Spinel MnCo2O4 Research Articles

Synthesis of urchin-like MnCo2O4 nanospheres as electrode material for supercapacitors

The morphology of MnCo2O4 has a significant effect on the electrochemical performance. In this paper, urchin-like MnCo2O4 nanospheres was successfully fabricated by a simple hydrothermal process and post-annealing treatment. The effects of addition of surfactant (Hexadecy ltrimethyl ammonium bromide) on the crystal structure, surface morphology and electrochemical performance of MnCo2O4 have been investigated. The results show that all the synthesized manganese cobalt oxides are composed of cubic spinel MnCo2O4. The addition of surfactant leads to the change of the morphology of MnCo2O4 from nanoarray to urchin-like nanospheres and increases the specific surface area, which is beneficial to improve the electrochemical performance of the MnCo2O4 electrode. The electrochemical test reveals that the urchin-like MnCo2O4 nanospheres delivered a high specific capacity of 2019 F/g at a 1 A/g and 1144 F/g at 5 A/g, respectively. The specific capacity of MnCo2O4 electrode reaches 512 F/g at 10 A/g and retains 96 % of the initial capacity after 2000 cycles at 10 A/g, which maintains an extraordinary cycling performance. In addition, an asymmetric supercapacitor (MnCo2O4//AC) with urchin-like MnCo2O4 nanospheres as a cathode and activated carbon (AC) as an anode was also assembled. Impressively, the assembled MnCo2O4//AC asymmetric supercapacitor exhibits a high energy density of 69 Wh/kg at a power density of 793 W/kg. The above research shows that the urchin-like MnCo2O4 nanospheres synthesized by adding surfactants are expected to be excellent high-performance energy storage electrode materials, which provides a new strategy for the synthesis of high-capacity nanoelectrode materials.

Effect of bias voltage on high-temperature oxidation resistance and electrical properties of Mn–Co coating with metal interconnects for solid oxide fuel cell

Abstract This study investigated the effects of bias voltage on the microstructure, high-temperature oxidation resistance, electrical conductivity, element diffusion, and barrier of chromium poisoning cathode of Mn–Co coating on the surface of SOFCs metal interconnect SUS441 ferritic stainless steel. A series of Mn–Co coatings were prepared by magnetron sputtering technique at different bias voltages (−10, −50, −90 V) and oxidized at high temperatures for 175 h at 850 °C in an air environment. The results showed that the surface of each coating before oxidation exhibited a cauliflower-like morphology, with the crystallinity of the coating increasing with higher bias voltage. After high-temperature oxidation, especially the Mn–Co coatings prepared at −90 V bias, a dense and stable MnCo2O4 spinel structure was formed, which is crucial in inhibiting the growth of the Cr2O3 oxide layer. In addition, the coating also exhibits excellent electrical conductivity (Ea = 0.35 eV), good high-temperature oxidation resistance (1.182 mg cm−2), and a stronger ability to prevent the diffusion of Cr elements.

Optimizing the defect engineering of MnCo2O4 spinel structure through Zn-substitution as a cathode for high-performance Zinc-ion batteries

Zinc-ion batteries are regarded as an effective alternative for energy storage because of their low flammability, affordability, inherent safety, and high theoretical capacity. However, manganese-based materials are limited due to a relatively narrow tunneling pathway, causing low-rate capacity and low life cycle stability. Hence, an effective strategy using defect-engineered crystal structure promoted by Zn-substituted MnCo2O4 to achieve a high-performance ZIB is proposed. The microspheres, assembled with interconnected micro- and nanoflake structures of ZnxMn1-xCo2O4 (with the Zn-substitution of x = 0, 0.2, 0.4, 0.6, and 0.8), are hydrothermally synthesized, followed by calcination, which serves as the cathode for ZIBs. At the optimal Zn0.4Mn0.6Co2O4 cathode, ZIBs battery possesses a superior discharged specific capacity of 660 mAh g-1 at 0.05 A g-1, a high-rate performance (energy density of 260–528 Wh kg−1 at a power density of 800–40 W kg−1), and good capacity retention of 70 mAh g-1 after 800 cycles at 0.2 A g–1. Ex-situ SEM-EDX and XPS results through charge/discharge cycles confirm the high stability and reversibility of Zn0.4Mn0.6Co2O4 in its electron state. Such improved rate capacity and long-life cycles originate from efficient defect engineering using Zn-substitution and oxygen vacancies. These lead to improved ion insertion and Zn2+ transport kinetics, along with enhanced electrical conductivity, resulting in the reversibility reactions of Mn4+/Mn2+ and Co2+/Co3+ upon Zn2+insertion/extraction.

Pt-decorated spinel MnCo2O4 nanosheets enable ampere-level hydrazine assisted water electrolysis

Coupling hydrazine oxidation reaction (HzOR) with hydrogen evolution reaction (HER) has been widely concerned for high efficiency of green hydrogen preparation with low energy consumption. However, the lacking of bifunctional electrodes with ampere-level performance severely limits its industrialization. Herein, we put forward an efficient active site anchored strategy for MnCo2O4 nanosheet arrays on nickel foam (NF) by introducing Pt species (denoted as Pt-MnCo2O4/NF), which is standing for excellent bifunctional electrodes. The Pt-MnCo2O4/NF delivers ultralow potentials of −195 mV and 350 mV at 1000 mA cm−2 as well as robust stability for HzOR and HER, respectively. The study of in-situ Raman and reaction kinetics reveal that the formation of key adsorbed *NH2 and *N2H4 intermediates and the rapidly oxidization of intermediates with a fast interfacial charge transfer on Pt-MnCo2O4/NF. Remarkably, the Pt-MnCo2O4/NF assembled two-electrode hydrazine assisted water electrolyzer realizes current density of 100 mA cm−2 and 1000 mA cm−2 at 0.16 V and 0.62 V with over 80 h stability. This work provides a promising way to design efficient electrodes for energy-saving H2 generation under ampere-level current density.

Controllable preparation of MnCo2O4 spinel and catalytic persulfate activation in organic wastewater treatment: Experimental and immobilized evaluation

Transitional metal oxides are excellent candidates as heterogeneous catalysts for activating persulfate towards organics degradation. In this study, MnCo2O4 spinel was successfully prepared using a solvent-free molten method. The catalytic performance was systematically investigated and MnCo2O4 powder catalyst was successfully immobilized on polyurethane (PU) membrane through electrospinning to assess its application potential. The results showed that peroxymonosulfate (0.1 ​g ​L−1) activated by MnCo2O4 (0.1 ​g ​L−1) reached 99.92 ​% degradation in 10 ​min when treating 0.04 ​g ​L−1 rhodamine B as target pollutant. The abundant oxygen vacancies formation, synergistic effect of Co and Mn ions and high electron transfer mobility are contributing to production of reactive oxygen species. Combining with quenching experiment and time-resolved EPR, the contribution of various active species was proposed, of which 1O2 exhibited the dominant role. The flowing reaction run by the MnCo2O4-PU membrane activating PMS exhibited universal degradation on different target pollutants.

Interplay of lattice-spin-orbital coupling and Jahn–Teller effect in noncollinear spinel Ti x Mn1−x (Fe y Co1−y )2O4: a neutron diffraction study

Local magnetostructural changes and dynamical spin fluctuations in doubly diluted spinel Ti x Mn1‒x (Fe y Co1‒y )2O4 has been reported by means of neutron diffraction and magnetization studies. Two distinct sets of compositions (i) x(Ti) = 0.20 and y(Fe) = 0.18; (ii) x(Ti) = 0.40 and y(Fe) = 0.435 have been considered for this study. The first compound of equivalent stoichiometry Ti0.20Mn0.80Fe0.36Co1.64O4 exhibits enhanced tetragonal distortion across the ferrimagnetic transition temperature T C = 258 K in comparison to the end compound MnCo2O4 (T C ∼ 180 K) with a characteristic ratio c t/√2a t of 0.99795(8) demonstrating robust lattice-spin-orbital coupling. However, in the second case Ti0.40Mn0.60Fe0.87Co1.13O4 with higher B-site compositions, the presence of Jahn–Teller ions with distinct behavior appears to counterbalance the strong tetragonal distortion thereby ceasing the lattice-spin-orbital coupling. Both the investigated systems show the coexistence of noncollinear antiferromagnetic and ferrimagnetic components in cubic and tetragonal settings. On the other hand, the dynamical ac-susceptibility, χ ac(T) reveals a cluster spin-glass state with Gabay–Toulouse (GT) like mixed phases behaviour below T C. Such dispersive behaviour appears to be sensitive to the level of octahedral substitution. Further, the field dependence of χ ac(T) follows the weak anisotropic GT-line behaviour with crossover exponent Φ lies in the range 1.38–1.52 on the H–T plane which is in contrast to the B-site Ti substituted MnCo2O4 spinel that appears to follow irreversible non-mean-field AT-line behaviour (Φ ∼ 3 + δ). Finally, the Arrott plots analysis indicates the presence of a pseudo first-order like transition (T < 20 K) which is in consonance with and zero crossover of the magnetic entropy change within the frozen spin-glass regime.

Plant-Cell mediated synthesis of MnCo2O4 nanoparticles and their activation of peroxymonosulfate to remove Tetracycline

Nanosized bimetallic oxides can efficiently activate peroxymonosulfate (PMS) to degrade organic pollutants attributed to their synergetic electron transfer between the two metals. However, their scalable and controllable synthesis remains challenging. In this study, small and regular MnCo2O4 nanoparticles (NPs) were successfully synthesized via a facile bio-templating method. Leaf cells were used as structure-directing agents, and the nucleation and growth of MnCo2O4 were restricted in the confined space of cells, resulting in MnCo2O4 spinel with an average size of 22 nm. The MnCo2O4 NPs can activate PMS to achieve 99 % degradation of TC (C0 = 20 mg·L−1) within 10 min. Moreover, the MnCo2O4 NPs also show a wide applicable pH range (3.0 − 11.0, RE > 94 %), excellent reusability (RE = 96 % after four cycles), and good adaptability in the complex water matrix. Analysis of the catalytic mechanisms suggests that radical O2•− and non-radical 1O2 dominate this MnCo2O4 + PMS + TC system. Besides, 17 major degradation intermediates of TC were identified (most of them were predicted to be harmless), and 3 possible degradation pathways were proposed. This study provides a feasible strategy for synthesizing spinel-structured MnCo2O4 NPs, which show great potential in removing antibiotics from wastewater.

Design of morphology-controlled cobalt-based spinel oxides for efficient X-band microwave absorption

The cobalt-based spinel structure oxides with synergistic effect of magnetic loss and dielectric loss have important applications in electromagnetic wave absorption. And the excess 0.5 oxygen atoms in MnCo2O4.5 provide more vacancies than traditional MnCo2O4 spinel structure and improve the electrical conductivity. In the current study, MnCo2O4.5 microsphere clusters, MnCo2O4.5 microcubic spheres and MnCo2O4.5 flowery spheres were prepared by solvothermal method and annealing process. Among the final samples with different morphologies, MnCo2O4.5 microcubic spheres showed outstanding microwave absorption capabilities, with a minimum reflection loss (RLmin) of -51.52 dB at 2.2 mm. When the thickness was further increased to 2.3 mm, the effective absorption bandwidth could be as wide as 5.36 GHz, covering most of the X-band. The excellent absorption performance of electromagnetic waves is related to the modulability of the complex dielectric parameters, the optimization of impedance matching, and the enhancement of the polarization relaxation process through the improvement of the morphologies. This work provides guidance and support for refining the electromagnetic wave absorption potential of cobalt-based spinel oxides and for designing highly efficient electromagnetic wave absorbers in the X-band.

Ce-doping at Mn site to enhance resistive switching performance of spinel MnCo2O4 resistive random access memory devices

The spinel Ce-doping MnCo2O4 (MCO) thin films were fabricated on Pt/Ti/SiO2/Si substrates for resistive switching (RS) layer using sol-gel spin-coating deposition method. The Pt/Mn0.925Ce0.075Co2O4/Pt (Pt/7.5MCC/Pt) device exhibits stabler and superior bipolar RS performance, the concentrated distribution of Reset/Set voltage as low as – 0.62/1.175 V, good cycle endurance and excellent time retention capability. The improvement in the RS performance of the Pt/7.5MCC/Pt devices can be attributable to the effective limitation of the random formation and rupture of conductive filaments by appropriate Ce doping. The carrier transport mechanism of the device at high resistance state can be dominated by the Schottky emission, whereas the carrier transport mechanism at low resistance state consistent with the Ohmic conduction. This work provides a potential performance improvement approach to design the resistive memory devices for data storage applications.

Radical-driven selective oxidation of benzyl alcohol on MnCoOx catalysts with no oxidant other than air in reactor

Mn reinforced Co3O4 catalysts (MnCoOx) were prepared by a facile solid phase mixed foaming method with an in-situ heating enhancement for the formation of spinel phase mixed oxide species, and studied in the selective oxidation of benzyl alcohol just the air in reactor as oxygen donor. It was found that the MnCoOx catalysts are composed of relatively minimal spinel MnCo2O4 mixed oxide and massive Co3O4 to form MnCo2O4-Co3O4 oxide pair. The micro-domains of MnCo2O4-Co3O4 oxide pair present two redox couples of Mn3+/Mn2+ and Co3+/Co2+ instead of the single one of Co3+/Co2+ in Co3O4, and then dramatically enhance the formation of superoxide radicals (•O2–) species from the O2 in air, which can efficiently initiate the conversion of benzyl alcohol to benzaldehyde in a Fenton-like processes. With no oxidant other than air in reactor, the interaction between MnCo2O4 and Co3O4 in MnCoOx catalysts leads to a benzyl alcohol conversion up to 98 % with a 100 % benzaldehyde selectivity at atmospheric pressure while single component Co3O4 can only present a benzyl alcohol conversion at 37 %. This embodiment of highly efficient heterogeneous selective oxidation just with air as oxidant provides a probability for developing a low-cost and super-facile radical-induced selective oxidation process for alcohols.

Suspension and process parameters selection for electrophoretic deposition of Mn–Co spinel coating on steel interconnects

Metallic interconnect coatings, consisting of MnCo2O4 spinel, were effectively applied to Crofer 22 APU using the electrophoretic deposition (EPD) method in both H2O: ethanol and pure ethanol solvents. The primary goal of this method was to prevent chromium migration, minimize evaporation, and control the oxidation rate. The study aimed to assess the quality, adhesion, and thickness of the Mn–Co coating, with the objective of achieving a consistent and uniform layer. The results indicated a preference for pure ethanol solvent over H2O: ethanol (40:60 %Vol) for Mn–Co particles. Furthermore, the agglomeration of Mn–Co particles was notably lower (approximately 7 times) in ethanol compared to H2O: ethanol. The morphology and surface roughness of the sintered Mn–Co coating on the alloy were examined using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). A uniform and dense coating was successfully attained using pure ethanol solvent at a solid concentration of 10 g/L, with 0.5 g/L of iodine serving as a disperser. The deposition process, carried out at a voltage of 30V for 20 s, resulted in a coating with a thickness of 7.4 ± 0.3 μm and a surface roughness of 0.75 ± 0.5 μm.

Influence of conductive carbon and MnCo2O4 on morphological and electrical properties of hydrogels for electrochemical energy conversion.

In this work, a strategy for one-stage synthesis of polymer composites based on PNIPAAm hydrogel was presented. Both conductive particles in the form of conductive carbon black (cCB) and MnCo2O4 (MCO) spinel particles were suspended in the three-dimensional structure of the hydrogel. The MCO particles in the resulting hydrogel composite acted as an electrocatalyst in the oxygen evolution reaction. Morphological studies confirmed that the added particles were incorporated and, in the case of a higher concentration of cCB particles, also bound to the surface of the structure of the hydrogel matrix. The produced composite materials were tested in terms of their electrical properties, showing that an increase in the concentration of conductive particles in the hydrogel structure translates into a lowering of the impedance modulus and an increase in the double-layer capacitance of the electrode. This, in turn, resulted in a higher catalytic activity of the electrode in the oxygen evolution reaction. The use of a hydrogel as a matrix to suspend the catalyst particles, and thus increase their availability through the electrolyte, seems to be an interesting and promising application approach.

Cu- and Ce-doped MnCo2O4 spinel coatings on ferrite interconnects by electrophoretic deposition

MnCo2O4 spinel coating is considered as one of the most promising protective coatings on the surface of ferritic stainless steel interconnects in solid oxide fuel cells (SOFCs). And the doping of metallic elements and active rare earth elements may further improve the electrical conductivity and antioxidant properties of spinel coatings. In this work we firstly prepare the Cu-doped and Ce-doped MnCo2O4 spinel coatings (abbreviated as MCCu, MCCe) on the surface of SUS430 substrate by Sol-Gel and electrophoretic deposition methods. The optimal doped ratio of Cu and Ce based on the results of oxidized mass gain and area-specific resistance (ASR) tests are determined respectively. Then we deposit Cu-Ce co-doped MnCo2O4 spinel coatings (abbreviated as MCCuCe) accordingly. The successful deposition of the target modified spinel coating on the substrate surface is confirmed using SEM-EDS, XRD, XPS characterization. The performance test results of the MCCuCe coating on the SUS430 surface show that the mass gain after 500 h oxidation at 800 °C in air is 1.3564 × 10−3 mg cm−2, and the ASR at 800 °C after 500 h oxidation is 9.80mΩ cm2, which is much lower than those of the bare SUS430 substrate and the substrate with deposited MnCo2O4 spinel coating. And the MCCuCe protective coating plays a better role in preventing the diffusion of Cr from the substrate. Further analysis prove that the doping Cu mainly contributes to the electrical conductivity and adhesion to the substrate while the doping Ce mainly improve the anti-oxidation and Cr diffusion resistance. This work determines the optimal doped ratio of Cu and Ce and provides a simple way to prepare the Cu-Ce co-doped MnCo2O4 spinel coatings on the ferritic interconnects, which effectively improve comprehensive performances of MnCo2O4 spinel coatings and helps to accelerate the industrial application of SUS430 ferrite in the SOFCs.

Investigation of non-precious metal cathode catalysts for direct borohydride fuel cells.

Borohydride crossover in anion exchange membrane (AEM) based direct borohydride fuel cells (DBFCs) impairs their performance and induces cathode catalyst poisoning. This study evaluates three non-precious metal catalysts, namely LaMn0.5Co0.5O3 (LMCO) perovskite, MnCo2O4 (MCS) spinel, and Fe-N-C, for their application as cathode catalysts in DBFCs. The rotating disk electrode (RDE) testing shows significant borohydride tolerance of MCS. Moreover, MCS has exhibited exceptional stability in accelerated durability tests (ADTs), with a minimal reduction of 10 mV in half-wave potential. DFT calculations further reveal that these catalysts predominantly adsorb over , unlike commercial Pt/C which preferentially adsorbs . In DBFCs, MCS can deliver a peak power density of 1.5 W cm-2, and a 3% voltage loss after a 5 hours durability test. In contrast, LMCO and Fe-N-C have exhibited significantly lower peak power density and stability. The analysis of the TEM, XRD, and XPS results before and after the single-cell stability tests suggests that the diminished stability of LMCO and Fe-N-C catalysts is due to catalyst detachment from carbon supports, resulting from the nanoparticle aggregation during the high-temperature preparation process. Such findings suggest that MCS can effectively mitigate the fuel crossover challenge inherent in DBFCs, thus enhancing its viability for practical application.

Cation defect engineering of core–shell spinels nanoelectrocatalyst for enhanced oxygen evolution reaction

Defect engineering is a promising approach to address the inherently low conductivity and limited number of reaction sites of manganese-based spinel oxides as electrocatalysts. However, high formation energies make it challenging to controllably generate cation defects in such spinel oxides. Herein, we report a heterogeneous core–shell electrocatalyst [Mn3O4@MnxCo3−xO4–Co2(OH)3Cl, MCIL] based on a facile cation-deficiency strategy. The addition of ionic liquid (1-butyl-3-methylimidazole hexafluorophosphate) to the reaction system can simply and quickly control the octahedral field defects in spinel MnCo2O4. The results show that the selective generation of defects in the Co(Oh) octahedral field can accelerate the OER reaction kinetics and provide excellent OER electrocatalytic performance. Specifically, the MCIL series catalysts can exhibit the lowest overpotential of 332 mV at 10 mA cm−2 and Tafel slope of 50 mV dec−1, compared with that of pristine samples [i.e., Mn3O4 (890 and 343 mV dec−1) and Mn3O4@MnCo2O4 (357 and 56 mV dec−1)]. This work highlights the importance of cation defect engineering to enhance the catalytic activity of materials.

Phase change caused by Jahn-Teller distortion in Ni doped MnCo2O4 spinel

Polycrystalline NixMnCo2−xO4 (x = 0, 0.25, 0.5, 0.75, and 1) powders were produced. The addition of nickel to the MnCo2O4 system modifies the magnetic ion concentration and regulates the Jahn-Teller distortion of the system. We have intended to replace octahedral Co with Ni. Beyond expectation, we found that the different types of Co were replaced by Ni with the doping concentration increasing. When the concentration of Ni doping is low, replacing the non-magnetic octahedral Co3+ (3d6, t2 g6eg0), Ni3+ (3d7, t2 g6eg1) enters octahedral sites. The bond angle between tetrahedral Co and octahedral Mn enlarges and the Neel temperature increases from 164 to 207 K. As Ni enters the octahedral site, the net magnetic moment at low temperature increases, which is believed that the sample exhibits a non-collinear magnetic configuration. As the doping Ni concentration is further increased, Ni2+ (3d8, eg4t2 g4) unexpectedly replaces the tetrahedral Co2+ (3d6, eg4t2 g4). The replacement makes the non-collinear frustrated transition temperature increase from 74 K to 87 K. The interaction between Co2+Tet-Ni3+Oct and Ni3+Oct-Mn3+Oct competes with each other to form a spin frustration at low temperature. An antiferromagnetic-dominated spin-glass phase occurs at low temperatures in the NiMnCoO4 system. The saturation magnetization in the NixMnCo2−xO4 system increases from 0.40 to 0.67 μB/formular (2 K).

Silver-induced adsorption optimization of adjacent Co tetrahedral sites for enhanced oxygen reduction/evolution reaction

Physical structure change of catalysts based on the electronic metal-support interaction (EMSI) effects is a prospective strategy to regulate the surface electronic structure of catalysts and further enhance their catalytic performance. To optimize the constrained intrinsic oxygen evolution reaction/oxygen reduction reaction (OER/ORR) activity of spinel MnCo2O4, we present a facile hydrothermal and photoreduction strategy to synthesize the Ag and MnCo2O4 supported on N-doped carbon nanotubes (Ag-MnCoO/NCNTs) with the EMSI effect. Ag-MnCoO/NCNTs as catalyst shows enhanced performance for OER (overpotential of 340 mV) and ORR (half-wave potential of 0.80 V). Furthermore, a zinc-air battery is assembled based on Ag-MnCoO/NCNTs cathode, which affords an open circuit potential of 1.49 V and favorable cycling performance for 200 h. Theoretical calculations illustrate the introduction of Ag reduces the charge density of the tetrahedral Co site along the direction of the dangling bonds and optimizes the adsorption of oxygen intermediates on tetrahedral Co, thus lowering the reaction activation energy and improving its oxygen catalytic activity. This work provides new insights to guide the fabrication of advanced oxygen electrocatalysts.

Three birds, one-stone strategy for synthesis of hierarchically arrayed defective MnCo2O4@NF catalyst for photothermal preferential oxidation of CO in H2-rich streams

A novel strategy with the “three birds, one stone” effect has been proposed to enhance the catalytic performance of cobalt manganese spinel catalysts for photothermal CO-PROX in H2 streams. The approach involves fabricating hierarchically arrayed defective MnCo2O4@ Nickel foam (NF) through a simple hydrothermal post-treatment and partial recrystallization process. Three synergetic effects were induced by the hydrothermal posttreatment of MnCo2O4: (i) the creation of a hierarchically arrayed morphology that strengthens light absorption and photo-to-thermal conversion, supported by finite-element method (FEM) simulations; (ii) the increased vacancy structures to alleviate significant electron-hole recombination; and (iii) abundant oxygen vacancy to facilitate oxygen adsorption and activation. These effects result in the unique hierarchically arrayed morphology and superior structural properties of MnCo2O4 spinel, which significantly enhances the photothermal synergism and catalytic activity of MnCo2O4@NF in photothermal CO-PROX driven by simulated solar light. This work provides a simple and facile strategy for developing hierarchical and defective MnCo2O4 spinel photothermal materials.

Fe-modified Mn2CuO4 spinel oxides: coatings based on abundant elements for solid oxide cell interconnects

The current state of the art steel interconnect coating materials are based on critical raw material - Co-oxide spinels. Replacing Co-oxide spinels with alternative, abundant materials can reduce the dependence on the critical raw materials. Cobalt-free coatings with the general formula Mn2-xCuFexO4, where x = 0, 0.1, 0.3, were electrophoretically deposited on a ferritic stainless-steel support and evaluated. Prior to deposition, the powders were prepared by a soft chemistry process and studied in terms of crystallographic phase analysis, electrical conductivity, thermal expansion, and sinterability behaviour. Coated steel samples were oxidised in an air atmosphere at 750 °C for 3000 h. In parallel, a state-of-the-art MnCo2O4 spinel oxide was tested as a reference. The coatings and oxide scale microstructures of the surfaces and cross-sections were examined by XRD, and SEM-EDX. TEM-EDX, XRF, and micro-XRD were also performed on the cross-section lamellae. The electrical properties of the steel-coating system were evaluated by Area Specific Resistance measurement. The results confirm that Mn–Cu–Fe oxides exhibit higher conductivity and lower TEC than Mn–Co oxide. Based on the obtained results, it might be concluded that the proposed coatings are a promising alternative to coatings that contain cobalt.

Facile in-situ grown spinel MnCo2O4/MWCNT and MnCo2O4/Ti3C2 MXene composites for high-performance asymmetric supercapacitor with theoretical insight

The logical construction of electrode materials along with greater electrochemical features and solid architectural design is a strategic approach for boosting the electrochemical performance of supercapacitors. However, it is tough and complicated to develop diverse composite materials with better electronic conductivity and greater specific capacitance via rapid and cost-effective synthesis procedures. Herein, we propose a straightforward and simple approach by employing the hydrothermal technique for the synthesis of spinel MnCo2O4 composite nanostructures using 1D MWCNT and 2D MXene (Ti3C2Tx) materials with detailed analysis of the supercapacitor performance as compared to existing literature on similar studies. The MCO/TCX (MnCo2O4/Ti3C2Tx) composite shows an impressive capacitance of 860.22 F/g at a current density of 2 A/g after electrochemical optimization. Furthermore, an asymmetric supercapacitor device (ASCs) was constructed using MCO and its composites MCO/MWCNT and MCO/TCX as a positive, and AC was employed as a negative electrode to test its device capability. Comparatively, the MCO/TCX//AC SC device demonstrated exceptional energy storage properties with a better specific capacitance value of 126.58 F/g at 0.8 A/g of current density, an elevated energy density of 40 Wh/kg, with a power density of 4828 W/kg along a capacitance retention rate of 87 % over 5000 cycles, suggesting better cycle life. Whereas, the MCO/MWCNT//AC device shows a better cycling performance of 91 % after 5000 cycles with a superior energy and power density of 27.04 Wh/kg and 1448 W/kg respectively. Also the theoretical insight for further understanding of the charge-storage mechanism through DFT calculations provides an estimate of electronic properties and quantum capacitance calculated for the pristine MCO and its hybrids with CNT and Ti3C2Tx MXene and information on the interactions between orbitals, the bonding process, and the charge transfer capabilities of each electrode material. The theoretical studies also confirm that the electronic properties and therein charge storage performance have an increasing trend in the order of MCO < MCO/CNT < MCO/TCX consistent with the experimental findings. Additionally, these simulations conclude that the hybrid MCO/TCX has the largest quantum capacitance which is in accordance with the findings of the experiments. The improved performance of MCO/TCX is due to the enlarged surface area that allows higher charge transfer from TCX to MCO. The charge transferred from the C 2p orbital of TCX to the Mn 3d orbital of MCO is the leading cause for the capacitance improvement mechanism of hybrid MCO/TCX. This work offers a simple procedure for developing energy storage devices using spinel MnCo2O4-based composite electrode materials supported by 1D carbon nanotube and 2D MXene that offer superior electrochemical performance and the fabricated electrodes that could be employed further for energy storage-based applications.