Graphene-based Catalysts Research Articles

In Situ and Simultaneous Synthesis of a Novel Graphene-Based Catalyst for Deep Hydrodesulfurization of Naphtha

In this research, a novel graphene-supported catalyst was prepared through which, a simultaneous chemical exfoliation of graphite and MoS2 powder performed preparing a new composite species and evaluated for the hydrodesulfurization reaction of naphtha and no sulfidation pretreatment was performed upon the catalyst. Also, the influences of the operating parameters such as temperature, and liquid hourly space velocity on HDS conversion evaluated.

Graphene-Based Oxygen Reduction Reaction Catalysts for Metal Air Batteries

In the past few years, the metal air batteries developed fast due to their remarkably high theoretical energy output. So far, the oxygen reduction reaction catalysts still have been the bottleneck for high power application of metal air batteries because of their sluggish kinetics. Recently, the graphene-based oxygen reduction reaction catalysts (GORRC) with high catalytic activity have been intensively reported. In this review, we focus on the recent progress and current situation of GORRC, and divide them into three categories, graphene as catalyst support, nitrogen doped graphene as the catalyst, and hybrids of nitrogen doped graphene and other catalysts as the catalyst. As an outstanding catalyst support, graphene can not only decrease the application amount of active components but also improve their catalytic activity and long-term stability. After doped by nitrogen, the graphene catalysts exhibit enhanced catalytic activity for the oxygen reduction reaction. In addition, the excellent catalysts can be obtained as the nitrogen doped graphene and other type of catalysts are hybridized. The catalytic activity and long-term stability of the hybrids are even better than that of the commercial Pt/C catalyst. Furthermore, the remarks on the challenges and perspectives of research directions are proposed for further development of GORRC which can be used in the metal air batteries.

Synthesis of metallic Ni-Co/graphene catalysts with enhanced hydrodesulfurization activity via a low-temperature plasma approach

Graphene sheets (GS) supported monometal (Ni, Co) or bimetal (Ni-Co) nanoparticle composites have been conveniently prepared with the assistance of dielectric barrier discharge (DBD) plasma at low temperature. Both graphene oxide and the metal ions (Ni2+, Co2+) can be simultaneously reduced during the DBD plasma treatment in H2 atmosphere, which gives rise to the uniformly distributed metal nanoparticles on the surface of GS. The graphene-based catalysts are used in the catalytic hydrodesulfurization (HDS) of carbonyl sulfide (COS). It is revealed that the bimetallic Ni-Co/GS catalyst exhibits outstanding performance for higher COS conversion compared with the monometal catalysts, suggesting the synergetic effect between Ni and Co active species in the HDS reaction. The presented strategy demonstrates a new pathway for the preparation of graphene-based catalysts with high HDS catalytic performance.

Optimization of catalyst layer composition for PEMFC using graphene-based oxygen reduction reaction catalysts

The focus in recent years is on developing high performance non-precious metal catalysts (NPMCs) to reduce the catalyst cost in fuel cells. However, little attention has been paid to improve the utilization of NPMCs. Thus, this study focuses on the optimization of electrode component, particularly the Nafion content. With the synthesized graphene based oxygen reduction reaction (ORR) catalyst, the catalyst inks were prepared at various Nafion contents with suitable amounts of catalysts sprayed on the gas diffusion media. Twenty different single cells were assembled and measured for polarization, resistance and electrochemical impedance. Electrodes of 66.7 and 50.0% Nafion contents showed the highest performance for hydrogen/oxygen and hydrogen/air operation, respectively. These results were explained using the electrochemical impedance spectra, where the highest performance electrode resulted with the lowest charge transfer resistance. Moreover, negligible change in performance was observed during the 80 h of stability test. The optimization compositions of NPMC-based MEAs were very different to Pt-based MEAs, indicating the importance of optimization studies for the practical use of NPMCs.

CuAu–ZnO–graphene nanocomposite: A novel graphene-based bimetallic alloy-semiconductor catalyst with its enhanced photocatalytic degradation performance

The bimetallic alloy CuAu nanoparticles (NPs) can produce more photogenerated electrons when compared with single metal Au NPs. Moreover, graphene (Gr) sheets can help the charge separation and slow down the recombination of the electron hole pairs of ZnO. Hence, a novel graphene-based bimetallic alloy-semiconductor catalyst: CuAu–ZnO–Gr nanocomposite is synthesized. Due to the synergistic effect among CuAu NPs, ZnO nanopyramids, and Gr sheets, CuAu–ZnO–Gr behaves an enhanced photocatalytic activity for the photocatalytic degradation of synthetic colorants methyl orange (MO), methylene blue (MB), indigotin (IN), sunset yellow (SY), and tartrazine (TT) under the simulated sunlight irradiation. Furthermore, the apparent rate constants (kapp) of MO, MB, IN, SY, and TT degradation are estimated respectively. In addition, the as-prepared CuAu–ZnO–Gr nanocomposite is characterized by X-ray diffraction, UV–vis spectrum, transmission electron microscopy, energy dispersive X-ray analysis (EDX), and EDX mapping. As a result of the facile synthesis route and the enhanced photocatalytic activity, this new material CuAu–ZnO–Gr can be a promising photocatalyst for the degradation of dyes.

Effect of Nitrogen Doping on the Migration of the Carbon Adatom and Monovacancy in Graphene

Nitrogen-doped graphene (N-graphene) has important implications in graphene-based devices and catalysts. Nitrogen incorporation into graphene via postsynthetic treatment is likely to produce a non-negligible amount of defects and bond disorders, and the resulting nitrogen content is usually dominated by graphitic N and pyridinic N. To understand the kinetic stability of doped N and the effect of doped N on the self-healing of monovacancy in graphene, we have performed density functional theory calculations to study the adsorption and migration of an adsorbed C atom on undoped and N-doped graphene with and without a monovacancy (MV). The effects of N doping and hydrogenation on the migration of a MV in graphene are also studied. Our results suggest that the graphitic N doped in the vicinity of MV is kinetically unstable, and it could be transformed into a pyridinic N due to the migration of MV when N-graphene is through high-temperature annealing. The presence of a C adatom would easily repair the vacancy ...

Silicon phthalocyanine covalently functionalized N-doped ultrasmall reduced graphene oxide decorated with Pt nanoparticles for hydrogen evolution from water.

To improve the photocatalytic activity of graphene-based catalysts, silicon phthalocyanine (SiPc) covalently functionalized N-doped ultrasmall reduced graphene oxide (N-usRGO) has been synthesized through 1,3-dipolar cycloaddition of azomethine ylides. The obtained product (N-usRGO/SiPc) was characterized by transmission electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, Raman spectra, X-ray photoelectron spectroscopy, fluorescence, and UV-vis spectroscopy. The results demonstrate that SiPc has been successfully grafted on the surface of N-usRGO. The N-usRGO/SiPc nanocomposite exhibits high light-harvesting efficiency covering a range of wavelengths from the ultraviolet to visible light. The efficient fluorescence quenching and the enhanced photocurrent response confirm that the photoinduced electron transfers from the SiPc moiety to the N-usRGO sheet. Moreover, we chose Pt nanoparticles as cocatalyst to load on N-usRGO/SiPc sheets to obtain the optimal H2 production effect. The platinized N-usRGO/SiPc (N-usRGO/SiPc/Pt) demonstrates good hydrogen evolution performance under both UV-vis and visible light (λ>400 nm) irradiation. The apparent quantum yields are 1.3% and 0.56% at 365 and 420 nm, respectively. These results reveal that N-usRGO/SiPc/Pt nanocomposite, consolidating the advantages of SiPc, N-usRGO, and Pt NPs, can be a potential candidate for hydrogen evolution from water under UV-vis or visible light irradiation.

One-step fabrication of RGO/HNBR composites via selective hydrogenation of NBR with graphene-based catalyst

Enhanced mechanical and electrical RGO/HNBR composite was prepared by hydrogenation of NBR with grapheme-based catalyst.

A Review of Graphene Supported Electrocatalysts for Direct Methanol Fuel Cells

As a fascinating two-dimensional nanomaterial, graphene is attractive for electrocatalytical application in direct methanol fuel cells due to its unique structure and outstanding physical properties. Graphene and its derivatives have been widely used as a support material to improve electrocatalytical activity of catalyst particles for methanol and ethanol oxidations. In this review, discussion is focused on the graphene supported monometallic and bimetallic nanocrystals hybrid materials for electrocatalysts. Additionally, the nitrogen-doped graphene utilized for promising support material in electrocatalysts was also mentioned. We believe that the article will be useful to researchers interested in graphene-based catalyst and related materials for direct methanol fuel cells and provide the present status of the subject.

Graphene–NHC–iridium hybrid catalysts built through –OH covalent linkage

Graphene oxide (GO) and thermally reduced graphene oxide (TRGO) were covalently modified with imidazolium salts through their hydroxyl surface groups. The selective reaction of the –OH groups with p-nitrophenylchloroformate produced labile intermediate organic carbonate functions which were used for the covalent anchoring of a hydroxy-functionalized imidazolium salt. Nanohybrid materials containing iridium N-heterocyclic carbene (NHC)-type organometallic complexes were prepared by causing the imidazolium-functionalized materials to react with [Ir(μ-OMe)(cod)]2. The iridium content of the graphene-based hybrid catalysts, as determined by XPS and ICP-MS was the order of ∼5 and 10wt.%, for the TRGO and GO-based materials, respectively. The graphene-supported iridium hybrid materials were active in the heterogeneous hydrogen-transfer reduction of cyclohexanone to cyclohexanol with 2-propanol/KOH as the hydrogen source. The thermally reduced graphene–NHC–iridium hybrid catalyst showed the best catalytic performance with an initial TOF of 11.500h−1, slightly better than the related acetoxy-functionalized NHC iridium homogeneous catalyst. A good catalyst recyclability and stability were achieved.

Graphene-Based Porous Catalyst with High Stability and Activity for the Methanol Oxidation Reaction

Due to its large specific surface area and extraordinary carrier mobility, graphene has been widely used as the supporting material for metal particles in catalysis. A platinum-based catalyst with a graphene-based porous matrix as the supporting material was prepared by one-step hydrothermal synthesis, which produces a uniform distribution of platinum nanoparticles on the support. This catalyst material shows excellent antipoison ability and superior electrocatalytic stability for the methanol oxidation reaction. It was also found that further annealing treatment could modify the morphology of platinum particles attached to the graphene, and an appropriate annealing temperature contributed to an improvement of its electrocatalytic activity.

Metal-Free and Pt-Decorated Graphene-Based Catalysts for Hydrogen Production in a Sulfur–Iodine Thermochemical Cycle

Graphene oxide (GO), GO reduced by hydrazine hydrate (rGO-HH), GO reduced by ethylene glycol (rGO-EG), Pt-decorated rGO-HH composite (Pt/rGO-HH), and Pt-decorated rGO-EG composite (Pt/rGO-EG), are fabricated for the heterogeneous catalytic decomposition of HI in a sulfur–iodine thermochemical cycle. Corresponding material characterization on various catalysts are performed to gain insight into the catalytic mechanism. rGO-HH presents better catalytic activity than the GO and rGO-EG counterparts, due to the increase of active sites (unsaturated carbon atoms) with the reduction of oxygen-containing groups and the formation of edge planes. Homogeneously dispersed fine Pt nanoparticles are obtained with employing rGO-EG as the support. The corrugation morphology and graphene edges benefit the nucleation, dispersion, and immobilization of Pt nanoparticles. As a consequence, Pt/rGO-EG presents better catalytic activity and stability than the convenient Pt/activated-carbon (Pt/AC) counterpart. Results indicate t...

Long-range electron transfer over graphene-based catalyst for high-performing oxygen reduction reactions: importance of size, N-doping, and metallic impurities.

N-doped carbon materials are considered as next-generation oxygen reduction reaction (ORR) catalysts for fuel cells due to their prolonged stability and low cost. However, the underlying mechanism of these catalysts has been only insufficiently identified, preventing the rational design of high-performing catalysts. Here, we show that the first electron is transferred into O2 molecules at the outer Helmholtz plane (ET-OHP) over a long range. This is in sharp contrast to the conventional belief that O2 adsorption must precede the ET step and thus that the active site must possess as good an O2 binding character as that which occurs on metallic catalysts. Based on the ET-OHP mechanism, the location of the electrode potential dominantly characterizes the ORR activity. Accordingly, we demonstrate that the electrode potential can be elevated by reducing the graphene size and/or including metal impurities, thereby enhancing the ORR activity, which can be transferred into single-cell operations with superior stability.

Water Splitting over Graphene-Based Catalysts: Ab Initio Calculations

We present first-principles modeling of water oxidation over various graphene systems, such as nitrogen-doped graphene; graphene monolayers on iron, nickel, and copper surfaces; and bi- and trilayer graphene on copper surfaces. It is shown that nitrogen-doped graphene and graphene over copper are better for this reaction than those over platinum at temperatures below 100 °C. Bi- and trilayer graphene on copper have catalytic properties similar to those of a monolayer on copper.

Origin of the Electrocatalytic Oxygen Reduction Activity of Graphene-Based Catalysts: A Roadmap to Achieve the Best Performance

The mutually corroborated electrochemical measurements and density functional theory (DFT) calculations were used to uncover the origin of electrocatalytic activity of graphene-based electrocatalysts for oxygen reduction reaction (ORR). A series of graphenes doped with nonmetal elements was designed and synthesized, and their ORR performance was evaluated in terms of four electrochemical descriptors: exchange current density, on-set potential, reaction pathway selectivity and kinetic current density. It is shown that these descriptors are in good agreement with DFT calculations, allowing derivation of a volcano plot between the ORR activity and the adsorption free energy of intermediates on metal-free materials, similarly as in the case of metallic catalysts. The molecular orbital concept was used to justify this volcano plot, and to theoretically predict the ORR performance of an ideal graphene-based catalyst, the ORR activity of which is comparable to the state-of-the-art Pt catalyst. Moreover, this study may stimulate the development of metal-free electrocatalysts for other key energy conversion processes including hydrogen evolution and oxygen evolution reactions and largely expand the spectrum of catalysts for energy-related electrocatalysis reactions.

Tuning the catalytic property of non-noble metallic impurities in graphene

The stable configuration, electronic structure, magnetic property and catalytic activity of single-atom non-noble-metal (NNM) catalysts on graphene are investigated using the first-principles method. In contrast to the pristine graphene, a vacancy defect in graphene strongly stabilises the NNM adatom and makes it more positively charged. The charging leads to the CO adsorption unfavourable, while facilitate the O2 adsorption, thus alleviating the CO poisoning and improving the reaction possibility for CO oxidation. Besides, there are more electrons transferred between NNM doped-graphene and O2 molecule, which enhance their interaction and induce changes in the electronic structures and magnetic properties of the systems. Moreover, the sequential processes of CO oxidation on the Co–, Al– and Zn–graphene systems have lower enough energy barriers (<0.4eV) by the Langmuir–Hinshelwood (LH) reaction (CO+O2→OOCO→CO2+Oads) than that on the Ni–graphene substrate. Among the reaction processes, the rate-controlling step is the breaking of the O–O bond of the OOCO complex to form the CO2 molecule and the atomic Oads. The results validate the reactivity of NNM catalysts at the atomic scale and initiate a clue for fabricating graphene-based catalysts with low cost and high activity.

ChemInform Abstract: Versatilities of Graphene‐Based Catalysts in Organic Transformations

AbstractReview: 108 refs.

Nitrogen-self-doped graphene-based non-precious metal catalyst with superior performance to Pt/C catalyst toward oxygen reduction reaction

A new, simple and scalable synthesis methodology is invented for an N-self-doped graphene-based non-precious Fe catalyst (Fe–N-graphene) for the oxygen reduction reaction (ORR) both in acidic and alkaline media. The electrochemical characterization shows that this Fe–N-graphene catalyst possesses outstanding electrocatalytic ORR activity (similar to Pt/C catalyst in alkaline media and slightly lower in acidic media), and both superior stability and fuel (methanol and CO) tolerance to Pt/C catalysts. We believe that this is the first time for a non-precious metal catalyst to have superior ORR performance to Pt/C catalyst. In addition, our synthesis methodology can be scaled up for the mass production of N-self-doped graphene-based fuel cell non-noble metal catalysts and other nanomaterials.

Sulfur-doped graphene as a potential alternative metal-free electrocatalyst and Pt-catalyst supporting material for oxygen reduction reaction

In this study, sulfur-doped graphene (S-graphene) was synthesized by thermal treatment of exfoliated graphene under CS2 gas flow. Its electrocatalytic activity as a metal-free catalyst was evaluated and compared with other doped-graphenes and commercial platinum nanoparticles loaded on carbon black (Pt/C) catalysts for oxygen reduction reaction (ORR) in fuel cell cathodes. The resultant S-graphene was shown to act as a viable catalyst for ORR and its limiting current density and durability were improved compared to those of the commercial Pt/C catalyst. The current density at -1.0 V for the commercial Pt/C catalyst, pristine graphene, nitrogen-doped graphene (N-graphene) and S-graphene was 4.7, 0.15, 6.26 and 6.99 mA cm(-2), respectively. The durability of S-graphene (70.3%) was much better compared to commercial Pt/C (37.2%) and N-graphene (67.9%). When S-graphene was used as a supporting material for Pt nanoparticles, its catalytic performance was significantly higher than other Pt catalysts supported on different doped graphenes. Here, we demonstrate that S-graphene can be used as a novel graphene-based efficient metal-free ORR catalyst in fuel cells.

Research Progress of Graphene and Its Composites in Organic Synthesis

As a novel carbon nanomaterial, graphene based composite has received much attention in catalysis due to its unique characterisics such as large surface area, good thermal and chemical stability, strong hydrophobicity, easy modifica- tion, etc. Graphene and its composites have been applied in the catalysis of different organic reactions, such as Su- zuki-Miyaura, Heck, and reduction of nitroarenes. The research progress of graphene-based composites catalyst is briefly reviewed in the paper.