Graphite Support Research Articles

Nitrogen-rich graphitic carbon stabilized cobalt nanoparticles as an effective heterogeneous catalyst for hydrogenation of CO2 to formate

In this article, we report a catalytic reduction of CO2 to formate in the presence of metallic cobalt nanoparticles as an elegant heterogeneous catalyst. The aforementioned cobalt nanoparticles was prepared by the pyrolysis of impregnated cobalt precursor on cucurbit[6]uril (CB[6]). During the pyrolysis process, CB[6] framework transform to the nitrogen-rich graphitic carbon support in which cobalt nanoparticles were present in their metallic state. The synthesized catalyst was highly active for the catalytic hydrogenation of CO2 with 1 M KOH solution at 120 °C by applying 1:1 partial pressure of pCO2/pH2 to obtain a high TON of 82,265 in 24 h. Moreover, the influence of all the catalytic parameters was investigated with the reusability of the catalyst. In sort, the catalytic protocol shows excellent activity and robust nature for the CO2 utilization reaction with economical/ abundant metal source, in aqueous media and with molecular hydrogen.

Effect of different promoter precursors in a model Ru-Cs/graphite system on the catalytic selectivity for Fischer-Tropsch reaction

The effect of using two different promoter precursors on the Fischer-Tropsch synthesis was studied over cesium promoted ruthenium catalysts supported on a high surface area graphite support. In this work we reveal significant modifications in the selectivity values for Fischer-Tropsch reaction depending on the Cs promoter precursor (CsCl vs CsNO3). Specifically the bimetallic catalyst (4Ru-4Cs), prepared from nitrates both for metal and promoter precursors, showed a high selectivity to CO2 during reaction. By modifying the cesium precursor, it was possible to inhibit the water gas shift reaction, decreasing significantly the selectivity to CO2. In order to understand the chemical origin of these modifications a careful characterization of the materials was performed including: X-ray absorption near edge spectroscopy, transmission electron microscopy measurements, temperature programmed reduction studies, determination of the CO uptakes on the catalysts and the evolution of the CO adsorption heats as a function of surface coverages. It was found that upon reduction and under reaction atmosphere the promoter in the ex-nitrate catalyst appears as Cs2O which is considered responsible of the CO2 production, while in the catalysts prepared with Cs chloride the promoter remains as CsCl suffering a slight partial reduction.

Role of Carbon Support for Subnanometer Gold-Cluster-Catalyzed Disiloxane Synthesis from Hydrosilane and Water

We studied the mechanism for the formation of disiloxane from hydrosilane precursor using plane-wave density functional theory (DFT). Si–O–Si bond linkage of disiloxane is an essential framework of many useful materials. The reactions are catalyzed by the presence of subnanometer Au cluster on graphitic support. Graphene support lowers the energy barrier of the rate-limiting O–H bond activation of water by ∼4.0–9.0 kcal/mol. The rate-limiting step is shown to be accelerated by the presence of defects in graphene support. Such high activity of Au cluster over carbon support is attributed to the enhanced charge transfer from cluster to the adsorbed substrate in the presence of the support. Regeneration of the catalyst through dehydrogenation of H2 from (H2)Aun···Gn is shown to be facile.

CeO2 nanowires stretch-embedded in reduced graphite oxide nanocomposite support for Pt nanoparticles as potential electrocatalyst for methanol oxidation reaction

A novel hybrid composite RGO-CeO2 NWS with the nanowire-sheet structure was synthesized by a facile hydrothermal process using ethanol/water as the solvent without any organic additives. The graphene oxide proceeds to reduce to graphene and chemical bonds form between graphene oxide and CeO2 NWS. Pt-based catalysts with the RGO-CeO2 NWS composite as the support were then prepared by a microwave-assisted polyol process. The resultant catalysts were characterized by X-ray diffraction, Raman spectroscopy, Scanning tunneling microscopy, X-ray photoelectron spectroscopy, High resolution transmission electron microscopy and electrochemical tests. The results show that the hybrid Pt/RGO4-CeO2 NWS exhibits the best catalytic activity and the increased catalytic efficiency of Pt in the hybrid catalysts is evidence that CeO2 NWS are anchored onto the chemical defects in the wrinkles and edges of the graphene surface. This avoids the restacking of graphene oxide, thus hindering the Pt nanoparticles embedded in folding and increasing the exposed active sites. The changed valence state from Ce4+ to Ce3+ in CeO2 NWS will introduce oxygen vacancies and thus promote the tolerance of intermediate species in methanol oxidation.

PtBi Alloy Nanoparticles on Reduced Graphitic Oxide Support for Electrocatalysis

PtBi Alloy Nanoparticles on Reduced Graphitic Oxide Support for Electrocatalysis

Correction to “A Smorgasbord of Carbon: Electrochemical Analysis of Cobalt–Bis(benzenedithiolate) Complex Adsorption and Electrocatalytic Activity on Diverse Graphitic Supports”

Correction to “A Smorgasbord of Carbon: Electrochemical Analysis of Cobalt–Bis(benzenedithiolate) Complex Adsorption and Electrocatalytic Activity on Diverse Graphitic Supports”

Carbon Nitride Grafted Cobalt Complex (Co@npg‐C3N4) for Visible Light−Assisted Esterification of Aldehydes

AbstractAzide containing bipyridine complex of cobalt was grafted to the propargylated nanoporous graphitic carbon nitride (npg‐C3N4) via click reaction to obtain heterogenized photocatalyst which could efficiently provide direct esterification of aldehydes under visible light irradiation at room temperature. The use of click reaction as grafting strategy provided covalent attachment of the cobalt complex to support which not only provided higher loading but also precluded the leaching. Furthermore, the presence of carbon nitride support exhibited synergistic effect to enhance the reaction rate. In addition, the milder basic nature of nitrogen containing graphitic support provided efficient ester synthesis without the need for an external base. The synthesized photocatalyst was found to be quite robust which could easily be recovered and reused several times without significantly losing activity.

Nafion functionalized carbon nanohorns as catalyst support for proton exchange membrane fuel cells

Carbon nanohorns (CNHs) are synthesized by DC arc-discharge method in helium atmosphere. The synthesized CNHs are heat treated and then functionalized with Nafion. Platinum is reduced onto Nafion functionalized CNHs through ethylene glycol reduction method. Pt/Nafion-CNHs catalysts are prepared by varying deposition times from 1 to 7h. Detailed characterization of CNHs and the catalyst is performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). Membrane electrode assemblies are prepared by decal method and electrode performance is analyzed using hydrogen pumping technique. SEM and TGA analysis of soot indicates relatively high level purity of CNHs. TEM and XRD analysis of catalyst with 6h deposition time reveals that Pt nanoparticles are uniformly deposited on multiwall CNHs surface with particle size of 3–4nm. Hydrogen pumping studies reveals that Nafion functionalized CNHs act as good catalyst support without hindering electron transfer at electrodes. Hence, these graphitic carbon supports have potential application for high power density applications.

A Smorgasbord of Carbon: Electrochemical Analysis of Cobalt-Bis(benzenedithiolate) Complex Adsorption and Electrocatalytic Activity on Diverse Graphitic Supports.

Heterogeneous dihydrogen production manifolds comprised of bulk graphite, pencil graphite, graphite powder in Nafion films, graphene, and glassy carbon electrodes with adsorbed proton reduction catalyst TBA[Co(S2C6Cl2H2)2] have been prepared and tested for their efficiency to generate dihydrogen in acidic aqueous media. The catalyst adsorbed on these inexpensive graphitic surfaces consistently displays similar electrocatalytic profiles compared to the same catalyst on highly ordered pyrolytic graphite (HOPG) supports, including high activity in moderately acidic aqueous solutions (pH < 4), moderate overpotentials (0.42 V vs platinum), and some of the highest reported initial turnover frequencies under electrolysis conditions (96 s(-1)). The exceptions are glassy carbon and single-layer graphene surfaces, which only weakly adsorb the catalyst, with no sustained catalytic current upon acid addition. In particular, the improved stability and good activity observed for the catalyst adsorbed on graphite powder embedded in a Nafion film shows that this is a promising H2 production system that can be assembled at minimal cost and effort.

Adsorption of hexavalent chromium by graphite–chitosan binary composite

Graphite chitosan binary (GCB) composite was prepared for hexavalent chromium adsorption from studied water. GCB was characterized by TGA, FTIR, SEM and X-ray diffraction techniques. Wide porous sorptive surface of 3.89 m2 g−1 and absorptive functionalities of GCB was due to 20% (w/w) graphite support on chitosan evidenced from FTIR and SEM that impart maximum adsorption at pH 4, agitation with 200 rpm for 180 min. Adsorption studies revealed intraparticle diffusion models and best-fitted kinetics was pseudo 2nd order one. A well-fitted Langmuir isotherm model suggested monolayer adsorption with an adsorption capacity (q m ) of 105.6 mg g−1 and R 2 = 0.945. Sorption mechanisms based on metal ionic interactions, intrusion/diffusion and chemisorptions onto composite. This graphite chitosan binary composite improve sorbent capacity for Cr(VI).

Palladium Nanoparticles Supported on 3D-Graphene Nanosheets for Oxygen Reduction Reactions in Alkaline Media

Fuel cells are considered to be one the most promising sustainable energy technologies for energy conversion and electric power generation. Due to their high electrical efficiency, low operating temperatures and zero tailpipe emissions, fuel cells have become ideal candidates for both transportation and residential applications. The electro-reduction of oxygen in the cathode compartment of fuel cells is an important reaction that determines the overall performance. As a result, understanding the oxygen reduction reaction (ORR) mechanistic pathways in terms of developing efficient, high performing and stable catalysts has been the main research interest over several decades. With the recent developments in high-performance anion-exchange membranes, there has been increased interest towards studying ORR in alkaline media due to faster kinetics. Currently, Platinum/Carbon (Pt/C) based catalysts are regarded as the most active electrocatalysts for ORR. However, Pt/C catalysts are relatively expensive and lack long term stability. In addition, commercial amorphous carbon-supports such as Vulcan XC-72 utilized for Pt nanoparticles undergo severe carbon corrosion during aggressive fuel cell operating conditions, inevitably leading to Pt dissolution and loss in fuel cell efficiency. Therefore, the development alternative electrocatalysts with improved performance and durability has become a high research priority. Recently, much more attention has been directed to the use of palladium (Pd) and Pd-based alloys deposited on graphitic supports such as carbon nanotubes and graphene oxide. However, the underlying relationship between catalytic activity, surface morphology and physiochemical properties of these heterogeneous materials are not well characterized. As a result, the knowledge related to understanding the influence of the supports on the performance of the electrocatalysts (e.g Pd) for ORR is still quite limited. In the present study, we report the synthesis, characterization and electrochemical performance of Palladium nanoparticles deposited on porous three dimensional graphene nanosheets (Pd/3D-GNS) as efficient electrocatalysts for ORR in alkaline media. In order to understand the influence of the supports chemical properties on Pd nanoparticle dispersion, 3D-Graphene sheets were thermally and chemically reduced using 7 at.% H2 at 800C and hydrazine hydrate ( N2H4) respectively. The morphology of the 3D-GNS support was also modified by adopting the Sacrificial Support Method (SSM) [1] developed at UNM for controlled synthesis of highly ordered materials, where sacrificial silica templates are infused with the 3D-GNS support and etched out to leave a network of porous channels within the matrix. Pd nanoparticles were then deposited on the chemically and morphologically modified supports using a previously established Soft Alcohol Reduction method. [2] The physical-chemical and electrochemical properties of these as-prepared materials were investigated using various surface analysis and cyclic voltammetry techniques. TEM particle micrographs are shown in Fig 1A, where Pd nanoparticles supported on thermally reduced 3D-GNS can be seen to exist in the form of spherical agglomerates with an average particle size of 4.3 nm. The RDE results in Fig. 1A shows significantly enhanced electrocatalytic activity of Pd/3D-GNS-H2_800C catalysts towards ORR, with an onset potential 0.93 V vs RHE , in addition to higher current densities compared to Pd/Vulcan and Pd/3D-GNS-N2H4. The RDE data obtained at different rotation speeds ( =600 to 2500 RPM) were analyzed using the Koutecky-Levich (K-L) equation the number of transferred electrons (n) from the K-L slope was found to be n=4, indicating the Pd/3D-GNS-H2_800 materials catalyze a 4-electron reduction of oxygen. The remarkable activity of these catalysts can attributed to the uniform distribution of Pd nanoparticles within the porous 3D-Graphene matrix providing high surface area and efficient charge transfer ability, making these hybridized Pd/3D-Graphene engineered materials a promising candidate for electrocatalysis in sustainable energy fields. References. 1. Serov, A., et al., Original Mechanochemical Synthesis of Non-Platinum Group Metals Oxygen Reduction Reaction Catalysts Assisted by Sacrificial Support Method. Electrochimica Acta, 2015. 179: p. 154-160. 2. Serov, A., et al., Palladium Supported on 3D Graphene as an Active Catalyst for Alcohols Electrooxidation. Journal of The Electrochemical Society, 2015. 162(12): p. F1305-F1309. Figure 1

Atomically isolated nickel species anchored on graphitized carbon for efficient hydrogen evolution electrocatalysis.

Hydrogen production through electrochemical process is at the heart of key renewable energy technologies including water splitting and hydrogen fuel cells. Despite tremendous efforts, exploring cheap, efficient and durable electrocatalysts for hydrogen evolution still remains as a great challenge. Here we synthesize a nickel–carbon-based catalyst, from carbonization of metal-organic frameworks, to replace currently best-known platinum-based materials for electrocatalytic hydrogen evolution. This nickel-carbon-based catalyst can be activated to obtain isolated nickel atoms on the graphitic carbon support when applying electrochemical potential, exhibiting highly efficient hydrogen evolution performance with high exchange current density of 1.2 mA cm−2 and impressive durability. This work may enable new opportunities for designing and tuning properties of electrocatalysts at atomic scale for large-scale water electrolysis.

Combined Balanced Magnetron Sputtering and Substrate-Annealing Synthesis for Pt and Pt/C Oxygen Reduction Catalysts

The objective of this work is to enhance the understanding of magnetron-sputtered electrocatalytic films as a technological approach for proton exchange membrane fuel cell catalyst development especially with Pt and Pt/C sputtered layers on glassy carbon electrodes and gas diffusion electrodes. We have developed a dual-magnetron process for the deposition of Pt catalyst and a graphitic C catalyst support onto glassy carbon at elevated substrate temperatures. We characterized the different layers by XRD, XPS, SEM, cyclic voltammetry and linear sweep voltammetry. The electrocatalytic activity of Pt and Pt/C sputtered layers for the oxygen reduction reaction was found to be enhanced at higher temperatures. It was possible to synthesize carbon layers with slight graphitic characteristics as Pt support. Comparisons of the electrochemical properties of Pt and Pt/C sputtered layers showed a higher oxygen reduction activity for Pt deposited directly onto glassy carbon. However, the Pt structure was also observed to be significantly influenced by temperature, agglomeration occured. Pt deposition onto the graphitic carbon support on the other hand resulted in deposition of small Pt crystals, which were also stable at high temperatures. The catalyst structure before and after electrochemical testing indicates an increased stability at higher substrate temperatures during deposition and more crystal-like Pt assemblies versus an higher Pt mobility with particle-like Pt assemblies deposited at room temperature.

In-situ synthesis of Ni/N-doped CNFs-supported graphite disk as effective immobilized catalyst for methanol electrooxidation

In this study, a facile, controllable, and efficient process (electrospinning followed by calcination at 1100 °C under argon atmosphere) is developed for in-situ synthesis of Ni/N-CNFs catalyst as thin film immobilized on graphite disk. Moreover, the influence of nitrogen content on the catalytic activity of the supported Ni-doped CNFs toward methanol oxidation was investigated. The composition and morphology of the prepared catalysts were characterized by XRD, EDX, FE-SEM and TEM techniques. The electrocatalytic activity and stability were evaluated by cyclic voltammetry (CV) and chronoamperometry, respectively. Compared to the powder form, the results indicated that the proposed in-situ immobilization of the introduced nanofibers on graphite disk reveals distinct enhancement in the electrocatalytic activity due to merging of the underneath nanofibers with the graphite support which eliminates the interfacial resistance. Numerically, the detected maximum current density was 270.44 and 80.59 mA/cm2 for Ni/N-CNFs/graphite and unsupported nanofibers, respectively. Moreover, the obtained results have also showed that nitrogen doping effectively enhances the electrocatalytic activity and stability of Ni/CNFs toward methanol oxidation in the alkaline medium. However, due to the influence of methanol content on the water-alcohol mixture fluidity, the optimum methanol concentration was observed to be 0.5 and 5.0 M for the supported and unsupported nanofibers, respectively. Overall, this study opens new avenue to prepare one-pot current collector/electrode plate to be utilized in the fuel cell technology.

Electrocatalytic Activity and Durability of Pt-Decorated Non-Covalently Functionalized Graphitic Structures

Carbon graphitic structures that differ in morphology, graphiticity and specific surface area were used as support for platinum for Oxygen Reduction Reaction (ORR) in low temperature fuel cells. Graphitic supports were first non-covalently functionalized with pyrene carboxylic acid (PCA) and, subsequently, platinum nanoparticles were nucleated on the surface following procedures found in previous studies. Non-covalent functionalization has been proven to be advantageous because it allows for a better control of particle size and monodispersity, it prevents particle agglomeration since particles are bonded to the surface, and it does not affect the chemical and physical resistance of the support. Synthesized electrocatalysts were characterized by electrochemical half-cell studies, in order to evaluate the Electrochemically Active Surface Area (ECSA), ORR activity, and durability to potential cycling and corrosion resistance.

Synthesis and characterization of wires-like ZnO structures grown on a graphite support by microwave irradiation

Wires-like ZnO structures supported on graphite plates were synthesized by a microwave-assisted method using zinc oxide as precursor which was previously obtained from a chemical oxidation of zinc nitrate hexahydrate. Characterization was made by X-ray diffraction, scanning and high resolution transmission electron microscopy. X-ray diffraction results revealed that homemade ZnO showed the same diffraction peaks as its commercial counterpart, all reflections corresponds to a ZnO wurtzite hexagonal phase. After an irradiation process done at 2.45GHz and an output power of 1200W for 7min, homemade ZnO showed a morphological transformation which can be appreciated in SEM micrographs resulting in the formation of the wires-like ZnO structures; these ones present a broadness between 150 to 200 nm and a variable length from 0.4 to 5µm. Moreover, energy dispersive spectroscopy reveals that these structures present an entirely elemental zinc oxide composition. Wires-like ZnO structures use carbon plates as a support medium to perform their oriented growing. Finally, high resolution transmission electron microscopy showed that wires-like ZnO structures presents a crystalline arrangement with an interplanar distance of 2.4Å corresponding to a preferential crystallographic orientation (101).

Graphite-supported ultra-small copper nanoparticles – Preparation, characterization and catalysis applications

A convenient preparation of graphite-supported ultra-small copper nanoparticles (Cu NPs) has been developed. Ultra-small Cu NPs, generated by reduction of Cu(OAc)2 with H2, were well dispersed onto the graphite support and possess a very narrow distribution in size, ranging from 1.6 to 2.6nm. The catalytic activity of these ultra-small graphite-supported Cu NPs was evaluated for the Meerwein arylation of pyrroles and the multicomponent synthesis of 1,2,3-triazoles via click reaction.

Effective Strategy for Improving Electrocatalyst Durability by Adhesive Immobilization of Catalyst Nanoparticles on Graphitic Carbon Supports

We have found that Ta-based additive films in our catalyst system act as adhesives, which improves electrocatalyst durability by immobilizing the catalyst Pt NPs on the graphitic Vulcan carbon support. Furthermore, we suggest that this can be a general design principle in producing higher-durability electrocatalysts on graphitic supports. By electrochemically probing the contributing roles of the tantalum oxide (Ta2O5) and the polyphosphate (PPA) components in separate samples, we show that these combine to produce the observed improvement in activity and durability of our best catalyst, the tantalum polyphosphate (TaOPO4)-treated sample. To control variables for a valid electrochemical comparison, such as dissimilar catalyst particle size distributions and variations in surface coverage, four new catalyst samples closely matched in every way were prepared: (1) Pt/VC, (2) Pt/[PPA/VC], (3) Pt/[Ta2O5/VC], and (4) Pt[TaOPO4/VC]. We present HR-TEM/HAADF-STEM, EDS elemental mapping, PXRD, XPS, and electrochemi...

Cu₂O Nanoparticles Anchored on Amine-Functionalized Graphite Nanosheet: A Potential Reusable Catalyst.

Synthesis of Cu2O-amine-functionalized graphite nanosheet (AFGNS) composite has been accomplished at room temperature. In the first step, AFGNS is synthesized by wet chemical functionalization where the -NH2 groups formed on nanosheet surface help to anchor the Cu(2+) ions homogeneously through coordinate bonds. Reduction of Cu(2+) (3.4 × 10(-2) mmol) in the presence of NaBH4 (1.8 mmol) can be restricted to Cu(1+) on AFGNS surface at room temperature. This leads to the formation of uniform Cu2O nanoparticles (NP) on AFGNS. The role played by the -NH2 groups in anchoring Cu(2+) ions and followed by stabilizing the Cu2O NP on AFGNS was understood by controlled reactions in the absence of -NH2 groups and without any graphitic support, respectively. The prepared Cu2O-AFGNS composite shows excellent catalytic activity toward degradation of an azo dye, methyl orange, which is an environmental pollutant. The dye degradation proceeds with high rate constant value, and the composite shows high stability and excellent reuse capability.

Detection of cardiac biomarker proteins using a disposable based on a molecularly imprinted polymer grafted onto graphite

A low-cost disposable was developed for rapid detection of the protein biomarker myoglobin (Myo) as a model analyte. A screen printed electrode was modified with a molecularly imprinted material grafted on a graphite support and incorporated in a matrix composed of poly(vinyl chloride) and the plasticizer o-nitrophenyloctyl ether. The protein-imprinted material (PIM) was produced by growing a reticulated polymer around a protein template. This is followed by radical polymerization of 4-styrenesulfonic acid, 2-aminoethyl methacrylate hydrochloride, and ethylene glycol dimethacrylate. The polymeric layer was then covalently bound to the graphitic support, and Myo was added during the imprinting stage to act as a template. Non-imprinted control materials (CM) were also prepared by omitting the Myo template. Morphological and structural analysis of PIM and CM by FTIR, Raman, and SEM/EDC microscopies confirmed the modification of the graphite support. The analytical performance of the SPE was assessed by square wave voltammetry. The average limit of detection is 0.79 μg of Myo per mL, and the slope is −0.193 ± 0.006 μA per decade. The SPE-CM cannot detect such low levels of Myo but gives a linear response at above 7.2 μg · mL−1, with a slope of −0.719 ± 0.02 μA per decade. Interference studies with hemoglobin, bovine serum albumin, creatinine, and sodium chloride demonstrated good selectivity for Myo. The method was successfully applied to the determination of Myo urine and is conceived to be a promising tool for screening Myo in point-of-care patients with ischemia.