Palladium nanoparticle and decorated carbon nanotube for electrochemical hydrogen storage

This study proposes a multicomponent system for hydrogen storage. An electrochemical evaluation was used as a simple and accurate technique to assess the storage capacity. A porous silicon substrate was fabricated using an electrochemical anodization process and decorated with palladium nanoparticles using the electroless method. The hybrid substrate underwent chemical vapor deposition for 45 min. Since the deposited palladium nanoparticles could act as potential catalysts, carbon nanotubes grew properly over hybrid structure. The final sample was obtained through post-treatment by palladium nanoparticles using the same electroless method. This triplet sample was characterized using field emission scanning electron microscopy and X-ray diffraction. Galvanostatic charge/discharge experiments were used to conduct electrochemical evaluations of proposed electrode. A maximum hydrogen storage capacity of 537 mAh/g (～2.05 wt.%) was achieved for the triple-structure sample. The measurements demonstrate that the storage capacity of the triple-structure sample was reduced by a factor of 0.05% after 100 cycles. Although the obtained storage capacity is far from DOE targets, optimized structures based on the proposed electrode may be further developed as an efficient storage system.     

Graphene decorated Pd-Ag nanoparticles for H2 sensing

Hydrogen sensor based on graphene nano-composite with Pd-Ag nanoparticles was fabricated by MEMS process. Structural and morphological properties of the sensing film were studied by an energy dispersive spectroscopy (EDS) and field emission scanning electron microscopy (FESEM), respectively. The H₂ sensing properties of as-formed sensor were investigated by measuring the resistance changes at different H₂ concentrations. The maximum gas response was 16.2% at 1000 ppm of H₂ gas. The gas sensitivity of the as-formed H₂ sensor showed linear behavior with the hydrogen concentration. Experimental results showed that the coupling of graphene with Pd/Ag alloy enhanced significantly hydrogen sensing performance.     

Electrocatalytic hydrogen production on GCE/RGO/Au hybrid electrode

We have prepared a nanocomposite hybrid film to produce a collaborative network of gold (Au) nanoparticles that are highly dispersed on reduced graphene oxide (RGO) sheets, and tested it for electrocatalytic hydrogen production. The RGO/Au nanocomposite film synthesized on glassy carbon electrode (GCE) allows significant improvements to the electron-transfer process. The Au nanoparticles decorated on the surface of graphene increases the electron density, which synergistically promote the adsorption of hydrogen atoms on the graphene sheets and consequently enhance the hydrogen evolution reaction (HER) activity. The surface properties of the composite was characterized by field-emission scanning electron microscopy (FE-SEM) and the electrocatalytical performances evaluated as-prepared electrocatalyst toward (HER) by linear sweep voltammetry (LSV), Tafel polarization curves and electrochemical impedance spectroscopy (EIS) analyses. The GCE/RGO/Au nanohybrid electrode exhibited good catalytic activity for HER with an onset potential of ?0.3 V and a Tafel slope of 136 mV dec^?1, achieving a current density of 10 mA cm^?2 at an overpotential of ?0.43 V.     

Hydrogen liberation from the dehydrocoupling of dimethylamine–borane at room temperature by using novel and highly monodispersed RuPtNi nanocatalysts decorated with graphene oxide

Addressed herein, we reported the fabrication of the graphene oxide (GO) supported monodispersed ruthenium–platinum–nickel (RuPtNi) nanomaterials (3.40 ± 0.32 nm) to be utilized as a catalyst in the process of dimethylamine borane (DMAB) dehydrogenation. The nanoparticles were fabricated through the ultrasonication method by co-reducing the Ru³⁺, Pt²⁺ and Ni²⁺ cations and then the nanomaterials were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), inductively coupled plasma optical emission spectrometry (ICP-OES), and X-ray photoelectron spectroscopy (XPS). The fabricated nanomaterials showed outstanding efficiency and remarkable reusability in addition to their record catalytic activity at low temperatures and with extreme low concentrations. They had a significantly high turnover frequency (TOF) (727 h^?1) and low activation energy (E_a) (49.43 ± 2 kJ mol^?1) for DMAB dehydrocoupling. To the best of our knowledge, RuPtNi@GO NPs become a very promising candidate as the best catalyst ever.     

Enhanced photoelectrochemical water splitting in hierarchical porous ZnO/Reduced graphene oxide nanocomposite synthesized by sol-gel method

Today the utilization of solar energy to split water and its conversion to hydrogen and oxygen has been considered as a powerful way to solve the environmental crisis. Hierarchical porous nanostructured ZnO and ZnO/reduced graphene oxide (rGO) composite photoanodes are synthesized by innovated sol-gel method using triethylenetetramine (TETA) as a stabilizer. The hierarchical porous ZnO structure containing large agglomerates each consisting of tiny nanoparticles are formed. The X-ray diffraction analysis and Raman spectroscopy confirm the in-situ reduction of graphene oxide sheets during synthesis and formation of ZnO/rGO nanocomposite. Although the band gap and transmittance of the porous nanocomposites do not dramatically change by rGO addition, the main photoluminescence peak quenches entirely showing prolonging exciton lifetime. The ZnO/rGO porous structure achieved remarkably improved current density (1.02 mA cm^?2 at 1.5 V vs. Ag/AgCl) in 1 wt% rGO, up to 12 times higher compared to the bare ZnO (0.09 mA cm^?2 at 1.5 V vs. Ag/AgCl), which attributes to positive role of ZnO hierarchical porous structure and rGO electron separation/transportation. These findings provide new insights into the broad applicability of this methodology for promising future semiconductor/graphene composite in the field of photoelectrochemical water splitting.     

Preheated self-aligned graphene oxide for enhanced room temperature hydrogen storage

This study explored the hydrogen adsorption capacity of self-assembled aligned graphene oxide at room temperature. The characteristics of as-prepared graphene oxide were determined by scanning electron microscopy, Raman spectroscopy, and X-ray diffractometry techniques. Three different temperatures were taken for preheating, i.e., 25, 250, and 400 °C. The maximum adsorption pressure was given to 20 bar, and we evaluated the hydrogen adsorption competency at room temperature (25 ± 2 °C). The maximum hydrogen storage capacity was achieved ~2.5 wt%, which was found for the graphene oxide sample preheated at 400 °C. This hydrogen storage capacity was 67% and 40% more than the graphene oxide samples preheated at 25 and 250 °C, respectively. Such an enhancement of hydrogen storage capacity in the self-aligned graphene oxide samples at room temperature is attributed to reduced interlayer spacing and increased topological defects in preheated graphene oxide samples at 400 °C.     

Vertically-heterostructured TiO2-Ag-rGO ternary nanocomposite constructed with {001} facetted TiO2 nanosheets for enhanced Pt-free hydrogen production

TiO₂ nanosheets with high ratio of {001} facets were coupled with reduced graphene oxide (rGO) nanosheets through the link of silver (Ag) nanoparticles, forming a novel ternary nanocomposite photocatalyst with a vertical heterostructure, TiO₂-Ag-rGO. The vertical anchoring of TiO₂-Ag nanosheets between rGO sheets was confirmed by transmission electron microscopy (TEM), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Due to excellent separation of electron-hole pairs in the TiO₂ nanosheets, enhanced electron transfer to rGO via Ag nanoparticles, the TiO₂-Ag-rGO nanocomposite exhibited an outstanding performance in photocatalytic hydrogen production, with a hydrogen production rate of 593.56 μmol g^?1 h^?1. This study provides new insights to the development of Pt-free photocatalysts for hydrogen production.     

Tubular graphene architectures at the macroscopic scale: fabrication and properties

Specific graphene architectures at the macroscopic scale are paramount for exploring new functions and practical uses of graphene. In this study, macroscopic, freestanding, and tubular graphene (TG) architectures were successfully fabricated through a versatile and robust process based on the annealing of cellulose acetate (CA) on Ni templates. These TG architectures can be obtained as woven tubes with diameters of approximately 50 μm; they possess high graphitic crystallinity, strong electrical conductivity, and favorable corrosion resistance. The effects of processing parameters, such as annealing temperature, annealing time, and amount of CA, on the graphene properties of these architectures were investigated and are discussed in this paper. The graphene properties were characterized through field emission scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, four-point probe resistivity, and electrochemical measurements.     

Investigation of the effect of carbonaceous supports on the activity and stability of supported palladium catalysts for methanol electro-oxidation reaction

In this study, nitrogen doped graphene (NG) and multi-walled carbon nanotubes (MWCNT) were used as supporting materials for palladium active phase to investigate their performance in direct methanol fuel cells (DMFCs). The facile and low temperature solvothermal method was used for the synthesis of NG. Palladium nanoparticles were deposited on the surface of NG and MWCNT by a modified polyol reduction method. The morphologies and microstructures of the prepared catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Also, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy were carried out to evaluate the electrocatalytic activity and the durability of the obtained catalysts towards methanol oxidation reaction. Pd/NG catalyst had a better activity and durability of methanol electrocatalytic oxidation rather than Pd/MWCNT catalyst, which is related to good dispersion of Pd nanoparticles on the surface of nitrogen doped graphene and the physicochemical characteristics of NG.     

Hydrogen uptake of cobalt and copper oxide-multiwalled carbon nanotube composites

Hydrogen storage capacity of a pristine multi-walled carbon nanotubes is increased 10-fold at 298 K and an equilibrium hydrogen pressure of ～23 atm, upon addition of a hydrogen spillover catalyst cobalt- and copper oxide, from 0.09 to 0.9 wt.%. In situ reduction method is utilized to synthesize Co-oxide/MWCNTs and Cu-oxide/MWCNTs composite. Blocking of channels and pores of MWCNTs by oxide nanoparticles during preparation method is responsible for low BET specific surface area of composites compared to pristine sample. X-ray diffraction, scanning, and transmission electron microscopy demonstrates nanostructural characterization of MWCNTs and composites. Thermogravimetric analysis of two oxide/MWCNTs composites showed a single monotonous fall related to MWCNTs gasification. Enhancement of hydrogen storage of both composites is attributed to the spillover mechanism due to decoration of Co and Cu-oxide nanoparticles on the outer surface of MWCNTs.     

“Green” electrochemical synthesis of Pt/graphene sheet nanocomposite film and its electrocatalytic property

Nanocomposite films of platinum nanoparticle-deposited expandable graphene sheet (Pt/EGS) are fabricated on conductive indium tin oxide glass electrodes via a “green” electrochemical synthetic route involving a series of electrochemical processes. The microstructure and morphology of the prepared film samples are characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, three-dimensional non-contact surface mapping, and field emission scanning electron microscopy. At the same time, the catalytic activity and stability of the Pt/EGS film for the oxidation of methanol are evaluated through cyclic voltammetry and chronoamperometry tests. The Pt nanoparticles in the Pt/EGS nanocomposite film are found to be uniformly distributed on the EGS. The as-synthesized Pt/EGS nanocomposite exhibits high catalytic activity and good stability for the oxidation of methanol, which may be attributed to its excellent electrical conductivity and the high specific surface area of the graphene sheet catalyst support.     

Enhanced room-temperature hydrogen storage capacity in Pt-loaded graphene oxide/HKUST-1 composites

Series of Pt-loaded graphene oxide (GO)/HKUST-1 composites were synthesized by the reaction between Pt@GO and precursors of HKUST-1. The parent materials and composites have been characterized by powder X-ray diffraction (XRD), Infrared (IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and gas adsorption analyzer. The XRD and IR analysis showed that the incorporation of Pt@GO did not prevent the formation of HKUST-1 units. SEM, TEM and EDS results revealed that Pt nanoparticles were well-dispersive and anchored tightly into composites. Meanwhile, the percentage of Pt@GO has an obvious effect on morphologies, crystallinities and surface areas of composites. More importantly, the significant enhancement of hydrogen storage capacity at ambient temperature for the composite with low Pt@GO content can be ascribed to the hydrogen spillover mechanism in such system.     

Fabrication of flexible polypyrrole/graphene oxide/manganese oxide supercapacitor

A flexible polypyrrole/graphene oxide/manganese oxide‐based supercapacitor was prepared via an electrodeposition process. The polypyrrole, graphene oxide, and manganese oxide were deposited onto a flexible and highly porous nickel foam, which acted as a current collector to enhance the electrochemical performances. The good coverage of the polypyrrole, graphene oxide, and manganese oxide onto the scaffold of the nickel foam was evidenced using field emission scanning electron microscopy and X‐ray diffraction. The manganese species, which were present in the oxidation states of Mn³⁺ and Mn⁴⁺, were shown using X‐ray photoelectron spectroscopy. The presence of Mn₂O₃ and MnO₂ polymorphs was detected using Fourier transform infrared and Raman spectroscopies. The cyclic stability of the ternary supercapacitor was consistent regardless of its geometry and curvature. In contrast, an activated carbon supercapacitor possesses limited energy storage capability compared to a ternary supercapacitor, which suppresses the electrochemical performances of activated carbon. The ternary as‐fabricated supercapacitor could retain a specific capacitance of 96.58% after 1000 cycles, and the as‐synthesized energy storage device was able to light up a light emitting diode. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of UV irradiation on PC membrane and use of Pd nanoparticles with/without PVP for H2 selectivity enhancement over CO2 and N2 gases

The hydrogen-based economy is one of the possible approaches toward to eliminate the problem of global warming, which are increases because of the gathering of greenhouse gases. Palladium (Pd) is well-known material having a strong affinity to the hydrogen absorbing property and thus appropriate material to embed in the membrane for the improvement of selective permeation of hydrogen gas. In present work, we have functionalized polycarbonate (PC) membranes with the help of UV irradiation to embed the Pd nanoparticles in pores as well as on the surface of the PC membrane. Use of Pd Nanoparticles is helpful to enhance the H₂ selectivity over other gases (CO₂, N_2, etc.). Also, the UV based modification of membrane increases the attachment of Pd Nanoparticles. Further to enhance the Pd nanoparticles attachment, we used PVP binder with Pd nanoparticles solution. Gas permeability measurements of functionalized PC membranes have been carried out, and better selectivity of hydrogen has been found in the functionalized and Pd nanoparticle binded membrane. PC membrane with 48 h UV irradiated and Pd NPs with PVP have been found to have maximum selectivity and permeability for H₂ gas. All the samples being characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and UV–Vis spectroscopy for their morphological and structural investigation.     

An efficient photocatalytic system containing Eosin Y, 3D mesoporous graphene assembly and CuO for visible-light-driven H2 evolution from water

In the present work, 3D mesoporous graphene assembly was fabricated in a hydrothermal process using triethylenetetramine molecules as cross-linkers. And CuO nanoparticles were introduced in the graphene assembly via in-situ photodeposition. Then, a photocatalytic system containing Eosin Y as a sensitizer, graphene assembly as a supporter material and electron transfer channel, and CuO nanoparticles as an active center of H₂ evolution from water was prepared. Meanwhile, photocatalytic hydrogen evolution from water over the as-prepared photocatalytic system was explored under visible irradiation. Furthermore, for practical purposes, the durability of the photocatalytic system was also studied. And the photocatalytic mechanism was preliminarily discussed. The experimental results indicate that the as-prepared photocatalytic system is an efficient photocatalyst for visible-light-driven H₂ evolution from water. The rate of H₂ evolution over the photocatalytic system is up to 5.85 mmol g^?1 h^?1 under optimal conditions, which is 2.3 times higher than that over reduced graphene oxide loaded with CuO. The 3D porous graphene assembly plays an important role in the photocatalytic process. It can not only efficiently enhance the electron transfer in the photocatalytic system, but also result in fast diffusion of sacrificial reagent and timely release of H₂ bubbles. This work provides us with new possibility for designing an efficient Pt-free visible photocatalyst for H₂ evolution from water.     

Electrochemical hydrogen evolution and storage studies on bismuth nano hexagons

Bismuth nano hexagons were synthesized using potentiostatic electrodeposition and studied for their performance towards electrochemical hydrogen storage and evolution. Regular hexagons with edge length ≈ 500 nm and thickness ≈ 80 nm were observed in scanning electron microscopy (SEM). X-ray diffraction (XRD) pattern indicates the presence of poly-crystalline bismuth and bismuth oxide in rhombohedral and cubic phases respectively. X-ray photoelectron spectroscopy (XPS) studies further confirm the presence of two phases of bismuth i.e. elemental bismuth and bismuth (III) oxide. Results indicate that these nano hexagons show good hydrogen ion (H⁺) storage and successive hydrogen gas (H₂) evolution characteristics.     

Trimetallic PdRuNi nanocomposites decorated on graphene oxide: A superior catalyst for the hydrogen evolution reaction

In this work, we report an improved catalyst which is superior to known heterogeneous catalysts for dehydrocoupling of dimethylamine-borane (DMAB). The prepared three metallic nanocomposites consist of graphene oxide supported monodisperse palladium, ruthenium and nickel nanomaterials (3.78 ± 0.43 nm). The monodisperse PdRuNi nanoparticles decorated with graphene oxide (PdRuNi@GO) were synthesized according to the microwave synthesis method and characterized by TEM (Transmisson Electron Microscopy), HR-TEM (High Resolution Transmisson Electron Microscopy), XPS (X-ray photoelectron spectroscopy), XRD (X-ray diffraction) and Raman spectroscopy. The prepared trimetallic nanocomposites have shown outstanding performance and stability as a catalyst for the dehydrocoupling of dimethylamine-borane. To the best of our knowledge, the prepared monodisperse PdRuNi@GO nanoparticles have one of the best catalysts with outstanding TOF (Turnover Frequency) value (737.05 1/h) and E_a (55.47 kJ/mol) (activation energy) among all catalysts prepared for dehydrogenation of dimethylamine-borane at low temperatures.     

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.     

Fabrication of three-dimensional structured graphene for supercapacitors

以氧化石墨为原料,采用电化学还原和超声剥离法制备了三维网状石墨烯,电化学法是在交变场中用方波实现的,最终制得的石墨烯具有明确的三维连通多孔网络结构,孔的大小在亚微米至数微米之间,孔壁由非常薄的石墨烯片堆积而成.用该材料做超级电容器电极材料,用循环伏安法,恒流充放电,交流阻抗法测试电极的电容性能,当扫描速率为10 mV/s时,电容器比电容为140 F/g,等效电阻小于1 Ω,三维网状石墨烯具有性能稳定,充放电效率高,循环性能好,适合于大电流充放电等优良性能.     

Reduced graphene oxide–coated anode gas diffusion layer for performance enhancement of proton‐exchange membrane fuel cell

In this study, we produced reduced graphene oxide (RGO) by reduction of graphene oxide (GO) in Teflon‐lined autoclave, maintained at 100°C for 12 hours, and coated on the anode gas diffusion layer (GDL) of a proton‐exchange membrane fuel cell (PEMFC) to improve the cell performance. Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy analysis showed the presence of residual oxygen‐containing functional groups in RGO. Field‐emission scanning electron microscopy images revealed the uniform and adequate coating of the GDLs with RGO. The wettability of RGO‐coated GDL was determined by the sessile drop method and has optimum contact angle 117°. The power densities for the membrane electrode assembly (MEA) with RGO coated on the anode GDL were 30.92%, 41%, and 36.20% higher than those for the MEA without the RGO coating at anode gas humidified temperatures of 25°C, 45°C, and 65°C, respectively.