Vertically-aligned graphene nanowalls grown via plasma-enhanced chemical vapor deposition as a binder-free cathode in Li-O_2 batteries

In the present report, vertically-aligned graphene nanowalls are grown on Ni foam (VA-G/NF) using plasma-enhanced chemical vapor deposition method at room temperature. Optimization of the growth conditions provides graphene sheets with controlled defect sites. The unique architecture of the vertically-aligned graphene sheets allows sufficient space for the ionic movement within the sheets and hence enhancing the catalytic activity. Further modification with ruthenium nanoparticles (Ru NPs) drop-casted on VA-G/NF improves the charge overpotential for lithium–oxygen (Li–O_2) battery cycles. Such reduction we believe is due to the easier passage of ions between the perpendicularly standing graphene sheets thereby providing ionic channels

Vertically-aligned graphene nanowalls grown via plasma-enhanced chemical vapor deposition as a binder-free cathode in Li-O_2 batteries

In the present report, vertically-aligned graphene nanowalls are grown on Ni foam (VA-G/NF) using plasma-enhanced chemical vapor deposition method at room temperature. Optimization of the growth conditions provides graphene sheets with controlled defect sites. The unique architecture of the vertically-aligned graphene sheets allows sufficient space for the ionic movement within the sheets and hence enhancing the catalytic activity. Further modification with ruthenium nanoparticles (Ru NPs) drop-casted on VA-G/NF improves the charge overpotential for lithium–oxygen (Li–O_2) battery cycles. Such reduction we believe is due to the easier passage of ions between the perpendicularly standing graphene sheets thereby providing ionic channels

Flower-Like Nickel–Cobalt Oxide Decorated Dopamine-Derived Carbon Nanocomposite for High Performance Supercapacitor Applications

The highly open space flower, coin, peony flower, and leaf-like nickel–cobalt oxide nanostructured materials with and without dopamine as a carbon source (D_1.5NiCo₂O₄, D_1.0NiCo₂O₄ (D-NiCo₂O₄), D_0.5NiCo₂O₄, and D_0.0NiCo₂O₄ (D- free NiCo₂O₄)) are prepared by a low temperature chemical synthesis method with improved electrical conductivity, providing the longtime electron pathway, and high surface area for high performance supercapacitors. The structure and morphology of the as-synthesized samples were characterized by X-ray diffraction pattern, X-ray photoelectron spectroscopy, scanning electron microscope, field emission-transmission electron microscope, and N₂ adsorption–desorption isotherms. Electrochemical properties of the electrodes were analyzed by cyclic voltammetry and galvanostatic charge–discharge methods. Notably, the as-synthesized flower-like D-NiCo₂O₄ nanocomposite exhibited a maximum specific capacitance of 667 F g^–1, which is superior to D- free NiCo₂O₄ viz. 202 F g^–1 at 5 A g^–1 with excellent cyclic stability of about 95% and 86% at 10 A g^–1 after 2000 charge–discharge cycles in 2.0 M KOH aqueous electrolyte solution for D-NiCo₂O₄, and D-free NiCo₂O₄, respectively. In addition, an asymmetric supercapacitor device is fabricated through D-NiCo₂O₄ as a positive electrode and biomass-derived AC as a negative electrode with the potential range of 0–1.5 V in PVA-KOH gel electrolyte solution. These results indicate that the as-prepared electrodes have high specific capacitance, excellent cycle stability, and good rate capability, which surpass several related metal oxide electrodes

Palladium Nanoparticle Incorporated Porous Activated Carbon: Electrochemical Detection of Toxic Metal Ions

A facile method has been developed for fabricating selective and sensitive electrochemical sensors for the detection of toxic metal ions, which invokes incorporation of palladium nanoparticles (Pd NPs) on porous activated carbons (PACs). The PACs, which were derived from waste biomass feedstock (fruit peels), possess desirable textural properties and porosities favorable for dispersion of Pd NPs (ca. 3–4 nm) on the graphitic PAC substrate. The Pd/PAC composite materials so fabricated were characterized by a variety of different techniques, such as X-ray diffraction, field-emission transmission electron microscopy, gas physisorption/chemisorption, thermogravimetric analysis, and Raman, Fourier-transform infrared, and X-ray photon spectroscopies. The Pd/PAC-modified glassy carbon electrodes (GCEs) were exploited as electrochemical sensors for the detection of toxic heavy metal ions, viz., Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, which showed superior performances for both individual as well as simultaneous detections. For simultaneous detection of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, a linear response in the ion concentration range of 0.5–5.5, 0.5–8.9, 0.5–5.0, and 0.24–7.5 μM, with sensitivity of 66.7, 53.8, 41.1, and 50.3 μA μM^–1 cm^–2, and detection limit of 41, 50, 66, and 54 nM, respectively, was observed. Moreover, the Pd/PAC-modified GCEs also show perspective applications in detection of metal ions in real samples, as illustrated in this study for a milk sample

Honeycomb-like Porous Carbon–Cobalt Oxide Nanocomposite for High-Performance Enzymeless Glucose Sensor and Supercapacitor Applications

Herein, we report the preparation of Pongam seed shells-derived activated carbon and cobalt oxide (∼2–10 nm) nanocomposite (PSAC/Co₃O₄) by using a general and facile synthesis strategy. The as-synthesized PSAC/Co₃O₄ samples were characterized by a variety of physicochemical techniques. The PSAC/Co₃O₄-modified electrode is employed in two different applications such as high performance nonenzymatic glucose sensor and supercapacitor. Remarkably, the fabricated glucose sensor is exhibited an ultrahigh sensitivity of 34.2 mA mM^–1 cm^–2 with a very low detection limit (21 nM) and long-term durability. The PSAC/Co₃O₄ modified stainless steel electrode possesses an appreciable specific capacitance and remarkable long-term cycling stability. The obtained results suggest the as-synthesized PSAC/Co₃O₄ is more suitable for the nonenzymatic glucose sensor and supercapacitor applications outperforming the related carbon based modified electrodes, rendering practical industrial applications

Honeycomb-like Porous Carbon–Cobalt Oxide Nanocomposite for High-Performance Enzymeless Glucose Sensor and Supercapacitor Applications

Herein, we report the preparation of Pongam seed shells-derived activated carbon and cobalt oxide (∼2–10 nm) nanocomposite (PSAC/Co₃O₄) by using a general and facile synthesis strategy. The as-synthesized PSAC/Co₃O₄ samples were characterized by a variety of physicochemical techniques. The PSAC/Co₃O₄-modified electrode is employed in two different applications such as high performance nonenzymatic glucose sensor and supercapacitor. Remarkably, the fabricated glucose sensor is exhibited an ultrahigh sensitivity of 34.2 mA mM^–1 cm^–2 with a very low detection limit (21 nM) and long-term durability. The PSAC/Co₃O₄ modified stainless steel electrode possesses an appreciable specific capacitance and remarkable long-term cycling stability. The obtained results suggest the as-synthesized PSAC/Co₃O₄ is more suitable for the nonenzymatic glucose sensor and supercapacitor applications outperforming the related carbon based modified electrodes, rendering practical industrial applications

Nickel Nanoparticle-Decorated Porous Carbons for Highly Active Catalytic Reduction of Organic Dyes and Sensitive Detection of Hg(II) Ions

High surface area carbon porous materials (CPMs) synthesized by the direct template method via self-assembly of polymerized phloroglucinol-formaldehyde resol around a triblock copolymer template were used as supports for nickel nanoparticles (Ni NPs). The Ni/CPM materials fabricated through a microwave-assisted heating procedure have been characterized by various analytical and spectroscopic techniques, such as X-ray diffraction, field emission transmission electron microscopy, vibrating sample magnetometry, gas physisorption/chemisorption, thermogravimetric analysis, and Raman, Fourier-transform infrared, and X-ray photon spectroscopies. Results obtained from ultraviolet–visible (UV–vis) spectroscopy demonstrated that the supported Ni/CPM catalysts exhibit superior activity for catalytic reduction of organic dyes, such as methylene blue (MB) and rhodamine B (RhB). Further electrochemical measurements by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) also revealed that the Ni/CPM-modified electrodes showed excellent sensitivity (59.6 μA μM^–1 cm^–2) and a relatively low detection limit (2.1 nM) toward the detection of Hg­(II) ion. The system has also been successfully applied for the detection of mercuric ion in real sea fish samples. The Ni/CPM nanocomposite represents a robust, user-friendly, and highly effective system with prospective practical applications for catalytic reduction of organic dyes as well as trace level detection of heavy metals

Metal organic framework derived nickel phosphide/graphitic carbon hybrid for electrochemical hydrogen generation reaction

Development of efficient hydrogen evolution reaction (HER) catalyst composed of earth-abundant elements is scientifically and technologically important for water splitting associated with the conversion and storage of renewable energy. Herein, we report a new class of nickel-phosphide/graphitic carbon (NiP@GC) hybrid prepared by a two-step strategy: first pyrolyzing of Ni-based metal–organic frameworks (Ni-MOFs) and then phosphating. The HER performance of the as-prepared material was tested using linear sweep voltammetry (LSV) method in 0.5 M HSO electrolyte solution. Unexpectedly, the NiP@GC exhibited superior HER performance with the onset potential started at ∼93 mV and good durability due to the synergistic interaction of active NiP nanoparticles and graphitic carbon support. This study offers an attractive electrocatalyst toward the power-efficient electrochemical preparation of hydrogen energy