Experimental and computational investigation on the charge storage performance of a novel Al2O3-reduced graphene oxide hybrid electrode.

The advancements in electrochemical capacitors have noticed a remarkable enhancement in the performance for smart electronic device applications, which has led to the invention of novel and low-cost electroactive materials. Herein, we synthesized nanostructured Al2O3 and Al2O3-reduced graphene oxide (Al2O3-rGO) hybrid through hydrothermal and post-hydrothermal calcination processes. The synthesized materials were subject to standard characterisation processes to verify their morphological and structural details. The electrochemical performances of nanostructured Al2O3 and Al2O3- rGO hybrid were evaluated through computational and experimental analyses. Due to the superior electrical conductivity of reduced graphene oxide and the synergistic effect of both EDLC and pseudocapacitive behaviour, the Al2O3- rGO hybrid shows much improved electrochemical performance (~ 15-fold) as compared to bare Al2O3. Further, a symmetric supercapacitor device (SSD) was designed using the Al2O3- rGO hybrid electrodes, and detailed electrochemical performance was evaluated. The fabricated Al2O3- rGO hybrid-based SSD showed 98.56% capacity retention when subjected to ~ 10,000 charge-discharge cycles. Both the systems (Al2O3 and its rGO hybrid) have been analysed extensively with the help of Density Functional Theory simulation technique to provide detailed structural and electronic properties. With the introduction of reduced graphene oxide, the available electronic states near the Fermi level are greatly enhanced, imparting a significant increment in the conductivity of the hybrid system. The lower diffusion energy barrier for electrolyte ions and higher quantum capacitance for the hybrid structure compared to pristine Al2O3 justify improvement in charge storage performance for the hybrid structure, supporting our experimental findings.

Enhanced Oxygen Evolution Reaction with a Ternary Hybrid of Patronite-Carbon Nanotube-Reduced Graphene Oxide: A Synergy between Experiments and Theory.

This work reports the hybridization of patronite (VS4) sheets with reduced graphene oxide and functionalized carbon nanotubes (RGO/FCNT/VS4) through a hydrothermal method. The synergistic effect divulged by the individual components, i.e., RGO, FCNT, and VS4, significantly improves the efficiency of the ternary (RGO/FCNT/VS4) hybrid toward the oxygen evolution reaction (OER). The ternary composite exhibits an impressive electrocatalytic OER performance in 1 M KOH and requires only 230 mV overpotential to reach the state-of-the-art current density (10 mA cm-2). Additionally, the hybrid shows an appreciable Tafel slope with a higher Faradaic efficiency (97.55 ± 2.3%) at an overpotential of 230 mV. Further, these experimental findings are corroborated by the state-of-the-art density functional theory by presenting adsorption configurations, the density of states, and the overpotential of these hybrid structures. Interestingly, the theoretical overpotential follows the qualitative trend RGO/FCNT/VS4 < FCNT/VS4 < RGO/VS4, supporting the experimental findings.

Novel Magnetic Retrievable Visible-Light-Driven Ternary Fe3O4@NiFe2O4/Phosphorus-Doped g-C3N4 Nanocomposite Photocatalyst with Significantly Enhanced Activity through a Double-Z-Scheme System.

Nickel ferrite (NiFe2O4) and magnetite (Fe3O4) are established earth-abundant materials and get tremendous attention because of magnetic and high photocatalytic activity. First we fabricated novel Fe3O4@20 wt % NiFe2O4/phosphorus-doped g-C3N4 (M@NFOPCN) using a convenient simple coprecipitation method followed by calcination at 400 °C. Then M@NFOPCN composites were prepared by the in situ growth of Fe3O4 nanorods and cubes on the surfaces of a porous agglomerated NFOPCN nanostructure, varying the weight percentage of Fe3O4. A series of characterizations like X-ray diffraction, UV-vis diffuse-reflectance spectroscopy, photoluminescence, Fourier transform infrared, thermogravimetric analysis-differential thermal analysis, vibrating-sample magnetometry, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques confirm that changing weight percentage of M can constructively control the textural characteristics, internal strain, size of the crystals, and other aspects meant for photocatalytic activity. When M was coupled with NFOPCN, magnetic loss was lowered and also an appreciable saturation magnetization (Ms) was obtained. 40 wt % M@NFOPCN showed admirable photostability and was capable of evolving 924 µmol h-1 H2 when irradiated under visible light. The percentage of degradation for ciprofloxacin (CIP) by this ternary nanocomposite was almost 2-fold greater than those of the pure M and NFOPCN photocatalysts. A plausible photocatalytic mechanism for the degradation of CIP antibiotic was established. Hence, this study presents a reusable, low-cost, noble-metal-free, environmentally friendly, fast, and highly efficient 40 wt % M@NFOPCN photocatalyst, achieving 90% degradation of CIP antibiotic under visible light. The double-Z scheme triggers charge separation and migration, enhances visible-light harvesting, and helps in internal electric-field creation, thus headed toward dramatic augmentation of the photocatalytic activity.

Urea-Assisted Room Temperature Stabilized Metastable ß-NiMoO4: Experimental and Theoretical Insights into its Unique Bifunctional Activity toward Oxygen Evolution and Supercapacitor.

Room-temperature stabilization of metastable ß-NiMoO4 is achieved through urea-assisted hydrothermal synthesis technique. Structural and morphological studies provided significant insights for the metastable phase. Furthermore, detailed electrochemical investigations showcased its activity toward energy storage and conversion, yielding intriguing results. Comparison with the stable polymorph, α-NiMoO4, has also been borne out to support the enhanced electrochemical activities of the as-obtained ß-NiMoO4. A specific capacitance of ∼4188 F g-1 (at a current density of 5 A g-1) has been observed showing its exceptional faradic capacitance. We qualitatively and extensively demonstrate through the analysis of density of states (DOS) obtained from first-principles calculations that, enhanced DOS near top of the valence band and empty 4d orbital of Mo near Fermi level make ß-NiMoO4 better energy storage and conversion material compared to α-NiMoO4. Likewise, from the oxygen evolution reaction experiment, it is found that the state of art current density of 10 mA cm-2 is achieved at overpotential of 300 mV, which is much lower than that of IrO2/C. First-principles calculations also confirm a lower overpotential of 350 mV for ß-NiMoO4.

3D cuboidal vanadium diselenide embedded reduced graphene oxide hybrid structures with enhanced supercapacitor properties.

The electrochemical supercapacitor performance of a VSe2-reduced graphene oxide (RGO) hybrid has been reported for the first time. The hybrid was synthesized via a one-step hydrothermal route at different concentrations of graphene oxide, i.e. 0.15, 0.3, and 0.75 wt%. Enhanced supercapacitor performances were observed in the case of the hybrid obtained at 0.3 wt% of GO. It showed a specific capacitance of ∼680 F g-1 at a mass normalised current of 1 A g-1 which was ∼6 and ∼5 fold higher than those of bare VSe2 and bare RGO, respectively. Furthermore, a high energy density of ∼212 W h kg-1, power density of ∼3.3 kW kg-1, and ∼81% retention of the initial capacitance even after 10 000 cycles of charge-discharge were observed.

Supercapacitor electrodes based on layered tungsten disulfide-reduced graphene oxide hybrids synthesized by a facile hydrothermal method.

We report here the synthesis of layer structured WS2/reduced graphene oxide (RGO) hybrids by a facile hydrothermal method for its possible application as supercapacitor materials in energy storage devices. The prepared two-dimensional materials are characterized thoroughly by various analytical techniques to ascertain their structure and to confirm the absence of any impurities. Two-electrode capacitance measurements have been carried out in aqueous 1 M Na2SO4. The WS2/RGO hybrids exhibited enhanced supercapacitor performance with specific capacitance of 350 F/g at a scan rate of 2 mV/s. The obtained capacitance values of WS2/RGO hybrids are about 5 and 2.5 times higher than bare WS2 and RGO sheets. Because of the unique microstructure with combination of two layered materials, WS2/RGO hybrids emerge as a promising supercapacitor electrode material with high specific capacitance, energy density, and excellent cycling stability.