Photodiodes based on graphene oxide–silicon junctions

Schottky barrier diode based on graphene oxide (GO) with the structure of Al/GO/n-Si/Al was fabricated. The current–voltage characteristics of the diode were investigated under dark and various light intensity. It was observed that generated photocurrent of the diode depends on light intensity. Various junction parameters were presented using I–V characteristics. The transient photocurrent measurement indicated that the Al/GO/n-Si/Al diode was very sensitive to illumination. The photocurrent of the diode increases with increase in illumination intensity. The capacitance–voltage–frequency (C–V–f) measurements indicated that the capacitance of the diode depends on voltage and frequency. The capacitance decreases with increasing frequency due to a continuous distribution of the interface states. These results suggest that the Al/GO/n-Si/Al diode can be utilized as a photosensor.     

Reliability of hydrogen sensing based on bimetallic Ni–Pd/graphene composites

Graphene-supported nickel–palladium (Ni–Pd) bimetallic nanoparticles (Ni–Pd/Gr) were synthesized using a simple chemical method, followed by a post-thermal annealing process. The characteristics of resistivity-type hydrogen (H₂) sensors composed of Pd–Gr composites (with small amounts of Ni added to the Pd nanoparticles (Pd NPs)) were investigated in detail. Pd NPs with various amounts of Ni embedded into the Pd lattice were synthesized by varying the molar ratios of the Ni/Pd precursors. The results from this work indicate that the addition of Ni not only enhances performance, but also reduces the hysteresis behavior of the Pd–Gr composite based H₂ sensors. H₂ was detectable from 1 to 1000 ppm based on a rapid recovery response with suitable Ni/Pd percentages. At the optimal Ni/Pd percentage of 7% (Ni/Pd ∼7%), sensors showed a small enhancement of sensitivity, fast recovery, and minimum hysteresis effect. From our experiment, the addition of Ni to Pd NPs results in a reduction of the hysteresis effect and reliability on H₂ sensors based on Pd–Gr composites.     

Efficient method to obtain Platinum–Cobalt supported on graphene oxide and electrocatalyst development

We have prepared a highly efficient and stable platinum–cobalt catalyst supported on graphene oxide by using a one-step synthesis microwave-irradiation process. The structure and composition of two different compositions (Pt:Co(2.5:1)/rGO, Pt:Co(2:1)/rGO) have been investigated by Fourier infrared spectroscopy (FT-IR), X-ray Photoelectron spectroscopy (XPS), specific surface area (BET), Raman spectroscopy. Their electrocatalytic activity was investigated and the electrochemical response from cyclic voltammetry revealed the high efficiency and stability as well as the potential application as cathode electrode. The electrocatalysts exhibited a superior durability comparing with commercial Pt/C catalyst after accelerated stress test, indicating a lower loss of electrochemical surface area in the case of prepared samples. Moreover, this study extends the applicability of this synthesis method for the preparation of other noble or transitional metal nanoparticles decorated on reduced graphene oxide.     

Hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticles for highly efficient methanol electrooxidation

Exploiting highly efficient electrocatalysts through simple methods is very critical to the development of energy conversion technologies. Herein, we develop a hierarchical reduced graphene oxide supported dealloyed platinum–copper nanoparticle catalyst (Pt–Cu/RGO) by a facile one-step electrodeposition of graphene oxide in the presence of H₂PtCl₆ and copper ethylenediamine tetraacetate. The nanostructure and composition were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. Meanwhile, the electrocatalytic performance was investigated by cyclic voltammetry and chronoamperometry, showing that the Pt–Cu/RGO catalyst not only equips with an outstanding electrocatalytic activity for the methanol oxidation reaction (2.3 times that of commercial Pt/C catalyst), but also shows a robust durability and superior tolerance to CO poisoning. The excellent electrocatalytic performance could be attributed to the three-dimensional hierarchical structure, porous dealloyed nanoparticles and synergistic effect between each component.     

TiO2–graphene nanocomposites for photocatalytic hydrogen production from splitting water

TiO₂ (P25)–graphene (P25–GR) hybrids were prepared via solvothermal reaction of graphene oxide and P25 using ethanol as solvent. The as-prepared P25–GR nanocomposites were characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, photoluminescence emission spectroscopy and ultraviolet-visible (UV–vis) diffuse reflectance spectroscopy. The results indicated that P25–GR nanocomposites possessed enhanced light absorption ability and charge separation efficiency. As photocatalysts, P25–GR hybrids were much better than the bare P25, when they were used in the hydrogen evolution from aqueous methanol solution under Xe-lamp illumination. A significant enhancement in the rate of hydrogen production was achieved through using P25–GR as photocatalysts, comparing to bare P25. The optimum mass ratio of GR to P25 in the hybrids was 0.5 wt%. The higher mass ratio of GR in P25–GR would decrease the photocatalytic activity of P25.     

Bipotential deposition of nickel–cobalt hexacyanoferrate nanostructure on graphene coated stainless steel for supercapacitors

Graphene oxide (GO) was deposited on inexpensive and mechanically stable stainless steel (SS) electrode by electrophoretic deposition (EPD) technique. GO was reduced electrochemically in NaNO₃ to obtain electrochemically reduced graphene oxide (ERGO). Next, Hybrid nickel–cobalt hexacyanofarrate (NiCoHCF) nanoparticles were deposited from solution containing Ni⁺² and Co⁺² with ratio of 1:1 on ERGO/SS by bipotential method. Morphological investigation of prepared sample by scanning electron microscopy showed the presence of nanoparticles with diameters in the range of 15–50 nm. Crystal structure of nanocomposite was investigated by X-ray diffraction technique. Electrochemical behavior of prepared film indicates that hybrid nanocomposite has higher specific capacitance (411 F g⁻¹) than ERGO (185.2 F g⁻¹) in KNO₃ solution at current density of 0.2 A g⁻¹. In other words, pseudocapacitor that is formed based on the faradaic behavior of NiCoHCF can improve the capacitive performance of ERGO.     

Synthesis and electrocatalytic alcohol oxidation performance of Pd–Co bimetallic nanoparticles supported on graphene

Magnetic Pd–Co bimetallic nanoparticles supported on reduced graphene oxide sheets (Pd–Co/RGO) with excellent electrocatalytic performance have been synthesized by a rapid reducing method, using sodium hypophosphite as the reducing agent. The loading and crystalline phase of cobalt in the Pd–Co/RGO hybrids varied as to the initial amount of cobalt salt and reducing agent. Transmission electron microscopy images show that the mean size of the Pd–Co bimetallic nanoparticles was about 10–13 nm and without significant agglomeration. At the same Pd loading on graphene, the current densities of the forward anodic peak of the different Pd–Co/RGO catalysts was decreased by about 25% when compared with that of the pure Pd nanoparticles supported on reduced graphene oxide for both methanol and ethanol oxidation. However, chronoamperometry tests confirmed that the stability was increased by up to 240% and 225% for methanol oxidation and ethanol oxidation, respectively. It is hypothesized that the Co layer on Pd partially blocks Pd sites sacrificing a small portion of the activity of the catalysts, but it leaves the remaining Pd more active and thus enhances alcohol oxidation kinetics and tolerance to poisoning intermediates. Catalytic performance of the Pd–Co/RGO hybrids for alcohol oxidation is primarily affected by the interaction among Pd, Co, and graphene.     

One-pot calcination preparation of graphene/g–C3N4–Co photocatalysts with enhanced visible light photocatalytic activity

Photocatalytic technology for hydrogen evolution from water splitting and pollutant degradation is one of the most sustainable methods. Here, the graphene/g–C₃N₄–Co composite materials have been prepared by one-pot calcination method. The results show that g-C₃N₄ grow on the surface of graphene and form a sandwich structure, meanwhile, the introduction of Co increases the active sites, which promotes the photocatalytic performance. The influences of graphene and Co content on photocatalytic activity were also studied by UV–visible spectrophotometry (DRS), photoluminescence spectroscopy (PL), photocurrent, degradation MB, and hydrogen production. The apparent reaction rate constant k of graphene/g–C₃N₄–Co (3%) is 0.946 h⁻¹, which is 4.90 and 2.18 times faster than g-C₃N₄ and graphene/g-C₃N₄, respectively. And the hydrogen production rate of graphene/g–C₃N₄–Co (3%) (892.3 μmol h⁻¹ g⁻¹) is 3.53 and 1.61 times higher than g-C₃N₄ and graphene/g-C₃N₄, respectively.     

Surfactant-free Pd–Fe nanoparticles supported on reduced graphene oxide as nanocatalyst for formic acid oxidation

Herein, a novel surfactant-free nanocatalyst of Pd–Fe bimetallic nanoparticles (NPs) supported on the reduced graphene oxide (Pd–Fe/RGO) were synthesized using a two-step reduction in aqueous phase. Electrochemical studies demonstrate that the nanocatalyst exhibits superior catalytic activity towards the formic acid oxidation with high stability due to the synergic effect of Pd–Fe and RGO. The optimized Pd–Fe/RGO (Pd:Fe = 1:5) nanocatalyst possess an specific activity of 2.72 mA cm^?2 and an mass activity of 1.0 A mg^?1_(Pd), which are significantly higher than those of Pd/RGO and commercial Pd/C catalysts.     

Layered MoS2–graphene composites for supercapacitor applications with enhanced capacitive performance

Layered molybdenum disulfide (MoS₂)–graphene composite is synthesized by a modified l-cysteine-assisted solution-phase method. The structural characterization of the composites by energy dispersive X-ray analysis, X-ray powder diffraction, Fourier transform infrared spectroscopy, XPS, Raman, and transmission electron microscope indicates that layered MoS₂–graphene coalescing into three-dimensional sphere-like architecture. The electrochemical performances of the composites are evaluated by cyclic voltammogram, galvanostatic charge–discharge and electrochemical impedance spectroscopy. Electrochemical measurements reveal that the maximum specific capacitance of the MoS₂–graphene electrodes reaches up to 243 F g⁻¹ at a discharge current density 1 A g⁻¹. The energy density is 73.5 Wh kg⁻¹ at a power density of 19.8 kW kg⁻¹. The MoS₂–graphene composites electrode shows good long-term cyclic stability (only 7.7% decrease in specific capacitance after 1000 cycles at a current density of 1 A g⁻¹). The enhancement in specific capacitance and cycling stability is believed to be due to the 3D MoS₂–graphene interconnected conductive network which promotes not only efficient charge transport and facilitates the electrolyte diffusion, but also prevents effectively the volume expansion/contraction and aggregation of electroactive materials during charge–discharge process. Taken together, this work indicates MoS₂–graphene composites are promising electrode material for high-performance supercapacitors.     

Experimentally measured thermal transport properties of aluminum–polytetrafluoroethylene nanocomposites with graphene and carbon nanotube additives

Reactive materials such as aluminum (Al) and polytetrafluoroethylene (Teflon) are used for energy generation applications and specifically in ordnance technologies. With the advent of nanotechnology various nano-scale additives have become incorporated into reactive material formulations with the hope of enhanced performance. An important component to the study of energy generation is an examination of energy transport through a reactant matrix. This study examines an experimental approach to quantifying thermal properties of an Al/Teflon nanocomposite reactant matrix that has been impregnated with carbon additives. Various structures of carbon are investigated and include amorphous nanoscale carbon spheres (nano C), graphene flakes and unaligned multiwalled carbon nanotubes (CNTs). The additives were selected based on their completely different structures with the hypothesis that the structure of the additive will influence the thermal transport properties of the matrix. Results show graphene has the greatest influence on the thermophysical properties. For example, thermal conductivity of the composites containing graphene increased by 98%. Graphene similarly enhanced the thermal diffusivity and specific heat of the Al/Teflon matrix. Conversely, nano C and CNTs decreased the thermal conductivity and thermal diffusivity of the samples significantly.     

Preparation and characterization of core–shell-like PbPt nanoparticles electro-catalyst supported on graphene for methanol oxidation

PbPt core–shell-like nanoparticles supported on graphene is successfully synthesized by a simply galvanic displacement reaction method. The composition, morphology, structure of the catalyst and activity towards methanol oxidation are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Chronoamperometric and CV results reveal that PbPt core–shell-like nanoparticles catalyst has better activity towards methanol oxidation than the pure platinum prepared under the same conditions. These behaviors are attributed to an electronic effect of the inner Pb or the increase in the d-orbital vacancy of Pt in core–shell-like PbPt catalyst.     

Use of Pd–MnMoO4–graphene hybrids as efficient and CO poisoning tolerant electrocatalysts for methanol oxidation

40 wt%Pd-x wt%MnMoO₄/Graphene (GNS) (0 ≤ x ≤ 20) hybrids have been synthesized for use as efficient and CO poisoning tolerant anode materials in methanol fuel cells. Investigations revealed that the addition of MnMoO₄ increases the electrocatalytic activity of the base electrode (40 wt%Pd/GNS) towards the methanol oxidation reaction (MOR) in 1 M KOH significantly. The catalytic activity of the electrode is found to be the greatest with 8 wt%MnMoO₄. The addition of MnMoO₄ also improves CO poisoning tolerance of the base electrode by 11–73%. The MOR activity and CO poisoning tolerance of the 40 wt%Pd-8 wt%MnMoO₄/GNS hybrid electrode were superior to other electrodes of the investigation.     

ZnO–Bi2O3/graphene oxide photocatalyst with high photocatalytic performance under visible light

Abstract

Photocatalytic nanomaterials are attracting more and more attention because of their potential for solving environmental problems. ZnO, as one of the most promising photocatalysts, can only be excited by ultraviolet (UV) or near UV radiation. The objective of the study is to describe an efficient visible light driven ZnO based photocatalyst. In this regard, we communicate the preliminary research on the synthesis, characterisation and photocatalytic properties of ZnO–Bi₂O₃/graphene oxide (GO) composite materials. It was found that the photodegradation of methylene blue in the presence of ZnO–Bi₂O₃/GO reached 99·62% after irradiation with visible light for 2 h. The presence of GO enhances the stability of ZnO–Bi₂O₃ and reduces the recombination of charge carriers. ZnO–Bi₂O₃/GO also shows high photocatalytic activity for the degradation of acid blue, acid yellow, reactive red, acid red, reactive yellow and reactive blue under visible light irradiation. The novel aspect is the combination of GO and Bi₂O₃ doped ZnO. The use of GO enhances the efficiency of photocatalysis, and Bi₂O₃ doping ZnO excites the absorption of visible light. The impact of the research concerns the study of ZnO–Bi₂O₃/GO, which can be used as a promising photocatalyst for the treatment of textile wastewater.     

Hydrolytic dehydrogenation of ammonia borane and methylamine borane catalyzed by graphene supported Ru@Ni core–shell nanoparticles

Ru@Ni core–shell nanoparticles (NPs) supported on graphene have been synthesized by one-step in situ co-reduction of aqueous solution of ruthenium (III) chloride, nickel (II) chloride, and graphene oxide (GO) with ammonia borane (AB) as the reducing agent under ambient condition. The as-synthesized NPs exhibit much higher catalytic activity for hydrolytic dehydrogenation of AB than the monometallic, bimetallic alloy (RuNi/graphene), and graphene-free core–shell (Ru@Ni) counterparts. Additionally, the Ru@Ni/graphene NPs facilitate the hydrolysis of AB, with the turnover frequency (TOF) value of 340 mol H₂ min⁻¹ (mol Ru)⁻¹, which is among the highest value reported on Ru-based NPs so far, and even higher than the reversed Ni@Ru NPs. Furthermore, the as-prepared NPs exert satisfied durable stability and magnetically recyclability for the hydrolytic dehydrogenation of AB and methylamine borane (MeAB). Moreover, this simple synthetic method can be extended to other Ru-based bimetallic core–shell systems for more applications.     

Platinum–Iron nanoparticles supported on reduced graphene oxide as an improved catalyst for methanol electro oxidation

Platinum–Iron nanoparticles supported on reduced graphene oxide powder are synthesized by chemical reduction method as an anode catalyst for the methanol electro oxidation. The characterization of the catalyst has been investigated using physical and electrochemical methods. Prepared catalyst was characterized by scanning electron microscopy (SEM), TEM (Transmission electron microscopy), FT-IR (Fourier-transform infrared spectroscopy), Raman spectroscopy and, X-ray diffraction (XRD) and energy dispersive analysis of X-ray (EDX). Pt and Pt-Fe nanoparticles are uniformly dispersed on the surface of reduced graphene oxide (rGO) powder nanocomposite support. The catalytic properties of the catalyst for methanol electro-oxidation were thoroughly studied by electrochemical methods that involved in the cyclic voltammetry, linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The Pt-Fe/rGo exhibits high electrocatalytic activity, catalyst tolerance for the CO poisoning and catalyst durability for electro-oxidation of methanol compared to the Pt/rGo and commercial Pt/C catalyst. Therefore, the Pt-Fe/rGo catalyst is a good choice for application in direct methanol fuel cells.     

Strategic synthesis of graphene supported trimetallic Ag-based core–shell nanoparticles toward hydrolytic dehydrogenation of amine boranes

We reported the synthesis and characterization of two trimetallic (Ag@CoFe, and Ag@NiFe) core–shell nanoparticles (NPs), and their catalytic activity toward hydrolytic dehydrogenation of ammonia borane (AB) and methylamine borane (MeAB). The as-synthesized trimetallic core–shell NPs were obtained via a facile one-step in situ procedure using methylamine borane as a reducing agent and graphene as the support under ambient condition. The as-synthesized NPs are well dispersed on graphene, and exhibit higher catalytic activity than the catalysts with other conventional supports, such as the SiO₂, carbon black, and γ-Al₂O₃. Additionally, compared with NaBH₄ and AB, the as-synthesized Ag@CoFe/graphene NPs reduced by MeAB exhibit the highest catalytic activity, with the turnover frequency (TOF) value of 82.9 (mol H₂ min⁻¹ (mol Ag)⁻¹), and the activation energy (E_a) value of 32.79 kJ/mol. Furthermore, the as-prepared NPs exert good durable and magnetically recyclability for the hydrolytic dehydrogenation of AB and MeAB. Moreover, this simple strategic synthesis method can be easily extended to the facile preparation of other graphene supported multi-metal core–shell NPs.     

Intermittent microwave synthesis of nanostructured Pt/TiN–graphene with high catalytic activity for methanol oxidation

A one-step and fast microwave technique was developed to synthesize graphene-supported TiN nanoparticles (TiN–G) directly from graphene and dihydroxybis (ammonium lactato) titanium (IV). During the synthesis graphene served as a reductant and template to reduce the Ti-precursor into TiN and then uniformly disperse TiN nanoparticles on it. Pt/TiN–G catalyst was also successfully prepared with the portion of Pt nanoparticles was anchored at the interface of TiN and graphene. Electrochemical measurements showed that the Pt/TiN–G catalyst exhibited improved catalytic activity for methanol oxidation and enhanced CO tolerance than those of Pt/G catalyst, attributed to the formation of –OH groups on the surface of TiN. And the –OH attached TiN assisted the conversion of CO into CO₂.     

Monodisperse palladium–nickel alloy nanoparticles assembled on graphene oxide with the high catalytic activity and reusability in the dehydrogenation of dimethylamine–borane

Herein, a highly efficient and stable palladium nickel nanoparticles (PdNi NPs) supported on graphene oxide (GO) was synthesized, characterized and applied for the dehydrogenation of dimethyl ammonia borane (DMAB). The monodisperse PdNi NPs has been synthesized via the ultrasonic double solvent reduction method in the presence of oleylamine and GO as support matrices. The structure morphology and properties of PdNi@GO NPs were characterized by using different techniques such as UV–VIS, XPS, TEM, HRTEM and XRD methods. The PdNi@GO NPs was found to be highly effective and stable in the dehydrogenation of DMAB. This catalyst with the turnover frequency of 271.9 h^?1 shows one of the best results among the all prepared catalysts in literature for the dehydrogenation of DMAB. The apparent activation parameters of the catalytic dehydrogenation reaction were also calculated; apparent activation energy (E_a,app) = 38 ± 2 kJ mol^?1, activation enthalpy (ΔH^#_,app) = 35 ± 1 kJ mol^?1 and activation entropy (ΔS^#_,app) = ?102 ± 1 J K^?1 mol^?1.     

In-situ assemblage of Fe–V–P/graphene aerogel based on prussian blue analogue as a high-performance electrocatalyst for oxygen evolution reaction

The carbon scaffold with high conductivity is suitable to enhance the catalytic activity of prussian blue analogues (PBAs) in oxygen evolution reaction (OER) of water splitting. Herein, a two-step strategy is developed to synthesize Fe–V–P/graphene aerogel based on prussian blue analogue (Fe–V–P/GA) electrocatalysts, which possess dense arrangement of anomalous octahedron structure. In the vanadium-modified PBAs (FeV–PBAs), Fe/V with a series of different molar ratios has been investigated and when the molar ratio of Fe/V is 1:1, the catalyst achieves a fairly high specific surface area expressed by the double-layer capacitance of 5.29 mF cm⁻² and requires overpotentials of only 234.0 and 314.3 mV to attain the benchmark current density of 10 and 50 mA cm⁻² during OER process. Besides, the catalyst owns satisfactory stability and the current density remains almost constant during stability tests lasting up to 70 h. As revealed via electrochemical kinetics analysis and the spectroscopic measurement, embellished FeV–PBAs not only lead to larger tangible area, more accessible sites and higher durable stability, but also provide formation of high valence state of iron and vanadium species, strong modification of electronic state and faster kinetics. This study provides a novel mode of thinking to consummate the design of 3D construction so as to boost the catalytic effect of transition metal catalysts for efficient oxygen evolution.