Graphene–CeO2 hybrid support for Pt nanoparticles as potential electrocatalyst for direct methanol fuel cells

A Comprehensive Review on Adsorption, Photocatalytic and Chemical Degradation of Dyes and Nitro-Compounds over Different Kinds of Porous and Composite Materials

Dye and nitro-compound pollution has become a significant issue worldwide. The adsorption and degradation of dyes and nitro-compounds have recently become important areas of study. Different methods, such as precipitation, flocculation, ultra-filtration, ion exchange, coagulation, and electro-catalytic degradation have been adopted for the adsorption and degradation of these organic pollutants. Apart from these methods, adsorption, photocatalytic degradation, and chemical degradation are considered the most economical and efficient to control water pollution from dyes and nitro-compounds. In this review, different kinds of dyes and nitro-compounds, and their adverse effects on aquatic organisms and human beings, were summarized in depth. This review article covers the comprehensive analysis of the adsorption of dyes over different materials (porous polymer, carbon-based materials, clay-based materials, layer double hydroxides, metal-organic frameworks, and biosorbents). The mechanism and kinetics of dye adsorption were the central parts of this study. The structures of all the materials mentioned above were discussed, along with their main functional groups responsible for dye adsorption. Removal and degradation methods, such as adsorption, photocatalytic degradation, and chemical degradation of dyes and nitro-compounds were also the main aim of this review article, as well as the materials used for such degradation. The mechanisms of photocatalytic and chemical degradation were also explained comprehensively. Different factors responsible for adsorption, photocatalytic degradation, and chemical degradation were also highlighted. Advantages and disadvantages, as well as economic cost, were also discussed briefly. This review will be beneficial for the reader as it covers all aspects of dye adsorption and the degradation of dyes and nitro-compounds. Future aspects and shortcomings were also part of this review article. There are several review articles on all these topics, but such a comprehensive study has not been performed so far in the literature.

One-Pot Synthesis of Pt High Index Facets Catalysts for Electrocatalytic Oxidation of Ethanol

Direct ethanol fuel cell (DEFC) has attracted wide attention due to its wide range of fuel sources, cleanliness, and high efficiency. However, the problems of low catalytic efficiency and poor catalyst stability still exist in DEFC catalysts, which restrict its rapid development. With chloroplatinic acid (H₂PtCl₆·6H₂O) as the precursor, Polyvinylpyrrolidone (PVP) plays the role of surfactant, stabilizer, and reducing agent in the experiment. Glycine is the surface control agent and co-reducing agent. Pt high-index facets nanocatalyst was prepared with the one-pot hydrothermal method by adjusting the amount of PVP and glycine. X-Ray Diffraction (XRD), transmission electron microscope (TEM), and scanning electron microscope (SEM) were used to characterize the micro-structure of the nanocatalyst, and the influence of PVP and glycine on the synthesis of high-index facets catalyst was studied. The electrocatalytic performance of the catalyst was tested with an electrochemical workstation, and it was found that the performance of the prepared catalyst was better than that of the commercial catalyst. When the mass ratio of PVP and Pt was 50:1 and the molar ratio of glycine and Pt was 24:1, Pt nanocatalysts with {310}, {520} and {830} high exponential facets were prepared. The electrochemical test results showed that the peak current density of ethanol oxidation was 2.194 m²/g, and the steady-state current density was 0.241 mA/cm², which was 5.7 times higher than that of commercial catalyst. The results of this paper show that due to the defects such as steps and kinks on the surface of the high-index facets, the active sites are increased, thus showing excellent electrocatalytic performance. This study provides a theoretical basis for the development and commercial application of high index facets nanocatalysts.

Cerium functionalized graphene nano-structures and their applications; A review

Graphene-based nanomaterials with remarkable properties, such as good biocompatibility, strong mechanical strength, and outstanding electrical conductivity, have dramatically shown excellent potential in various applications. Increasing surface area and porosity percentage, improvement of adsorption capacities, reduction of adsorption energy barrier, and also prevention of agglomeration of graphene layers are the main advantages of functionalized graphene nanocomposites. On the other hand, Cerium nanostructures with remarkable properties have received a great deal of attention in a wide range of fields; however, in some cases low conductivity limits their application in different applications. Therefore, the combination of cerium structures and graphene networks has been widely invesitaged to improve properties of the composite. In order to have a comprehensive information of these nanonetworks, this research reviews the recent developments in cerium functionalized graphene derivatives (graphene oxide (GO), reduced graphene oxide (RGO), and graphene quantum dot (GQD) and their industrial applications. The applications of functionalized graphene derivatives have also been successfully summarized. This systematic review study of graphene networks decorated with different structure of Cerium have potential to pave the way for scientific research not only in field of material science but also in fluorescent sensing, electrochemical sensing, supercapacitors, and catalyst as a new candidate.

One-Step Preparation of Nitrogen-Doped Platinum-Based Catalysts for Electrocatalytic Oxidation of Ethanol

Pt/nitrogen-doped reduced graphene oxide (N-GO) catalysts were prepared by one-step microwave-assisted ethylene glycol reduction using N-methyl-2-pyrrolidone (NMP) as the nitrogen source. Nitrogen doping in GO and the deposition of highly dispersed platinum nanoparticles were completed at the same time. The effect of adding NMP on the microstructure and the electrocatalytic performance of Pt/N-GO catalysts were studied. The results show that Pt/N-GO catalysts have better particle size distribution and electrocatalytic performance than undoped catalysts. When the ratio of GO to NMP reaches 1:200, the peak current density of the catalyst is about 3 times that of the non-nitrogen-doped Pt/GO and Pt/C(JM) catalysts, indicating that the electrocatalytic performance of this catalyst is the best. Therefore, the development of a one-step synthesis of Pt/N-GO catalysts has a broad application prospects in direct ethanol fuel cells (DEFCs).

Europium oxide nanorod-reduced graphene oxide nanocomposites towards supercapacitors

Fast charge/discharge cycles are necessary for supercapacitors applied in vehicles including, buses, cars and elevators. Nanocomposites of graphene oxide with lanthanide oxides show better supercapacitive performance in comparison to any of them alone. Herein, Eu₂O₃ nanorods (EuNRs) were prepared through the hydrothermal method and anchored onto the surface of reduced graphene oxide (RGO) by utilizing a sonochemical procedure (in an ultrasonic bath) through a self-assembly methodology. The morphologies of EuNRs and EuNR-RGO were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and IR spectroscopy. Then, we used EuNRs and EuNR-RGO as electrode materials to investigate their supercapacitive behavior using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy techniques. In a 3.0 M KCl electrolyte and with a scan rate of 2 mV s⁻¹, EuNR-RGO exhibited a specific capacity of 403 F g⁻¹. Galvanostatic charge–discharge experiments demonstrated a specific capacity of 345.9 F g⁻¹ at a current density of 2 A g⁻¹. The synergy between RGO's flexibility and EuNR's high charge mobility caused these noticeable properties.

Fast charge/discharge cycles are necessary for supercapacitors applied in vehicles including, buses, cars and elevators.

Etching high-Fe-content PtPdFe nanoparticles as efficient catalysts towards glycerol electrooxidation

Great effort has been made to improve the activity and stability, as well as increase the utilization efficiency of noble metal-based electrocatalysts.

Atomic Carbon Layers Supported Pt Nanoparticles for Minimized CO Poisoning and Maximized Methanol Oxidation

Maximizing activity of Pt catalysts toward methanol oxidation reaction (MOR) together with minimized poisoning of adsorbed CO during MOR still remains a big challenge. In the present work, uniform and well-distributed Pt nanoparticles (NPs) grown on an atomic carbon layer, that is in situ formed by means of dry-etching of silicon carbide nanoparticles (SiC NPs) with CCl₄ gas, are explored as potential catalysts for MOR. Significantly, as-synthesized catalysts exhibit remarkably higher MOR catalytic activity (e.g., 647.63 mA mg^-1 at a peak potential of 0.85 V vs RHE) and much improved anti-CO poisoning ability than the commercial Pt/C catalysts, Pt/carbon nanotubes, and Pt/graphene catalysts. Moreover, the amount of expensive Pt is a few times lower than that of the commercial and reported catalyst systems. As confirmed from density functional theory (DFT) calculations and X-ray absorption fine structure (XAFS) measurements, such high performance is due to reduced adsorption energy of CO on the Pt NPs and an increased amount of adsorbed energy OH species that remove adsorbed CO fast and efficiently. Therefore, these catalysts can be utilized for the development of large-scale and industry-orientated direct methanol fuel cells.

One-pot synthesis of PtIn/3D-GNs composites with high alloying degree for electro-photo synergistic catalysis

Alloyed PtIn/3D-GNs composites exhibit efficient electro-photo-catalysis under irradiation, deriving from the synergy between the charge separation of In₂O₃ and SPR excitation of In(0).

Nanofence Stabilized Platinum Nanoparticles Catalyst via Facet-Selective Atomic Layer Deposition

A facet-selective atomic layer deposition method is developed to fabricate oxide nanofence structure to stabilize Pt nanoparticles. CeO_x is selectively deposited on Pt nanoparticles' (111) facets and naturally exposes Pt (100) facets. The facet selectivity is realized through different binding energies of Ce precursor fragments chemisorbed on Pt (111) and Pt (100), which is supported by in situ mass gain experiment and corroborated by density functional theory simulations. Such nanofence structure not only has exposed Pt active facets for carbon monoxide oxidation but also forms ceria-metal interfaces that are beneficial for activity enhancement. The composite catalysts show excellent sintering resistance up to 700 °C calcination. CeO_x anchors Pt nanoparticles with a strong metal oxide interaction, and nanofence structure around Pt nanoparticles provides physical blocking that suppresses particles migration. The study reveals that forming oxide nanofence structure to encapsulate precious metal nanoparticles is an effective way to simultaneously enhance catalytic activity and thermal stability.

Graphene oxide based nanohybrid proton exchange membranes for fuel cell applications: An overview

In the context of many applications, such as polymer composites, energy-related materials, sensors, 'paper'-like materials, field-effect transistors (FET), and biomedical applications, chemically modified graphene was broadly studied during the last decade, due to its excellent electrical, mechanical, and thermal properties. The presence of reactive oxygen functional groups in the grapheme oxide (GO) responsible for chemical functionalization makes it a good candidate for diversified applications. The main objectives for developing a GO based nanohybrid proton exchange membrane (PEM) include: improved self-humidification (water retention ability), reduced fuel crossover (electro-osmotic drag), improved stabilities (mechanical, thermal, and chemical), enhanced proton conductivity, and processability for the preparation of membrane-electrode assembly. Research carried on this topic may be divided into protocols for covalent grafting of functional groups on GO matrix, preparation of free-standing PEM or choice of suitable polymer matrix, covalent or hydrogen bonding between GO and polymer matrix etc. Herein, we present a brief literature survey on GO based nano-hybrid PEM for fuel cell applications. Different protocols were adopted to produce functionalized GO based materials and prepare their free-standing film or disperse these materials in various polymer matrices with suitable interactions. This review article critically discussed the suitability of these PEMs for fuel cell applications in terms of the dependency of the intrinsic properties of nanohybrid PEMs. Potential applications of these nanohybrid PEMs, and current challenges are also provided along with future guidelines for developing GO based nanohybrid PEMs as promising materials for fuel cell applications.

TiO2 Nanotube-Carbon (TNT-C) as Support for Pt-based Catalyst for High Methanol Oxidation Reaction in Direct Methanol Fuel Cell

In this study, TiO₂ nanotubes (TNTs) were synthesized via a hydrothermal method using highly concentrated NaOH solutions varying from 6 to 12 M at 180 °C for 48 h. The effects of the NaOH concentration and the TNT crystal structure on the performance for methanol oxidation were investigated to determine the best catalyst support for Pt-based catalysts. The results showed that TNTs produced with 10 M NaOH exhibited a length and a diameter of 550 and 70 nm, respectively; these TNTs showed the best nanotube structure and were further used as catalyst supports for a Pt-based catalyst in a direct methanol fuel cell. The synthesized TNT and Pt-based catalysts were analysed by FESEM, TEM, BET, EDX, XRD and FTIR. The electrochemical performance of the catalysts was investigated using cyclic voltammetry (CV) and chronoamperometric (CA) analysis to further understand the methanol oxidation in the direct methanol fuel cell (DMFC). Finally, the result proves that Pt-Ru/TNT-C catalyst shows high performance in methanol oxidation as the highest current density achieved at 3.3 mA/cm² (normalised by electrochemically active surface area) and high catalyst tolerance towards poisoning species was established.

Electro-catalysis of carbon black or titanium sub-oxide supported Pd–Gd towards formic acid electro-oxidation

Carbon black supported Pd–Gd catalysts (Pd–xGd/C, x is weight percent in catalyst) with different amounts of Gd were prepared by a simultaneous reduction reaction with sodium borohydride in aqueous solution.

Sonochemical preparation of a ytterbium oxide/reduced graphene oxide nanocomposite for supercapacitors with enhanced capacitive performance

Decoration of graphene with different nanostructures can result in fundamental advancements in versatile technologies, especially in the fast growing fields of catalysts, sensors and energy storage.

Ruthenium and ruthenium oxide nanofiber supports for enhanced activity of platinum electrocatalysts in the methanol oxidation reaction

Ru and RuO₂ nanofiber composites arranged into nanosized grains as Pt catalyst supports are synthesized by electrospinning and post-calcination, which show excellent electrochemical activity.

Facile synthesis of magnetically separable reduced graphene oxide/magnetite/silver nanocomposites with enhanced catalytic activity

In this study, the combination of magnetite (Fe3O4) with reduced graphene oxide (RGO) generates a new hybrid substrate for the dispersion of noble metal nanoparticles. Well-dispersed silver (Ag) nanoparticles loaded on the surface of Fe3O4 modified RGO are achieved by an efficient two-step approach. Through reducing Ag(+) ions, highly dispersed Ag nanoparticles are in-situ formed on the RGO/Fe3O4 substrate. It is found that the existence of Fe3O4 nanocrystals can significantly improve the dispersity and decrease the particle size of the in-situ formed Ag nanoparticles. Magnetic study reveals that the as-prepared RGO/Fe3O4/Ag ternary nanocomposites display room-temperature superparamagnetic behavior. The catalytic properties of the RGO/Fe3O4/Ag ternary nanocomposites were evaluated with the reduction of 4-nitrophenol into 4-aminophenol as a model reaction. The as-synthesized RGO/Fe3O4/Ag ternary catalysts exhibit excellent catalytic stability and much higher catalytic activity than the corresponding RGO/Ag catalyst. Moreover, the RGO/Fe3O4/Ag catalysts can be easily magnetically separated for reuse. This study further demonstrates that nanoparticles modified graphene can act as an effective hybrid substrate for the synthesis of multi-component and multifunctional graphene-based composites.

A general method for the fabrication of graphene-nanoparticle hybrid material

We describe a simple and general approach to conjugate nanoparticles on pristine graphene. The method takes advantage of the high reactivity of perfluorophenyl nitrene towards the C[double bond, length as m-dash]C bonds in graphene, where perfluorophenyl azide-functionalized nanoparticles are conjugated to pristine graphene through the [2+1] cycloaddition reaction by a fast photoactivation.

A high performance supercapacitor based on a ceria/graphene nanocomposite synthesized by a facile sonochemical method

In this work, we have developed a novel nanocomposite material of ceria (CeO₂)–reduced graphene oxide (RGO) by a sonochemical route for application as a symmetric supercapacitor.

Pt–Ru/Al2O3–C nanocomposites as direct methanol fuel cell catalysts for electrooxidation of methanol in acidic medium

We have employed different ratios of Al₂O₃ and Vulcan carbon as supporting matrices for a Pt–Ru catalyst for direct methanol fuel cell catalysts.

Monolayer of close-packed Pt nanocrystals on a reduced graphene oxide (RGO) nanosheet and its enhanced catalytic performance towards methanol electrooxidation

A close-packed monolayer composed of (111)-orientated Pt nanocrystals was fabricated on reduced graphene oxide, exhibiting excellent electrocatalytic activity and stability towards methanol oxidation, ~3 times better mass activity than the commercial Pt/C.

Facile green synthesis of palladium quantum dots@carbon on mixed valence cerium oxide/graphene hybrid nanostructured bifunctional catalyst for electrocatalysis of alcohol and water

Electrocatalytic oxidation of ethylene glycol at Pd quantum dots@C–CeOx/RGO electrode.

Pt–CeO2/reduced graphene oxide nanocomposite for the electrooxidation of formic acid and formaldehyde

The Pt–CeO₂/reduced graphene oxide nanocomposite on the carbon-ceramic electrode (Pt–CeO₂/RGO/CCE) was prepared by a two-step electrodeposition process.

Electrodeposition of PtNi bimetallic nanoparticles on three-dimensional graphene for highly efficient methanol oxidation

In the present work, platinum–nickel (PtNi) bimetallic nanoparticles with a uniform diameter of 40 nm were anchored onto a three-dimensional graphene (3DGN) by using the method of electrodeposition.

Facile sonochemical synthesis and electrochemical investigation of ceria/graphene nanocomposites

We have developed a self-assembly approach to anchor CeO₂ nanoparticles onto reduced graphene oxide (RGO) through a sonochemical method. We found that a suitable loading content of CeO₂ on RGO can induce a synergistic effect for optimizing the electro-catalytic activity of the nanocomposites.