Metal Oxide-based Electrode Materials Research Articles

Synthesis of ZnO and NiO nano ceramics composite high-performance supercapacitor and its catalytic capabilities

NiO and ZnO mixed nanocomposites were manufactured using the solution combustion process. As-prepared samples were analyzed using XRD. The XRD shows an average crystallite size of 35–40 nm. The elemental composition determined by EDS indicates a nearly equal proportion of Ni and Zn, with an atomic ratio of Ni/Zn = 0.96. The specific capacitances of NiO is 295.5 Fg-1, ZnO is 117.3 Fg-1 and ZnO/NiO nanocomposites is 561.75 Fg-1 which are more than NiO and ZnO alone. This study shows that constructing binary oxide nanocomposites is an approach for developing high-performance supercapacitor electrode materials. Experimental observations on catalytic activity revealed that NiO/ZnO increased catalytic activity. Furthermore, adding NiO to ZnO in the composite increased the overall amount of oxygen vacancies in the samples. Our research lays the door for a simple, inexpensive, nontoxic, and quick technique to synthesize binary transition metal oxide-based electrode materials for high-performance supercapacitors.

Recent progress in metal oxide-based electrode materials for safe and sustainable variants of supercapacitors.

A significant amount of energy can be produced using renewable energy sources; however, storing massive amounts of energy poses a substantial obstacle to energy production. Economic crisis has led to rapid developments in electrochemical (EC) energy storage devices (EESDs), especially rechargeable batteries, fuel cells, and supercapacitors (SCs), which are effective for energy storage systems. Researchers have lately suggested that among the various EESDs, the SC is an effective alternate for energy storage due to the presence of the following characteristics: SCs offer high-power density (PD), improvable energy density (ED), fast charging/discharging, and good cyclic stability. This review highlighted and analyzed the concepts of supercapacitors and types of supercapacitors on the basis of electrode materials, highlighted the several feasible synthesis processes for preparation of metal oxide (MO) nanoparticles, and discussed the morphological effects of MOs on the electrochemical performance of the devices. In this review, we primarily focus on pseudo-capacitors for SCs, which mainly contain MOs and their composite materials, and also highlight their future possibilities as a useful application of MO-based materials in supercapacitors. The novelty of MO's electrode materials is primarily due to the presence of synergistic effects in the hybrid materials, rich redox activity, excellent conductivity, and chemical stability, making them excellent for SC applications.

Soft-template assisted morphology tuning of NiMoO4 for hybrid supercapacitors

The electrochemical performance of electrode materials depends on various physicochemical properties like particle size, morphology, porosity, etc. of materials. Herewith, a facile surfactant assisted hydrothermal route using cetyltrimethylammonium bromide (CTAB) and hexamethylenetetramine (HMT) is used to successfully synthesize nanostructured nickel molybdate (NiMoO4) with various morphologies. It is found that NiMoO4 possesses different morphologies when synthesized by using these surfactants. With change in morphology, there is a significant increase in diffusion coefficient for sample synthesized with CTAB. It is interesting to note that NiMoO4 synthesized by using CTAB exhibit a high specific capacitance of 947 F g−1 when cycled at 1 A g−1 in 1 M KOH solution as compared to that of 322 F g−1 (synthesized without CTAB), which can be ascribed to its flower-like shape with uniform porosity. Both Ni2+/Ni3+ and Mo6+/Mo4+ redox couples are involved in the capacitive characteristic of NiMoO4, as found from the XPS study. Additionally, a hybrid supercapacitor has been assembled using NiMoO4 as positive electrode and reduced grapgene oxide (rGO) as negative electrode, which can exhibit 107 F g−1 with an operating voltage of 1.6 V with excellent cycling stability of maintaining 94 % capacitance retention after 6000 cycles in 1 M KOH solution. The hybrid supercapacitor can possess an energy density of 37.7 Wh kg−1 and a power density of 8 kW kg−1. Thus, this study enables the importance of tuning the morphology to enhance the capacitance property of transition metal oxide based electrode materials for supercapacitor applications.

Ammonium ion intercalation and oxygen-rich vacancies in birnessite-type MnO2 for supercapacitors and oxygen evolution applications

Defect engineering is an effective strategy to improve the electrochemical and electrocatalytic properties of transition metal oxide-based electrode materials.

Binary mixed metal oxide sphere-like structures for hybrid supercapacitor electrode with improved electrochemical properties

The facile fabrication of stable and highly efficient metal oxide-based electrode materials by regulating the electroactive sites is crucial for supercapacitor applications. In this work, a two-step synthesis strategy comprising hydrothermal and heat treatment was employed to prepare the NiWO4/WO3 (NW/W-O) as electrode materials for supercapacitors. Moreover, the heat treatment temperature influences and alters the physicochemical and electrochemical properties of the obtained NW/W-O products. The material prepared at 500 °C (NW/W-O(A)) unveils low crystallinity, small particle size, and a large surface area with a narrow porous feature than the material obtained at 600 °C (NW/W-O(B)). Thus, the NW/W-O(A) electrode could be anticipated for effective charge transfer and better capacitive behavior. Notably, the NW/W-O(A) material exhibited a superior specific capacitance of 825 F g−1 than NW/W-O(B) with 536 F g−1 at a current density of 1 A g−1. Further, the NW/W-O(A) displayed a higher rate capability of 60% (@ 20 A g−1) than that of NW/W-O(B) (49%). The designed hybrid supercapacitor (NW/W-O(A)//AC) showed a high specific capacitance of 108 F g−1 and energy density of 33.77 Wh kg−1 at a power density of 896.39 W kg−1 with long-term cyclic retention of only <12% deterioration over 10,000 cycles. Hence, this work demonstrates that the influence of heat treatment temperature is a crucial parameter in tailoring electrode materials with promising energy storage capability.

Construction of CuO/Cu-nanoflowers loaded on chitosan-derived porous carbon for high energy density supercapacitors.

Copper oxide (CuO) and copper (Cu) have been viewed as the prospective pseudocapacitive electrode materials for supercapacitors. Nevertheless, the poor electron transfer capacity, loading amount, and cycling stability limit their wide applications, which can be addressed by developing the CuO based heterojunction on conductive carbons. Here, a CuO/Cu@C comprising CuO/Cu nanoflowers and chitosan-derived N-doped porous carbon was compounded by simple mechanical mixing, freeze-drying, and carbonization. The composite heated at 700°C exhibited a high specific capacitance of 2479F/g at 0.5 A/g and excellent cycling stability with capacitance retention of 82.43% after 10 000 charge-discharge cycles. In addition, the asymmetric supercapacitor (ASC), i.e., CuO/Cu@C-700//AC assembled by CuO/Cu@C (as a positive electrode) and activated carbon (AC, as a negative electrode) displayed a great energy density of 76.87Whkg-1 at 374.5Wkg-1 and kept as high as 25.83Whkg-1 even at 14998Wkg-1. Our work provides a new pathway to preparing transition metal oxide-based electrode materials with distinguished electrochemical performances.

Rational design of metal oxide based electrode materials for high performance supercapacitors – A review

Supercapacitors have emerged as the most integral energy devices due to their unexampled countenance like high power and energy density, long cyclic life and environmentally friendly nature. Electrode materials play a critical role in determining the supercapacitor performance. Due to their rich valence states, excellent redox properties and high energy density, transition-metal oxides have demonstrated to be promising candidates for high performance supercapacitors, however, the relatively low conductivity limits their applications. Therefore, incorporating with carbon-based materials or conductive polymers is a promising strategy to further improve the performance of transition-metal oxide based supercapacitors. Here in, we have a comprehensive review on the advances and progress of transition-metal oxides materials applied in supercapacitors, such as copper oxide (CuO), nickel oxide (NiO), cobalt oxide (Co3O4), zinc oxide (ZnO), manganese dioxide (MnO2), iron oxide (Fe2O3, Fe3O4, FeO), and their composites incorporated with carbon-based materials or conductive polymers. Finally, the current challenges and future perspectives of these electrode materials for supercapacitors have been summarized and anticipated.

Structure-engineering of core-shell ZnCo2O4@NiO composites for high-performance asymmetric supercapacitors.

The implementation of a structure-designed strategy to construct hierarchical architectures of multicomponent metal oxide-based electrode materials for energy storage devices is in the limelight. Herein, we report NiO nanoflakes impregnated on ZnCo2O4 nanorod arrays as ZnCo2O4@NiO core–shell structures on a flexible stainless-steel mesh substrate, fabricated by a simple, cost-effective and environmentally friendly reflux condensation method. The core–shell structure of ZnCo2O4@NiO is used as an electrode material in a supercapacitor as it provides a high specific surface area (134.79 m2 g−1) offering high electroactive sites for a redox reaction, reduces the electron and ion diffusion path, and promotes an efficient contact between the electroactive material and electrolyte. The binder-free ZnCo2O4@NiO electrode delivers a high specific capacitance of 882 F g−1 at 4 mA cm−2 current density and exhibits remarkable cycling stability (∼85% initial capacitance retention after 5000 charge–discharge cycles at 10 mA cm−2). The asymmetric supercapacitor device ZnCo2O4@NiO//rGO delivered a maximum energy density of 46.66 W h kg−1 at a power density of 800 W kg−1. The device exhibited 90.20% capacitance retention after 4000 cycles. These results indicate that the ZnCo2O4@NiO architecture electrode is a promising functional material for energy storage devices.

Scrutinizing the charge storage mechanism in SrO based composites for asymmetric supercapacitors by diffusion-controlled process

Optimization of suitable electrode material flashing high electrochemical performance is the main hindrance in energy storage applications. Metal oxide-based electrode materials are promising candidate which greatly promotes the sustainable development. Herein, strontium oxide (SrO) is synthesized from sonochemical method followed by calcination. Incorporating polyaniline (PANI) and graphene (Gr) intensify the materials performance. Three asymmetric devices are designed using SrO, its composites (SrO/PANI and SrO/PANI/Gr) and activated carbon (AC) as an electrode and electrolyte-soaked separators are sandwiched in solidly packed cell assembly. Electrochemical measurements are performed to scrutinize the inherent properties. After that, Dunn’s model is applied to evaluate the capacitive and diffusion-controlled contributions. The obtained result divulges that SrO/PANI/Gr//AC exhibits more diffusive-controlled contribution and reveals a battery type behavior due to the contribution of PANI in redox reactions. Thus, this work delivers a route to synthesize metal oxides-based composites and a systematic approach to analyze the charge storage mechanism in asymmetric supercapacitors.

Bowl-shaped NiCo2O4 nanosheet clusters as electrode materials for high-performance asymmetric supercapacitors

The development of transition metal oxide-based electrode materials with proper controlled structures is highly desirable for high-performance supercapacitors. However, it remains a major challenge. Here, we present the first synthesis of bowl-like NiCo2O4 nanosheet clusters through a simple soft template guided hydrothermal strategy. The resulting bowl-like clusters consist of numerous NiCo2O4 nanosheets with an average thickness of 19 nm and possess a mean diameter of 1 µm along with a specific surface area of 40 m2 g−1. Remarkably, serving as an electrode material in a three-electrode system, the bowl-like NiCo2O4 nanosheet clusters exhibit a high specific capacity of 1068 F g−1 at a current density of 1 A g−1 and excellent cycling stability with 90% capacitance retention after 5000 charge-discharge cycles. Meanwhile, an asymmetric supercapacitor (ASC) assembled with the NiCo2O4 clusters and activated carbon (AC) as the two electrodes exhibits a high specific capacitance of 129 F g−1 at 1 A g−1, along with a high energy density of 33 W h kg−1 at a power density of 0.66 kW kg−1. Such performance is superior to those of many commercial supercapacitors. This study opens a new avenue for the construction of ordered complex particles with controlled architectures for energy storage and conversion applications.

Research progress on transition metal oxide based electrode materials for asymmetric hybrid capacitors

In the past few years, the increasing energy consumption of traditional fossil fuels has posed a huge threat to human health. It is very imperious to develop the sustainable and renewable energy storage and conversion devices with low cost and environment friendly features. Hybrid supercapacitors are emerging as one of the promising energy devices with high power density, fast charge-discharge process and excellent cycle stability. However, morphology and structure of the electrode materials exert serious effect on their electrochemical performances. In this review, we summarized recent progresses in transition metal oxide based electrode materials for supercapacitors. Different synthesis routes and electrochemical performances of electrode materials and storage mechanisms of supercapacitor devices have been presented in details. The future developing trends of supercapacitor based on metal oxide electrode materials are also proposed.

Commercial-Level Energy Storage via Free-Standing Stacking Electrodes

Summary Pseudocapacitors with a fast faradic redox reaction during the electrochemical charge/discharge process hold great promise for delivering high power and high energy. Here, we used emerging oxygenated carbon nitride (OCN) as a model for nitrogen- and oxygen-enriched carbons and found an anion-selective charging behavior in aqueous electrolytes. The N- and O-mediated hydroxyl anion-selective charging originates from inbuilt surface-positive electrostatic potential localized at heptazine and quaternary N atom structural units. The carbon atoms in heptazine adjacent to pyridinic N act as the electron transfer active sites for faradic pseudocapacitance. The OCN free-standing films (FSFs) were developed as current collector-free electrodes, and stacking OCN FSFs can confer a cell with loading weight over a commercial level. For demonstration, a symmetrical cell with 17.7 mg cm−2 delivers an energy of 140.9 mW h at a high power of 2,499.9 mW, and almost 100% capacitance retention after 20,000 charge/discharge cycles at 50 mA.

Sol–gel synthesized BiFeO3–Graphene nanocomposite as efficient electrode for supercapacitor application

In the present work, bismuth iron oxide–graphene composite has been explored as electrode material for electrochemical supercapacitor application. Bismuth iron oxide (BFO) nanoparticles, synthesized by sol–gel process, are mixed with the graphene sheets in a solution. The electrodes are prepared by coating the resulted slurry on stainless steel (SS) substrate, by drop casting process. The morphology and structure of the BFO–graphene composite are characterized by XRD, FIB-SEM, HRTEM and Raman spectroscopy, which show that the nanoparticles with diameter 100–200 nm are randomly distributed on and around the graphene sheets. The composite electrode exhibits significantly enhanced capacitance as compared to BFO. In this structure, the electrons generated by the surface based Faradaic reactions from the BFO nanoparticles can be transported by the graphene nanosheets toward the current collector. The electrochemical characteristic of the electrodes is investigated through cyclic voltammetry and charging/discharging process. The specific capacitance of the electrode measured at 5–100 mV/s was found to be 17–4 mF/cm2 which is comparable to the most commonly used metal oxide based electrode materials. It shows better cycling stability with 95% retention of capacitance after 2000 cycles.

Fabrication, formation mechanism and the application in lithium-ion battery of porous Fe2O3 nanotubes via single-spinneret electrospinning

Porous Fe2O3 nanotubes have been fabricated by annealing the electrospun precursor nanofibers. Moreover, the mechanism for the formation of the controllable Fe2O3 nanostructures is investigated through manipulating the concentration of the electrospun precursor solution and also discussed based on their morphological evolution processes. When evaluated as anode materials for lithium-ion batteries, the porous Fe2O3 nanotubes exhibit good lithium storage performance with high specific capacity of 1407.9mAhg−1 and good cycling stability (stable up to 250 cycles), which is attributed to the unique morphology of the porous, hollow and continuous one dimensional (1D) nanostructures. These results demonstrate that further improvement or optimization of electrochemical performance in metal oxide-based electrode materials could be realized by the design of 1D nanostructures with unique morphologies.