Calcium Manganese Oxide Research Articles

Quantum Chemical Understanding of the O2 Release Process from Nature's Water Splitting Cofactor.

Natural photosynthesis plays a vital role in the supply of energy and oxygen necessary for the survival of biological organisms. The current leading proposal of the O-O bond formation in photosystem II suggests the coupling between the central μ-oxo (O5) and the additional oxygenic ligand (Ox) of the manganese-calcium oxide cofactor. However, the subsequent process through which molecular dioxygen is formed and released remains elusive. In this report, quantum chemical calculations reveal that the O2 release process is initiated by the cleavage of the Mn-O5 bond, without a preliminary conformational change of the peroxide [O5-Ox]2- group. Subsequently, the [O5-Ox] moiety is converted from the superoxide to the weakly bound quasi-O2 where the Mn-Ox bond is cleaved, and after a twist of the quasi-O2 unit, the free O2 is ultimately released. Alternative pathways display significantly slower kinetics, due to the lower structural stabilities of the rate-limiting transition states. The cause of the difference is associated with the Jahn-Teller axial orientation and the local ring strain within the Mn cluster. These findings contribute to unravelling the intricate mechanism involved in an important step of photosynthetic oxygen evolution for a deeper understanding of nature's water oxidation catalysis.

Iron Doped Calcium Manganese Oxide Cathode Materials for Aqueous Zinc Secondary Batteries

In recent years, zinc secondary batteries, which utilize a water-based electrolyte and offer high safety, have attracted attention as post-lithium-ion batteries. Zn has a high specific capacity (820 mAh/g) and a redox potential of -0.76 V (versus the standard hydrogen electrode) as a cathode. Furthermore, combining it with new cathode materials could significantly enhance performance. In particular, layered compounds containing manganese are inexpensive, widely used in industry, and considered promising candidates. This study synthesized calcium manganese oxide with a layered structure and investigated its potential as a cathode material for zinc secondary batteries. It is already known that Ca₂Mn₃O₈ has a layered structure and can be synthesized with a Mn/Ca atomic ratio ranging from 1.5 to 2.5. This research examined the effect of adding Fe and Al to this calcium manganese oxide on battery performance. When Fe was added, the battery capacity increased by 20%, reaching 177 mAh/g compared to the sample without Fe. This increase is believed to result from an increased interlayer distance, promoting the incorporation of structural water and enhancing ion conversion reactions during charge and discharge. However, adding Al was found to have no beneficial effect on battery performance.

Advancements in AEM Anode Catalysts: Calcium Manganese Oxide as a High Performing Bioinspired Electrocatalyst for Oxygen Evolution Reaction Applications

Anion exchange membrane water electrolyzers (AEMWE) have garnered significant attention over the past decade among researchers worldwide due to their economical electrolyzer components, including bipolar plates, flow fields, electrocatalysts, and membrane materials. They represent a cost-effective alternative to high-performing yet expensive proton exchange membrane water electrolyzers (PEMWE). The allure of AEMWE lies in their affordable cell hardware and components, albeit at the expense of somewhat reduced durability and overall performance compared to PEMWE systems. While AEMWE anodes may not match the activity levels of noble metal catalysts, their abundance and cost-effectiveness render them compelling options. Interest in this domain revolves around utilizing earth-abundant metal oxides, binary and ternary metal oxides featuring transition metals like iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), and other readily available materials boasting various oxidation states and coordination configurations. Among these, manganese-based oxides such as MnO2 and its derivatives have been extensively explored for their oxygen evolution reaction (OER) activity. Intriguingly, the complexation of manganese with calcium (Ca) to yield CaMnOx electrodes mirrors the active site complexes found in natural metalloenzymes involved in facilitating OER processes, such as those seen in photosynthetic enzymes like photosystem II. These bioinspired electrocatalysts, mimicking nature's design, hold immense promise for integration into AEMWE setups as cost-effective, durable, and efficient OER catalysts [1], [2], [3], [4]. In this study, we investigate CaxMnyOxz electrocatalysts with varying atomic ratios through comprehensive performance and durability evaluations via Rotating Disk Electrode (RDE), Gas Diffusion Electrode (GDE) half-cell, and Membrane Electrode Assembly (MEA) testing. In-house MEA stability testing out to 25 hours at 1 A/cm2 demonstrated steady state voltages of 1.87 V and 1.90 V for CaMn3Ox and CaMn4Ox, respectively. Additionally, polarization curves at 0 h and 20 h reveal an improvement in performance from 1.9 V at 1 A/cm2 down to 1.8 A/cm2 for both CaxMnyOxz catalysts, suggesting an activation of the CaxMnyOxz with use. Our findings reveal that these CaMnOx-based anodes perform comparably to benchmarked commercially available NiFeOx counterparts for AEMWE applications, underscoring their potential as viable alternatives in the pursuit of sustainable hydrogen production.

Spinel-type calcium manganese oxide adorned on g-CN composite: A highly proficient electrocatalyst for oxygen evolution reaction (OER)

Spinel-type calcium manganese oxide adorned on g-CN composite: A highly proficient electrocatalyst for oxygen evolution reaction (OER)

Influence of carbon template and ultrasound irradiation on combustion design of nanostructured calcium manganese oxides used in biodiesel production

Influence of carbon template and ultrasound irradiation on combustion design of nanostructured calcium manganese oxides used in biodiesel production

Perfectly dense ceramics of highly pure calcium manganese oxide

Perfectly dense ceramics of highly pure calcium manganese oxide

Crafting advanced supercapacitor electrodes with calcium manganese oxide in synergy with rGO and MWCNTs

Crafting advanced supercapacitor electrodes with calcium manganese oxide in synergy with rGO and MWCNTs

Exploring Calcium Manganese Oxide as a Promising Cathode Material for Calcium-Ion Batteries.

The dependence on lithium for the energy needs of the world, coupled with its scarcity, has prompted the exploration of postlithium alternatives. Calcium-ion batteries are one such possible alternative owing to their high energy density, similar reduction potential, and naturally higher abundance. A critical gap in calcium-ion batteries is the lack of suitable cathodes for intercalating calcium at high voltages and capacities while also maintaining structural stability. Transition metal oxide postspinels have been identified as having crystal structures that can provide low migration barriers, high voltages, and facile transport pathways for calcium ions and thus can serve as cathodes for calcium-ion batteries. However, experimental validation of transition metal oxide postspinel compounds for calcium ion conduction remains unexplored. In this work, calcium manganese oxide (CaMn2O4) in the postspinel phase is explored as an intercalation cathode for calcium-ion batteries. CaMn2O4 is first synthesized via solid-state synthesis, and the phase is verified with X-ray diffraction (XRD). The redox activity of the cathode is investigated with cyclic voltammetry (CV) and galvanostatic (GS) cycling, identifying oxidation potentials at 0.2 and 0.5 V and a broad insertion potential at -1.5 V. CaMn2O4 can cycle at a capacity of 52 mAh/g at a rate of C/33, and calcium cycling is verified with energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) and modeled with density functional theory (DFT) simulations. The results from the investigation concluded that CaMn2O4 is a promising cathode for calcium-ion batteries.

Synthesis of Calcium Manganese Oxide Films Using a Sol–Gel Method and Evaluation of Color and Photocatalytic Properties

Herein, for developing colored photocatalysts, calcium manganese oxide (Ca–Mn–O) film and powder samples are synthesized by a sol–gel method using acetylacetone (acac) or citric acid as a chelating agent, and their color and photocatalytic properties are evaluated. Thin‐film X‐ray diffraction experiments clarify the precipitation of Ca–Mn–O phases, such as Ca3Mn2O7 (Ca/Mn = 1.5) and Ca2MnO4 (Ca/Mn = 2), in the film samples with drop‐cast coating. These films strongly absorb all visible light due to the interband transition between O 2p and Mn 3d orbitals, resulting in dark gray coloration. By testing photocatalytic activities using methylene blue dyes, it is revealed that the film sample (acac, 4‐drops) exhibits photocatalytic activities, which makes Ca–Mn–O films dual functional with photocatalytic functions and coloration.

A facile synthesis of calcium manganese oxide for supercapacitor application

A facile synthesis of calcium manganese oxide for supercapacitor application

Investigation of Transition Metal Oxide Post-Spinels for Calcium-Ion Batteries

The dependence on lithium for rising global energy demand coupled with the scarcity of lithium necessitates the exploration of post-lithium strategies. Calcium-ion batteries are one such post-lithium strategy that can mitigate rising costs owing to calcium’s natural abundancy. A critical gap in this field is the lack of cathodes capable of intercalating calcium at high voltages and capacities while also retaining structural stability. The handful of candidates evaluated thus far have been plagued by low capacities and poor cycling performance due to intercalation–induced phase changes and instability. Transition metal oxide post–spinel–type materials have been identified as potential candidates for reversible Ca–ion storage owing to their crystal structures and high theoretical energy densities. However, experimental validation of these theoretical predictions remains largely unaddressed. In this work, post-spinel Calcium Iron Oxide (CaFe2O4) and Calcium Manganese Oxide (CaMn2O4) are explored as cathodes for calcium-ion batteries. The redox activity of each cathode is investigated using galvanostatic (GS) cycling while their structural stabilities are evaluated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The use of GS in tandem with XRD and SEM provides insights into the evolution of crystal structure with Ca–ion–transport within each cathode. Our results reveal that these post–spinel systems can cycle with a reversible capacity of 56 mAh/g, making them promising cathode candidates for Ca–ion batteries and warrant further investigation.

Enhancing the thermoelectric properties of CaMnO3-δ via optimal substituent selection

Enhancing the thermoelectric properties of CaMnO3-δ via optimal substituent selection

Reversible Structural Isomerization of Nature's Water Oxidation Catalyst Prior to O-O Bond Formation.

Photosynthetic water oxidation is catalyzed by a manganese–calcium oxide cluster, which experiences five “S-states” during a light-driven reaction cycle. The unique “distorted chair”-like geometry of the Mn4CaO5(6) cluster shows structural flexibility that has been frequently proposed to involve “open” and “closed”-cubane forms from the S1 to S3 states. The isomers are interconvertible in the S1 and S2 states, while in the S3 state, the open-cubane structure is observed to dominate inThermosynechococcus elongatus (cyanobacteria) samples. In this work, using density functional theory calculations, we go beyond the S3+Yz state to the S3nYz• → S4+Yz step, and report for the first time that the reversible isomerism, which is suppressed in the S3+Yz state, is fully recovered in the ensuing S3nYz• state due to the proton release from a manganese-bound water ligand. The altered coordination strength of the manganese–ligand facilitates formation of the closed-cubane form, in a dynamic equilibrium with the open-cubane form. This tautomerism immediately preceding dioxygen formation may constitute the rate limiting step for O2 formation, and exert a significant influence on the water oxidation mechanism in photosystem II.

Synthesis of calcium manganese oxide with different constructions as potential materials for electrochemical hydrogen storage

Synthesis of calcium manganese oxide with different constructions as potential materials for electrochemical hydrogen storage

Synthesis, characterization and thermoelectric properties of Ca substituted nanostructured SrMnO3 by sol-gel hydrothermal method

Synthesis, characterization and thermoelectric properties of Ca substituted nanostructured SrMnO3 by sol-gel hydrothermal method

Dual enzymes-mimic activity of nanolayered manganese-calcium oxide for fluorometric determination of metformin

Dual enzymes-mimic activity of nanolayered manganese-calcium oxide for fluorometric determination of metformin

Thickness dependent electrical resistivity modulation in tensile-strained epitaxial thin films of calcium manganese oxide

We report our studies of the thickness dependence of electrical resistivity and lattice constants in strained epitaxial thin films of calcium manganese oxide. Our results indicate the potential of bi-axial lattice mismatch strain as a handle for modulating electrical resistivity. We observe thickness dependence of lattice constants consistent with what is expected for strain relaxation for films thicker than 400 Å. At lower thickness values, anomalies are observed suggestive of reduced oxygen stoichiometry. We observe a remarkable decrease in electrical resistivity with decreasing film thickness. The resistivity of our thinnest films (5–7 nm) is about three orders of magnitude lower than the resistivity of bulk CaMnO3. Resistivity increases as the film thickness increases, along with the progression of strain relaxation. It is noteworthy that the thickness dependence of resistivity we observe in CMO thin films is the opposite of what has been reported for their hole-doped rare earth manganite counterpart La0.67Ca0.33MnO3 (LCMO), where tensile lattice mismatch strain suppresses metallicity, leading to the increase in resistivity with film thickness. We believe that the enhanced conductivity in our thinnest films is related to the possible oxygen deficiency promoted by tensile strain. Recent x-ray absorption measurements have revealed reduced oxygen content and associated changes in Mn valence states in tensile-strained CMO thin films, as also predicted by density functional theory calculations. This report is the first observation of electrical transport behavior possibly indicative of strain–oxygen stoichiometry coupling.

Sol-gel synthesis and photocatalytic activity of biomimetic calcium manganese oxide catalysts

The water contaminations by dye residues are increasingly becoming serious concerns worldwide due to dye toxicity and persistent characteristics. Manganese oxide-based catalysts having similar structures with manganese compounds found in nature (biomimetic) have been considered as a very promising and effective photocatalyst for the degradation of organic pollutions in wastewater. This paper focuses on the synthesis of calcium manganese oxide catalysts from the octahedral layered birnessite-type manganese oxide and calcium carbonate via sol-gel method with citric acid as the complexing agent. The as-synthesized oxide was then tested as a photocatalyst for the degradation of methylene blue (MB) dye. The calcium manganese oxides prepared by the two different mole ratios of CaCO3/MnO2 resulted in the similar crystallinity and crystal phases but difference in the crystal sizes. The photocatalytic activities of the prepared calcium manganese oxides for the degradation of methylene blue are compared to that of the calcium manganese oxide prepared from tunnel cryptomelane-type manganese oxide. Both the calcium manganese oxides prepared from the different manganese oxide phases show the remarkable performance for the photocatalytic degradation of methylene blue after 10 minutes of reaction times. The birnessite-prepared calcium manganese oxide displays slightly higher photocatalytic performance than cryptomelane-prepared calcium manganese oxide.

Functions of MnOx in NaCl Aqueous Solution for Artificial Photosynthesis.

SummaryPhotoelectrochemical water splitting has been intensively investigated as artificial photosynthesis technology to convert solar energy into chemical energy. The use of seawater and salted water has advantages for minimum environmental burden; however, the oxidation of Cl− ion to hypochlorous acid (HClO), which has toxicity and heavy corrosiveness, should occur at the anode, along with the oxygen evolution. Here, O2 and HClO production in aqueous solution containing Cl− on photoanodes modified with various metal oxides was investigated. The modification of MnOx resulted in the promotion of the O2 evolution reaction (OER) specifically without HClO production over a wide range of conditions. The results will contribute not only to the practical application of artificial photosynthesis using salted water but also to the elucidation of substantial function of manganese as the element for OER center in natural photosynthesis.

A study of calcium ion intercalation in perovskite calcium manganese oxide

A study of calcium ion intercalation in perovskite calcium manganese oxide