Mixed Transition Metal Oxides Research Articles

Screening Transition-Metal-Incorporated β-AgVO3 for Augmented Oxygen Reduction Activity.

Exploring cost-effective alternatives to Pt-based catalysts for the oxygen reduction reaction (ORR) in fuel cells is crucial for their large-scale deployment in green energy applications. Silver vanadate (AgVO3) is a well-studied material for photocatalytic applications. Here, we investigate the electrocatalytic ORR activity of the thermodynamically stable β phase of AgVO3 through computational modeling based on DFT. It is found that β-AgVO3 exhibits weak catalytic activity for the ORR, with vanadium being the preferable active site. Incorporating single atoms of transition metals at surface-level vacancies in β-AgVO3 significantly modifies the ORR activity. We study the scaling of free energy changes for the ORR intermediates *OOH, *OH, and *O for various transition metals incorporated, which leads to an optimal overpotential for the system. The optimal overpotential thus obtained is remarkably lower than that of pristine β-AgVO3. For the transition metal atoms we consider here, Co-incorporated β-AgVO3 exhibits the best ORR catalytic activity due to its optimal binding of ORR species to the vanadium site. It is also observed that some of the transition metals considered like Re, Rh, Os, or Mn show weak activity, either due to strong or weak binding. Analysis of the electronic structure of the adsorbate-catalyst interface shows a strong correlation between optimal activity and evolution of midgap states in β-AgVO3, due to transition metal incorporation. Our study concludes that the ORR activity of a stable mixed transition metal oxide like β-AgVO3 can be enhanced with a minimal loading of transition metals, which could help in developing a novel series of ORR catalysts.

Ultrasensitive electrochemical detection of 4-nitrophenol through flower-like mixed transition metal oxide anchored on reduced graphene oxide composites

4-Nitrophenol or para-nitrophenol is an organic water pollutant that has a direct impact on environmental pollution and human health. Therefore, developing sensitive electrochemical sensors is vital for monitoring environmental water samples to detect hazardous 4-nitrophenol. Herein, template-free zinc vanadate (ZV) micro-flowers were synthesized and anchored on reduced Graphene oxide (RGO) to modify the electrode surface for sensing and quantification of 4-nitrophenol. The fabrication of the as-prepared electrode modifier was confirmed by physicochemical and morphological characterizations. The synthesized ZV/RGO/GCE displayed well-defined reductive peak current at the potential of −0.7 V due to the hydrogenation of 4-nitrophenol. The increase in active sites and the larger surface area acquired by ZV and RGO were responsible for efficient sensing toward 4-nitrophenol. Under the optimized experimental parameters, CV and DPV techniques were carried out to investigate the electrochemical performance of ZV/RGO/GCE for the detection of 4-nitrophenol. The resultant cathodic current response was related linearly (0.01 µM to 1955 µM) to the concentration with the LOD of 0.009 µM. The developed sensor exhibited a good recovery range in the real-sample analysis in multiple water systems. The proposed ZV/RGO/GCE functions well as an effective electrode material for the determination of the perilous pollutant 4-nitrophenol in water samples by an electrochemical approach.

Cryo-Assisted Nitrogen Treatment for the Fabrication of Nanoengineered, Mixed Transition Metal Oxide Anode from Inorganic Domestic Waste, for Lithium-Ion Batteries

A novel method for the fabrication of nanoengineered, mixed transition metal oxide anode active material is proposed based on implementing liquid nitrogen treatment during the chemical precipitation process, for the first time in open literature. Such interference in the precipitation is believed to change the surface energy of the nuclei leading to differentiation in the growth process. To exemplify this hypothesis with an environmentally friendly approach, kitchen scourer pads, an existing waste, are used as a starting material instead of using a mixture of primary quality metals’ salts. Therefore, in this study, firstly, an optimization is realized to leach the scouring pad with 100% efficiency. Then, by applying a conventional chemical precipitation to this leachate at pH 5.5, Sample 1-P is produced. Herein, innovatively liquid nitrogen treatment is carried out during the chemical precipitation to produce Sample 2-P. Lastly, these precipitates (Samples 1-P, 2-P) are calcinated in the air to form mixed transition metal oxide powders: Samples 1 and 2, respectively. Structural, chemical, and morphological characterizations are carried out to examine the effect of liquid nitrogen treatment on the powders’ properties. To discuss the effect of nitrogen treatment on the electrochemical performances of the anode active materials (Sample 1 and Sample 2), galvanostatic tests are realized. The results show that Sample 2 demonstrates a higher 1st discharge capacity (1352 mAh/g) and retains 62% of its performance after 200 cycles when 50 mA/g current load is applied. Moreover, this electrode delivers around 500 mAh/g at 1 A/g current load. The remarkable cycle performance of Sample 2 is believed to be related to the superior chemical, structural, and physical properties of the electrode active material.Graphical

Mesoporous Mn-substituted MnxZn1-xCo2O4 ternary spinel microspheres with enhanced electrochemical performance for supercapacitor applications.

Extensive investigations have been carried out on spinel mixed transition metal oxide-based materials for high-performance electrochemical energy storage applications. In this study, mesoporous Mn-substituted MnxZn1-xCo2O4 (ZMC) ternary oxide microspheres (x = 0, 0.3, 0.5, 0.7, and 1) were fabricated as electrode materials for supercapacitors through a facile coprecipitation method. Electron microscopy analysis revealed the formation of microspheres comprising interconnected aggregates of nanoparticles. Furthermore, the substitution of Mn into ZnCo2O4 significantly improved the surface area of the synthesized samples. The electrochemical test results demonstrate that the ZMC3 oxide microspheres with an optimal Mn substitution exhibited enhanced performance, displaying the largest specific capacitance of 589.9Fg-1 at 1Ag-1. Additionally, the ZMC3 electrode maintained a capacitance retention of 92.1% after 1000 cycles and exhibited a significant rate capability at a current density of 10Ag-1. This improved performance can be ascribed to the synergistic effects of multiple metals resulting from Mn substitution, along with an increase in the surface area, which tailors the redox behavior of ZnCo2O4 (ZC) and facilitates charge transfer. These findings indicate that the incorporation of Mn into mixed transition metal oxides holds promise as an effective strategy for designing high-performance electrodes for energy storage applications.

Amorphous mixed transition metal oxides: A novel catalyst for boosting dehydrogenation of MgH2

Magnesium hydride (MgH2) has been recognized as a promising hydrogen storage material. However, the sluggish hydrogen desorption kinetics is one of the main factors hindering its practical applications. To enhance the dehydrogenation kinetics of MgH2, an amorphous mixed TiO2-ZrO2-V2O5 catalyst is synthesized in this work. After adding the as-synthesized catalyst into MgH2 by ball milling, the dehydrogenation activation energy can be decreased to 65.7 kJ mol−1. Meanwhile, the catalyzed MgH2 shows excellent cycling stability after fifty hydrogen absorption-desorption cycles. The significant improvement of hydrogen desorption kinetics is attributed to the synergistic effect of abundant oxygen vacancies and in situ formed multivalent species in the catalyst. This highlights the importance of designing and synthesizing efficient catalysts for dehydrogenation of MgH2.

Oxalate-mediated synthesis of hybrid nickel cobalt-based nanostructures for boosting water and urea electrooxidation efficiency

The utilization of urea during electrolysis presents an appealing option for anodic oxidation, offering environmental benefits by converting waste into energy. The present work focuses on synthesizing mixed transition metal oxide (MMO) nanostructures composed of nickel rich nickel cobaltite electrode materials. Interesting, cobalt rich nickel cobaltite have been widely studied; however, the nickel-rich nickel cobaltite remains relatively unexplored. For stabilization of nickel rich nickel cobaltite, we have designed a process for synthesizing three-dimensional (3D) Ni-Co oxalate as a precursor via the coprecipitation method using diammonium oxalate monohydrate as a precipitating agent. The as obtained precursor was further subjected to thermal decomposition which results in the formation of Ni2CoO4. Microstructural analysis of Ni-Co oxalate indicates that oxalate-assisted synthesis leads to anisotropic ultrafine nanoparticle growth, forming hierarchically arranged 3D microflowers. Interestingly, the use of NaOH as a precipitating agent induces a significant change in the morphology of Ni2CoO4, (nanoparticles). Furthermore, the effect of morphology changes over the electrochemical performance was investigated. Ni2CoO4 microflower demonstrates an overpotential of 330 mV@25 mA/cm2 for O2 and −190 mV@10 mA/cm2 for H2 production during water oxidation in 1 M KOH, exhibiting excellent stability for up to 24 h. During urea oxidation, the potential required by Ni2CoO4 microflowers was 1.31 V@10 mA/cm2. Ni2CoO4 nanoparticles' performance is significantly poor during water and urea oxidation compared to the microflower counterpart. Therefore, this work provides detailed insights into designing MMOs with high porosity, increased exposed active sites, and unique structural features that enhance electrocatalytic activity.

In-situ synthesis of SnO2/CoFe2O4/Fe3O4 nanograss array composite: A redox-active electrode material for battery-type supercapacitors

Nanocomposites containing mixed transition metal oxides demonstrate significant promise as materials for supercapacitors, specifically due to their enhanced surface area, synergistic effect of multiple metal cations, excellent electrical conductivity, and improved electrochemical properties. In this study, we synthesized a nanocomposite with a nanograss array morphology consisting of SnO2/CoFe2O4/Fe3O4 using an in-situ sol-gel method. For comparison, we synthesized a composite (CoFe2O4/Fe3O4) without SnO2. Through a systematic characterization employing various analytical techniques, we examined the structural, morphological, and textural attributes of the resulting composites. The results reveal that the phase percentages of CoFe2O4, SnO2, and Fe3O4 were 38%, 33%, and 29% in the SnO2/CoFe2O4/Fe3O4 composite. Also, the nanograss array of SnO2/CoFe2O4/Fe3O4 is composed of nano-sized primary particles, while CoFe2O4/Fe3O4 showed spherical-like nanoparticle morphology. The BET surface area of the SnO2/CoFe2O4/Fe3O4 composite was found to be seven times higher than that of CoFe2O4/Fe3O4. We also evaluated the electrochemical performance of the SnO2/CoFe2O4/Fe3O4 composite as a cathode material for battery-type supercapacitors. The synergistic combination of SnO2 and CoFe2O4/Fe3O4 in the SnO2/CoFe2O4/Fe3O4 electrode resulted in a high specific capacity of 465C g−1 at 1 A g−1, which is 2.5 times higher than the CoFe2O4/Fe3O4 electrode. Additionally, the SnO2/CoFe2O4/Fe3O4 electrode exhibited a remarkable rate capability of 87% at 10 A g−1 and excellent cyclic performance with 96% capacity retention after 5000 cycles. A hybrid supercapacitor was fabricated, featuring a cathode composed of a composite electrode consisting of SnO2/CoFe2O4/Fe3O4 and an anode comprising activated carbon (AC). This fabricated SnO2/CoFe2O4/Fe3O4//AC HSC device configuration exhibited impressive performance characteristics, boasting a notable energy density of 38.4 Wh kg−1 at 1468.2 W kg−1. These findings underscore the significant impact of SnO2 on the physio/electrochemical properties of the CoFe2O4/Fe3O4 composite. The outstanding electrochemical performance of this electrode underscores its potential for application in next-generation hybrid supercapacitors.

Binary NiCu oxide nanoparticles onto graphite as promoting nanocatalysts for ethanol electro‐oxidation process

A facile and reduced cost fabrication protocol was followed to have a series of nickel oxide nanospecies onto graphite support with introducing varied copper oxide wt.% values (NiCuO/T). The co‐precipitation of metallic hydroxide particles onto carbonaceous surfaces and their subsequent burning at 400°C were sufficient to prepare mixed transition metal oxides. Suitable analysis tools were exploited to fully characterize the obtained nanopowders using scanning electron microscopy, transmission electron microscopy, X‐ray diffraction spectroscopy, X‐ray photoelectron spectroscopy, and energy dispersive X‐ray analysis. Outstanding performances of the formed nanocatalysts for catalyzing ethanol electro‐oxidation reaction were measured especially in presence of 15 wt.% copper oxide content. The onset potential (Eonset) value of alcohol oxidation process was negatively shifted at dispersed NiO nanoparticles onto graphite after doping with copper oxide nanospecies. This promoted activity of prepared nanomaterials could be explained by their increased active sites when binary metallic oxides were incorporated. Electrochemical impedance spectroscopy studies demonstrated much lowered resistances in alkaline solution containing ethanol molecules to ascertain the enhanced behavior of NiCuO/T nanocatalysts. Moreover, their good stability attitude encouraged the application of doped nanomaterials with copper oxide for fuel cells application.

ZnO/RuO2 nanocomposite modified glassy carbon electrode as sensor for determination of exercise-induced myoglobin biomarkers

A novel ZnO/RuO2 nanocomposite modified electrochemical sensor was developed for the rapid and ultrasensitive quantification of Mb biomarkers related to exercise-induced muscle injury. The sensor demonstrated a wide linear range from 0.1 to 100 nM along with an ultra-low detection limit down to 30 pM Mb under optimal conditions. A rapid response time below 10 s was achieved. The sensor surface showed excellent electrocatalytic activities towards Mb oxidation, attributing to the synergistic properties of the mixed transition metal oxide interface. Systematic investigations revealed reversible electrochemical behavior and diffusion controlled electron transfer kinetics governing the oxidation process. Negligible interferences were observed against potentially co-existing species. Spike-recovery experiments using real human serum samples yielded excellent recovery rates between 97.3% and 103.1%. Significantly enhanced post-exercise Mb levels up to 8.2 nM were successfully detected in clinical specimens, confirming the sensor's ability to sensitively monitor muscular trauma via minimally invasive blood tests. The sensor provided tangible analytical advantages over previous Mb detectors and immunoassays in terms of detection limit, sensitivity, simplicity and cost-effectiveness. Findings validate the feasible adoption of the sensor technology to facilitate prompt diagnosis of exercise-induced myoglobinemia in sports medicine clinics.

Influence of metal cations on 3D MCoMnO4 microstructures (M = Ni and Zn) for battery-type supercapacitors: A comprehensive study

Mixed transition metal oxides (MTMOs) with high conductivity and multiple metal centers are promising for energy storage. We synthesized self-assembled three-dimensional (3D) flower-like NiCoMnO4 (NCMO) and cube-like ZnCoMnO4 (ZCMO) microstructures via the hydrothermal method. These structures effectively utilize synergistic interactions among MTMOs, offering abundant electro-active sites, and enabling efficient redox reactions. The influence of the metal cation (Ni/Zn) on the physicochemical attributes of the synthesized materials was comprehensively investigated using a diverse set of analytical techniques. When assessing their electrochemical performance in the context of battery-type supercapacitors at a current density of 1 A g−1, the NCMO electrode outperformed with a significantly higher specific capacity of 170.2 mAh g−1 (612.2 C g−1) in contrast to the 145 mAh g−1 (522 C g−1) for the ZCMO electrode. Remarkably, the NCMO electrode displayed exceptional cyclic stability, preserving 91% of its capacity even when subjected to a high current density of 20 A g−1 over 5000 cycles. This innovative approach holds substantial potential for advancing energy storage technologies.

ZnMn2O4 spinel nanocrystals-decorated multi-walled carbon nanotubes for oxygen reduction: Experimental and theoretical studies on the strong coupling facilitated four-electron selectivity

In this work, we have successfully formulated a single-step hydrothermal synthesis of mixed transition metal oxide nanocrystals (ZnMn2O4) strongly coupled on carbon support (MWCNTs) that acts as an efficient electrocatalyst for the electrochemical oxygen reduction reaction (ORR). The results depict that the composite, MWCNTs@ZnMn2O4 shows better electrocatalytic activity as compared to the activity exhibited by its individual components MWCNTs and ZnMn2O4 combined, attributed to the strong coupling between the two components. Transmission electron images of the composite depict that ZnMn2O4 nanocrystals have been successfully integrated on MWCNTs resulting in high conductivity and activity. The composite, MWCNTs@ZnMn2O4 exhibits an onset potential of 0.9 V vs. RHE, 99 % four-electron ORR selectivity, and high stability. The high selectivity and stability are assigned due to the strong coupling of ZnMn2O4 to MWCNTs through Zn/Mn–O–C bonds which are proved from DFT studies. The presence of Zn/Mn–O–C bonds is verified from X-ray photoelectron spectroscopy.

(Invited) Metal Oxide Nanoparticles for Stable Alkaline Oxygen Evolution Reaction in an Anion Exchange Membrane Electrolyser Cell

One of the key challenges to develop efficient water electrolysis system is to find effective and robust electrocatalysts for the oxygen evolution reaction (OER). Mixed transition metal oxides provide immense possibilities for such purpose.1 , 2 Abundant catalytically active sites could be generated via engineering the defects and oxygen vacancies within the transition metal oxides.3 The catalyst stability could also be improved by incorporating self-healing component into the catalysts .4 In this work, we adopt cobalt oxides as substrate materials to prepare mixed transition metal oxides. The catalysts are synthesized via a combined approach of hydrothermal and annealing processes. The final products are characterized thoroughly by a broad range of characterization techniques, including XRD, TEM, SEM, EDX, and XPS. The OER activities are initially evaluated in a three-electrode system. The results show that the as-prepared catalysts demonstrate high current density at a relatively low overpotential. Moreover, the catalysts exhibit excellent robustness for an 8-hours stability test in a three-electrode testing system. The stability and activity of the catalysts is further assessed in a lab-scale anion exchange membrane (AEM) electrolyser cell setup. Only a small degradation is observed for the best performing catalyst in 12 hours period. The details of the catalyst characterization and electrochemical measurements will be discussed. Acknowledgements This work was funded by European Union’s Horizon 2020 projects FlowPhotoChem (Grant agreement number 862453) and European Innovation Council Pathfinder ANEMEL (Grant agreement number 101071111). References Mohammed-ibrahim, J. & Moussab, H. Tuning the electronic structure of the earth-abundant electrocatalysts for oxygen evolution reaction (OER) to achieve efficient alkaline water splitting – A review. J. Energy Chem. 56, 299–342 (2021).Plevová, M., Hnát, J. & Bouzek, K. Electrocatalysts for the oxygen evolution reaction in alkaline and neutral media. A comparative review. J. Power Sources 507, (2021).Zhang, R. et al. Tracking the Role of Defect Types in Co3O4 Structural Evolution and Active Motifs during Oxygen Evolution Reaction. J. Am. Chem. Soc. (2023) doi:10.1021/JACS.2C10515.Silva, A. L. et al. Mn-doped Co3O4 for acid, neutral and alkaline electrocatalytic oxygen evolution reaction. RSC Adv. 12, 26846–26858 (2022).

Surface engineering of ternary mixed transition metal oxides for highly efficient catalytic oxidation of low concentration VOCs

With the widespread application of waterborne painting process, effective removal technologies for low concentration volatile organic compounds (VOCs) is a major concern of the painting industries due to the low mass transfer efficiency. This work presents a unique approach for the molecular-level preparation of precious-metal-free mixed aliovalent-substituted, CeCuOx binary oxide and NiO-modified yNi/CeCuOx ternary mixed metal oxide catalysts. In addition, the excellent catalytic selectivity (no catalytic activity decreases under 5.0 vol% water vapor) of the catalysts was successfully achieved by microstructures optimization and grafting octadecyltrichlorosilane (OTS). Its catalytic activity in the oxidation of toluene at low concentrations (50 ppm) was studied. The 3Ni/CeCuOx sample exhibits the best performance, which achieve 90 % catalytic oxidation of toluene at 197 °C without using noble metals. This results from that the ternary doping and the growth of NiO increases the specific surface area, active lattice oxygen species, activates molecular oxygen species, and provides more catalytic sites, which improve the adsorption and catalysis of toluene. Furthermore, the catalytic stability of the catalysts is also significantly improved by the addition of the hydrophobic coating. Therefore, the unique catalysts have great potential in practical applications for low concentration VOCs removal of painting industries.

Facile preparation of CoMoO4/NiCo2O4 nano-sphere anode materials and their performance in asymmetric supercapacitors

CoMoO4/NiCo2O4 electrodes with a three-dimensional nano-sphere structure have been successfully prepared by a combination of hydrothermal and calcination methods. The electrode material exhibits a high specific capacitance of 1175 F g−1 at 1 A/g, excellent multiplicative performance (74.2 % capacity at 15 A/g) and good cycling stability (85.9 % specific capacitance retention after 10,000 cycles). The asymmetric supercapacitor was constructed using activated carbon (AC) as the negative electrode, showing excellent energy density (27.7 wh kg−1) and power density (806 W kg−1). It also has an extremely long operating life, maintaining a specific capacitance of 78.3 % after 5000 cycles at current densities up to 6 A/g. The results indicate that the synthesized mixed transition metal oxides CoMoO4/NiCo2O4 are promising as composite electrode materials for high-performance asymmetric supercapacitors.

Three-Dimensional Porous Flower-like CoMoO4 As Cathode for Li-O2 Batteries

Lithium-oxygen batteries (LOBs) are considered to be the next-generation energy storage systems due to their high energy density (~ 3500 Wh kg-1).1 However, the insulating and bulk lithium peroxide discharge product causes sluggish decomposition, increasing overpotential and reducing cycle stability, so it is necessary to find cathode materials with excellent oxygen reduction reaction and oxygen evolution reaction performance.2 Mixed transition metal oxides have attracted much attention because of their feasible oxidation states, high energy density, and high conductivity. Here, Three-Dimensional Porous flower-like CoMoO4 (3DF-CM) was synthesized via a universal and low-cost hydrothermal method, which is to be used as an efficient electrocatalyst in an oxygen electrode for high-performance LOBs. Morphologically, the 3DF-CM with high electrical conductivity has a large surface that can improve charge transport and promote delithiation during recharge. As a result, the battery based on 3DF-CM as a cathode exhibited an outstanding discharge capacity and a long-term life performance.

Improving the structural and transport properties of cadmium ferrites with the addition of cerium for high frequency applications

Due to their outstanding properties, low cost, and environmental friendliness, mixed transition metal oxides are frequently used in various applications. In this study, Ce3+ doped CdFe2O4 powder samples were prepared through the co-precipitation process. A peak shift was observed towards a lower 2 θ angle with the substitution of Ce3+ at their lattice site and the lattice constant has a maximum value for the x = 0.06 sample with the crystallite size of 34 nm. Moreover, for x = 0.06 sample, the resistivity was found in the order of 106 Ω cm and the dielectric tangent loss had a smaller value. The electrical and dielectric analysis of the as-prepared x = 0.06 sample indicate that it is the best for high-frequency applications.

Synthesis of Zn doped CrV spinel oxide nanostructures for flexible supercapacitor and hydrogen evolution reaction

Nanostructures containing mixed transition metal oxides with various architectures have been used as promising materials in supercapacitors due to their excellent capacitive contributions. The present work reports on the spinel zinc chromium vanadate ZnCrVO4 (ZCV) nanostructures fabricated via the facile hydrothermal method, for the first time. The pseudocapacitive nature and promising electrocatalytic hydrogen evolution of the prepared ZCV in activated carbon electrodes were confirmed by electrochemical tests. The maximum specific capacitance (Cs) of 448 F g−1 at 1 mA was determined for the ZCV nanostructures s which is far better than pure chromium vanadate (CrV). ZCV containing supercapacitor exhibited the specific energy of 54.5 Wh kg−1 at a power of 1350 W kg−1 and the remarkable coulombic efficiency of the device was recorded at around 99% at 10.000 cycles. In addition, excellent electrochemical hydrogen evolution reaction (HER) kinetics for ZCV were revealed by the Tafel slope (118 mV dec−1) which is quite comparable to the slope of the Pt–C electrode (54 mV dec−1) under the same operating conditions.

Catalytic Hydrogenation of Organic Polymers by Mixed Transition Metal Oxides

Catalytic Hydrogenation of Organic Polymers by Mixed Transition Metal Oxides

Unravelling the Supercapacitive Potential of Zn-Ni-Co Mixed Transition Metal Oxide

Objective: A promising Zn-Ni-Co mixed transition metal oxide was successfully synthesized by means of the sol-gel route and its super capacitive behavior was studied. Methods: The structural, morphology, and functional groups were deduced via XRD, SEM, EDX, and FTIR analysis. The super capacitive performance of the hybrid and ternary mixed transition metal oxides was executed through a three-electrode system, in a 2M KOH electrolyte. Results: The specific capacitance of Zn-Ni-Co O was reckoned to be 415 Fg-1 at 50 mVs-1, thrice as much as the specific capacitance of ZnCo2O4 hybrid transition metal oxide (139 Fg-1). The synergistic effects benefited from multiple metal constituents and low activation energy for electron transportation plays an important role in boosting the electrochemical performance. Conclusion: The obtained results proved that Zn-Ni-Co O ternary composite has a promising future as an alternative for supercapacitor electrodes.

Electrochemical Performance of Chemically Integrated N-Doped Carbon Dots/Bi2MoO6 Nanocomposites for Symmetric Supercapacitors

Mixed transition-metal oxides (MTMOs) are attracting tremendous attention as a battery-type electrode due to their high electrical conductivity and structural stability. However, utilizing these electrodes in practical applications is hindered by capacity degradation, especially during the long-term cycle. These limitations could be overcome by constructing electrodes by introducing the carbonaceous material into the MTMO matrix. Accordingly, in this work, a facile hydrothermal method is employed to develop nitrogen-doped carbon dots (NCDs)-integrated bismuth molybdenum oxide (Bi2MoO6; BMO) (NCD/BMO) composites, where the concentration of NCDs is varied, such as 2, 5, 10, and 15 wt %. The structural and chemical state analyses of the samples confirm the formation of the orthorhombic BMO system and the chemically integrated NCD/BMO composites. The morphology analysis revealed a brick-like structure for bare-BMO with an average size of ∼100 nm and a rod-like morphology for the NCD/BMO composites, which is attributed to the interaction of NCDs with growing BMO particles leading to the rod-like formation of the resultant composites. The electrochemical performance of the developed materials is studied in a three-electrode and symmetric assembly system. Among the composites, the 10 wt % NCD/BMO (BMO–C10) composite exhibited an enhanced specific capacity of 561 C g–1 (155.8 mA h g–1) at a current density of 1 A g–1 in 6 M KOH electrolyte. Besides, the assembled symmetric device achieved an energy density and a power density of 44.2 W h kg–1 and 720 W kg–1, respectively, at a current density of 1 A g–1. In addition, the assembled symmetric device maintained excellent cyclic stability of ∼87.3% up to 10,000 cycles at 20 A g–1 current density. The obtained results demonstrate that the NCD/BMO composite could be an efficient battery-type electrode material for promising supercapacitor applications.