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In this study, an electrospinning method was used to produce highly conductive freestanding carbon nanofibers (CNFs). The freestanding CNFs are compatible with hierarchical growth techniques, such as hydrothermal processes, for the nanostructure engineering of supercapacitor electrodes with enhanced electrochemically active sites. Therefore, the flower-like FeMoO 4 @CNF nanosheets were investigated to improve the electrochemical performance using aqueous and neutral electrolytes (Na 2 SO 4 and K 2 SO 4). The optimized FeMoO 4 @CNF electrode exhibits areal capacitances of 252 and 220 mF·cm−2 at a high current density of 2.5 mA·cm−2 with Na 2 SO 4 and K 2 SO 4 electrolytes, respectively. The wide potential window (1.6 V) of the symmetric supercapacitor delivered maximum energy densities of 22.4 and 19.6 μWh·cm−2 at a power density of 2 mW·cm−2 for Na 2 SO 4 and K 2 SO 4 electrolytes, respectively. [ABSTRACT FROM AUTHOR]

Currently, lightweight wearable energy storage devices are in great demand owing to their use in wearable electronics and energy-efficient electric vehicles. Freestanding carbon nanofibers replace the need for metal substrates while providing a rapid electrical network owing to their excellent electrical properties. Bimetallic oxides with multivalent oxidation states facilitate the rapid transfer of electrolytic ions owing to efficient Faradaic reactions, thereby enhancing the overall energy storage capability. In this study, CoOx@CNF was derived from ZIF-67 (zeolitic-imidazolate framework) @PAN-2MI fibers that were stabilized in air at 280°C and then annealed in argon at 900°C. Subsequently, Co was seeded on the annealed CoOx@CNF and subjected to a hydrothermal process in sodium molybdate dihydrate solution to grow CoMoO4 nanosheets, eventually forming bimetallic CoMoO4@CNF. The concentration of sodium molybdate solution was varied to determine the optimal growth conditions for CoMoO4 nanosheets. The energy density of the optimal bimetallic CoMoO4@CNF sample was 166.5 μWh cm-2 at a power density of 200 μW cm-2; this represented a nearly twofold increase compared to that of the single metallic CoOx@CNF. Powering humidity sensors using only one CoMoO4@CNF supercapacitor was demonstrated. The optimal sample remained stable during long-term galvanostatic charge and discharge cycles ( N cyc = 30,000) and retained 100% of its specific capacitance. [ABSTRACT FROM AUTHOR]

Summary: Flexible, lightweight, and freestanding zinc‐manganese oxide carbon nanofibers are promising materials for the fabrication of portable electronic devices. Composite nanofibers were synthesized using terephthalic acid and sodium dodecyl sulfate. Terephthalic acid improves the flexibility of the composite fibers and facilitates the diffusion of electrolytic ions. Meanwhile, sodium dodecyl sulfate aids to elevate the metal (zinc) oxide particles to the surface of the nanofibers during annealing. The texturing of the carbon nanofiber surface with ZnO enhances the electrochemical activity of the composite fibers. Parametric studies were conducted by varying the weight ratio of zinc and manganese acetates from zero to unity. The optimal case with a ratio of 0.75 produces specific capacitances of 1080 and 817 F·g−1 at current densities of 1 and 10 A·g−1, respectively, with a wide potential window of 1.6 V, indicating outstanding energy storage capabilities. The capacitance retention was 92% after 10 000 galvanostatic charge‐discharge cycles. The bending angle test confirmed the mechanical durability of the freestanding carbon nanofiber electrodes, and the corresponding change in the cyclic voltammetry curve was negligible. [ABSTRACT FROM AUTHOR]

Summary: A water‐based iron oxide/cobalt/reduced graphene oxide (Fe2O3/Co/rGO) precursor was spray‐coated via supersonic spraying onto a flexible substrate to fabricate supercapacitor electrodes. The inclusion of Co in Fe2O3 increased the number of electrochemical reaction sites and enhanced the local electron mobility, which in turn improved the overall energy storage capability of the electrodes. The Co salt concentration was varied to determine the optimal electrochemical performance. Supersonic spraying was utilized to coat rGO sheets, on which the bimetallic CoFe2O3 particles were evenly distributed. The uniform coating of rGO and its excellent electrical conductivity increased the electron mobility of the electrode and provided shorter ionic diffusion pathways. Furthermore, the catastrophic impact of supersonic spraying led to the exfoliation of the rGO sheets, which increased the surface area and enhanced the adherence of the CoFe2O3 particles to the substrate. This rGO exfoliation also enabled the accommodation of the CoFe2O3 particles between the exfoliated graphene sheets, thereby enhancing electron transport throughout the electrode. The optimal sample exhibited a specific capacitance of 1.11 F·cm−2 at a current rate of 2 mA·cm−2, energy density of 0.62 mWh·cm−2 at a power density of 8 mW·cm−2, and capacitance retention of 89% after 10,000 charge‐discharge cycles. [ABSTRACT FROM AUTHOR]

In this study, freestanding carbon nanofibers embedded with bimetallic manganese-iron oxide are fabricated for flexible supercapacitor applications via electrospinning. A polyacrylonitrile solution is used as the carbon source, and poly(methyl methacrylate) functions as a sacrificial template to produce microporous carbon nanofibers. The concentrations of manganese acetate and iron acetylacetonate are varied to determine the fabrication conditions for maximal electrochemical performance. The optimized supercapacitor cell exhibits a capacitance of 467 F g−1 at a current density of 1 A g−1 and a capacitance retention of 94% at the end of N = 10,000 cycles. The higher mechanical durability of the electrode is confirmed by the absence of electrochemical deterioration at the end of performing 500 bending cycles. Overall, the sample comprising carbon nanofibers, in which the optimal amount of manganese-iron oxide is embedded, has the required pseudocapacitive characteristics and is an interesting choice for high-energy-storage supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Iron oxide (Fe 2 O 3) nanoparticles and reduced graphene oxide (rGO) sheets were supersonically sprayed onto a nickel substrate to fabricate flexible supercapacitors. The supersonic impact velocity was adjusted by varying the air chamber pressure from 2 to 6 bar, which facilitated the self-healing of Stone-Wall defects in rGO sheets. Supersonic spraying caused exfoliation of the rGO sheets, which in turn increased the surface area and adherence of the Fe 2 O 3 nanoparticles. The optimal case exhibited a specific capacitance of 1.44 F⋅cm-2 at a current rate of 1.5 mA⋅cm-2 and the energy density was 14.23 mWh⋅cm-3 at 250 mW⋅cm-3. The width of the potential window increased to 1.4 V, implying a significant increase in the energy storage capability. The energy density of the supersonically sprayed Fe 2 O 3 /rGO electrode also showed no signs of deterioration even when the increased current density interfered with the electrode performance. • Supersonically sprayed Fe 2 O 3 /rGO flexible electrodes were fabricated. • The fabricated electrodes had large surface areas and high volumetric energy and power densities. • The optimal case exhibited specific capacitance of 1.44 F cm-2 at a current rate of 1.5 mA cm-2. • The volumetric energy density of the optimal case was 14.23 mWh·cm-3 at 250 mW cm-3. [ABSTRACT FROM AUTHOR]

Summary: Wearable electronic devices such as health monitors, sensors, and e‐skin can be powered by lightweight, high‐power supercapacitors. Using a binder‐free and low‐temperature hydrothermal method, polyhedral ZnO nanoparticles were grown on carbon nanotube (CNT)‐decorated cotton fabric, which is friendly to human skin and highly wearable, inexpensive, and thus commercially viable. The concentration of the starting material, zinc acetate, was varied to optimize the electrochemical performance. The evenly spaced polyhedral ZnO facilitated efficient permeation of the electrolyte into the active material. The fabric filaments were decorated with CNTs to enhance electron transfer and the overall electrochemical processes. The symmetric cell comprised of cotton fabric decorated with ZnO polyhedron/CNT showed no discernible change in the cyclic voltammetry curves even after 500 bending cycles, demonstrating the mechanical durability of the electrode. The potential window of 1.6 V using a Na2SO4/K2SO4 aqueous dual‐ion electrolyte improved the long‐term electrochemical stability and increased the energy storage capacity. The capacitance retention was 94% after 5000 cycles at a current density of 1 A·g−1, indicating long‐term electrochemical stability. A specific capacitance of 375 F·g−1 at a current density of 5 A·g−1 and energy density of 33.3 Wh·kg−1 at a power density of 2000 W·kg−1 were recorded for the optimized electrode. Highlights: Polyhedral ZnO was grown on cotton fabric using a hydrothermal process.The electrochemical performance was optimized by varying the zinc acetate concentration.The highest specific capacitance was 375 F·g−1 at a current density of 5 A·g−1.Under optimal conditions, the capacitance retention was 94% at N = 5000 cycles.The energy density of the electrode was as high as 33.3 Wh·kg−1. [ABSTRACT FROM AUTHOR]

The electrostatic spray method is a promising nonvacuum technique for efficient deposition of thin films from solutions or dispersions. The multitude of electrostatic spray process parameters, including surface tension, viscosity, and conductivity of the liquid, applied voltage, nozzle size, and flow rate, make electrostatic spray deposition very versatile for the morphological engineering of nanostructured films. The current state‐of‐the‐art in electrostatic spraying can produce exceptional morphologies. Such tailoring of morphologies is notably useful in electrochemical applications where high electrolyte‐accessible surface area often improves performance. Interesting morphologies of metal oxides and their composites are highlighted, including nanopillars, nanoferns, and porous microspheres produced by electrostatic spraying to enhance energy conversion and storage performance. The physics associated with the electrostatic spray process and morphology control using it are also presented. The manuscript highlights the potential of electrospray processing for producing thin films of controlled microstructure, from ultrasmooth layers in organic photovoltaics and perovskite photovoltaics to hierarchical nanostructured films for anodes and photoanodes. It aims to help researchers appreciate essential aspects of electrostatic spray deposition efficiency, process control, and morphology engineering for energy conversion (e.g., solar cell, fuel cell, and photoelectrochemical cell) and energy storage (e.g., lithium‐ion battery and supercapacitor) electrodes. [ABSTRACT FROM AUTHOR]

• Fabricating transparent flexible metallic fibers (TMFs) is discussed. • The importance of lightweight, flexible, and scalable TMFs for soft electronics has been stressed. • Challenges associated with the fabrication and integration of TMFs in practical applications are addressed. The use of transparent metallic fibers (TMFs) in various applications, including touchscreens, solar cells, and transparent heaters, is gradually increasing, thereby emerging as a state-of-the-art technology in advanced portable and self-powered wearable electronics. This review discusses several novel approaches for fabricating TMFs that exhibit excellent transparency, flexibility, and low sheet resistance. TMFs are aim to meet the increasing demand for soft and wearable electronic and optoelectronic devices. Lightweight and flexible TMFs are alternatives to indium tin oxide, which is expensive, brittle, and possesses low optical transmittance in near-infrared spectra. Moreover, TMF fabrication is scalable. This review focuses on crucial techniques employed in the fabrication of metallic fibers and presents key parameters in a tabular format. In addition, the insights of developing high-performance TMFs for various applications are provided. Finally, challenges associated with the fabrication and integration of TMFs in practical applications are discussed and addressed. [ABSTRACT FROM AUTHOR]

• Electrospun nanofiber mats are surface-decorated with Mn-doped ZIF-8 nanoparticles. • Freestanding flexible Mn@ZnO/CNF is demonstrated as a promising supercapacitor electrode. • Enhanced capacitance of 501 F·g−1 and 92% capacitance retention after 10,000 cycles are obtained. We demonstrate freestanding, flexible, and cost-effective supercapacitor electrodes comprising carbon nanofibers (CNFs) decorated with metal oxide framework (MOF)-derived manganese-doped zinc oxide (Mn@ZnO). Nanoparticles of manganese-doped zeolitic imidazolate framework (ZIF-8) were grown directly on electrospun polyacrylonitrile nanofibers by a simple solution-phase synthesis. Carbonization of these composite fibers produced high surface area dodecahedral Mn@ZnO on core CNFs that provide fast electron-transfer pathways. The synergy between Mn@ZnO (active sites for Faradaic reactions) and the highly electrically conductive carbon nanofiber improves the performance of the supercapacitor electrode. The Mn@ZnO/CNF electrodes exhibit a high specific capacitance of 501 F·g−1 and retain >92% of their initial capacitance after 10,000 cycles. The optimized Mn@ZnO/CNF electrodes deliver impressive energy densities of 72.1 W·h·kg−1 and 33.3 W·h·kg−1 at power densities of 500 W·kg−1 and 5000 W·kg−1, respectively. This electrochemical performance demonstrates that the Mn@ZnO/CNF nanostructured composite is a robust electrode material for long-lifetime high-rate energy storage/delivery devices. [ABSTRACT FROM AUTHOR]

Highlights • Breakthrough demonstration of freestanding flexible high-performance photoanodes. • Uniform growth of ZnO nanowires improves photoelectrochemical performance. • ZnO NW/Ni fiber photoanode produces photocurrent density of 1.14 mA/cm2 at 0.4 V vs Ag/AgCl. • Unique morphology provides exceptional stability even after 1000 bending cycles. Abstract We demonstrate impressive performance of photoanodes comprising ZnO nanowires grown over nickel fibers for efficient water splitting. The photoanode is substrate-free and flexible, exhibiting excellent stability (∼98%) in photocurrent density even after 1000 bending cycles. The hierarchically structured ZnO nanowires on nickel microfibers synergistically provide many accessible electrochemical sites and enhance the photocurrent density to 1.14 mA/cm2 at a voltage of 0.4 V vs. Ag/AgCl. The one- and two-dimensional structures of the ZnO nanowires over nickel microfibers enable an efficient charge-transport mechanism that supports high light-harvesting efficiency. Scanning and transmission electron microscopy are used to study the morphologies of the samples in detail, while X-ray diffraction confirms the metallic state of Ni and the crystallinity of ZnO. [ABSTRACT FROM AUTHOR]

Abstract Bimetallic (zinc-iron) oxide with a pillar-like morphology is decorated over graphene films. The electrosprayed composite demonstrates good electrochemical performance as an anode material for lithium-ion batteries. Scanning and transmission electron microscopy images confirm the effective decoration of graphene sheets with bimetallic Zn-Fe oxide particles. The composite shows a high capacity of 1601 mAh⋅g−1 at 100 mA·g−1 owing to its unique layer-particle morphology. The anode material exhibits excellent capacity retention of 77% (∼1235 mAh⋅g−1 at 100 mA·g−1) after 100 cycles, due to buffering of volumetric strain in the metal oxide by flexible conductive graphene sheets. Zinc forms an alloy with the lithium ions, and the graphene sheets prevent particle agglomeration, keeping transport distances within particles small. Thus, synthesizing a composite of graphene with Zn-Fe oxides via electrospray deposition is a promising method for preparing high-performance anode materials for lithium-ion batteries. Highlights • G/ZnFe 2 O 4 as an anode for LIB, it exhibits 1235 mAh·g-1 after 100 cycles. • The excellent electrochemical performance, high capacity and cycling stability were achieved. • Graphene decorated nanostructured ZnFe 2 O 4 attributed to numerous active sites and interspaces. • Facile electro-spraying of active material straightaway on stainless steel spacer. [ABSTRACT FROM AUTHOR]

Highly flexible freestanding carbon nanofibers were electroplated with silver for use in supercapacitor applications. The brittle carbon nanofibers were encased within bendable silver shells to provide superior flexibility and resilience of the supercapacitors. The enhanced electrical conductivity derived from the silver shell structure dramatically increased the capacitance of the supercapacitor. The silver shell also conferred structural stability to the carbon core, thus furnishing stable, long-term electrode performance. Nearly 100% of the specific capacitance was retained after N  = 10,000 galvanostatic charge-discharge cycles. The mechanical endurance or stability of the fabricated electrode was evaluated using 1,000 bending cycles, demonstrating that the electrode performance remained unchanged. Cyclic voltammetry and galvanostatic discharge curves were measured at various scan rates and current densities. The fabricated electrodes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, which clearly illustrated the carbon-core and silver-shell structure. [ABSTRACT FROM AUTHOR]

Abstract Electrosprayed BiVO 4 adopts a nanopillar structure formed by diffusion-limited aggregation, which maximizes the surface area of the nanopillars. However, increasing the interfacial area between an electrode and the electrolyte through nanostructuring enhances the overall interfacial activity for solar water splitting. For this purpose, the pH of the precursor solution used for electrospraying BiVO 4 was altered by adding ammonium hydroxide, thereby inducing a drastic change in the morphology of BiVO 4. The previously demonstrated nanopillar morphology of electrosprayed BiVO 4 was transformed into a nanofern structure that increased the photocurrent density of BiVO 4 from 0.82 to 1.23 mA·cm−2 at 1.2 V vs. Ag/AgCl. The produced films were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and electrochemical impedance spectroscopy. Highlights • BiVO 4 nanopillar morphology were tuned to nanoferns with a facile one-pot method. • Nanoferns showed the fast photoresponse due to enhanced photoelectrochemical sites. • The photocurrent density of BiVO 4 nanoferns reached to 1.23 mA·cm−2 at 1.2 V vs Ag/AgCl. • The structural and morphological properties of BiVO 4 nanoferns were characterized. [ABSTRACT FROM AUTHOR]

Abstract This manuscript reports the preparation, characterization, and testing of stable high-capacity lithium-ion battery anodes based on graphitic carbon nitride (g-CN) nanosheets hosting ZnFe 2 O 4 nanoparticles (ZFCN). The ZFCN is prepared by a one-pot thermal process, then supersonic cold spraying is used to rapidly deposit films with a lamellar morphology that allows enhanced capacity retention by preventing particle agglomeration. The presence of g-CN nanosheets minimizes degradation of ZnFe 2 O 4 by providing a buffering space during the lithiation/delithiation process. The ZFCN composite anodes exhibit first reversible capacities of 1550 mAh·g−1 at 50 mA·g−1 and up to 934 mAh·g−1 at 1000 mA·g−1 after 20 cycles. The superior electrochemical performance and capacity retention (88% after 160 cycles at 100 mA·g−1 relative to the first reversible capacity) are attributed to highly reversible alloying/conversion mechanisms. The combination of high performance and stability with the use of low-cost earth-abundant elements and scalable processing approaches gives this ZFCN composite immense potential for use as a stable high-performance anode material for lithium-ion batteries. • ZnFe 2 O 4 /g-C 3 N 4 films were fabricated as LIB anode via rapid supersonic spraying. • Lamellar morphology prevented particle agglomeration ensuing enhanced capacity retention. • High capacity retention of 93% is observed at 100 mA·g-1 after 70th cycle. • The ZFCN composite shows high capacity of 934 mAh·g-1 at 1000 mA·g-1 current rate. [ABSTRACT FROM AUTHOR]

We present a uniform rhombohedral Ni@ZnO bimetallic oxide host over carbon nanofibers (CNF) as an anode material for Li-ion batteries. Ni@ZnO was produced by annealing a Ni@zeolitic imidazolate framework (ZIF-8) hierarchically decorated over CNFs. The rationally-designed freestanding composite exhibited promising stability in electrochemical performance. A first reversible capacity of 1051 mA·h·g −1 was measured at a current density of 100 mA·g −1 , and 88% of this capacity was retained after 100 cycles. We attribute this high capacity retention to the hierarchical structure of the Ni@ZnO-enwrapped carbon framework encapsulating the conductive CNFs, as demonstrated by scanning and transmission electron microscopy. The composite electrode also showed a high specific capacity of ∼497 mA·h·g −1 in high-rate testing at 1000 mA·g −1 , because the cage-like framework of the material allowed rapid charge transfer and Li-ion diffusion in the anode. [ABSTRACT FROM AUTHOR]

Abstract Highly flexible, binder-free, scalable, and high-capacity lithium ion battery anodes were fabricated by ball-milling SnO 2 and ZnO 2 particles to form Zn 2 SnO 4 /SnO 2 ternary oxide particles that were supersonically sprayed over a large area of a flexible copper foil without using any binders. The addition of rGO promoted uniform distribution of the particles and enhanced the overall performance of the composite anodes, which showed excellent long-term stability and a reversible capacity of 1316 mAh·g−1 at a specific current of 100 mA g−1 after 100 cycles. The supersonic deposition promoted inter-particle cohesion as well as adhesion of the coating materials onto the flexible substrate. Without added binder, the potential adverse effects of using binders on the electrical properties of the anodes were eliminated. The morphology and composition of the samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The low-cost and scalable synthesis and deposition methods used here may offer a pathway for achieving commercially viable high-capacity anodes for various flexible electronic devices. Highlights • SnO 2 and ZnO 2 were ball-milled to form Zn 2 SnO 4 /SnO 2 ternary oxide particles. • Reduced graphite oxide (rGO) promoted uniform distribution of the particles. • The uniform distribution enhanced the overall electrode performance. • Supersonic deposition promoted interparticle cohesion & particle−substrate adhesion. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework-derived carbon and metal oxide composites are promising for applications in lithium-ion batteries due to their morphology and porous structure. Herein, we report freestanding carbon nanofibers grafted with amorphous ZnO where the rhombic dodecahedral morphology of the parent (ZIF8) is maintained. The impacts of ZIF8 loading temperature on particle size after pyrolysis and on the electrochemical properties of these hybrid structures for LIBs are investigated. Polyacrylonitrile nanofiber loaded with ZIF8 at 45 °C exhibits a perfect sodalite topology and optimized particle size. The carbonized freestanding composite fibers have a high specific capacity of 818 mAh·g −1 at a current density of 100 mA·g −1 after 100 cycles. This remarkable performance of ZIF8-derived ZnO is due to its loading and coordination chemistry, which facilitates flexible volume changes and continuity in electrical conductivity through a continuous carbon nanofiber. [ABSTRACT FROM AUTHOR]

Piezoelectric nanogenerators (PENGs) are the core components of self-powered devices used in sensors, ecofriendly wearable gadgets, and biomedical implants. This study introduces and demonstrates a flexible PENG with supersonically cold-sprayed films of cobalt titanate (CTO) and polyvinylidene fluoride (PVDF). An electrically poled PENG produces a maximum output voltage of 34.8 V under a tapping force of 20 N, whereas a CTO/PVDF-based PENG exhibits 25.4 V across a loading resistance ( R L ) of 50 MΩ and generates a short-circuit current of 30 μA at 0.1 MΩ. Furthermore, the maximum power density is 25 μW·cm-2 at R L = 0.6 MΩ. Cyclic tapping and bending test results show that open-circuit voltages (Voc) of 25.4 and 5.8 V are produced under the tapping cycle of N tap = 4200 and bending cycle of N bend = 750 , respectively, confirming the mechanical durability of the PENG. Thus, the potential of CTO/PVDF films for use in PENGs with various functionalities can be confirmed based on the V oc values generated from bending, mobile tapping, walking, and lifting movements. [ABSTRACT FROM AUTHOR]

We demonstrate the synthesis of a highly stable, freestanding and flexible anode material for lithium-ion batteries created by depositing a conformal coating of TiO 2 on a SnZnO/carbon nanofiber (CNF) composite using atomic layer deposition. The term SnZnO is used here because metallic Sn is observed in the SnZnO/CNF composites after annealing under argon gas. The elemental composition of the material was confirmed by energy-dispersive X-ray spectroscopy, while the oxidation states of the elements were determined by X-ray photoelectron spectroscopy. Cross-sectional transmission electron microscopy showed that the core regions of the composite nanofibers were almost uniformly covered by a TiO 2 shell. The specific capacities of the TiO 2 -coated and uncoated samples at a high current density (5C) were 413 and 159 mAh·g −1 , respectively. An analysis of the surface morphology after cycling indicated that the stability of the solid electrolyte interface layer increased after the formation of the protective conformal TiO 2 layer. As a result, no signs of anode degradation were observed even after 700 cycles at a current density of 5C. We attribute this exceptional stability to the buffering of the anode material by the protective coating during volumetric expansion. [ABSTRACT FROM AUTHOR]

A binder-free nanocomposite consisting of ZnO nanoparticles (NPs) grown directly on graphene sheets by electrospraying was fabricated for use as an electrode material in supercapacitors. The optimal concentrations of graphene and ZnO NPs were determined from the capacitive characteristics of the composite. Scanning electron microscopy confirmed that the ZnO NPs grew in a uniformly distributed manner on the graphene sheets and that they exhibited negligible agglomeration. Further, X-ray diffraction analysis confirmed that ZnO growth was preferentially oriented along (100) plane in the ZnO/graphene composite. A symmetric supercapacitor fabricated using this composite exhibited an energy density of 67 mWh·cm −3 and power density of 6000 mW·cm −3 . The composite also showed good long-term cycling performance, retaining 90% of its capacitance after 1000 galvanostatic charge/discharge cycles. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of core-shell SnO x /carbon nanofiber (CNF) composite mats via single-nozzle one-step electrospinning for use as flexible freestanding electrodes in supercapacitors. The freestanding and flexible nature of the composites is essential for their use in lightweight, portable, and foldable electronic devices and eliminates the need for a separate current collector. We fully characterized the structural and morphological properties of the SnO x /CNF mats and optimized the SnO x to CNF precursor ratio. The optimized SnO x /CNF-based symmetric supercapacitor exhibited a capacitance of 289 F·g −1 at a scan rate of 10 mV·s −1 . Moreover, it retained more than 88% of its initial capacitance after 5000 cycles, highlighting the long-term stability of supercapacitors based on these SnO x /CNF mats. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of a MnO x /carbamide carbon nanofiber (CCNF) composite consisting of MnO particles embedded in CCNFs as a highly flexible and freestanding electrode material for supercapacitors. A sacrificial polymer component, polymethylmethacrylate, included in the precursor solution, pyrolyzes during heating, resulting in pores in the fibers, some of which are filled by the MnO nanocrystals. Carbamide is added to control the size of the MnO x particles as well as to increase the carbon content of the composite and hence its conductivity. The X-ray diffraction and Raman spectra of the composite show that the MnO particles formed have low crystallinity. Transmission electron microscopy confirms that the MnO particles are distributed very uniformly over the CCNFs. Symmetric supercapacitors constructed using electrodes of this composite exhibit specific capacitances of 498 F∙g −1 at a scan rate of 10 mV∙s −1 and 271 F∙g −1 at a current density of 1 A∙g −1 . They also exhibit excellent long-term cycling performance, retaining 93% of their initial capacity after 5000 cycles of galvanostatic charging/discharging. [ABSTRACT FROM AUTHOR]

We have produced flexible, freestanding, and light weight mats of FeO x -decorated carbon nanofibers (CNFs) and demonstrated their use in supercapacitors with high energy and power density and excellent long term capacitance retention. Highly flexible carbon-iron oxide nanofibers were synthesized by electrospinning a solution of polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), and iron acetylacetonate (FeAcAc), followed by annealing to carbonize the PAN, pyrolyze the PMMA to produce pores, and convert FeAcAc to FeO nanoparticles. The morphology of the FeO x /CNF composite was determined by scanning and transmission electron microscopies, which showed that the embedded FeO x nanoparticles were well distributed in the CNF electrode. We employed cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy to evaluate the electrochemical performance of symmetric supercapacitors prepared from the FeO x /CNF composite. The supercapacitors exhibited high specific capacitance (427 F·g −1 at 10 mV·s −1 and 436 F·g −1 at 1 A·g −1 in the optimal case) and good stability, retaining 89% of their initial capacitance after 5000 cycles at a current density of 1 A·g −1 . The optimal device achieved an energy density of 167 Wh·kg −1 at a power density of 0.75 kW·kg −1 , and an energy density of 66 Wh·kg −1 at a power density of 7.5 kW·kg −1 . These combinations of energy and power densities can meet the needs of many emerging supercapacitor applications. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of flexible electrospun carbon nanofibers (CNFs) containing uniformly distributed carbon nanotubes (CNTs) and iron oxide (FeO x ) nanoparticles (NPs) as a composite material for lithium-ion battery (LIB) anodes. The uniform incorporation of CNTs and FeO x NPs within the CNFs was confirmed by transmission electron microscopy. Embedding even a small amount of CNTs (0.1 wt%) in the CNFs increased the LIB performance by a factor of two compared with pure CNFs. The specific capacity was also increased, by 25%, when an iron source (iron (III) acetylacetonate) was added at a concentration of 2 wt%. The FeO x -CNT/CNF electrode maintained a capacity of 1008 mAh∙g −1 at a current density of 100 mA∙g −1 after 100 cycles. Further, the high-performance anode material was freestanding, flexible, and lightweight. This makes it suitable for next-generation LIBs, which must deliver high power over long periods while also being light and flexible. [ABSTRACT FROM AUTHOR]

Titania (TiO 2 ) nanoparticles were uniformly distributed on and are well attached to reduced graphene oxide (rGO) by supersonic cold spraying. The process facilitated rapid production of lithium ion battery (LIB) anodes. Integration of TiO 2 with rGO not only enhanced the conductivity of the anode, but also prevented agglomeration of the titania nanoparticles, which facilitated uniform distribution of the nanoparticles and thus consistently reduced the electron diffusion length. Integration of rGO with TiO 2 widened the characteristic voltage range of the resulting rGO-TiO 2 composite (0.01–3 V) relative to that of pure TiO 2 , which enhanced the capacity during the lithiation process. Therefore, the LIB cell exhibited superior performance with long cycle durations even under high current rate. The optimal weight ratio of rGO to TiO 2 was found to be 1:1, which produced a retention capacity of 203 mA h g −1 at N = 300 cycle under a current rate of 1 C = 336 mA g −1 . Rapid production of rGO/TiO 2 nanocomposites via supersonic cold spraying may facilitate commercialization of high-quality LIB cells. [ABSTRACT FROM AUTHOR]

• Prominent MIL-related morphologies, designs, and synthesis methods are reviewed. • MIL- and MIL-derived porous carbons, and composites are thoroughly discussed. • Performance of MIL-based LIB electrodes are compared. • Perspectives, challenges, and prospects for commercialization are discussed. Developing high-performance energy storage and conversion devices is critical for implementing renewable and sustainable energy technologies. Nanoporous Matériaux de l′Institut Lavoisier (MIL)-type metal–organic framework materials can accommodate porous carbonaceous substances, metal oxides, or chalcogenides or can be fashioned into porous composites. Several of these structures show great potential for use in energy storage devices. Most MILs include high-valent cations, such as iron, vanadium, and chromium, and can accommodate abundant redox-active species in their scaffolds. Substantial recent research on MIL-based lithium-ion-battery (LIB) electrodes has highlighted the synergistic impact of restructuring the MIL morphology on enhancing specific lithium uptake capacities. Several studies have also explored the rate capabilities of MIL-based electrodes with different energy storage mechanisms. In this review, advanced MIL-based composites for LIBs compatible with electric vehicles are comprehensively analyzed, focusing on achieving rapid charging and long-term cycling performance under high-current-loading conditions. The challenges, future prospects, and research directions for design and synthesis of MIL-based composites are also discussed. [ABSTRACT FROM AUTHOR]

We demonstrate the fabrication of freestanding and flexible MnO-decorated carbon nanofiber (CNF) composites as lithium-ion battery anode materials. They showed an initial capacity of 1131 mAh·g −1 and a retention capacity of 923 mAh·g −1 after 90 charge-discharge cycles under a current rate of 123 mA·g −1 . Decoration of MnO nanocrystals on the CNFs enhanced the lithium storage capacity of the composites. The optimal concentration of MnO was identified by varying its weight percentage from 0 to 7%. When the concentration was increased, more reaction sites for lithium ions were formed, which in turn increased the overall specific capacity. The intensity of the D band in the Raman spectra of the decorated CNFs was higher than that of the G band, indicating the enhanced diffusion of lithium ions. The plateau region of the discharge curve observed in the cases of higher MnO concentrations indicated the active reduction of MnO; consequently, a higher reversible capacity was achieved. These flexible and freestanding MnO-CNF nanocomposites can be used in lightweight, portable, and flexible batteries. [ABSTRACT FROM AUTHOR]

A flexible piezoelectric nanogenerator (PENG) was developed to convert ambient mechanical energy into electrical energy. Highly crystalline template-free zinc oxide (ZnO) microrods were prepared using a wet chemical method at a low temperature. As-synthesized ZnO microrods were blended with polyvinylidene fluoride (PVDF) to prepare a piezoelectric composite film using the supersonic spraying method. A PENG electrode comprising ZnO microrods (0.5 g) produced 15.2 V under a tapping force of 20 N at 5 Hz. In addition, an output current of 32 μA was produced with a maximum power density of 12.5 μW cm–2. The output voltage considering various body movements was investigated to demonstrate the flexibility and durability of the proposed PENG. Furthermore, the supercapacitive properties of ZnO/reduced graphene oxide were studied. [ABSTRACT FROM AUTHOR]

• The review focuses on potential of flexible, freestanding binder-free nanofiber electrodes for real time applications. • The advancement of the hollow/porous composite nanofibers, and process parameters are presented. • Morphology engineering over composite nanofibers for enhancing electrochemical performance is reviewed. • Current challenges and future prospect of binder free composite nanofibers for flexible SCs are suggested. The versatile electrospinning technique is scalable and suitable to fabricate highly conducting freestanding carbon nanofiber composite electrodes for energy storage devices. Freestanding/flexible electrodes hold enormous potential for use in wearable electronic devices. Carbon-yielding polymers and the optimal use of sacrificial polymers, metal oxides, and sulfides retain the flexibility and enhance the surface area and pseudocapacitance of electrodes. Both as-prepared electrospun fibers and carbonized nanofibers are compatible with surface decoration via various chemical and electrochemical routes. Metal oxides/sulfides with various morphologies, such as nanocones and nanosheets, can be grown on the carbon nanofibers or on the as-prepared electrospun fibers using chemical synthesis methods such as electrodeposition, hydrothermal processes, and chemical impregnation to enhance the pseudocapacitance of the electrodes. Similarly, the deposition of metal organic frameworks on as-prepared electrospun fibers embellishes these fibers with nanostructures of specific morphologies such as dodecahedral and spindle-shaped structures. Under optimal conditions, these morphologies do not hamper the flexibility of the fibers, and binders are not required to retain them or maintain the electrode integrity. The engineering of electrodes with various morphologies and process parameters is presented systematically. Electrospinning-derived electrodes that have demonstrated significant electrochemical performance are highlighted and critically analyzed, and the energy storage mechanisms of these supercapacitors are described in detail. [ABSTRACT FROM AUTHOR]

The effect of annealing temperature on sol-gel deposited thin films have been studied. The average crystallite size determined from XRD shows that the deposited films are nanocrystalline. FTIR confirms deposition of thin films. The transmittance of annealed thin films is greater than 80% in visible region with bandgap ranging from 3.25-3.19 eV. The films annealed at 450°C temperature shows lower resistivity value of 527.241 Ωm. The deposited nanocrystalline films are suitable for biosensing applications due to its higher surface area. [ABSTRACT FROM AUTHOR]

• Flexible, freestanding, binder-free nanofiber electrodes for lithium-ion batteries are introduced. • Significance and limitations of electrospinning for fabrication of freestanding electrodes are discussed. • Parameters and polymers for the design of porous and core–shell nanofibers are analyzed. • Feasibility of decorating fibers with nanosheets, nanocones, and polyhedra of active materials is discussed. Carbon nanofibers derived from electrospun precursors show great promise for electronic applications owing to their flexibility, conductivity, high surface area, and open structure. The integration of metal oxides and sulfides in carbon nanofibers, rather than using them with other binders, eliminates many problems caused by poor adhesion, nanomaterial agglomeration, excess mass contributed by inactive binders, and low conductivity of embedded active materials. The engineering of electrospun fibers with novel morphologies, such as core–shell, hollow, or porous structures, and the use of decorated carbon nanofibers (e.g. , by electrodeposition or co-precipitation) are discussed in this review. Representative schematic illustrations of the lithium-storage mechanism for these binder-free electrodes are presented. We describe how the electrospinning technique can offer a cost-effective strategy for fabrication of lightweight lithium-ion batteries with high capacity and excellent bendability. This review presents the fascinating morphologies of these specially designed carbon nanofiber electrodes, which enhance the electrochemical performance of metal oxides and sulfides, illustrating their enormous potential for use in wearable electronic devices and hybrid electric vehicles. [ABSTRACT FROM AUTHOR]

High capacity, rapid-charging, and long-term recyclability are the essential characteristics of high-performance lithium-ion battery (LIB) electrodes, which are particularly important in the electric vehicle industry. Bimetallic Zn2SnO4 nanoparticles wrapped in carbon shells were supersonically sprayed with reduced graphene oxide (rGO) nanosheets to fabricate rapid-charging, binder-free, and long-term-stable LIB anodes. The fabricated Zn2SnO4/C@rGO composite exhibited high capacity retention and specific capacity over a wide range of current densities. Zn2SnO4 was first reduced to metal oxides (ZnO and SnO2) and then to metals (Zn and Sn) during the lithiation process. The reduced metals were successively alloyed with Li+ ions, which in turn formed LiZn and LiSn. These cyclic conversions and alloying processes enhanced the performance of the LIBs, resulting in a high capacity of 1126 mAh⋅g-1 after 400 cycles at a high current density of 1000 mA·g-1; such high performance indicates the rapid-charging capability of the fabricated LIB anodes. The agglomeration of identical oxide particles was reduced during the long-term cycling process by introducing bimetallic Zn2SnO4, which was reduced to ZnO and SnO2 in the first cycle. Metal formation through the conversion and subsequent alloying processes caused the pulverization of ZnO and SnO2, whose mixture favorably alleviated agglomeration of identical oxides owing to the distinct grain boundaries of ZnO and SnO2. In addition, ZnO and SnO2 particles were confined within a carbon shell, which originated from the introduction of polyvinylpyrrolidone. The carbon shell further alleviated the particle agglomeration for Zn2SnO4/C@rGO, which is identified as the optimal case, yielding a capacity retention of 106% for the first reversible capacity at a current density of 1000 mA⋅g-1 after 400 cycles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Wearable fabric supercapacitors decorated with ultrathin manganese oxide nanorods are fabricated. • MnSO 4 , MnNt, and MnAc salts are used to grow ultrathin MnO 2 nanorods on the wearable fabrics. • The MnSO 4 -based supercapacitor demonstrates 90% retention after 10,000 cycles. We present the fabrication (using a hydrothermal process) and the properties of wearable fabrics decorated with ultrathin manganese oxide (MnO 2) nanorods for supercapacitor applications. The superior mechanical durability of the supercapacitor was confirmed by cyclic voltammetry (CV) curves, which showed little change during 1000 bending cycles. The pseudocapacitive properties of the ultrathin MnO 2 nanorods were confirmed by recording the CV curves at various scan rates. The galvanostatic charge–discharge curves at various specific currents confirmed the pseudocapacitance of MnO 2. The ultrathin MnO 2 nanorods exhibited a superior capacitance of 508 F·g−1 and an energy density of 35.3 Wh·kg−1. The MnO 2 electrode with optimal properties demonstrated stable long-term cycling performance with 90% retention after 10,000 galvanostatic cycles. [ABSTRACT FROM AUTHOR]

• Flexible supercapacitors were fabricated using Ni-electroplated carbon nanofibers with NiGa 2 S 4 nanosheets. • The impact of the Ni/Ga ratio on the electrochemical performance of the supercapacitor was studied. • The NiGa 2 S 4 nanosheets promoted electrolyte diffusion and intensified the charge transport rate. • The specific capacitance was the highest at 488F·g−1 at a current rate of 0.5 A·g−1. Herein, high-power flexible supercapacitor electrodes were fabricated by decorating Ni-electroplated carbon nanofibers (Ni@CNF) with two-dimensional NiGa 2 S 4 nanosheets. The electrical conductivity of carbon nanofibers was enhanced by the addition of nickel, and the energy storage capability was enhanced by decoration with NiGa 2 S 4. The impact of metal (Ni/Ga) ratio on the overall electrochemical performance of the supercapacitor was studied by varying the Ga concentration. The NiGa 2 S 4 nanosheets promoted diffusion of the electrolyte into the electrode, thereby improving the electrochemical activity. The nanosheets also intensified the charge transfer rate within the composite electrode, which contributed to the overall improvement in the electrochemical performance. The optimal Ga concentration was the concentration at which the specific capacitance was the highest at 488 F·g−1 with a potential window of 1.1 V and current rate of 0.5 A·g−1. The long-term stability test revealed that the capacitance retention of the electrode with this optimal Ni/Ga ratio was 109% after 20,000 cycles. This flexible supercapacitor electrode was subjected to 2000 bending cycles, and the corresponding cyclic voltammetry performance was assessed. In combination, the outstanding electrochemical performance and durable mechanical properties render the NiGa 2 S 4 /Ni@CNF electrode highly suitable for flexible energy storage applications. [ABSTRACT FROM AUTHOR]

• Flexible supercapacitors were fabricated using Ni-electroplated carbon nanofibers with NiGa 2 S 4 nanosheets. • The impact of the Ni/Ga ratio on the electrochemical performance of the supercapacitor was studied. • The NiGa 2 S 4 nanosheets promoted electrolyte diffusion and intensified the charge transport rate. • The specific capacitance was the highest at 488F·g−1 at a current rate of 0.5 A·g−1. Herein, high-power flexible supercapacitor electrodes were fabricated by decorating Ni-electroplated carbon nanofibers (Ni@CNF) with two-dimensional NiGa 2 S 4 nanosheets. The electrical conductivity of carbon nanofibers was enhanced by the addition of nickel, and the energy storage capability was enhanced by decoration with NiGa 2 S 4. The impact of metal (Ni/Ga) ratio on the overall electrochemical performance of the supercapacitor was studied by varying the Ga concentration. The NiGa 2 S 4 nanosheets promoted diffusion of the electrolyte into the electrode, thereby improving the electrochemical activity. The nanosheets also intensified the charge transfer rate within the composite electrode, which contributed to the overall improvement in the electrochemical performance. The optimal Ga concentration was the concentration at which the specific capacitance was the highest at 488 F·g−1 with a potential window of 1.1 V and current rate of 0.5 A·g−1. The long-term stability test revealed that the capacitance retention of the electrode with this optimal Ni/Ga ratio was 109% after 20,000 cycles. This flexible supercapacitor electrode was subjected to 2000 bending cycles, and the corresponding cyclic voltammetry performance was assessed. In combination, the outstanding electrochemical performance and durable mechanical properties render the NiGa 2 S 4 /Ni@CNF electrode highly suitable for flexible energy storage applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrodeposited ZnFe 2 O 4 nanosheets enhanced the electrochemical performance. • The ZnNt:FeSO 4 electrolyte concentration was varied to control the thickness of these nanosheets. • The optimal case exhibited a specific capacitance of 1093 F·g−1 at a current rate of 1 A·g−1. • The energy density of the optimal case was 54 Wh·kg−1 at 600 W·kg−1. Binder-free bimetallic ZnFe 2 O 4 nanosheets were fabricated using one-step electrodeposition, which facilitated excellent electrical contact between the ZnFe 2 O 4 nanosheets and the nickel substrate. The resultant numerous ZnFe 2 O 4 nanosheets with their cubic spinel structures promote interfacial activity to enhance the electrochemical and Faradaic redox reactions. The metallic Zn and Fe from the cubic spinel structure of ZnFe 2 O 4 attract electrolytic ions and increase the energy-storage capability, thus yielding a specific capacitance of 1093 F·g −1 at a current rate of 1 A·g−1. Different samples were prepared by varying the amount of metal salts in the electrodeposition solution while maintaining a constant ZnNt:FeSO 4 concentration ratio of 1:2 for all cases. The optimal electrode composition, which yielded an energy density of 54 Wh·kg−1 and a capacitance retention of 93.5% at N = 5000 charge-discharge cycles, was identified. [ABSTRACT FROM AUTHOR]

Flexible supercapacitors are preferred for small wearable electronics owing to their sustainability and high power density. These systems can be fabricated using low-density, conductive, flexible carbon materials, which are primarily obtained using cotton fabrics. For instance, cotton-fabric-derived carbon cloth comprises a three-dimensional network of conductive fibers that can hierarchically accommodate electrochemically active materials. In this context, the present article reports the decoration of a cotton fabric with two-dimensional ZIF-8 nanoplates by wet chemical impregnation followed by high-temperature annealing. Tailoring the ratio of the zinc salt to 2-methylimidazole enhances the exposure of electrochemically active sites. The optimal specimen exhibits the highest capacitance among the samples (982.8 mF cm−2), as ascertained by cyclic voltammetry at a scan rate of 10 mV s−1, whereas in terms of electrochemical stability, it shows a capacitance retention of 91% after 10,000 galvanostatic charge–discharge cycles. Furthermore, in a potential window of 0–1.6 V, ZnO nanoplates anchored to low-density carbon fabric aids in storing an energy density of 261.3 μW h·cm−2 at a high power density of 11.2 mW cm−2. • ZIF-8 was synthesized via water-based impregnation at a low temperature. • Low-density conductive flexible carbon was decorated with ZnO nanoplates. • The ratio of zinc salt to 2-methylimidazolate (1:10) yielded a capacitance of 982.8 mF cm−2. • A high energy density of 261.3 μW h·cm−2 was obtained at a potential window of 1.6 V. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) decorated with tin oxide (SnO 2) is deposited on a fabric via supersonic spraying to produce wearable supercapacitor textiles. rGO improves the electrical conductivity of textiles, while SnO 2 provides energy storage capabilities. The synergetic effect of the combination of rGO and SnO 2 on the overall electrochemical performance of the supercapacitor was studied by varying the SnO 2 concentration. The intermixed rGO flakes and SnO 2 nanoparticles enhanced the charge transport within the composite electrode, ultimately improving the overall electrochemical performance. The porous structure of the fabric enables sufficient electrolyte diffusion into the deposited rGO and SnO 2 , to promote the interfacial activity between the active electrode and electrolyte. The optimal sample exhibited the highest specific capacitance of 1008 mF⋅cm−2 at a current loading of 1.5 mA⋅cm−2, with a capacitance retention of 93% after 10,000 cycles. Stretching and relaxing cyclic tests up to N = 1100 demonstrate the mechanical durability of the wearable supercapacitor. These promising results confirm that supersonic spraying is suitable for producing energy storage devices on wearable fabrics. Image 1 • Wearable supercapacitors comprising reduced graphene oxide and tin oxide were fabricated. • The intermixed rGO flakes and SnO 2 nanoparticles enhanced the charge transport. • The optimal sample exhibited the highest specific capacitance of 1008 mF cm−2 at a current loading of 1.5 mA cm−2. • The capacitance retention of 93% after 10,000 cycles was obtained. • Bending cycles up to N = 1100 demonstrated the mechanical durability of the wearable supercapacitor. [ABSTRACT FROM AUTHOR]

Herein, we present the facile growth of beehive-like NiFe 2 O 4 nanosheets over Ni nanocones for shorter electron transport distances in supercapacitor electrodes. The electrodeposited ultrathin nanosheets provide excellent electrode–electrolyte interfacial areas, thereby enabling superior electrochemical performances. Notably, the deposition duration is tuned to achieve abundant energy storage sites and controlled cavities for adequate electrolytic ion diffusion. The synergy of these advantageous cavities and active sites of beehive-like NiFe 2 O 4 nanosheets yields excellent stability with a capacitance retention of 95.3% after 10, 000 charging and discharging cycles of the nanosheet-based supercapacitor electrodes. At a high galvanostatic current rate of 5 A g−1, the capacitance was 483 F g−1. The optimal two-dimensional ultrathin NiFe 2 O 4 beehive nanostructure exhibits immense potential for high-energy-storage supercapacitor electrodes, paired with the required pseudocapacitive characteristics. • Facile growth of uniform beehive-like NiFe 2 O 4 nanosheets using electrodeposition. • Ultrathin beehive-like nanosheets with cavities show high electrochemical stability. • One-step synthesized NiFe 2 O 4 showed 95.3% capacitance retention after 10, 000 cycles. • High energy density of 40.3 Wh·kg−1 and power density of 5 kW kg−1 were achieved. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) decorated with dodecahedral ZIF8 was prepared using an easy and cost-effective co-precipitation method and deposited over nickel nanocones by a scalable supersonic cold spraying technique. The structure and morphology of ZIF8 were retained even after post-annealing under argon at 500 °C. Cyclic voltammetry analyses confirmed the excellent electrochemical performance of the rGO/ZIF8 composite, attributed to the dodecahedral structure of ZIF8, high electrical conductivity of rGO, and the nanocone textured substrate. The hierarchical morphology of ZIF8, the rGO nanosheets, and the nanocones (Ni) was confirmed by scanning and transmission electron microscopy. A three-fold enhancement of the specific capacitance (336 F⋅g‒1 at a current density of 1 A⋅g‒1) and long-term cycling performance with 96% retention were achieved after 10,000 cycles. The rGO/ZIF8 Ni-nanocone samples exhibited a high specific energy, capacitance, rate capability, and superior stability in comparison to previously reported supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

To prepare high-performance ZnO/C nanocomposite anode materials, dodecahedral ZIF-8 was first deposited on exfoliated reduced graphene oxide (rGO) by precipitation from methanol. The ZIF-8 was carbonized by annealing in argon to produce ZnO/C that retained the structure of the ZIF-8 template. ZIF-8-derived ZnO/C and ZnO/C/rGO were deposited over Cu substrates using low-cost, scalable supersonic cold spraying to facilitate the rapid production of Li-ion battery anodes. The synergy of the ZIF-8-derived dodecahedral nano-ZnO/C framework with rGO significantly enhanced conductivity, reduced aggregation, and shortened Li-ion transfer pathways. Electrochemical impedance spectroscopy showed enhanced Li-ion diffusion. The rGO/ZnO/C framework demonstrated a specific capacity of 1325 mAh·g−1 at a specific current of 100 mA·g−1. At a higher current of 2.5 A·g−1, the anode delivered a capacity of 525 mAh·g−1. The composite also showed a highly stable reversible capacity of 1063 mAh·g−1 after 300 cycles. The outstanding electrochemical performance of the rGO/ZnO/C sample was facilitated by the three-dimensional morphology of the exfoliated rGO and ZIF-8-derived dodecahedral porous ZnO/C structure. A quantitative comparison of specific capacity and capacity retention shows that the electrochemical performance of these rGO/ZnO/C composites exceeds that of previously-reported anodes based on ZnO, carbon, and/or rGO. • Dodecahedral ZIF-8 was deposited on exfoliated rGO by precipitation from methanol. • ZIF-8 derived ZnO/C and ZnO/C/rGO composites were produced by supersonic cold spraying. • The composite provided enhanced conductivity, reduced aggregation, and shortened Li-ion transfer pathways. • The composite showed 81% capacity retention after 300 cycles. [ABSTRACT FROM AUTHOR]

• Successful synthesis of Fe 2 O 3 /C/CNT with stable electrochemical performance. • Fe 2 O 3 /C/CNT anode exhibited high discharge capacity (901 mAh·g−1) after 1000 cycles at 1000 mA·g−1. • Carbon-coating reduced Fe 2 O 3 particle size, which increased capacity retention. • The CNTs intertwined with Fe 2 O 3 /C nanoparticles to form a 3D network. A synthesized Fe 2 O 3 /C composite integrated with carbon nanotubes (CNTs) is deposited via cold spraying and used as a highly stable Li-ion battery anode. The X-ray diffraction pattern of the anode material confirms the coexistence of CNTs and mixed Fe 2 O 3 phases (α and γ). Morphology and elemental mapping analyses are performed using scanning electron microscopy and transmission electron microscopy, respectively. The Fe 2 O 3 /C/CNT composite presents the high discharge capacity of 1598 mA·h·g−1 at the current density of 100 mA·g−1. The anode exhibits excellent capacity retention values of 83% and 88% after 100 and 1000 charge–discharge cycles under current densities of 100 and 1000 mA·g−1, respectively. The electrochemical performance of the synthesized Fe 2 O 3 /C/CNT composite is superior to that of the Fe 2 O 3 /CNT composite prepared by mixing commercially available Fe 2 O 3 and CNTs. This is attributed to the shorter diffusion path of the Li-ions in the relatively smaller Fe 2 O 3 particles and faster charge transfer through the highly conductive CNTs. [ABSTRACT FROM AUTHOR]

We demonstrate the supersonic cold-spray deposition of a Zn 2 SnO 4 /SnO 2 /carbon nanotube (CNT) composite as an exceptionally high-performance photoanode for photoelectrochemical water splitting. We optimized the photoanode thickness (number of deposition passes) and composition to achieve a maximum photocurrent density of 17.2 mA cm−2 at 1.78 V vs. reversible hydrogen electrode, with no additional catalysts or additives. The morphology of the deposited films, as characterized by scanning and transmission electron microscopy, comprises CNTs intermingled with Zn 2 SnO 4 and SnO 2 nanoparticles. The high electron concentration and charge transfer rate achieved by adding CNTs are demonstrated through Mott–Schottky and Nyquist analyses of electrochemical impedance spectroscopy (EIS) data. While we find no prior reports of Zn 2 SnO 4 /SnO 2 /CNT nanocomposites for water splitting, we demonstrate that this combination of ball-milled Zn 2 SnO 4 /SnO 2 nanoparticles mixed with CNTs is a promising candidate for high-performance solar water splitting with dramatically enhanced performance compared to previously-reported ZnO- and SnO-based photoanodes. • Supersonically-sprayed Zn 2 SnO 4 /SnO 2 /CNT photoanodes were fabricated for solar water splitting. • A maximum photocurrent density of 17.2 mA cm−2 at 1.78 V vs. RHE was recorded. • The PCD stabilized at a value above 6.5 mA cm−2 at a fixed voltage and remained constant. [ABSTRACT FROM AUTHOR]

[Display omitted] • PVP/ZIF-7/PAN nanofibers carbonized at 900 °C yielded flexible ZnO P /C. • A capacitance of 382.5 mF cm−2 was obtained at a current density of 1 mA cm−2. • ZnO P /C demonstrated a capacitance retention of ∼ 101 % over 10,000 cycles. • ZnO P /C delivered an energy density of 49 μWh cm−2 at a power density of 2 mW cm−2. This study investigates the carbonization of electrospun fibers derived from zeolitic imidazolate framework (ZIF)-7/polyacrylonitrile solutions containing urea or polyvinylpyrrolidone (PVP). The carbonization yields highly flexible composites comprising nitrogen-doped carbon nanofibers and ZnO. Notably, using PVP as a nitrogen source generates a composite exhibiting excellent electrochemical performance. Specifically, it delivers a high capacitance of 382.5 mF cm−2 at a current density of 1 mA cm−2. Furthermore, this composite demonstrates capacitance retentions of approximately 101 % and 80 % after 10,000 cycles and a 90° bending test, respectively. The charge-storage capability of the PVP-based ZnO P /C composite surpasses that obtained without PVP by 1.4 times. Additionally, a composite fiber mat of ZnO P /C obtained via one-step electrospinning exhibits exceptional electrical conductivity and an energy density of 49 μWh cm−2 at a power density of 2 mW cm−2. These findings highlight the potential of this material as an electrode for supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The FeVO 4 /rGO precursor was supersonically sprayed to fabricate supercapacitors. • The best FeVO 4 /rGO sample yielded an areal capacitance of 1240 mF·cm−2. • The capacitance retention was 90% at 8000 cycles. • An energy density of 0.3 mWh·cm−2 was obtained at 0–1.6 V potential window. High-energy–density supercapacitors exhibiting high power density and long-term stability are essential devices for energy storage applications, such as wearable electronics. In this study, we utilized supersonic spray deposition to exfoliate reduced graphene oxide (rGO). Additionally, a solvothermal process was employed to engineer the nanostructure of iron/vanadium oxides. Consequently, the resulting multivalent iron/vanadium oxide and rGO composites exhibited remarkably high energy densities. Three major parametric studies were conducted to investigate the electrochemical properties of iron oxide (FO), vanadium oxide (VO), and iron/vanadium oxide (FVO) composites with rGO. FVO/rGO emerged as the most promising sample, exhibiting an areal capacitance of 1240 mF·cm−2 at a current density of 2 mA·cm−2, as well as achieving a 90 % capacitance retention even after 8000 galvanostatic charge–discharge cycles. Furthermore, this sample delivered an energy density of 0.17 mWh·cm−2 at a power density of 4 mW·cm−2. [ABSTRACT FROM AUTHOR]

We demonstrate fabrication of films of highly textured bismuth oxide (Bi 2 O 3 ) pillars via electrostatic spray deposition and test the performance of these films as photoanodes in photoelectrochemical water splitting. The β-Bi 2 O 3 and α-Bi 2 O 3 phases were identified and distinguished using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The β-Bi 2 O 3 pillars of optimized thickness exhibited a photocurrent density of 0.97 mA⋅cm −2  at 0.5 V vs Ag/AgCl. The tetragonal β-Bi 2 O 3 pillars had enhanced visible light absorbance compared to α-Bi 2 O 3 as well as other metal oxides like ZnO and TiO 2 . Tauc plot analysis of film absorbance showed a decrease in the bandgap of the β-Bi 2 O 3 phase to 2.5 eV. In Na 2 SO 3 electrolyte, a hole scavenger, the onset voltage for the β-Bi 2 O 3 phase was shifted to a more negative value (−0.4 V), which increased photocurrent density. The electron concentration reached its highest value of 9.1 × 10 20  cm −3 for the film with the highest photocurrent density. [ABSTRACT FROM AUTHOR]

Zeolitic imidazole frameworks (ZIFs) are a class of metal organic frameworks (MOFs) with diverse energy-related applications. High-surface area materials derived from ZIFs can serve as electrodes with good long-term capacity retention. Herein, we demonstrate an electrospun ZIF7/carbon nanofiber (CNF) derived nanocomposite as a freestanding electrode for supercapacitors with excellent capacitance retention. The optimal ZIF7 composite nanofiber carbonized at 950 °C exhibited a specific capacitance of 202 F·g −1 at a current density of 1 A·g −1 and ~98% specific capacitance retention after 5000 charge–discharge cycles. N-doped nanoporous C and the Zn framework of ZIF7 composite fibers delivered an energy density of 42 W·h·kg −1 at a power density of 0.6 kW·kg −1 . These scalable ZIF7/CNF composite textiles (30 × 10 cm 2 ) can be used as freestanding supercapacitor electrodes without a separate substrate or current collector. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) loaded Fe-Fe 3 C composite nanofibers were prepared via a supersonic blowing technique. After high temperature annealing, the resulting electrodes delivered an excellent reversible capacity of 558 mAh·g −1 at a current rate of 1500 mA g −1 at the 200 th cycle. The supersonic blowing facilitated rapid and simultaneous coupling of exfoliated rGO with the solution-blown nanofibers, which is difficult to achieve by electrospinning methods. The performance of the fabricated electrode is remarkably high compared to the previously reported values; thus, these anodes are promising for application in lithium ion batteries. [ABSTRACT FROM AUTHOR]

Highly uniform, mechanically stable, dense, and water-adsorbing MIL-100(Fe) films were fabricated via supersonic spraying, a rapid, high-throughput, and scalable method compatible with roll-to-roll processing. The film surface area (1667 m 2 g −1 ) was comparable to that of the nanoparticles from which it was prepared (2009 m 2 g −1 ), and was higher than previously reported values for MIL-100(Fe) films. The gas and water adsorption abilities of the film were tested by nitrogen physisorption and water adsorption at 30 °C. The supersonically sprayed film was mechanically resistant up to a critical scratching load of 1.84 N, higher than the critical scratchability loads of dip-coated or spin-coated films. In humidity-sensing applications, films that incorporated conductive Ag nanowires were highly responsive to environmental humidity, demonstrating applicability as water vapor sensors. The fabricated films were characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. [ABSTRACT FROM AUTHOR]