Colloidal Graphene Oxide Research Articles

Nanoporosity changes of graphene oxide colloids on linkage-treatment with molecular linker and heating after the linkage-treating

This study examined the nanoporosity of graphene oxide (GO) and graphene colloids bridge-treated with amino linkers using comparative nanoporosimetry with N2 and Ar adsorption. The spectroscopic measurements revealed the linkage via amino linkers in the linkage-treated GO and graphene colloids. The linkage-treatment expanded the d-spacing of GO by 0.21 nm and the d-spacing of the linkage-treated GO colloid decreased from 1.01 to 0.35 nm upon heating. The linkage-treated graphene colloids exhibited significant adsorption and an adsorption hysteresis, regardless of the reduction of d-spacing. Heating of linkage bonds induced the local structural deformation, providing open pores and the assembled mesoscale structure.

Batch fabrication of ultrathin flexible pressure sensors enabled by full printed technique

Flexible pressure sensors have gained significant attention in recent years owing to their versatile applications in health monitoring, human-machine interfaces, and artificial robotics. Geometric microengineering of the active layer, including micropatterned structures, porous layers, and multilayered packed structures has been investigated to improve the sensing performance. However, accompanying challenges such as increased thickness and difficulties in achieving mass production still persist. This work presents a full printed technique for fabricating high-performance piezoresistive pressure sensors. Thermal-treated graphene oxide (TGO) colloid was selected as the printing ink. Combined with an in-situ chemical foaming strategy, structural microengineering of the piezoresistive layer was achieved. The obtained hierarchical protruding micro-domes endow the piezoresistive pressure sensors with a wide sensing range of 550 kPa and ultrathin features (18 μm). In addition, the full-printed manufacturing method enables the batch-producible fabrication of pressure sensors. These sensors can be employed for human motion detection and pressure mapping applications.

A novel electrochemical sensor based on phosphate-stabilized poly-caffeic acid film in combination with graphene nanosheets for sensitive determination of nitro-aromatic energetic materials

This work offers a novel approach and sensor electrode for electrocatalytic reduction of nitro-aromatic explosives (NAEs). This sensor was created by combining electrochemically reduced graphene nanosheets (GNSs) −through cyclic voltammetric reduction of a graphene oxide colloidal solution− with phosphate-stabilized poly-caffeic acid (pCAF) film-modified glassy carbon electrode (GCE). The poly-caffeic acid−modified nonconductive electrode was stabilized with a H2PO4-/HPO42− phosphate buffer at pH 7 and made conductive. The novel electrode, called phosphate stabilized-GC/GNSs/pCAF, was characterized by electrochemical methods and scanning electron microscopy (SEM). The sensor exhibited high performance for trinitrotoluene (TNT) detection with a linear response between 50 and 500 μg L− 1 and a detection limit of 6 μg L−1. In addition to TNT, precise determinations of NAEs such as 2,4-dinitrotoluene (2,4-DNT), tetryl (2,4,6-trinitrophenyl methyl nitramine), trinitro phenol (TNP or picric acid; PA), 2,4-dinitrophenol (2,4-DNP), and 4-amino dinitrotoluene (4A-DNT, an aerobic bacterial degradation product of TNT) were made using the developed sensor electrode and DPV technique. Simultaneous quantification of TNT and DNT was performed with the aid of a computational technique known as multiple linear regression (MLR). The optimized electrode was resistant to interference effects. Satisfactory results on real samples were obtained by applying the modified electrode to the determination of TNT, tetryl, and TNP in contaminated soil. The validation of the proposed method was made against a literature LC-MS/MS method. A statistical comparison of the obtained results was provided using F- and Student's t-tests.

Understanding the yielding behavior of graphene oxide colloids via experimental strain decomposition

Graphene oxide (GO) has attracted attention in materials science and engineering due to its large aspect ratio and dispersibility in polar solvent including water. It has recently been applied to direct-ink-writing (DIW) printing to realize the fabrication of three-dimensional structures, suggesting a wide variety of potential applications. Without post-processing, DIW printing requires yield stress fluids to fully build three-dimensional objects. The key properties of these inks are the yield stress and the viscoelastic properties during yielding. DIW ink rheology has therefore received significant interest in materials science, as well as mechanical and chemical engineering. Despite this interest, the yielding process has not been clearly elucidated and understanding yielding remains an outstanding problem. In this study, we discuss the yielding behavior of GO colloids via oscillatory rheology by decomposing the total strain into the recoverable and unrecoverable parts through iterative experimental techniques. The recoverable and unrecoverable responses represent viscoelastic solid and plastic properties, respectively, and they are used to determine the averaged storage and dissipation of energies. By mapping these contributions, we more clearly elucidate the yielding behavior of the GO colloids and suggest guidelines for energy efficiency. Beyond the specific lessons learned regarding the DIW-relevant rheology of GO colloids, our study contributes to an evolving development of material-centric and energy-focused methods for understanding the out-of-equilibrium rheological physics associated with the yielding of soft materials.

Improving the properties of nickel/graphene oxide coated copper plate by changing the electroplating process conditions

One of the attractive ways to improve the mechanical properties and prevent damage to the surface of the copper plate is to create a nickel/graphene coating on it. In this work, the effect of bath type and process conditions on mechanical and wettability properties of nickel/graphene oxide coated copper plate via electroplating, has been investigated. Ultrasonic stirring of the bath with a power of 200 W increased the hardness of the coating to 747 Vickers and the wetting angle with molten steel to 125° by uniformly distributing the graphene oxide layers among the nickel grains and preventing the growth of the grains. By using a chloride bath instead of a Watts bath, due to the adhesion and delamination mechanism, a slight weight loss occurred in the pin-on-disk wear test. The coating obtained by electroplating in a chloride bath containing 20 cc of colloidal graphene oxide had a structure with a thickness of 12–15 μm consisting of large and compact masses of cauliflower with a uniform distribution of graphene layers. This sample shown a contact angle of 130° with the surface tension of 25 × 10−6 N/m to the aluminum melt drop and a 135° and 120 × 10−6 N/m to the steel melt drop.

Viscosity-Controllable Graphene Oxide Colloids Using Electrophoretically Deposited Graphene Oxide Sheets.

Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the specific process requirements. Here, we report on the relatively rapid fabrication of viscosity-increased GO (VIGO) colloids mixed with electrophoretically deposited GO sheets (EPD-GO). As the GO colloid concentration, applied voltage, and deposition time increase, the viscosity of the GO colloids becomes high. The reason for the improved viscosity of GO colloids is because EPD-GO has parallel stacked GO sheets. The GO and VIGO colloids are compared and characterized using various chemical and structural analyzers. Consequently, our simple and fast method for the fabrication of GO colloids with enhanced viscosity can be used for producing inks for flexible and printed electronics.

Synthesis and Crosslinking Mechanism of Colloidal Graphene Oxide Crosslinker for Crosslinking Low-Concentration Hydroxypropyl Guar Gum Fracturing Fluids

Synthesis and Crosslinking Mechanism of Colloidal Graphene Oxide Crosslinker for Crosslinking Low-Concentration Hydroxypropyl Guar Gum Fracturing Fluids

Cooperative Electric Alignment of Colloidal Graphene Oxide Particles with Liquid Crystalline Niobate Nanosheets

Abstract Binary colloids of two morphologically different particle species cause phase separation containing liquid crystalline phases. Although electric alignment of colloidal nanosheets has been investigated for colloidal systems consisting of single nanosheet species, that of binary nanosheet colloids has scarcely been examined. We report herein the electric alignment of aqueous binary colloids composed of niobate (NB) nanosheets from K4Nb6O17 and commercially available graphene oxide (GO) platelets. The NB–GO binary colloids show multiphase coexistence involving liquid crystalline phases induced by the NB nanosheets, whereas the employed GO particles do not contribute to the liquid crystallinity. The NB nanosheets in the binary colloids are electrically aligned in parallel to an AC voltage (1 kV cm−1 peak to peak, 50 kHz) applied to the sample. When the concentration of GO in the binary colloids is low enough, the GO particles are also electrically aligned although they hardly respond to electric field in the absence of NB nanosheets. Combined optical microscopy of bright-field, polarized, and fluorescence observations demonstrates that isolated GO particles are dragged by the aligning motion of the NB nanosheets forming liquid crystalline domains. The results indicate that collective motions of colloidal nanosheets can induce participation of isolated particles.

Complementary combinative strategy of defect engineering and graphene coupling for efficient energy-functional materials.

The synergetic combination of defect engineering and graphene coupling enables to develop an effective way of exploring efficient bifunctional electrocatalyst/electrode materials. Defect-engineered amorphous MoO2 -reduced graphene oxide (rGO) nanohybrid was synthesized by soft-chemical reduction of K2 MoO4 in graphene oxide colloids. Mo K-edge X-ray absorption spectroscopy clearly demonstrates the rutile-type local atomic structure of amorphous MoO2 with significant oxygen vacancies and intimate electronic coupling with rGO. The defect-introduced MoO2 -rGO nanohybrid shows excellent bifunctionality as electrocatalyst for hydrogen evolution reaction and electrode for sodium-ion batteries, which are superior to those of crystalline MoO2 -rGO homologue. The beneficial effect of simultaneous defect control and rGO coupling can be ascribed to the provision of oxygen vacancies acting as active sites, the increase of electrical conductivity, and the improvement of reaction kinetics.

Graphene oxide synthesis using modified Tour method

Graphene oxide (GO) colloidal solution has been synthesised by the modified Tour method, in which the pH of the reaction medium has been increased to 2.0–2.2 at the final stage of graphite oxidation by adding NaOH solution. The solid-phase graphene oxide consists of multilayered graphene particles with a thickness of about 7.5 nm (9–10 layers of graphene) and an average size of about 7.7 nm. Reduced graphene oxide (rGO) has been prepared by hydrazine and microwave reduction. A comparative study of the structure, morphology, and electrical transport properties of rGO samples obtained by various methods has been carried out using XRD, SAXS, Raman spectroscopy, low-temperature nitrogen adsorption, and impedance spectroscopy. Structural analysis has shown the presence of two fractions of plate-like rGO particles for each reduction method, which consist of 4–6 layers of graphene in stacks and have a lateral size in the range of 7.1–7.6 nm. The BET specific surface area of the microwave-reduced rGO was higher than that of the chemically reduced one (296 and 237 m2 g−1 respectively). The frequency dependence (10−2–105 Hz) of the AC conductivity of the GO and rGO samples has been analysed in the temperature range of 25 °C–175 °C. For the GO sample, the proton exchange conductivity mechanism dominates. A Drude-like response of electrical conductivity at frequencies above 103 Hz with transition to Johnscher’s law response at 175 °C has been observed for rGO samples obtained using both chemical and microwave routes. Changes in activation energies and relaxation times have been interpreted using a model of a thermally activated frequency-dependent electron hopping mechanism between randomly coupled conducting sp 2 rGO packages separated by disordered sp 3 rGO regions with correspondingly higher resistivity.

Tunable surface enhanced Raman scattering of silver thin films by the graphene oxide

Silver thin films covered with a graphene oxide (GO) colloid layer were fabricated in this study. The coupling between GO and localized surface plasmons of the silver thin films was investigated by optical absorption and Raman scattering experiments. The absorption spectra showed that the intensity of the plasma edge peak at 320 nm decreased but the intensity of the interband transition peak at 350 nm was enhanced by an increase of the GO colloid concentration. The surface plasmon resonance attributed to the increased absorption of incident light by the GO layer caused an increase of the Raman scattering intensities. Theoretical calculations were performed for the surface plasmon resonance properties of the GO/silver thin films, and the results were in good agreement with the experiments.

Graphdiyne oxide and graphene oxide sense monovalent cations differently: The alkyne and alkene physicochemistry

Abstract The differences between graphdiyne oxide (GDYO) and graphene oxide (GO) in physicochemistry and functionalities are important for precisely selecting the most suitable carbon allotrope for specific proposes, and essential for our understanding of alkyne and alkene fundamentals. However, the precise distinctions between GDYO and GO in ion sieving and sensing are basically unknown. Here we show that GDYO senses monovalent cations differently from GO. The unique sp-hybridization in GDYO provides it with more affinity with H2O molecules and stronger Coulomb electrostatic repulsion to maintain zeta potential high enough to preserve its interfacial colloidal stability without changes in attachment kinetics in the presence of Na+ and K+. Na+ and K+ freely move through the rotatable triangular cavities of GDYO. By comparison, GO shows less H2O affinity and zeta potential. Colloidal GO aggregates with Na+ and K+. Both GO and GDYO sense concentration changes of bivalent and trivalent ions, resulting in interfacial instability that reaches zeta potential plateaus within narrow lower ion concentrations due to electrostatic force and van der Waals force. The present study discovers characteristics of GDYO sp-hybridization and its role in sensing monovalent cations, and elucidates physicochemical differences between GDYO and GO in sensing ions.

Graphene oxide functionalization via epoxide ring opening in bioconjugation compatible conditions

Graphene oxide (GO) functionalization has great importance for its practical application in many fields, and is a key step for GO bioconjugation. Polydispersity, limited colloidal stability and changeable extinction of GO complicates functional group quantification and the modification study. To bypass the mentioned limitations, we have used GO immobilization on glass support to quantify its epoxy groups surface load, and to study sustainability of the functional groups introduced through epoxy-amine reaction during hydrazine reduction. It was found out that GO contains near 1 epoxy group per nm2, and the major part of the functional groups are remaining after reduction process allowing to use this modification to make functionalized reduced graphene oxide (rGO). Then we modified colloidal GO with azide groups by aminotetraethylene glycol azide (H2N–TEG–N3) in mild conditions to avoid aggregation, and characterized it by means of immobilization on glass surface. Functional group surface load of the functionalized GO was determined as 0,7 groups per nm2. Finally, we proved capability of azide-functionalized GO for conjugation by strain promoted [3 + 2] azide-alkyne cycloaddition (SPAAC) with BCN derivative of organic fluorescent dye JOE.

Label-Free Homogeneous microRNA Detection in Cell Culture Medium Based on Graphene Oxide and Specific Fluorescence Quenching.

Label-free homogeneous optical detection of low concentration of oligonucleotides using graphene oxide in complex solutions containing proteins remains difficult. We used a colloidal graphene oxide (GO) as a fluorescent probe quencher to detect microRNA-21 spiked-in cell culture medium, overcoming previously reported problematic aspects of protein interference with graphene oxide. We used a “turn off” assay for specific quenching-based detection of oligo DNA-microRNA hybridization in solution. A fluorescein conjugated 30-mer single-stranded DNA (ssDNA) probe was combined with a complementary synthetic microRNA (18 nucleotides) target. The probe-target hybridization was detected by specific quenching due to photoinduced electron transfer (PET). On the next step, GO captures and quenches the unhybridized probe by fluorescence resonance energy transfer (FRET) in the presence of cell culture medium supplemented with platelet lysate, 0.1% sodium dodecyl sulfate (SDS), 0.1% Triton X-100 and 50% formamide. This resulted in sensitive measurement of the specific probe-target complexes remaining in solution. The detection is linear in the range of 1 nM and 8 nM in a single 100 μL total volume assay sample containing 25% cell culture medium supplemented with platelet lysate. We highlight a general approach that may be adopted for microRNA target detection within complex physiological media.

Microstructure Dictating Performance: Assembly of Graphene-Based Macroscopic Structures

ConspectusA wide range of groundbreaking advancements in electronics, photonics, nanocomposites, etc., have been achieved in the past decades due to the favorable attributes of single-layer graphene, including its record-breaking thermal conductivity, charge carrier mobility, fracture strength, and Young’s modulus. However, the realization of the potentials of macroscale graphene assemblies has remained challenging. The difficulties mainly lie within manipulating graphene sheets into an orderly intermolecular orientation and controlling the macroscopic ordering of the graphitic domains. Controlling the formation of graphene macroscopic structures and eliminating defects on both the nano- and microscales meanwhile optimizing performance is no easy feat. To address these microstructural issues in macroscopic graphene assemblies, multiple chemical, thermal, and mechanical approaches have been developed with a goal of overall performance enhancement. Therefore, in this Account we provide a brief review of our contributions in the microstructure engineering of macroscale graphene assemblies with the focus on graphene fibers (GFs), graphene papers (GPs), and other graphene-based assemblies with graphene oxide (GO) colloids as precursors.Building upon the developments in wet chemistry on assembling individual GO sheets into macroscopic structures, we successfully intercalated large GO sheets with small GO sheets, which increased compactness for wet-spun GFs without disturbing the sheet orientation and alignment of the large GO sheets. Increasing GO compactness during wet assembly allows for the increase of thermal and electrical conductivities as well as the mechanical strength of GFs at a single stroke. A high degree of alignment of graphene sheets with abundant sp2 carbon atoms is also necessary for achieving high thermal and electrical conductivities in graphene assemblies. Fine control of GO sheet alignment and orientation during the wet-spinning assembly is demonstrated through the shape and size confinement of fluidic flow channels. Utilizing this shear-stress-induced self-alignment strategy, the core–shell nonuniformity problem of GFs is addressed. Also, a correlation between the rheological properties and flow patterns of GO during wet-spinning and the microstructure of the GF assemblies is established.In addition to the orientation of graphene sheets, the crystallite size and macroscopic ordering within graphene assemblies also play important roles in determining their performances. Larger and highly oriented graphitic crystalline domains allow for higher thermal and electrical conductivities. By manipulating crystallite domain size and arrangement through high temperature graphitization, the electrical and thermal conductivities and Young’s modulus of GFs can be significantly enhanced. Fine temperature control can also help retain residual covalent cross-links between neighboring graphene sheets, meeting the need for balancing tensile strength, and thermal and electrical conductivities.The enhancement of GF mechanical, thermal, and electrical properties through optimizing the compactness and alignment of graphene sheets and the orientation of graphene crystallite domains have significantly improved the engineering capability of GFs. Such an improvement has been largely beneficial to flexible electronics research and has shown great potential in multifunctional composite materials. Similar strategies have also been emulated on related graphene-based materials such as graphene papers (GPs) and graphene fiber meshes (GFMs), yielding unique and favorable properties and performances.

Effects of phosphate on the transport of graphene oxide nanoparticles in saturated clean and iron oxide-coated sand columns

In this study, transport behaviors of graphene oxide (GO) in saturated uncoated (i.e., clean sand) and goethite-coated sand porous media were examined as a function of the phosphate. We found that phosphate enhanced the transport of GO over a wide range of solution chemistry (i.e., pH 5.0–9.0 and the presence of 10 mmol/L Na+ or 0.5 mmol/L Ca2+). The results were mainly ascribed to the increase of electrostatic repulsion between nanoparticles and porous media. Meanwhile, deposition site competition induced by the retained phosphate was another important mechanism leading to promote GO transport. Interestingly, when the phosphate concentration increased from 0.1 to 1.0 mmol/L, the transport-enhancement effect of phosphate in goethite-coated sand was to a much larger extent than that in clean sand. The observations were primarily related to the difference in the total mass of retained phosphate between the iron oxide-coated sand and clean sand columns, which resulted in different degrees of the electrostatic repulsion and competitive effect of phosphate. When the background solution contained 0.5 mmol/L Ca2+, phosphate could be bind to sand/ goethite-coated sand surface by cation bridging; and consequently, promoted competition between phosphate and nanoparticles for deposition sites, which was an important mechanism for the enhanced effect of phosphate. Moreover, the DLVO theory was applicable to describe GO transport behaviors in porous media in the absence or presence of phosphate. Taken together, these findings highlight the important status and role of phosphate on the transport and fate of colloidal graphene oxide in the subsurface environment.

Laser-driven self-exfoliation of graphene oxide layers on a fiber facet for Q switching of an Er-doped fiber laser at the longest wavelength

A new method to make an all-fiber nonlinear optic device for laser pulse generation is developed by depositing multi-layer graphene oxide (GO) selectively onto the core of the cleaved fiber facet by combining the electrical arc discharge and the laser-driven self-exfoliation. Using the GO colloid droplet with sub-nanoliter volume, we obtained a GO bulk layer deposited on a fiber facet of the order of milliseconds by using an electric arc. The prepared fiber facet was then included in an Er-doped fiber laser (EDFL) cavity and we obtained a few layers of GO having nonlinear optic two-dimensional (2D) characteristics selectively on the fiber core by the laser-driven self-exfoliation. The 2D GO layers on the fiber core served as a stable and efficient saturable absorber enabling robust pulse train generation at λ = 1600.5 nm , the longest Q -switched laser wavelength in EDFLs. Pulse characteristics were analyzed as we varied the pump power at λ = 980 nm from 105.2 mW to 193.6 mW, to obtain the maximum repetition rate of 17.8 kHz and the maximum output power of 2.3 mW with the minimum pulse duration of 7.8 μs. The proposed method could be further applied to other novel inorganic 2D materials opening a window to explore their novel nonlinear optic laser applications.

Oligonucleotide Detection and Optical Measurement with Graphene Oxide in the Presence of Bovine Serum Albumin Enabled by Use of Surfactants and Salts

As graphene oxide-based oligonucleotide biosensors improve, there is a growing need to explore their ability to retain high sensitivity for low target concentrations in the context of biological fluids. Therefore, we innovatively combined assay milieu factors that could influence the key performance parameters of DNA hybridization and graphene oxide (GO) colloid dispersion, verifying their suitability to enhance oligonucleotide–GO interactions and biosensor performance. As a model system, we tested single-strand (ss) DNA detection in a complex solution containing bovine serum albumin (BSA) and salts with surfactants. A fluorescein conjugated 30-mer oligonucleotide ssDNA probe was combined with its complementary cDNA target, together with solute dispersed GO and either non-ionic (Triton X-100 and Tween-20) or anionic sodium dodecyl sulfate (SDS) surfactants. In this context, we compared the effect of divalent Mg2+ or monovalent Na+ salts on GO binding for the quench-based detection of specific target–probe DNA hybridization. GO biosensor strategies for quench-based DNA detection include a “turn on” enhancement of fluorescence upon target–probe interaction versus a “turn off” decreased fluorescence for the GO-bound probe. We found that the sensitive and specific detection of low concentrations of oligonucleotide target was best achieved using a strategy that involved target–probe DNA hybridization in the solution with a subsequent modified “turn-off” GO capture and the quenching of the unhybridized probe. Using carefully formulated assay procedures that prevented GO aggregation, the preferential binding and quenching of the unhybridized probe were both achieved using 0.1% BSA, 0.065% SDS and 6 mM NaCl. This resulted in the sensitive measurement of the specific target–probe complexes remaining in the solution. The fluorescein-conjugated single stranded probe (FAM–ssDNA) exhibited linearity to cDNA hybridization with concentrations in the range of 1–8 nM, with a limit of detection equivalent to 0.1 pmoles of target in 100 µL of assay mix. We highlight a general approach that may be adopted for oligonucleotide target detection within complex solutions.

Colloidal graphene oxide enhances the activity of a lipase and protects it from oxidative damage: Insights from physicochemical and molecular dynamics investigations

Physical adsorption of lipase from Thermomyces lanuginosus onto single-layer sheets of graphene oxide (GO) was studied using the response surface methodology to evaluate the physicochemical factors – temperature, pH, ionic strength, and concentration – affecting the enzymatic activity and the immobilization efficiency. The immobilization efficiency and the activity of the enzyme were inversely proportional to each other. Specifically, higher pH values increased the immobilization efficacy, but produced changes in the aggregation state and secondary structure of the enzyme, thus decreasing its activity. Lower pH values, in turn, reduced the immobilization efficacy, but increased the activity of the adsorbed lipase. The adsorbed and the free lipase were followed during 600 ns and 3.5 μs, respectively, in molecular dynamics (MD) simulations. MD trajectories showed that irreversible adsorption freezes the enzyme in a state with a correctly opened catalytic cavity, while the active site remains without a direct interaction with the GO adsorbent. In contrast to the interfacial activation of lipases in a hydrophobic environment, where the catalytic pocket attaches to the hydrophobic surface, the adsorption onto GO made the active site of the lipase accessible by altering the tertiary structure of the enzyme, leading to a higher catalytic efficiency. Experimental investigations confirmed that the physical adsorption onto GO induces tertiary structure changes in the lipase and protects it from H2O2 by accepting the oxidative damage upon itself. In summary, the physical adsorption of the lipase onto GO is mainly affected by pH and could possibly provide a spreadable and robust catalytic interface for biotechnological applications.

Graphene Oxide Modified Pt/C and Pt2Ru3/C for Enhanced Carbon Monoxide Tolerable Fuel Cell Anode Catalyst

The commercial viability of residential fuel cell technology operating on reformed H2 strongly demands to find efficient, CO tolerable and long lasting anode catalyst.1 Currently, Pt-based electrocatalysts are widely used for this purpose. However, one of the major drawbacks of Pt-based anode is the surface poisoning by carbon monoxide (CO) leading to severe decrease in efficiency and long-term performance of catalyst.2 This problem has been mitigated by either (i) synthesis of catalysts with higher CO oxidation capability or (ii) suppressing the adsorption of CO on the catalyst surface. Within the first context, additives often partially cover the alloy surface and lead to a decrease in the electrochemically active Pt surface area and thus the HOR activity. Therefore, in the current work, the second strategy has been pursued. Here we use graphene oxide (GO) to improve the CO tolerance of Pt/C and Pt2Ru3/C catalysts by suppressing the adsorption of CO on the catalyst surface. Graphite oxide was prepared from graphite (Z-5F, Average particle size 4μm, ≥98.8 %, Ito Graphite Industry Co., Ltd.) by a modified Hummers' oxidation method.3 Graphite oxide was then dispersed in 2-propanol to exfoliate graphite oxide into GO. Commercial Pt/C (TKK TEC10E50E, 46.6 mass% Pt) and Pt2Ru3/C (TKK TEC61E54, 30 mass% Pt and 23.3 mass% Ru) were used as-received. GO–Pt/C and GO–Pt2Ru3/C were prepared by stirring, sonication and drying of a mixture of GO colloid with Pt/C and Pt2Ru3/C powder respectively. COad stripping measurement was performed by cyclic voltammetry (CV) at 10 mV s-1 in N2 saturated 0.1 M HClO4. Chronoamperometry (CA) was conducted in 0.1 M HClO4 saturated with either pure H2 or 250 ppm CO/H2 at 20 mV vs. RHE with 400 rpm rotation. Accelerated durability test (ADT) was conducted by square-wave potential stepping between 5 and 400 mV vs. RHE for 3000 cycles with a holding time of 3 seconds at each potential. TEM images confirm that GO wraps around Pt/C or Pt2Ru3/C and are distributed uniformly. XRD and XPS data support the co-existence of GO and Pt/C or Pt2Ru3/C. COad stripping of Pt/C and GO–Pt/C suggest that in contrast to Pt/C, in case of GO–Pt/C a pre-oxidation peak was observed at 0.5-0.7 V before the main CO oxidation peak (Fig. 1a). This pre-oxidation peak may be attributed to oxidation of weakly adsorbed CO. The apparent HOR activities in pure H2 for Pt/C (190 A (g-Pt)−1) and Pt2Ru3/C (148 A (g-PtRu)−1) do not change after the addition of GO, thus GO does not interfere with the HOR. Fig. 1b compares CA (HOR current) of Pt/C, GO–Pt/C, Pt2Ru3/C and GO–Pt2Ru3/C in 250 ppm CO/H2 saturated HClO4 after 3000 cycles of ADT. The HOR current for GO–Pt/C was 109 A (g-Pt)−1, which is 1.3 times higher than that of Pt/C (84 A (g-Pt)−1. The HOR current for GO–Pt2Ru3/C (89 A (g-PtRu)−1) is 1.3 times higher than that of commercial Pt2Ru3/C (68.4 A (g-PtRu)−1). The enhanced CO tolerance and durability of GO–Pt/C and GO–Pt2Ru3/C may be attributed to i) GO protects the coagulation of Pt particles and ensure the sufficient stability of Pt/C catalyst, ii) steric hindrances arise from oxygen-containing functional groups of GO surface decrease the adsorption of CO on Pt surface and iii) the electron transfer between the oxygen atoms and Pt nanoparticles could lead to the enhanced electron density of Pt via a ligand effect which in turns decrease the attraction towards CO. The current findings suggest that the prepared GO–Pt/C and GO–Pt2Ru3/C catalysts have great potential for use in fuel cell anode. Acknowledgments This work was supported in part by the ‘Polymer Electrolyte Fuel Cell Program’ from the New Energy and Industrial Technology Development Organization (NEDO), Japan. References E. Antolini, Appl. Catal. B Environ., 74, 324 (2007), E. Antolini, Appl. Catal. B Environ., 74, 337 (2007).M. Watanabe, T. Sato, K. Kunimatsu, and H. Uchida, Electrochem. Acta, 53, 6928 (2008).S. Hummers, R. E. Offeman, J. Am. Chem. Soc. 80, 1339(1958). Figure 1