Chemical vapor-deposited carbon nanofibers on carbon fabric for supercapacitor electrode applications

Entangled carbon nanofibers (CNFs) were synthesized on a flexible carbon fabric (CF) via water-assisted chemical vapor deposition at 800A degrees C at atmospheric pressure utilizing iron (Fe) nanoparticles as catalysts, ethylene (C2H4) as the precursor gas, and argon (Ar) and hydrogen (H-2) as the carrier gases. Scanning electron microscopy, transmission electron microscopy, and electron dispersive spectroscopy were employed to characterize the morphology and structure of the CNFs. It has been found that the catalyst (Fe) thickness affected the morphology of the CNFs on the CF, resulting in different capacitive behaviors of the CNF/CF electrodes. Two different Fe thicknesses (5 and 10 nm) were studied. The capacitance behaviors of the CNF/CF electrodes were evaluated by cyclic voltammetry measurements. The highest specific capacitance, approximately 140 F g(-1), has been obtained in the electrode grown with the 5-nm thickness of Fe. Samples with both Fe thicknesses showed good cycling performance over 2,000 cycles

Effective Infiltration of Gel Polymer Electrolyte into Silicon-Coated Vertically Aligned Carbon Nanofibers as Anodes for Solid-State Lithium-Ion Batteries

This study demonstrates the full infiltration of gel polymer electrolyte into silicon-coated vertically aligned carbon nanofibers (Si-VACNFs), a high-capacity 3D nanostructured anode, and the electrochemical characterization of its properties as an effective electrolyte/separator for future all-solid-state lithium-ion batteries. Two fabrication methods have been employed to form a stable interface between the gel polymer electrolyte and the Si-VACNF anode. In the first method, the drop-casted gel polymer electrolyte is able to fully infiltrate into the open space between the vertically aligned core–shell nanofibers and encapsulate/stabilize each individual nanofiber in the polymer matrix. The 3D nanostructured Si-VACNF anode shows a very high capacity of 3450 mAh g^–1 at C/10.5 (or 0.36 A g^–1) rate and 1732 mAh g^–1 at 1C (or 3.8 A g^–1) rate. In the second method, a preformed gel electrolyte film is sandwiched between an Si-VACNF electrode and a Li foil to form a half-cell. Most of the vertical core–shell nanofibers of the Si-VACNF anode are able to penetrate into the gel polymer film while retaining their structural integrity. The slightly lower capacity of 2800 mAh g^–1 at C/11 rate and ∼1070 mAh g^–1 at C/1.5 (or 2.6 A g^–1) rate have been obtained, with almost no capacity fade for up to 100 cycles. Electrochemical impedance spectroscopy does not show noticeable changes after 110 cycles, further revealing the stable interface between the gel polymer electrolyte and the Si-VACNFs anode. These results show that the infiltrated flexible gel polymer electrolyte can effectively accommodate the stress/strain of the Si shell due to the large volume expansion/contraction during the charge–discharge processes, which is particularly useful for developing future flexible solid-state lithium-ion batteries incorporating Si-anodes

Mesoporous Hybrids of Reduced Graphene Oxide and Vanadium Pentoxide for Enhanced Performance in Lithium-Ion Batteries and Electrochemical Capacitors

Mesoporous hybrids of V₂O₅ nanoparticles anchored on reduced graphene oxide (rGO) have been synthesized by slow hydrolysis of vanadium oxytriisopropoxide using a two-step solvothermal method followed by vacuum annealing. The hybrid material possesses a hierarchical structure with 20–30 nm V₂O₅ nanoparticles uniformly grown on rGO nanosheets, leading to a high surface area with mesoscale porosity. Such hybrid materials present significantly improved electronic conductivity and fast electrolyte ion diffusion, which synergistically enhance the electrical energy storage performance. Symmetrical electrochemical capacitors with two rGO–V₂O₅ hybrid electrodes show excellent cycling stability, good rate capability, and a high specific capacitance up to ∼466 F g^–1 (regarding the total mass of V₂O₅) in a neutral aqueous electrolyte (1.0 M Na₂SO₄). When used as the cathode in lithium-ion batteries, the rGO–V₂O₅ hybrid demonstrates excellent cycling stability and power capability, able to deliver a specific capacity of 295, 220, and 132 mAh g^–1 (regarding the mass of V₂O₅) at a rate of C/9, 1C, and 10C, respectively. The value at C/9 rate matches the full theoretical capacity of V₂O₅ for reversible 2 Li⁺ insertion/extraction between 4.0 and 2.0 V (vs Li/Li⁺). It retains ∼83% of the discharge capacity after 150 cycles at 1C rate, with only 0.12% decrease per cycle. The enhanced performance in electrical energy storage reveals the effectiveness of rGO as the structure template and more conductive electron pathway in the hybrid material to overcome the intrinsic limits of single-phase V₂O₅ materials

Self-Organization of Ions at the Interface between Graphene and Ionic Liquid DEME-TFSI

Electrochemical effects manifest as nonlinear responses to an applied electric field in electrochemical devices, and are linked intimately to the molecular orientation of ions in the electric double layer (EDL). Herein, we probe the origin of the electrochemical effect using a double-gate graphene field effect transistor (GFET) of ionic liquid <i>N</i>,<i>N</i>-diethyl-<i>N</i>-(2-methoxyethyl)-<i>N</i>-methylammonium bis­(trifluoromethylsulfonyl)­imide (DEME-TFSI) top-gate, paired with a ferroelectric Pb_0.92La_0.08Zr_0.52­Ti_0.48O₃ (PLZT) back-gate of compatible gating efficiency. The orientation of the interfacial molecular ions can be extracted by measuring the GFET Dirac point shift, and their dynamic response to ultraviolet–visible light and a gate electric field was quantified. We have observed that the strong electrochemical effect is due to the TFSI anions self-organizing on a treated GFET surface. Moreover, a reversible order–disorder transition of TFSI anions self-organized on the GFET surface can be triggered by illuminating the interface with ultraviolet–visible light, revealing that it is a useful method to control the surface ion configuration and the overall performance of the device

Nutrient and Water Use Efficiency in Soil:The Influence of Geological Mineral Amendments

Mineral amendments are known to improve the physical, chemical and biological properties of soil, which in turn can enhance the efficiency of nutrient and water use by plants. This chapter discusses the current state of the knowledge regarding the application of geological mineral amendments in soil which either helps to retain nutrients in soils or prevents losses of nutrients from soil and directly or indirectly contributes to improve the overall nutrient use efficiency (NUE). A critical analysis of the currently available research information recommends a site-specific (precision) management approach in order to explore the most beneficial effects of the mineral materials for increasing plants’ nutrient and water use efficiency. The management practices should include an integrated plant nutrition system (IPNS) for the best utilisation of resources including mineral materials, fertilisers and organic inputs. This holds the potential for leading to a reduced fertiliser input in modern agriculture and therefore may lower the cost of agricultural production without impacting the crop yield