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The rational design of free-standing hierarchic core–shell nanoporous architectures is a good strategy for fabricating next-generation electrode materials for application to electrochemical energy conversion/storage systems. Herein, hierarchical core–shell 3D Co9S8@Nix:Moy–Se nanowire arrays (NWAs) are constructed by a low-cost, straightforward two-step hydrothermal method and an effective electrodeposition process. The optimal 3D Co9S8@Ni0.5Mo0.5–Se NWAs electrode displays the excellent specific capacity of 460.81 mAh g-1 with a corresponding areal capacity of 0.93 mA h cm-2 at 1.5 mA cm-2. It also demonstrates superb rate capability (~68.4 % capacity retention at 20 mA cm-2) and remarkable cyclic stability (~ 94.3 % capacity retention after 10,000 charge and discharge cycles). Additionally, an asymmetric supercapacitor (ASC) is assembled using the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWAs as the positive electrode, and the as-obtained Fe2O3@PANNFs/N-rGO aerogel as the negative electrode. The assembled Co9S8@Ni0.5Mo0.5–Se//Fe2O3@PANNFs/N-rGO ASC shows a larger operating voltage range of 1.7 V, a high electrochemical energy storage capability (96.90 W h kg−1 at 1,158 W kg−1), and excellent cyclic stability (capacity remained ~ 94.47 % of the original capacity before 10,000 cycles). The all-solid-state ASC device that is also fabricated exhibits a high export working potential window of ~1.8 V, and an outstanding energy density of ~ 102.94 W h kg−1 at ~1,534 W kg−1, demonstrating that the hierarchical 3D Co9S8@Ni0.5Mo0.5–Se NWAs electrode materials are potential candidates for the high-performance energy storage device.

The flexible electrochromic Zn-ion battery (FE-ZiB), a newly born energy-storage technology having both electrochromic characteristics and energy-storage capability in a single device, will be a promising technology for the future transparent wearable electronics. However, the current technology limits the fabrication of FE-ZIB because the zinc (Zn) anode material is opaque and rigid. The development of a flexible and transparent Zn anode is the key factor to overcoming the current limitation. Here, for the first time, a flexible, transparent zinc-nanofiber network anode electrode (Zn@Ni@AgNFs) is reported for an FE-ZiB device that yields a remarkable electrochemical performance of a high areal capacity of 174.82 mA h m2 at 0.013 mA cm-2 applied current density, high optical contrast (50%), and excellent mechanical flexibility. The fabricated FE-ZiB device also exhibits a high volumetric energy density of 378.8 W h m-3 at a power density of 562.7 W m-3 . Besides, the FE-ZiB demonstrates excellent electrochromic capability with a reversible color transition from a transparent in a discharged state (0.3 V) to a dark bluish-violet in a charged state (1.6 V). These results highlight a new pathway for the development of transparent batteries for smart wearable electronic devices.

Hollow-structured Fex Co2-x P, Fex Co3-x O4 , and Prussian blue analogue (FeCo-PBA) microbuilding arrays on Ni foam (NF) are derived from Co-based metal-organic frameworks (Co-MOF) using a simple room temperature and post-heat-treatment route. Among them, Fex Co2-x P/NF shows excellent bifunctional catalytic activities by demonstrating very low oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) overpotentials of 255/114 mV at a current density of 20/10 mA cm-2 respectively, whereas Fex Co3-x O4 /NF and FeCo-PBA/NF demand higher overpotentials. Remarkably, for water electrolysis, Fex Co2-x P/NF requires only 1.61 V to obtain 10 mA cm-2 . In contrast to water electrolysis, urea electrolysis reduces overpotential and simultaneously purifies the urea-rich wastewater. The urea oxidation reaction at the Fex Co2-x P/NF anode needs just 1.345 V to achieve 20 mA cm-2 , which is 140 mV less than the 1.48 V potential required for OER. Moreover, the generation of H2 through urea electrolysis needs only 1.42 V to drive 10 mA cm-2 .

Energy storage devices that offer high energy storage capacity along with high electro-optical and mechanical performance is still a great challenge as a power source for transparent electronic gadgets. Here, we report the fabrication of an ultra-flexible, lightweight embedded PEDOT:PSS/AgNFs/NOA 63 hybrid transparent supercapacitor electrode (HTSE) film by using a peel-off transfer process technique. The HTSE film shows a good electro-optical performance, the sheet resistance of Rs ∼2.12 Ω/sq at 84.65% transmittance, along with excellent mechanical bending and flexibility characteristics. The HTSE film shows a negligible change in resistance, only a ∼1% increase in resistance is observed after 10,000 bending cycles at a bending radius of 2.0 mm. The HTSE film also exhibits good electrochemical performance with an areal capacitance of 3.64 mF/cm2 at 84.65% transmittance. The fabricated supercapacitor device also exhibits excellent mechanical flexibility, only

Metal oxides have attracted great attention as active materials for supercapacitor devices because of their high energy densities. However, their application for transparent supercapacitors is limited due to their opaqueness. The challenge remains to fabricate flexible transparent metal oxide supercapacitor electrodes. Here, in this paper, we report a novel technique to fabricate flexible transparent core–shell MnO2@AuNF network electrodes for flexible transparent supercapacitors. A high electro-optical performance AuNF network electrode (sheet resistance 9.58 Ω sq−1 and optical transparency ∼93.13%) was fabricated using a scalable electrospinning process and thermal vacuum deposition technique. With the AuNF network electrode as a current collector, a hierarchal MnO2 nanosheet was electrodeposited over the AuNF network, yielding a highly interconnected core–shell MnO2@AuNF network electrode structure with high transparency (∼86%). The fabricated MnO2@AuNF network electrode exhibited a high areal capacitance of 8.26 mF cm−2 at 5 mV s−1, along with high rate capability, long-term cycling stability, and excellent mechanical flexibility. Furthermore, the assembled flexible transparent supercapacitor device also showed high transparency (∼79%), a high energy density of 0.14 μW h cm−2 at a power density of 4 μW cm−2, along with excellent mechanical flexibility.

The development of new advanced nanostructures based on the hybridization of different carbon nanomaterials to obtain enhanced performance of energy storage devices has attracted considerable attention. Herein, a hierarchical nanostructure of carbon nanotubes supported electrospun carbon nanofiber networks (CNTs@CNFs) was successfully fabricated by using two facile techniques: – electrospinning and chemical vapor deposition (CVD). Such CNTs@CNFs hybrid showed the uniform and high density of CNTs directly grown on the surface of carbon nanofiber networks, leading to the formation of a hierarchical nanostructure with a large surface area and highly porous characteristics. The enhanced interactions between the CNTs and the CNFs networks were found to improve the electrical conductivity and electrochemical stability of the material. Owing to its unique nanoarchitectures and physicochemical properties, the CNTs@CNFs hybrid was demonstrated to be a potential electrode material for an electrochemical capacitor, in which a high specific capacitance of 464.2 F g−1 at 0.5 A g−1 and long-term stability with 97% retention after 10,000 repeated charge–discharge cycles were achieved. The obtained results suggest that the present CNTs@CNFs hybrid is a promising candidate for an electrochemical capacitor in energy storage technologies.

Flexible transparent conducting electrodes (TCEs) in replacement of brittle indium tin oxide (ITO) films are of ultimate importance in the production of flexible and stretchable displays, lighting devices, and solar panels with the ability to resist harsh weather conditions. Herein, the fabrication of an ultra-smooth, highly flexible transparent conducting electrode with a fully embedded structure of the silver coated electrospun polyvinyl alcohol (PVA) nanofiber (PVA@Ag NF) network is reported. These electrodes are fabricated using a scalable electrospinning and thermal evaporation process. The embedded PVA@Ag NF (E-PVA@Ag NF) network TCE structure provides several advantages, including a smooth surface, mechanical stability under high bending stress, and strong adhesion to the substrate with excellent flexibility, without sacrificing the electrical–optical properties. Ultrahigh aspect ratios with fused crossing at the junction points of the PVA@Ag NF network result in a high transmittance (∼90%) at a low sheet resistance (∼2.56 Ω □−1). The E-PVA@Ag NF network TCE structure shows a smooth surface topology (RRMS ∼ 2.0 nm) with excellent bending stability; the sheet resistance of the TCE remains almost constant after 10 000 bending cycles with a 1.0 mm bending radius. Finally, a flexible transparent heater is fabricated and its performance at low operating voltage is reported.

Hollow-structured Fe

Barium strontium titanate (Ba0.6Sr0.4TiO3) nanostructured thin films have been deposited on platinized silicon substrates by the sol-gel method. The as-fired films were found to be amorphous, which crystallize to cubic phase after annealing at 550°C in air for one hour. The low-frequency dielectric responses of the BST films were measured as functions of frequency range from 1 kHz to 1MHz. The thickness dependence dielectric constant of the BST thin films were measured in the temperature range from −150°C to 150°C at 100 kHz and discussed in the light of an interfacial dead layer. All the samples showed a diffuse type phase transitions. Both the dielectric constant and loss tangent showed anomaly peaks at about 10°C, which corresponds to a tetragonal ferroelectric-to-cubic paraelectric phase transition.

Nanocrystalline Bismuth ferrite (BiFeO3) thin films of different thickness were deposited on glass substrates using sol-gel processing technique. The effect of thickness on structural and optical properties of BiFeO3thin films has been studied. The as-fired films were found to be amorphous that crystallized to hexagonal structure after annealing at 500°C for 2hr in air. The XRD pattern shows that the samples are polycrystalline in structure. At low annealing temperature (400°C), the thick film samples show amorphous in nature while thinner film shows some crystallinity with the presences of impurity phases. At high annealing temperature, all the samples show single phase distorted perovskite BiFeO3structure. The AFM photograph reveals that there is an increase in the grain size with the increase in film thickness. Optical transmittance spectra shows that, with the increase in film thickness, there is a decrease in transmittance (T%). Further, it is observed that increase in film thickness would lead to the decrease in optical energy band gap of the samples. The effect of thickness on the photoluminescent properties of BiFeO3films have also been studied for their possible application in nanoscale optoelectronic devices.

Barium strontium titanate (Ba0.8Sr0.2TiO3) nanocrystalline thin film fabricated by a modified sol‐gel process was crystallized at low temperature 550 °C. The microstructure displayed a polycrystalline nature with average nanograin size of 11 nm. The BST thin film annealed at 550 °C show good dielectric properties. The BST thin films show a diffuse type phase transition. The room temperature dielectric constant and dissipation factors are 310 and 0.03 at 100 kHz, respectively. The capacitance‐frequency curves reveal that the film shows typical frequency dispersion at low frequency. The ferroelectric nature of the BST thin film was indicated by butterfly‐shaped C‐V curves. The effect of temperature on C‐V characteristic of the BST thin films has been investigated. The sample shows paraelectric nature well above the transition temperature as indicated by the absence of butterfly‐shaped C‐V curves.