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This study addresses the inferior performance of assembled supercapacitor devices, which can be attributed to the sluggish kinetics and poor structural stability of positive electrodes and lower capacitance of carbon-based negative electrodes. To overcome this challenge, we propose a sustainable approach that utilizes Ag embedded CoFe-Phosphate (CFPAg) and Ti3C2 MXene as positive and negative electrodes, respectively, to fabricate a hybrid supercapacitor (HS) device. The CFPAg sample, composed of porous nanoflakes decorated with nanospheres of CoFe-phosphate material, is binder-free deposited on Ni-foam using a facial hydrothermal route. In contrast, the MX sample is synthesized via a chemical route and deposited on Ni-foam as the negative electrode. Our results show that the CFPAg electrode exhibits a specific capacity of 1021 mF/cm2 with 80.5% cyclic stability over 10,000 cycles, while the MX electrode shows a specific capacity of 177.6 mF/cm2 with a cyclability of 84.7% over 10,000 cycles. The HS device, fabricated using CFPAg and MX electrodes, exhibits an areal capacitance of 79.6 mF/cm2 and provides excellent cyclic stability of 96% measured over ~39,000 cycles, with 12.43 μWh/cm2 energy at 0.75 mW/cm2 power density measured at 2 mA/cm2 applied current. Our work serves as a foundation for developing a range of electrode materials for next-generation energy storage devices, offering a sustainable and effective solution to improve supercapacitor device performance and longevity.

We have made a first attempt to build a novel Tin doped indium oxide@Manganese oxide (ITO@Mn3O4) nanocomposite electrode to overcome the detriments of Mn3O4 such as low conductivity and small potential window. Herein, we have synthesized the ITO@Mn3O4 nanocomposite by growing Mn3O4 nanoplates over ITO nanofibers synthesized by electrospinning technique. Benefitted from, the high conductivity and negative operating potential window of ITO exceptionally increased in the electrochemical performance of ITO@Mn3O4 was observed. The specific capacitance of optimized ITO@Mn3O4 nanocomposite reached up to 823 F/g at 1 mA/cm2 in a wide potential window of 2 V using Na2SO4 electrolyte. To determine the practical feasibility an ITO@Mn3O4//ITO@Mn3O4 all-solid-state symmetric device was developed, which operated very well in a 2.2 V voltage window. It was found to deliver a maximum energy density of 88 Wh/kg and a power density of 550 W/kg. This novel composite inferred the significance of using simple design to build a high-performance device.

In this study, the nanocomposite of manganese oxide (Mn2O3)/graphene oxide (GO) is deposited on a current collector using the single-nozzle electrospinning method. The effects of the GO concentration (volume %) of the Mn2O3 nanofibers (NFs) on the structural, morphological, and electrochemical properties are investigated systematically. The presence of GO in the Mn2O3 NF samples is confirmed using X-ray diffraction patterns, Raman spectroscopy, and X-ray photoelectron spectroscopy, where sp2 hybridization can be observed. The influence of the GO (volume %) in the Mn2O3 NF samples on the contribution of the capacitive and diffusion-controlled process has been calculated mathematically. GO at 5 vol% in the Mn2O3 sample exhibited a high specific capacitance of 588 Fg−1 at a current density of 0.5 mAcm−2 (2.5 Ag−1) in 1 M aqueous electrolyte with 98% cyclic stability up to 1000 cycles. Furthermore, a coin cell hybrid device was assembled using Mn2O3/GO and a Li-chip as an electrode, 1 M LiPF6 as an electrolyte, and a polypropylene sheet as a separator. This device exhibited a capacitance, an energy density, and a power density of 0.33 F (specific capacitance of 740 Fg−1), 925 Whkg−1, and 3.3 kWkg−1, respectively at a current density of 1 mAcm−2 (2.5 Ag−1) along with 90% retention in capacitance measured till 5000 cycles.

The present investigation deals with controlled synthesis of nanostructured NiCo2O4 thin films directly on stainless steel substrates by facile and economical chemical bath deposition technique, without adding a surfactant or a binder. The consequences of different compositions of solvents on morphological and electrochemical properties have been studied systematically. We used different solvent composition as Double Distilled Water (DDW), DDW:Ethanol (1:1) and DDW: N, N dimethylformamide (1:1). The films have been named as NCO-W for DDW, NCO-WE for DDW: Ethanol (1:1) solvent and NCO-WD for DDW: N, N dimethylformamide (1:1) solvent. The morphologies of NiCo2O4 thin films modify substantially with change in a solvent. NCO-W exhibited the spikes of Crossandra infundibuliformis like nanostructures. The NCO-WE favored the formation of uniformly distributed leaf-like nanostructure whereas NCO-WD showed randomly oriented nanoplates all over the surface area. The Electrochemical performance of these NiCo2O4 thin films were studied using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy techniques. The NCO-W, NCO-WE and NCO-WD electrodes showed specific capacitance values of 271, 553 and 140 F/g respectively at the current density of 0.5 mA/cm2 and excellent capacitance retention of 90%, 91% and 80% after 2000 cycles for NCO-W, NCO-WE and NCO-WD samples respectively. This result reveals that NiCo2O4 is a prominent electrode material for supercapacitor application.

The present investigation deals with controlled synthesis of nanostructured NiCo

Binary metal oxides are deposited via simple chemical routes for high-performance energy storage applications. In this work, we developed nanostructures of BiMnO3 on Ni foam using a hydrothermal method. Initially, the (0 1 0) and (1 1 0) planes confirmed the presence of the BiMnO3 phase. Snow fungus-like nanostructure was transferred to porous interconnected nanoflakes with an increase in deposition time. These nanoflakes serve as large active sites that are beneficial for the diffusion of electrolytic ions that enhance the charge storage and transport process. Consequently, the two-dimensional interconnected nanoflakes showed a high diffusion coefficient, standard rate constant, and minimum transfer coefficient. In addition, BiMnO3 exhibited an aerial capacitance of 6000 mF cm−2 (1500 Fg−1) with an energy density of 102 Wh kg−1 at an applied current density of 20 mA cm−2. For practical applications, an asymmetric coin cell (ACC) device was assembled using BiMnO3 as the positive electrode and activated carbon as the negative electrode in 3 M aqueous KOH as an electrolyte. The fabricated ACC device had an energy density of 14.4 Wh kg−1 at a power density of 50 W kg−1 with a 1.2 V potential; the capacitive retention was 90 %, with 97 % Coulombic efficiency up to 5000 cycles. Accordingly, the results determined that BiMnO3 can be used as an electrode material for high-performance energy storage applications.

In this study, novel binder-free copper-nickel-sulfur (CNS) nanostructures are deposited on 3D Ni foam (CNS/Ni) by a facile hydrothermal technique. A step-wise evaluation of the CNS nanostructures is systematically carried out by varying the hydrothermal reaction times (3, 6, 9, 18, and 27 h). The structural phase, chemical composition, and morphological evolution were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (SEM) respectively. The CNS deposited at 18 h shows interconnected 2D nanoflakes that provide maximum porosity, fast surface redox reaction sites, and improved ionic and electronic conductivity. The electrochemical measurements for CNS-18 show high areal capacitance (2589 mFcm−2), energy density (0.22 mWhcm−2), and power density (7.8 mWcm−2) at a current density of 20 mAcm−2 owing to its high diffusion-controlled contribution (97 %) to the total current as compared to the other CNS samples. The kinetics of the electrochemical measurements are undertaken by the Dunn and Trasatti method. The CNS-18 sample shows long cyclic stability of approximately 81 % up to 7500 cycles. A CNS/AC asymmetric capacitor was fabricated to demonstrate its practical performance. It is surmised that CNS deposited on Ni foam can be used as an efficient electrode in energy storage applications.

In the present work, we have designed and synthesized nanocomposite of IrO2@Mn3O4 with two-step simple and scalable chemical routes. In this route, nanofibers of IrO2 were synthesized by a single nozzle electrospinning technique onto which Mn3O4 was overlaid by a simple SILAR route. The ratio of Mn3O4 and IrO2 was varied by varying the SILAR cycles onto electrospun IrO2 thin film as 20, 40, 60, and 80 cycles. The structural, morphological, and energy storage performance of IrO2@Mn3O4 composite electrodes were investigated. A 2 V kinetic potential with a rectangular-shaped cyclic voltammogram was observed for the IrO2@Mn3O4 electrodes. Moreover, the specific capacitance of 1027 F/g at 1 mA/cm2 was observed for the optimized electrode which is superior as compared with other electrodes. The optimized electrode showed better current and voltage than the individual compounds which might be due to the synergic effect of IrO2 and Mn3O4. Finally, a PVA-LiClO4 gel electrolyte-based solid-state IrO2@Mn3O4//IrO2@Mn3O4 symmetric device was fabricated. The symmetric device possessed an energy density of 81 Wh/kg with a power delivery of 714 W/kg which was capable to light up a green LED. Hence, the 2D transition metal oxides laminated on 1D metal oxides with high conductivity can be promising electrodes for future research.

Quantum dot solar cells (QDSCs) are attractive technology for commercialization, owing to various advantages, such as cost effectiveness, and require relatively simple device fabrication processes. The properties of semiconductor quantum dots (QDs), such as band gap energy, optical absorption, and carrier transport, can be effectively tuned by modulating their size and shape. Two types of architectures of QDSCs have been developed: 1) photoelectric cells (PECs) fabricated from QDs sensitized on nanostructured TiO2 , and 2) photovoltaic cells fabricated from a Schottky junction and heterojunction. Different types of semiconductor QDs, such as a secondary, ternary, quaternary, and perovskite semiconductors, are used for the advancement of QDSCs. The major challenge in QDSCs is the presence of defects in QDs, which lead to recombination reactions and thereby limit the overall performance of the device. To tackle this problem, several strategies, such as the implementation of a passivation layer over the QD layer and the preparation of core-shell structures, have been developed. This review covers aspects of QDSCs that are essential to understand for further improvement in this field and their commercialization.

Herein, we have synthesized iridium oxide (IrO2) nanofibers using electrospinning technique and optimization of annealing temperature is undertaken in order to obtain high quality IrO2 nanofibers. The annealing temperature is varied as 200, 300, 400 and 500 °C. The synthesized material has hollow nanofibrous morphology with average diameter ~45 nm. The formed nanofibers are amorphous in nature. The X-ray Photoelectron Spectroscopy (XPS) result revealed that synthesized iridium is in +4 oxidation state. The electrochemical performance of IrO2 electrodes showed 2 V potential window in three electrode system using 1 M Sodium sulphate (Na2SO4) aqueous electrolyte. The maximum specific capacitance is obtained for sample annealed at 400 °C (705F/g at 1 mA/cm2) which is due to the well-developed morphology with complete removal of polymer content. Moreover, a novel solid state symmetric IrO2/IrO2 supercapacitor with a high operating voltage of 2 V is built. The symmetric supercapacitor exhibits an energy density of 59 Wh/kg at a power density of 714 W/kg and an excellent cycling stability. These results demonstrate the potentialities of using IrO2 for symmetric supercapacitor for building high energy and power density devices.

Nanofibers (NFs) Mn2O3 thin films are prepared by facial and cost effective single-nozzle electrospinning method. The effect of annealing temperature on structural, morphological and surface analysis of NFs coated thin films are investigated. XRD measurement reveals, the formation of cubic crystalline Mn2O3 above 400 °C annealing temperature. Vibration bonds at 515 and 624 cm−1 confirms the presence of Mn2O3 from Fourier transform infrared spectroscopy studies. Field emission scanning electron spectroscopy analysis shows the NFs like morphology of Mn2O3 are observed after heat treatment. The synthesized NFs have high specific surface area with pore size, which is beneficial for charge storage application. Electrochemical performance of electrospunn Mn2O3 NFs are evaluated by using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. The sample annealed at 300 °C shows maximum specific capacitance of 526 F g−1 at 0.5 mA cm−2 in 1 M aq. Na2SO4 electrolyte. In addition, the NFs sample shows 96% retention in specific capacitance measured up to 1000 CV cycles. The storage of charge due to diffusion and capacitive controlled process are analysed in detail with their percentage contribution. It confirms that, the amorphous Mn2O3 NFs structure have high specific surface area and excellent capacitive performance as compared to crystalline Mn2O3.

An exotic 3-D tungsten oxide (WO3) microflower was synthesized via low-cost and environmental-friendly hydrothermal strategy. The effect of structure-directing agent on the formation of 3-D microflowers from a 2-D nanosheets of WO3 and its gas sensing behavior are investigated. The as-synthesized WO3 powder was used in morphological, structural and phase studies by X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The WO3 samples were found to be polycrystalline with monoclinic crystal structure. The SEM micrographs revealed the formation of 3-D microflowers made up of two-dimensional (2-D) multi-directional dendritic nanoplates. The potassium hydroxide (KOH) acts as a structure-directing agent in the formation of 3-D microflowers of WO3 sample. To further understand the formation of 3-D microflowers of WO3 sample, concentration-dependent experiments were carried out by varying KOH concentration and the formation mechanism was investigated. The synthesized WO3 microstructures were subjected to detailed gas sensing tests for different gases at an optimized temperature. A selective, sensitive gas response was obtained for WO3 gas sensor. The lower detection limit is about 1 ppm at 150 °C working temperature for an optimized WO3 gas sensor. The gas sensing results indicate that the 3-D microflower-like WO3 nanostructures are highly promising for applications as gas sensors.

Symmetric supercapacitor is advanced over simple supercapacitor device due to their stability over a large potential window and high energy density. Graphene is a desired candidate for supercapacitor application since it has a high surface area, good electronic conductivity and high electro chemical stability. There is a pragmatic use of ionic liquid electrolyte for supercapacitor due to its stability over a large potential window, good ionic conductivity and eco-friendly nature. For high performance supercapacitor, the interaction between ionic liquid electrolyte and graphene are crucial for better charge transportation. In respect of this, a three-dimensional (3D) nanoporous honeycomb shaped sulfur embedded graphene (S-graphene) has been synthesized by simple chemical method. Here, the fabrication of high performance symmetric supercapacitor is done by using S-graphene as an electrode and [BMIM-PF6] as an electrolyte. The particular architecture of S-graphene benefited to reduce the ion diffusion resistance, providing the large surface area for charge transportation and efficient charge storage. The S-graphene and ionic liquid-based symmetric supercapacitor device showed the large potential window of 3.2 V with high energy density 124 Wh kg−1 at 0.2 A g−1 constant applied current density. Furthermore, this device shows good cycling performance (stability) with a capacitive retention of 95% over 20,000 cycles at a higher current density of 2 A g−1.