide materials for the environmental applications

Effect of doping nickel/cobalt ions on the structural and photocatalytic efficiency of magnesium manganese oxide materials for the environmental applications

Manganese containing oxides catalytic ozonation in aqueous solution: Catalytic mechanism on acid sites

• Protonation of hydroxyl groups on acid sites is a necessary condition for electron transfer reaction. • Solution pH is a significant variable in the linear sweep voltammetry test. • Electron transfer ability of acid sites in MgMn x O y is positively related to Mg content. Transition metal oxides and transition metal containing oxides have been extensively researched in heterogeneous catalytic ozonation for water treatment. However, catalytic mechanism for typical transition metal oxide – manganese oxide (MnO 2 ) in catalytic ozonation is still ambiguous. Herein, MnO 2 and magnesium manganese oxides (MgMn x O y ) with different molar ratios of Mg to Mn were analysed by linear sweep voltammetry (LSV) test to explore a necessary condition for electron transfer reaction between ozone and acid sites of the catalysts in aqueous solution. And their catalytic performances were investigated in ozonation of acetic acid aqueous solution at a neutral pH. It is found that electron transfer reaction occurs in manganese containing oxides catalytic ozonation when ozone is adsorbed on protonated surface hydroxyl groups of acid sites (Mn 2+ /Mn 3+ in the lattice). But ozone that is absorbed on protonated hydroxyl groups of Mg 2+ in the lattice cannot react with acid sites to generate reactive oxygen species in MgMn x O y catalytic ozonation. Protonation of hydroxyl groups on acid sites can be achieved by enhancement in point of zero charge (pH PZC ) of the catalysts or decrease in initial pH of aqueous solution. Protonation ability of hydroxyl groups on acid sites and electron transfer ability of acid sites are positively related to Mg content in MgMn x O y . MgMn x O y with 2:1 molar ratio of Mg to Mn (Mg 2 MnO y ) exhibits the highest catalytic activity and good stability in ozonation of acetic acid. On basis of catalytic mechanism on acid sites of manganese containing oxides, modification and application of manganese containing oxides would be further developed in heterogeneous catalytic ozonation for water treatment.

A Simplified Numerical Approach to Characterize the Thermal Response of a Moving Bed Solar Reactor

Abstract Concentrated solar thermochemical storage in the form of a zero-emission fuel is a promising option to produce long-duration energy storage. Solar fuel is produced using a cavity reactor that captures concentrated solar radiation from a solar field of heliostats. In this paper, heat transfer model of a tubular plug-flow reactor designed and manufactured for a solar fuel production is presented. Experimental data collected from a fixed bed tubular reactor testing are used for model comparison. The system consists of an externally heated tube with counter-current flowing gas and moving solid particles as the heated media. The proposed model simulates the dynamic behavior of temperature profiles of the tube wall, gas, and particles under various gas flowrates and residence times. The heat transfer between gas–wall, solid particle–wall, and gas–solid particle is numerically studied. The model results are compared with the results of experiments done using a 4 kW furnace with a 150 mm heating zone surrounding a horizontal alumina tube (reactor) with 50.8 mm outer diameter and thickness of 3.175 mm. Solid fixed particles of magnesium manganese oxide (MgMn2O4) with the size of 1 mm are packed within the length of 250 mm at the center of the tube length. Simulation results are assessed with respect to fixed bed experimental data for four different gas flowrates, namely, 5, 10, 15, and 20 standard liters per minute of air, and furnace temperatures in the range of 200–1200 °C. The simulation results showed good agreement with maximum steady state error that is less than 6% of those obtained from the experiments for all runs. The proposed model can be implemented as a low-order physical model for the control of temperature inside plug-flow reactors for thermochemical energy storage applications.

Spinel-MgMn2O4 nanofibers: An attractive material for high performance aqueous symmetric supercapacitor

It is a known fact that morphology greatly influences the energy storage performance of a material. In this work, spinel magnesium manganese oxide (MgMn2O4) having nanofibric morphology has successfully been prepared for the first time using a versatile and cost-effective electrospinning technique. The morphology and the pore size are altered and optimized by varying the process parameters in the electrospinning process, and their corresponding effect on supercapacitive properties are also studied thoroughly. The aligned, mesoporous, and high aspect ratio of spinel-MgMn2O4 nanofiber exhibit the specific capacitance of ∼345 Fg−1 at 1 Ag−1 and 250 Fg−1 at 4 Ag−1 as well as demonstrate an outstanding rate capability and good capacity retention (∼90%) after 10,000 successive cycles at 4 Ag−1 in a three-electrode configuration. The improved energy storage performance of MgMn2O4 active material on graphite substrate is ascribed to its nanofibric morphology with interconnected particles having pores/voids in between, which impart a higher diffusion coefficient (D= 3.226 × 10−10 cm2s−1) and a small relaxation time constant (τ = 0.1 s). The quantitative capacitive contribution generating from EDLC and/or the surface pseudocapacitance reactions and the contribution from diffusion-controlled redox reactions to the total current have also been determined. The assembled symmetric all-solid-state supercapacitor (ASSSC) shows the high specific energy of ∼30 W h kg−1 at the specific power of ∼510 W kg−1 in the potential window of 0.0 V to 2 V with PVA-H2SO4 gel electrolyte. This performance is superior to that exhibited by many ASSSC reported recently. Two ASSSC devices connected in series can light up parallelly connected 55 red LEDs for more than 3 min, indicating practical applicability of our designed symmetric supercapacitor in electronics appliances. The outstanding electrochemical performance of the MgMn2O4 nanofiber reveals its potential to be a promising electrode material for supercapacitors.

Water-in-salt electrolyte enabled active carbon||Mg-OMS-1 capacitor-batteries with high voltage and wide operating temperature

Aqueous lithium-ion batteries possess great potential due to their low cost and high safety. However, the narrow voltage window of the electrolyte significantly hinders their energy density and electrode materials selection. Herein, sheet-like todorokite-type magnesium manganese oxide molecular sieve (Mg-OMS-1) is synthesized and applied as cathode materials for aqueous lithium-ion batteries with water-in-salt electrolyte. The water-in-salt lithium difluorosulfonimide (LiTFSI) electrolyte enlarges the working window of the device and enhance the capacity of the Mg-OMS-1. Mg-OMS-1 displays a high capacity, remarkable rate ability, and stable cycling performance. Moreover, the water-in-salt electrolyte promises the device to work in the temperature range of 0–70 ℃. In addition, an active carbon (AC)|15 mol kg−1 LiTFSI|Mg-OMS-1 capacitor battery is designed and assembled. The device presents a capable electrochemical performance, demonstrating the potential application of the water-in-salt electrolyte and Mg-OMS-1 for the aqueous batteries with high energy density and wide operating temperature.

Ultra-High Temperature Thermal Conductivity Measurements of a Reactive Magnesium Manganese Oxide Porous Bed Using a Transient Hot Wire Method

Abstract Pelletized magnesium manganese oxide shows promise for high temperature thermochemical energy storage. It can be thermally reduced in the temperature range between 1250 °C and 1500 °C and re-oxidized with air at typical gas-turbine inlet pressures (1–25 bar) in the temperature range between 600 °C and 1500 °C. The combined thermal and chemical volumetric energy density is approximately 2300 MJ/m3. The rate at which a thermochemical storage module can be charged is limited by heat transfer inside the solid packed bed. Hence, the effective thermal conductivity of packed beds of magnesium-manganese oxide pellets is a crucial parameter for engineering Mg-Mn-O redox storage devices. We have measured the effective thermal conductivity of a packed bed of 3.66 ± 0.516 mm sized magnesium manganese oxide (Mn to Mg molar ratio of 1:1) pellets in the temperature range of 300–1400 °C. Since the material is electrically conductive at temperatures above 600 °C, the sheathed transient hot wire method is used for measurements. Raw data is analyzed using the Blackwell solution to extract the bed thermal conductivity. The effective thermal conductivity standard deviation is less than 10% for a minimum of three repeat measurements at each temperature. Experimental results show an increase in the effective thermal conductivity with temperature from 0.50 W/m °C around 300 °C to 1.81 W/m °C close to 1400 °C. We propose a dual porosity model to express the effective thermal conductivity as a function of temperature. This model also considers the effect of radiation within the bed, as this is the dominant heat transfer mode at high temperatures. The proposed model accounts for microscale pellet porosity, macroscale bed porosity, pellet size, solid thermal conductivity (phonon transport), and radiation (photon transport). The coefficient of determination between the proposed model and the experimental results is greater than 0.90.

To decarbonize industry, we must decarbonize heat

Summary Industry is often termed “hard to decarbonize” because a vast, inhomogeneous array of processes comprise the sector. But developing new, decarbonized process heating technologies represents a single, broadly applicable pathway to eliminating a large portion of sectoral emissions—and approximately one-fifth of global CO2 emissions, overall. We begin this perspective with a brief review of the demand for and cost of industrial heat. Then, we highlight key challenges and R&D needs in developing zero-carbon industrial heating technologies. Technologies in four pathways are discussed: (1) zero-carbon fuels, (2) zero-carbon heat sources, (3) electrification of heat, and (4) better heat management. Finally, we identify cross-cutting challenges to the development and adoption of zero-carbon industrial heat technologies, the solution to any of which would constitute a significant breakthrough on the path to industrial decarbonization.

Synthesis of Zero Carbon Solid-State Fuel for Long Duration Energy Storage

This work presents a unique thermochemical process for synthesizing magnesium manganese oxide-based zero carbon solid-state fuel, which can be used for long duration energy storage. High temperature (1450°C) heating of the processing furnace can be driven by either renewable electricity or concentrated solar power. The very simple fuel synthesis concept is based on a tubular falling bed reactor with countercurrent oxygen-depleted gas flow for complete heat recuperation. A sophisticated control strategy using pulsed width modulated gas flow and an L-valve maintains consistent magnesium manganese oxide (Mg-Mn-O) particle flow up to 1450°C. The measured extent of the thermal reduction reaction after cooling the Mg-Mn-O particles is more than 90% of the fully reduced state at equilibrium. The thermal to chemical efficiency (ratio of chemical energy stored to thermal energy input) and overall system efficiency are above 96% and 28%, respectively. Both, the solid particle reactor flow at the extreme temperature of 1450°C and the system efficiency of 28% are the highest reported for thermochemical fuels in the literature to date.

Ni-Doped magnesium manganese oxide as a cathode and its application in aqueous magnesium-ion batteries with high rate performance

Aqueous magnesium-ion batteries feature good safety and high energy density and represent promising energy storage systems.

Calorimetric method for determining the thermochemical energy storage capacities of redox metal oxides

Transition metal oxide compounds have been demonstrated to be promising candidates for thermochemical processes, particularly energy storage. A calorimetric method for measuring enthalpy of these materials is developed in this work. A combination of drop calorimetry and acid-solution calorimetry is used to measure the total enthalpy and standard enthalpy of formation of these materials for compounds that form at high temperatures (≥ 1000 °C) after undergoing thermal reduction. These measurements are used to compute the energy storage potential of these materials for a specified set of redox cycle operating temperatures. The construction and calibration of appropriate calorimeter devices are described. A novel approach to performing acid-solution calorimetry is introduced by including tin (II) chloride as a reducing agent for enhancing the dissolution rate of these compounds sufficiently so that acid-solution calorimetry can be implemented accurately. The general procedure is presented and applied to three variations of magnesium-manganese oxide materials for a redox cycle operating under an oxygen partial pressure of 0.2 atm between 1000 and 1500 °C. Using this method, the total energies stored by magnesium-manganese oxides of molar ratios Mn/Mg of 2/1, 1/1, and 2/3 were found to be 924 ± 56.7, 1029 ± 57.0, and 1070 ± 64.2 kJ kg−1, respectively.

Magnesium-manganese oxides for high temperature thermochemical energy storage

Abstract The reactive stability and energy density of magnesium-manganese oxides for high-temperature thermochemical energy storage have been investigated. Three variations of material with molar ratios of manganese to magnesium of 2/3, 1/1, and 2/1 were prepared using solid-state reaction synthesis and were tested for thermochemical reactive stability and energy storage capability. Results show that oxygen released and absorbed (standard cm3 g−1) by the materials remains unchanged over 20 cycles when cycled between 1200 and 1500 °C under an oxygen partial pressure (PO2) of 0.2 atm, indicating excellent reactive stability at high temperatures. Additional confirmation of reactive stability was obtained through testing over 10 energy storage cycles between 1000 and 1500 °C. The energy density of the material between 1000 and 1500 °C was determined through a combination of acid-solution calorimetry and drop calorimetry. The total volumetric energy densities (chemical, phase change, and sensible) obtained for samples of Mn/Mg of 2/3, 1/1, and 2/1 cycled between 1000 and 1500 °C are 1596, 1626 and 1654 MJ m-3, respectively.