Electrochemical materials are under rigorous search for building advanced energy storage devices. Herein, supercapacitive properties of highly crystalline and ultrathin cobalt oxide (Co3O4) nanowires ...(diameter ∼30–60 nm) synthesized using an aqueous polymeric solution based electrospinning process are reported. These nanowire electrodes show a specific capacitance (CS) of ∼1110 F g−1 in 6 M KOH at a current density of 1 A g−1 with coulombic efficiency ∼100%. Asymmetric supercapacitors (ASCs) (CS ∼175 F g−1 at 2 A g−1 galvanostatic cycling) are fabricated using the Co3O4 as anode and commercial activated carbon (AC) as cathode and compared their performance with symmetric electrochemical double layer capacitors (EDLCs) fabricated using AC (CS ∼31 F g−1 at 2 A g−1 galvanostatic cycling). The Co3O4//AC ASCs deliver specific energy densities (ES) of 47.6, 35.4, 20 and 8 Wh kg−1 at specific power densities (PS) 1392, 3500, 7000 and 7400 W kg−1, respectively. The performance of ASCs is much superior to the control EDLCs, which deliver ES of 9.2, 8.9, 8.4 and 6.8 Wh kg−1 at PS 358, 695, 1400 and 3500 W kg−1, respectively. The ASCs show nearly six times higher energy density (∼47.6 Wh kg−1) than EDLC (8.4 Wh kg−1) without compromising its power density (∼1400 W kg−1) at similar galvanostatic cycling conditions (2 A g−1).
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•Asymmetric supercapacitors were fabricated with electrospun Co3O4 nanowires and activated carbon.•Exhibited six fold higher energy density compared to commercial EDLC with no lowering of power density.•Showed good cycling behaviour with ∼97% retention in Cs at the end of 2000 cycles.
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In an effort to minimize the usage of non-renewable materials and to enhance the functionality of the renewable materials, we have developed thin metal oxide coated porous carbon ...derived from a highly abundant non-edible bio resource, i.e., palm kernel shell, using a one-step activation-coating procedure and demonstrated their superiority as a supercapacitive energy storage electrode. In a typical experiment, an optimized composition contained ~10 wt% of Mn2O3 on activated carbon (AC); a supercapacitor electrode fabricated using this electrode showed higher rate capability and more than twice specific capacitance than pure carbon electrode and could be cycled over 5000 cycles without any appreciable capacity loss in 1 M Na2SO4 electrolyte. A symmetric supercapacitor prototype developed using the optimum electrode showed nearly four times higher energy density than the pure carbon owing to the enhancements in voltage window and capacitance. A lithium ion capacitor fabricated in half-cell configuration using 1 M LiPF6 electrolyte showed larger voltage window, superior capacitance and rate capability in the ~10 wt% Mn2O3 @AC than the pure analogue. These results demonstrate that the current protocol allows fabrication of superior charge storing electrodes using renewable materials functionalized by minimum quantity of earthborn materials.
Nitrogen containing mesoporous carbon obtained by the pyrolysis of graphene oxide (GO) wrapped ZIF-8 (Zeolitic Imidazolate Frameworks-8) micro crystals is demonstrated to be an efficient catalyst for ...the oxygen reduction reaction (ORR). ZIF-8 synthesis in the presence of GO sheets helped to realize layers of graphene oxide over ZIF-8 microcrystals and the sphere-like structures thus obtained, on heat treatment, transformed to highly porous carbon with a nitrogen content of about 6.12% and surface area of 502 m2/g. These catalysts with a typical micromeso porous architecture exhibited an onset potential of 0.88Vvs RHE in a four electron pathway and also demonstrated superior durability in alkaline medium compared to that of the commercial Pt/C catalyst. The N-doped porous carbon derived from GO sheathed ZIF-8 core–shell structures could therefore be employed as an efficient electrocatalyst for fuel cell applications.
ABSTRACT
Bright-rimmed clouds (BRCs) are ideal candidates to study radiation-driven implosion mode of star formation as they are potential sites of triggered star formation, located at the edges of ...Hii regions, showing evidence of ongoing star formation processes. BRC 18 is located towards the eastern edge of relatively closer (∼400 pc) H ii region excited by λ Ori. We made R-band polarimetric observations of 17 candidate young stellar objects (YSOs) located towards BRC 18 to investigate any preferred orientation of the discs with respect to the ambient magnetic field and the direction of energetic photons from λ Ori. We found that the discs are oriented randomly with respect to the projected magnetic field. Using distances and proper motions from the Gaia EDR3 of the candidate YSOs, we investigated the possible acceleration of BRC 18, away from λ Ori due to the well-known ‘Rocket Effect’, by assuming that both the candidate YSOs and BRC 18 are kinematically coupled. The relative proper motions of the candidate YSOs are found to show a trend of moving away from λ Ori. We computed the offset between the angle of the direction of the ionization front and the relative proper motion of the candidate YSOs and found it to lie close to being parallel to each other. Additionally, we found 12 sources that are co-moving with the known candidate YSOs towards BRC 18. These co-moving sources are most likely to be young and are missed in previous surveys conducted to identify potential YSOs of the region.
A one-dimensional morphology comprising nanograins of two metal oxides, one with higher electrical conductivity (CuO) and the other with higher charge storability (Co3O4), is developed by ...electrospinning technique. The CuO–Co3O4 nanocomposite nanowires thus formed show high specific capacitance, high rate capability, and high cycling stability compared to their single-component nanowire counterparts when used as a supercapacitor electrode. Practical symmetric (SSCs) and asymmetric (ASCs) supercapacitors are fabricated using commercial activated carbon, CuO, Co3O4, and CuO–Co3O4 composite nanowires, and their properties are compared. A high energy density of ∼44 Wh kg–1 at a power density of 14 kW kg–1 is achieved in CuO–Co3O4 ASCs employing aqueous alkaline electrolytes, enabling them to store high energy at a faster rate. The current methodology of hybrid nanowires of various functional materials could be applied to extend the performance limit of diverse electrical and electrochemical devices.
In the electrocatalytic CO2 reduction reaction (CO2RR), tin-based catalysts are known for their high formate faradaic yield. However higher overpotentials are required to attain a high faradaic yield ...with high partial current density for formate. Here, we describe the increase in the electrocatalytic CO2RR activity of Sn nanoparticles decorated on nitrogen-doped carbon fibers (NCFs) by adding a small amount of Pd. Nitrogen-doped carbon fibers decorated with SnPd nanoparticles (Sn100−yPdy–NCF) of different Sn : Pd ratios were synthesized using the electrospinning method and their electrocatalytic CO2RR activity was studied. The Sn100−yPdy–NCF catalyst with 3 wt% (y = 3) Pd displayed superior activity for the CO2RR and attained a faradaic efficiency of 85%, whereas the NCF with Sn nanoparticles (Sn100–NCF) attained only 57% efficiency at the same potential. The surface electronic configuration, Tafel slope (79 mV dec−1) and bicarbonate reduction activity of the catalyst reveal that the combination of SnOx–PdO on the catalyst surface is responsible for the superior CO2RR activity.
Understanding the rheological behaviour of thermoplastic nanocomposites is important to obtain a concrete knowledge of their processability. The viscoelastic properties of nanocomposites are a ...reflection of their morphology. The study of flow and deformation of nanocomposites provides essential information related to prevalent interactions in the system as well as contribution from the dispersion of incorporated nanofillers. In the present study, plasticized polyvinyl chloride/reduced graphene oxide nanocomposites (PPVC/RGO) were fabricated using melt mixing technique with different filler concentration. Flow behaviour of the nanocomposites was analyzed using small amplitude oscillatory shear (SAOS) measurements and it indicated an enhancement in the storage modulus (
G
′), loss modulus (
G
′′) and complex viscosity (
η
*) with RGO content. This can be attributed to very good dispersion and reinforcing effect of RGO in PPVC matrix as supported by TEM and FTIR results. Weak gel model is used to fit the rheological parameters and is found to be in excellent agreement with the SAOS experiments. Thermal history of the prepared nanocomposites was learned using differential scanning calorimetry. A shift in glass transition temperature (
T
g
) to higher temperature region could be seen, that manifest the effect of RGO in the amorphous portion of PPVC. An interesting property called secondary crystallinity was also found in these materials.
Understanding the rheological behaviour of thermoplastic nanocomposites is important to obtain a concrete knowledge of their processability.
Porous carbon has been a commercial choice as supercapacitor electrode; however, a large fraction of micrometer-sized voids limits the charge storability. Here, we show that porous carbon derived ...from an agricultural byproduct (palm kernel shell) with their voids filled by flower-shaped 3D nanostructure of TiO2 (TiO2@AC) acts as a low-cost electrode material for high energy density lithium ion capacitors (LIC) and supercapacitors. The size of the TiO2 flowers here is ideally suited to fit in the voids (∼1 μm); thereby, the TiO2@AC offers larger available surface area than its components, enhanced cyclic stability due to the larger particle volume and enhanced ion diffusion pathways due to the hierarchical structure. The LIC fabricated using the TiO2@AC electrode with a lithium plate as counter electrode showed impressively larger potential window (2.0–4.5 V vs. Li/Li+) than that fabricated using pure porous carbon (2.0–4.0 V vs. Li/Li+), a high specific energy (ES) at high specific power (PS) (ES ∼113 W h kg−1 @ PS ∼3.3 kW kg−1). Symmetric supercapacitors fabricated using the TiO2@AC in a neutral aqueous electrolyte (1 M Na2SO4) showed three times higher energy density than that fabricated using pure porous carbon with similar power density.
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•Voids of porous carbon are activated by similar sized 3D TiO2 nanoflowers.•The TiO2@AC has electrode continuity, larger pores and lower electrical resistance.•Larger charge storability and potential window for TiO2@AC than pure AC.•A TiO2@AC//Li capacitor gave ∼113 W h kg−1 @ ∼3.3 kW kg−1.•Thrice energy density for TiO2@AC//TiO2@AC capacitors than pure AC.
High-density charge (energy) storage under supercapacitive mode requires an electrode that would deliver larger space for charge accumulation and offer a larger electrochemical potential difference ...at an electrode–electrolyte interface. Porous carbon has been a preferred electrode for commercial supercapacitors; however, its charge storability is much lower than that of state-of-the-art charge-storage devices such as lithium-ion batteries. We show that one of the primary limiting factors is the voids in porous carbon, which do not contribute to the capacitance because their sizes are much larger than the size of the solvated/unsolvated ions in the electrolyte. We partially activate these voids by filling them with a flower-shaped 3D hierarchical pseudocapacitive material (MnCo2O4) by assuming that flower-shaped fillers would provide an additional easily accessible surface for charge adsorption. Less than 10 wt % MnCo2O4 in the porous carbon from palm kernel shells through simple wet impregnation results in a five-fold increase in the charge storability. Laboratory prototypes of symmetric supercapacitors are fabricated using the MnCo2O4-filled carbon electrodes, which show five times higher specific energy than pure carbon and are cycled over 5000 times with >95% capacitance retention. The present strategy of activating the voids by hierarchical 3D nanostructures could be applied to build high-performance energy-storage devices.
Processing of suitable materials as sustainable, eco-friendly, and cheaper energy storing electrodes offer significant challenges to overcome the current thresholds. In this work, we demonstrate ...development of a thin metallic (cobalt, in this case) film over biowaste-resourced porous carbon (PC) as a high performing supercapacitor electrode in aqueous alkaline electrolyte and lithium ion capacitor (LIC) configuration in an ionic electrolyte. The hierarchical structure thus developed are characterized for their chemical (crystal structure, surface chemical configuration), surface (morphology, surface area, and porosity) and electrochemical (voltammetric, galvanostatic and impedance spectroscopic) properties. The cobalt coating favourably modified the surface of PC such that the charge storability is enhanced. An optimized metal concentration (10% Co over PC) delivers over 100% increase in the charge storability with 20% increase in the potential window than the pure PC electrode. The LIC and the aqueous alkaline supercapacitor deliver impressive energy and power densities.
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•A thin metallic cobalt film is optimized over porous carbon by a single step process.•The surface properties of carbon are enhanced with the Co film for charge storage.•Lithium ion capacitor and supercapacitors are fabricated using the PCCo electrode.•A PCCo//Li capacitor gave ~126 W h kg−1 @ ~3.2 kW kg−1.•Thrice energy density for PCCo//PCCo than pure PCCo0//PCCo0 supercapacitors.
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