A comparative study on the electrochemical properties of nanoporous nickel oxide nanowires and nanosheets prepared by a hydrothermal method

Modeling and experimental analysis of CO2 methanation reaction using Ni/CeO2 monolithic catalyst

In this study, the effect of the cell density of monolithic catalysts was investigated and further mathematically modeled on cordierite supports used in CO2 methanation. Commercial cordierite monoliths with 200, 400, and 500 cpsi cell densities were coated by immersion into an ethanolic suspension of Ni/CeO2 active phase. SEM-EDS analysis confirmed that, owing to the low porosity of cordierite (surface area < 1 m2 g-1), the Ni/CeO2 diffusion into the walls was limited, especially in the case of low and intermediate cell density monoliths; thus, active phase was predominantly loaded onto the channels' external surface. Nevertheless, despite the larger exposed surface area in the monolith with high cell density, which would allow for better distribution and accessibility of Ni/CeO2, its higher macro-pore volume resulted in some introduction of the active phase into the walls. As a result, the catalytic evaluation showed that it was more influenced by increments in volumetric flow rates. The low cell density monolith displayed diffusional control at flow rates below 500 mL min-1. In contrast, intermediate and high cell density monoliths presented this behavior up to 300 mL min-1. These findings suggest that the interaction reactants-catalyst is considerably more affected by a forced non-uniform flow when increasing the injection rate. This condition reduced the transport of reactants and products within the catalyst channels and, in turn, increased the minimum temperature required for the reaction. Moreover, a slight diminution of selectivity to CH4 was observed and ascribed to the possible formation of hot spots that activate the reverse water-gas shift reaction. Finally, a mathematical model based on fundamental momentum and mass transfer equations coupled with the kinetics of CO2 methanation was successfully derived and solved to analyze the fluid dynamics of the monolithic support. The results showed a radial profile with maximum fluid velocity located at the center of the channel. A reactive zone close to the inlet was obtained, and maximum methane production (4.5 mol m-3) throughout the monolith was attained at 350 °C. Then, linear streamlines of the chemical species were developed along the channel.

In situ preparation of a nickel-oxy-hydroxide decorated ITQ-2 composite: a hydrodeoxygenation catalyst

A layered zeolite precursor of MWW type (MCM-22) was successfully delaminated (ITQ-2) in situ in the presence of nickel oxy-hydroxide. The broadening of XRD peaks corresponding to the (100), (220), and (310) planes and the disappearance of the (002) plane confirm the delamination. The curled ITQ-2 sheets having uniform lattice fringes, and the slit-shaped layers illustrate the formation of nickel-oxy-hydroxide-decorated ITQ-2 (Ni-ITQ-2 composite). The Ni-ITQ-2 composite is efficient for hydrodeoxygenation (HDO) of m-cresol, with a 99% yield of methylcyclohexane and exhibits excellent hydrotreating abilities for various oxygenated aromatics and cycloalkanes.

High-Performance 3D Nanostructured Silver Electrode for Micro-Supercapacitor Application

In the current energy crisis scenario, the development of renewable energy forms such as energy storage systems among the supercapacitors is an urgent need as a tool for environmental protection against increasing pollution. In this work, we have designed a novel 3D nanostructured silver electrode through an antireplica/replica template-assisted procedure. The chemical surface and electrochemical properties of this novel 3D electrode have been studied in a 5 M KOH electrolyte. Microstructural characterization and compositional analysis were studied by SEM, energy-dispersive X-ray spectroscopy, XRD technique, and Kripton adsorption at -198 °C, together with cyclic voltammetry and galvanostatic charge-discharge cycling measurements, Coulombic efficiency, cycle stability, and their leakage current drops, in addition to the self-discharge and electrochromoactive behavior, were performed to fully characterize the 3D nanostructured electrode. Large areal capacitance value of 0.5 F/cm2 and Coulombic efficiency of 97.5% are obtained at a current density of 6.4 mA/cm2 for a voltage window of 1.2 V (between -0.5 and 0.8 V). The 3D nanostructured silver electrode exhibits excellent capacitance retention (95%) during more than 2600 cycles, indicating a good cyclic stability. Additionally, the electrode delivers a high energy density of around 385.87 μWh/cm2 and a power density value of 3.82 μW/cm2 and also displays an electrochromoactive behavior. These experimental results strongly support that this versatile combined fabrication procedure is a suitable strategy for improving the electrochemical performances of 3D nanostructured silver electrodes for applications as micro-supercapacitors or in electrochemical devices.

Modification of Flexible Electrodes for P-Type (Nickel Oxide) Dye-Sensitized Solar Cell Performance Based on the Cellulose Nanofiber Film

The preparation of flexible electrode, including working electrode (WE) and counter electrode (CE), for dye-sensitized solar cells (DSSCs) utilizing metal oxides using environmentally friendly sustainable TEMPO-oxidized cellulose nanofibers (TOCNFs) is reported in this work. A new type of flexible electrode for the DSSCs, which were made of cellulose nanofiber composites with nickel hydroxide [CNF/Ni(OH)₂] substrate films and cellulose nanofiber composites with polypyrrole (CNF/PPY). Nickel hydroxide, Ni(OH)₂, has been prepared hydrothermally in the presence of TOCNFs, [TOCNF@Ni(OH)₂]. Similarly, the conductive polymer substrate has also been prepared from a composite consisting of TOCNF and PPY, TOCNF@ PPY film, by means of polymerization for the CE. Overall, the prepared electrodes both WE from CNF/Ni(OH)₂ substrates and CE from the TOCNF@PPY substrate film were revealed as the novelty of this work and which no one has introduced previously. Although NiO nanoparticles (NPs) coated on the Ni(OH)₂/TOCNF electrode also produced a good power conversion efficiency, PCE (0.75%); nevertheless, the NiO NP treatment with carbon dots boosted the efficiency up to 1.3%.

Studies on nanomaterial-based p-type semiconductor gas sensors

The development of various metal oxide semiconductor materials has resulted in better performance of the gas sensors in terms of selectivity, sensitivity, and response time. Different types of nanostructured materials, i.e., 2D materials, carbon nanotubes, and metal oxides, are used in the gas sensing applications. Generally, the metal oxide-based gas sensor operates at higher temperature to activate the adsorption process between the material surface and the target gas. The higher operating temperature of the gas sensor leads to more power consumption and produces defects in the grain boundary of metal oxide. To improve the selectivity and minimize the power consumption, nanoparticle-based p-type semiconductor materials are being developed. P-type metal oxide-based semiconductor materials have the ability to produce a hole accumulation layer which can chemisorb the oxygen molecules of higher concentration and these materials are not affected by humidity. The structure of p-type nanomaterial-based gas sensor depends upon the fabrication techniques which can affect the sensing properties of semiconductor materials. The hole accumulation layer is also known as conduction layer which is developed in the outer shell of p-type semiconductor material and the sensing mechanism is controlled by grain boundaries which is different from the n-type semiconductor material. This paper reviews the preparation methods, morphological analysis, and sensing mechanisms of nanomaterial-based p-type metal oxide-based gas sensors.

Hydrothermal Synthesis and Photocatalytic Activity of NiO Nanoparticles under Visible Light Illumination

In this present study, Nickel oxide (NiO) nanoparticles (NPs) have been synthesized using the hydrothermal method and characterized using powder X-ray Diffraction (XRD), UV-vis and Fourier Transform Infra Red (FTIR) spectroscopies, Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray (EDX) methods. The result of the characterization indicates that the synthesized sample has a pure cubic phase of NiO with roughly spherical shape morphologies and respective estimated crystallinity and microstrain values of about 78% and 5.1. Test of the photocatalytic activity of the synthesized sample towards the model contaminant dye methylene blue (MB) shows a degradation efficiency of 46% in a period of 2 h under nature sunlight irradiation at natural pH and that the reaction could satisfactorily describe both pseudo-first-order and pseudo-second-order kinetic models. So, this synthesis method may potentially be used for the effective elimination of toxic organic pollutants from water and wastewater over prolonged exposure under natural sunlight without adding any oxidant or adjusting the pH of the reaction medium. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Interfacial interaction induced OER activity of MOF derived superhydrophilic Co3O4-NiO hybrid nanostructures

Electrocatalytic water splitting is one of the key technologies for future energy systems envisioned for the storage of energy obtained from variable renewables and green fuels. The development of efficient, durable, Earth-abundant and cheap electrocatalysts for the oxygen evolution reaction is a scorching area of research. The oxygen evolution reaction has huge potential for fuel cell and metal-air battery applications. Herein, we reported interfacially interacted and uniformly decorated Co₃O₄-NiO hybrid nanostructures formed by a metal-organic framework (Co₂-BDC(OH)₂) using BDC as a linker to the metal center. The fine nanosheets of Co₂-BDC(OH)₂ were first uniformly grown over the honeycomb-like structure of nickel foam (NF). After controlled calcination of these nanosheets/NF composites, a uniformly decorated, binder-free Co₃O₄-NiO/NF electrocatalyst was synthesized. The transformation of Co₂-BDC(OH)₂/NF into Co₃O₄-NiO/NF was characterized by several techniques such as powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy, transmission electron microscopy, etc. The catalyst exhibits a low overpotential of 311 mV vs. RHE at 10 mA cm^-2 current density. The catalyst also shows long-term stability (24 h) with a Tafel slope value of 90 mV dec^-1. The obtained experimental results are also in-line with the theoretical data acquired from model systems.

Synthesis and characterizations of (Mg, Co, Ni, Cu, Zn)O high-entropy oxides

High-temperature structural ceramic materials require stability in terms of thermal and mechanical properties. High entropy oxides (HEOs) are among the emerging novel family of advanced ceramic materials with peculiar functional properties. However, their thermal stabilities and mechanical properties are not well investigated. In this work, HEO systems were synthesized from binary oxides of MgO, CoO, NiO, CuO, and ZnO using solid-state reaction method at high temperature, after obtaining the individual oxides through co-precipitation methods. The phase purity of as-synthesized and sintered samples was characterized using X-ray powder diffraction, while the microstructural investigation was performed using Scanning electron microscopy. Mechanical property of the sintered samples at different sintering times and temperatures was investigated and the sample sintered at a sintering temperature of 1200 °C for 15 h sintering time showed a maximum Vickers hardness of about 16 GPa. This result is comparable with some of the hard ceramic materials, and therefore the materials could be a potential candidate for structural applications.

Room-temperature chemical synthesis of 3-D dandelion-type nickel chloride (NiCl2@NiF) supercapattery nanostructured materials

A simple, room-temperature operable, glycerol-supported single beaker-inspired, and binder-free soft-chemical protocol has been developed to synthesize 3-D dandelion flower-type nickel chloride (NiCl₂) supercapattery (supercapacitor + battery) nanostructured electrode material from solid 3-D nickel-foam (NiF). The dandelion flower-type NiCl₂@NiF labeled as B electrode, demonstrates a battery-type electrochemical performance as obtained 1551 F·g^-1 specific capacitance (SC) and 95% cyclability over 50,000 cycles is higher than that of a setaria viridis-type NiCl₂@NiF electrode, prepared without glycerol labeled as A electrode. As a commercial market product, assembled NiCl₂@NiF@ (cathode)// BiMoO₃ (anode) pouch-type asymmetric supercapacitor energy storage device demonstrates moderate energy density and power density (28 Wh·kg^-1 and 845 W·kg^-1). By utilizing three devices in series, three different colored LEDs can be operated at full brightness. The as-proposed low temperature protocol impeccably effective and efficient on account of the low-cost, easy synthesis methodology for scalability, and high crytallinity as well as solvent-free and non-toxic as pyrolated gases were used while synthesis processing.

Sr-Doped NiO3 nanorods synthesized by a simple sonochemical method as excellent materials for voltammetric determination of quercetin

A fabricated Sr-doped NiO₃ nanorod-modified GCE was developed for electrochemical sensing of quercetin.

Mono- and bimetallic metal catalysts based on Ni and Ru supported on alumina-coated monoliths for CO2 methanation

A bimetallic catalyst consisting of Ni nanoparticles interspersed with atomic Ru on alumina coated monolith afforded higher activity than other mono and bimetallic catalysts in CO₂ methanation, providing low pressure drop at high space velocity.

Fabrication of double-shell hollow NiO@N-C nanotubes for a high-performance supercapacitor

Rational fabrication of carbon-based materials hybridized with transition-metal oxides is crucial for the design of supercapacitor electrodes with superior properties.