Improvement and regeneration of Co–B amorphous alloy nanowires for the selective hydrogenation of cinnamaldehyde

Co–B amorphous alloy nanowires exhibited the improvement of catalytic hydrogenation activity and cycling life by plasma treatment.

Ni(OH)₂ and NiO Based Composites: Battery Type Electrode Materials for Hybrid Supercapacitor Devices

Nanocomposites of Ni(OH)₂ or NiO have successfully been used in electrodes in the last five years, but they have been falsely presented as pseudocapacitive electrodes for electrochemical capacitors and hybrid devices. Indeed, these nickel oxide or hydroxide electrodes are pure battery-type electrodes which store charges through faradaic processes as can be shown by cyclic voltammograms or constant current galvanostatic charge/discharge plots. Despite this misunderstanding, such electrodes can be of interest as positive electrodes in hybrid supercapacitors operating under KOH electrolyte, together with an activated carbon-negative electrode. This study indicates the requirements for the implementation of Ni(OH)₂-based electrodes in hybrid designs and the improvements that are necessary in order to increase the energy and power densities of such devices. Mass loading is the key parameter which must be above 10 mg·cm⁻² to correctly evaluate the performance of Ni(OH)₂ or NiO-based nanocomposite electrodes and provide gravimetric capacity values. With such loadings, rate capability, capacity, cycling ability, energy and power densities can be accurately evaluated. Among the 80 papers analyzed in this study, there are indications that such nanocomposite electrode can successfully improve the performance of standard Ni(OH)₂ (+)//6 M KOH//activated carbon (−) hybrid supercapacitor.

Boosted electrochemical properties from the surface engineering of ultrathin interlaced Ni(OH)2 nanosheets with Co(OH)2 quantum dot modification

Nanoscale surface engineering of electroactive architectures is of paramount importance in high-performance supercapacitor applications based on surface-controlled charge storage mechanisms. Herein, we exploit Co(OH)2 quantum dots (CoQDs) as a surface modifier and report a simple and effective strategy for anchoring CoQDs on ultrathin interlaced Ni(OH)2 nanosheets. Impressively, the 2D/0D heterostructure of CoQD-interspersed Ni(OH)2 nanosheets (Ni(OH)2-CoQD) exhibits greatly enhanced capacitive behavior compared with pristine Ni(OH)2 nanosheets, exhibiting a higher capacitance (3244 F g-1vs. 2124 F g-1 at 5 mA cm-2), superior rate capability and better cycling stability. Density functional theory (DFT) calculations reveal the accumulation of additional electrons and reduced adsorption energy of OH- at the Ni(OH)2-CoQD interphase, which are the primary reasons for the enhanced electrochemical performance. An asymmetric full cell with Ni(OH)2-CoQD as the positive electrode has been fabricated, achieving a maximum energy density of 46 W h kg-1 at 141 W kg-1, and excellent cycling stability, where 84.1% of the initial capacitance is retained over 5000 cycles. This work brings a new opportunity to pseudoactive electrode material design by employing semiconductive quantum dots for surface modification.

Complimentary effects of annealing temperature on optimal tuning of functionalized carbon–V2O5 hybrid nanobelts for targeted dual applications in electrochromic and supercapacitor devices

Herein, carbon nanosphere-decorated vanadium pentoxide (C@V₂O₅) hybrid nanobelts were grown via a single step hydrothermal route with improved electronic conductivity as compared to that of pristine oxide. This hybrid nanomaterial exhibits different complimentary ranges of optimum post-growth annealing temperatures, which are suitable for dual applications either in electro-chromic smart windows or in supercapacitors. C@V₂O₅ nanobelts annealed at 350 °C appear to favor electro-chromic applications. They exhibit maximum dynamic optical transmission modulation as they switch from yellow to dark green, fast switching response, and high visible transmittance. In contrast, C@V₂O₅nanobelts annealed at 250 °C have been found to be most suitable for supercapacitor applications. They display a high specific capacity and an enhanced diffusion coefficient. Moreover, they exhibit long lifetimes with a capacity retention of ∼94% even after 5000 cycles of operation. Therefore, the obtained results clearly indicate that optimization of the post-growth annealing temperatures is very important and rather complementary in nature in terms of determining the most favorable device functionalities. It enables us to optimally tune these hybrid nanomaterials for targeted, device-specific, energy applications in either electrochromic or supercapacitor technologies simply based on the annealing temperature alone.

Herein, carbon nanosphere-decorated vanadium pentoxide (C@V₂O₅) hybrid nanobelts were grown via a single step hydrothermal route with improved electronic conductivity as compared to that of pristine oxide.

High-Capacitance Hybrid Supercapacitor Based on Multi-Colored Fluorescent Carbon-Dots

Multi-colored, water soluble fluorescent carbon nanodots (C-Dots) with quantum yield changing from 4.6 to 18.3% were synthesized in multi-gram using dated cola beverage through a simple thermal synthesis method and implemented as conductive and ion donating supercapacitor component. Various properties of C-Dots, including size, crystal structure, morphology and surface properties along with their Raman and electron paramagnetic resonance spectra were analyzed and compared by means of their fluorescence and electronic properties. α-Manganese Oxide-Polypyrrole (PPy) nanorods decorated with C-Dots were further conducted as anode materials in a supercapacitor. Reduced graphene oxide was used as cathode along with the dicationic bis-imidazolium based ionic liquid in order to enhance the charge transfer and wetting capacity of electrode surfaces. For this purpose, we used octyl-bis(3-methylimidazolium)diiodide (C8H16BImI) synthesized by N-alkylation reaction as liquid ionic membrane electrolyte. Paramagnetic resonance and impedance spectroscopy have been undertaken in order to understand the origin of the performance of hybrid capacitor in more depth. In particular, we obtained high capacitance value (C = 17.3 μF/cm2) which is exceptionally related not only the quality of synthesis but also the choice of electrode and electrolyte materials. Moreover, each component used in the construction of the hybrid supercapacitor is also played a key role to achieve high capacitance value.