Fabrication and characterization of poly(phenylene oxide)/SBA-15/carbon molecule sieve multilayer mixed matrix membrane for gas separation

A novel multilayer mixed matrix membrane (MMM), consisting of poly(phenylene oxide) (PPO), large-pore mesoporous silica molecular sieve zeolite SBA-15, and a carbon molecular sieve (CMS)/Al₂O₃ substrate, was successfully fabricated using the procedure outlined in this paper. The membranes were cast by spin coating and exposed to different gases for the purpose of determining and comparing the permeability and selectivity of PPO/SBA-15 membranes to H₂, CO₂, N₂, and CH₄. PPO/SBA-15/CMS/Al₂O₃ MMMs with different loading weights of zeolite SBA-15 were also studied. This new class of PPO/SBA-15/CMS/Al₂O₃ multilayer MMMs showed higher levels of gas permeability compared to PPO/SBA-15 membranes. The permselectivity of H₂/N₂ and H₂/CH₄ combinations increased remarkably, with values at 38.9 and 50.9, respectively, at 10 wt% zeolite loading. Field emission scanning electron microscopy results showed that the interface between the polymer and the zeolite in MMMs was better at a 10 wt% loading than other loading levels. The increments of the glass transition temperature of MMMs with zeolite confirm that zeolite causes polymer chains to become rigid.     

Fabrication of highly dispersed palladium/graphene oxide nanocomposites and their catalytic properties for efficient hydrogenation of p-nitrophenol and hydrogen generation

In this report, graphene oxide (GO) nanosheets decorated with ultrafine Pd nanoparticles (Pd NPs) have been successfully fabricated through a reaction between [Pd₂(μ-CO)₂Cl₄]²⁻ and water in the presence of GO nanosheets without any surfactant or other reductant. The as-synthesized small Pd NPs with average diameter of about 4.4 nm were well-dispersed on the surface of GO nanosheets. The Pd/GO nanocomposites show remarkable catalytic activity toward the hydrogenation of p-nitrophenol at room temperature. The kinetic apparent rate constant (k_app) could reach about 34.3 × 10⁻³ s⁻¹. Furthermore, the as-prepared Pd/GO nanocomposites could also be used as an efficient and stable catalyst for hydrogen production from hydrolytic dehydrogenation of ammonia borane (AB). The catalytic activity is much higher than the conventional Pd/C catalysts.     

Fabrication of a highly efficient polymer electrolyte membrane by embedding nanofibrous metal oxide in cell components

In this work, a high-performance polymer electrolyte membrane based on sulfonated polyether ether ketone (SPEEK) loaded with zirconium oxide nanofibres (ZrN) was fabricated. ZrN with an average diameter of 182 nm were prepared by pyrolysing electrospun polyacrylonitrile fibres embedded with a zirconium precursor. The weight percentage of added ZrN and the relevant performance of the hybrid membrane (e.g., proton conductivity, methanol permeability and fuel cell performance) were experimentally determined and verified. It was found that the SPEEK-ZrN hybrid membrane exhibited sufficient proton conductivity (25.9 mS cm⁻¹), low methanol permeability (1.64 × 10⁻⁷ cm² s⁻¹) and superior selectivity (15.8 × 10⁴ S s cm⁻³) at room temperature. Compared to a pure SPEEK membrane, the SPEEK-ZrNT-1.5 membrane showed 1.3 and 1.7 times higher current density and power density, respectively.     

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.     

Experimental investigation of natural polysaccharide-based mixed matrix membrane modified with graphene oxide and Pd-nanoparticles for enhanced gas separation performance

In this work, we proposed a mixed matrix membrane prepared by using a glycerol modified guar gum (GGP) polymer matrix incorporated with graphene oxide (GO). The influence of varying GO concentration on the gas separation performance was investigated and 2 wt% was found to be the optimum concentration for high performance. The 2 wt% GO mixed matrix membranes were further modified with Pd nanoparticles. When GO, and Pd nanoparticles were mixed, CO₂ permeability increased by 49.94%, while the permeability of H₂ gas molecules decreased by 98.11%, respectively, compared to the pristine GGP membrane. The selectivity of CO₂/H₂ was obtained as 18.27. The glass transition temperature of the membrane increased from 85 to 95.2 °C, tensile strength and elongation of the break were significantly improved by 29.09% and 84.37% through the addition of Pd and GO into the membrane. The scanning electron microscopy revealed a dense top surface after GO nanosheets incorporation. Further, the thermogravimetric analysis proposes that the modified membrane is thermally stable than GGP. Henceforth, the study suggests GO incorporation and Pd nanoparticles modification of guar gum membrane is a promising gas separation membrane with potentially high selectivity for CO₂ gas.     

Fabrication of robust CoP/Ni2P/CC composite for efficient hydrogen evolution reaction and the reduction of graphene oxide

Developing the novel catalysts with an excellent performance of hydrogen generation is essential to facilitate the application of hydrogen evolution reaction (HER). Herein, a heterostructured cobalt phosphide/nickel phosphide/carbon cloth (CoP/Ni₂P/CC) composite was fabricated via an interfacial engineering strategy to achieve the modification of CoP nanoleaf on Ni₂P nanosheet skeleton supported by carbon cloth. By virtue of the unique heterostructure, abundant exposing active sites and the synergistic coupling effect of CoP and Ni₂P nanoparticles, the elaborated CoP/Ni₂P/CC composite exhibits a robust catalytic property. Among fabricated composites, the optimal CoP/Ni₂P/CC-4 catalyst behaves an excellent HER performance at a wide pH range (overpotentials of 67, 71 and 95 mV to afford 10 mA cm^?2 in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively). The HER current density of this composite shows a negligible degradation after continuous test for 24 h. Charmingly, the HER process of this catalyst was innovatively applied to reduce graphene oxide, and thus exploiting the fabrication route of reduced graphene oxide (rGO). We are sure that this work will provide a firm guideline for the exploitation of pH-universal HER catalysts and the exploration of HER application.     

Development of membrane reformer system for highly efficient hydrogen production from natural gas

A membrane reformer is composed of a steam reformer equipped with palladium-based alloy membrane modules and can perform steam reforming reaction of natural gas and hydrogen separation processes simultaneously, without shift converters and purification systems. We have developed a membrane reformer system with nominal hydrogen production capacity of 40 Nm³/h. The system has demonstrated the potential advantages of the membrane reformer: simple system configuration as benefited by single-step production of high-purity hydrogen (99.999% level), compactness, and high-energy efficiency of 70–76%. We are promoting development towards commercialization of the membrane reformer technology, focusing on further improvement of energy efficiency, proof of long-term durability and reliability, and establishment of system engineering technologies. The target of our current project is to develop a membrane reformer system that can produce 99.99% or higher-purity hydrogen from natural gas at a rate of 40 Nm³/h with hydrogen production energy efficiency of over 80%.     

Highly stable graphene oxide composite proton exchange membrane for electro-chemical energy application

Proton exchange membrane is a basic element for any redox flow battery. Nafion is the only commercial available proton exchange membrane used in different electro-chemical energy systems. High cost restrict it's used for energy generation devices. In present work, we synthesised styrene divinylbenzene based composite proton exchange membranes (PEMs) with varying sulfonated graphene oxide (sGO) content for redox flow battery (RFB). Synthesized copolymer PEMs were analyzed in terms of their chemical structure with the help of FT-IR spectroscopy to confirm desired functional groups at appropriate position. Electrochemical characterization was performed in terms proton-exchange capacity, protonic conductivity and water uptake. Membrane shows adequate proton exchange capacity with good proton conductivity. Vanadium ion permeability was also tested for the prepared membrane to assess capability for vanadium redox flow battery (VRFB) in contrast with commercially available Nafion 117 PEM. Higher VO⁺² ion cross-over resistance was found for CEM-4 with 7.17 × 10⁻⁷ cm² min⁻¹ permeability, which is about half of the CEM-1. Further CEM-4 was also evaluated for charging-discharging phenomenon for single cell VRFB. The values of columbic, voltage and energy efficiency for VRFB confirms prepared membrane as a good candidate for redox flow battery. Composite PEM also shows better mechanical and thermal stability. Results indicates that synthesized composite membrane can be used in vanadium redox flow battery.     

Highly selective 3D porous graphene membrane for organic gas separation derived from polyphenylene

In this paper, a 3D nanoporous carbon molecular sieve (CMS) membrane is proposed to investigate the diffusion and separation properties of ethylene/methane and ethylene/acetylene binary mixtures permeating through the structural deformated carbon nanotube (CNT) channels. Combining the results obtained from density functional theory (DFT) calculations and molecular dynamics (MD) simulations, we find that the organic gas permeability and selectivity can be effectively ameliorated by fine-tuning the geometric structure of CNTs gas separation channels. By virtue of the intrinsic structural characteristics, this hybrid CMS configuration established elliptical cylinder channels to separate the organic gas molecules with similar molecular size. Compared with channels with a circular cross section, the gas selectivity for channels with an elliptical cross section is larger, and it increases with an increasing pressure. The selectivity of ethylene over acetylene (methane) increased to ~13.8 (5.5) in deformed CNTs channels, which is more than doubled over the original CNT channels. This distinguished hybridization configuration may pave a promising avenue to utilize gas separation materials.     

Ultrafine Co6Mo6C nanocrystals on reduced graphene oxide as efficient and highly stable electrocatalyst for hydrogen generation

Up to now, it is still a great challenge to develop active, durable and low-cost non-precious metal catalysts toward hydrogen evolution reaction (HER). In this paper, we synthesized ultrafine Co₆Mo₆C nanocrystals on reduced graphene oxide (RGO) support (Co₆Mo₆C/RGO). The Co₆Mo₆C/RGO shows Pt-like HER performance, which exhibits almost zero onset overpotential, and very small overpotential of 64 mV at 10 mA cm^?2. In addition, the Co₆Mo₆C/RGO has a very small Tafel slope of 44 mV dec^?1 and a high exchange current density of 0.402 mA cm^?2, suggesting fast reaction kinetics. Furthermore, the Co₆Mo₆C/RGO demonstrates superior durability in acid electrolyte. The distinguished HER performance makes Co₆Mo₆C/RGO the promising candidate as non-precious metal catalyst for HER in acid electrolyte.     

Fabrication,characterization and application of three-dimensional copper nanodomes as efficient cathodes for hydrogen production

In this study, three-dimensional (3D) copper nanodomes (Cu-NDs) were fabricated by a combined method of nanosphere-soft lithography, electrochemical and physical vapor deposition (PVD) methods. The 3D Cu-NDs were characterized using surface characterization techniques. The hydrogen production performance and time-stability of the electrodes were examined in a concentrated alkaline solution (6 M KOH) using various electrochemical techniques. The experimental results showed that very uniformly and closely packed Cu-NDs were prepared by the combined methods. The hydrogen generation activity of the 3D Cu-NDs was significantly improved with respect to bulk Cu. Fabricating Cu-NDs does not effect of the hydrogen evolution mechanism and the reaction is activation controlled. The water splitting reaction starts at lower potentials and larger current densities at a fixed potential were appeared at the Cu-NDs electrode. The average reduction in the charge transfer resistance related to the reaction of hydrogen gas evolution is 91.9% at the Cu-NDs electrode with respect to the bulk Cu. The enhanced activity of the nanostructures was related to enlarging real surface area and available more active centers at the Cu-NDs surface. The Cu-NDs electrode has excellent time stability in alkaline solution.     

Polyoxomolybdate-derived MoS2/nitrogen-doped reduced graphene oxide hybrids for efficient hydrogen evolution

Integrating MoS₂ with carbon-based materials, especially graphene, is an effective strategy for preparing highly active non-noble-metal electrocatalysts in the hydrogen evolution reaction (HER). This work demonstrates a convenient hydrothermal method to fabricate molybdenum disulfide nanosheets/nitrogen-doped reduced graphene oxide (MoS₂/NGO) hybrids using polyoxomolybdate as the Mo precursor. Introducing more defects and expanding interlayer spacing of MoS₂ can be achieved through decreasing the pH value of the reactive system due to the existed high-nuclear polyoxometalate clusters. MoS₂/NGO hybrids prepared at low pH exhibit superior HER activity to those obtained at high pH. MoS₂/NGO-pH1.5 exhibits an ultralow overpotential of 81 mV at 10 mA cm⁻², a low Tafel slope of 60 mV·dec⁻¹ and good stability in alkaline electrolyte. Such excellent electrocatalytic activity is contributed by the abundant HER catalytic active sites, the increased electrochemically-accessible area and the synergetic effects between the active MoS₂ catalyst and NGO support.     

Preparation and characterization of PPSU/PBNPI blend membrane for hydrogen separation

Novel polymer blend membranes of poly(bisphenol A-co-4-nitrophthalic anhydride-co-1,3-phenylenediamine) (PBNPI) and polyphenylsulfone (PPSU) in different weight ratios were prepared by a solution casting technique with N-methyl-2-pyrrolidone (NMP) as solvent. The effects of blend polymer composition on the membrane structure and the H₂, CO₂ and CH₄ separation performance were investigated. The membranes appear macroscopically miscible but microscopically immiscible based on thin-film X-ray diffraction investigations. A remarkably and continuously enhanced permeability has been achieved for these gases with increasing PPSU content from 0 to 50%. The highest pure H₂, CO₂ and CH₄ permeability are, respectively, equal to 40.4, 34.1 and 8.0 barrer.     

Agent-free synthesis of graphene oxide/transition metal oxide composites and its application for hydrogen storage

Graphene oxide (GO) wrapped transition metal oxide composite materials were synthesized by a very simple route without any additional agents and the hydrogen adsorption properties of the materials were investigated. The morphologies of GO/V₂O₅ and GO/TiO₂ were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that single- or few-layered GO sheets wrapped throughout the V₂O₅ and TiO₂ particles. According to X-ray photoelectron spectroscopy (XPS), the C–OH species of GO and the surface-adsorbed oxygen of the transition metal oxide bond together via a dehydration reaction. The wrapping phenomenon of GO causes the enhancement of hydrogen storage capacity at liquid nitrogen temperature (77 K) compared with those of the pristine transition metal oxides and GO. The enhancement of hydrogen storage capacity of GO-wrapped transition metal oxide composite materials results from the existence of interspaces between the transition metal oxide particles and the thin GO layers.     

Nitrogen-phosphorus co-functionalized reduced graphene oxide supported NiCoPd-CeOx nanoparticles as a highly efficient and stable catalyst for formic acid dehydrogenation

Formic acid (HCOOH, FA), a common liquid hydrogen storage material, has attracted tremendous research interest. However, the development of efficient, low-cost and high-stable heterogeneous catalyst for selective dehydrogenation of FA remains a major challenge. In this paper, a simple co-reduction method is proposed to synthesize nitrogen-phosphorus co-functionalized rGO (NPG) supported ultrafine NiCoPd-CeO_x nanoparticles (NPs) with a mean size of 1.2 nm. Remarkably, the as-prepared Ni_0.2Co_0.2Pd_0.6-CeO_x/NPG shows outstanding catalytic activity for FA dehydrogenation, affording a high TOF value of 6506.8 mol H₂ mol Pd^?1 h^?1 at 303 K and a low activation energy of 17.7 kJ mol^?1, which is better than most of the reported heterogeneous catalysts, and can be ascribed to the combined effect of well-dispersed ultrafine NiCoPd-CeO_x NPs, modified Pd electronic structure, and abundant active sites. The reaction mechanism of dehydrogenation of FA is also discussed. Furthermore, the optimized Ni_0.2Co_0.2Pd_0.6-CeO_x/NPG shows excellent stability over 10^th run with 100% conversion and 100% H₂ selectivity, which may provide more possibilities for practical application of FA system on fuel cells.     

CuS-modified ZnO rod/reduced graphene oxide/CdS heterostructure for efficient visible-light photocatalytic hydrogen generation

Solar energy utilization is a promising strategy for the photocatalytic generation of H₂ from water. Herein, a CuS-modified ZnO rod/reduced graphene oxide (rGO)/CdS heterostructure was fabricated via Cu-induced electrochemical growth with Zn powder at room temperature. The resulting powder revealed good interfacial bonding and promoted photoexcited carrier transport. The CuS nanoparticles played a pivotal role in enhancing visible-light responses and demonstrated excellent catalytic performance. A high visible-light photocatalytic H₂ generation rate of 1073 μmol h⁻¹ g⁻¹ was obtained from the CuS–ZnO/rGO/CdS heterostructure containing 0.23% CuS and 1.62% CdS. Increased photoexcited electron lifetimes, improved carrier transport rates, and decreased fluorescence intensities confirmed the synergistic effects of each of the components of the heterostructure. This study provides an innovative strategy for constructing multi-component heterostructures to achieve efficient visible-light H₂ evolution.     

Highly efficient and durable phosphine reduced iron-doped tungsten oxide/reduced graphene oxide nanocomposites for the hydrogen evolution reaction

The design and development of inexpensive and highly efficient electrocatalysts for hydrogen production from water splitting are highly crucial for green energy and the hydrogen economy. Herein, we report phosphine reduced an iron-doped tungsten oxide nanoplate/reduced graphene oxide nanocomposite (Fe-WOxP/rGO) as an excellent electrocatalyst for the hydrogen evolution reaction. This electrocatalyst was synthesized using a hydrothermal method, followed by reduction with phosphine (PH₃), which was generated from sodium hypophosphite. The catalyst onset potential, Tafel slope, and stability were investigated. Accordingly, Fe-WOxP/rGO exhibited impressively high electrocatalytic activity with a low overpotential of 54.60 mV, which is required to achieve a current density of 10 mAcm^?2. The Tafel slope of 41.99 mV dec^?1and the linear sweep voltammetry curve is almost the same as 2000 cycles and electrolysis under static overpotential (54.60 mV) is remain for more than 24 h in 0.5 M H₂SO₄. The catalytic activity and conductivity of Fe-WOxP/rGO were higher than WO_XP, Fe-WOxP and WOxP/rGO. Such an outstanding performance of the Fe-WOxP/rGO nanocomposite is attributed to the coupled synergic effect between high oxygen vacancies formation on tungsten oxide in the nanoplate-like structure of Fe-WOxP and rGO nanosheet, making it as an excellent electrocatalyst for hydrogen evolution reaction.     

Experimental evaluation of graphene oxide/TiO2-alumina nanocomposite membranes performance for hydrogen separation

In recent years, graphene oxide membranes showed interesting performances in terms of high permeating flux and perm-selectivity in several applications of gas separation because of their inherent properties combined to a low energy consumption. In this paper, a graphene oxide layer is coated on modified TiO₂-alumina tubular substrate in order to prepare graphene oxide nanocomposite membranes useful for hydrogen separation. Nanocomposite graphene oxide membrane samples were obtained by using vacuum deep coating method, depositing the graphene oxide solution as single layers on TiO₂-alumina substrate. Temperature and pressure variations were evaluated to achieve high H₂ permeance, high H₂/CO₂ selectivity and membrane performance stability during the experimental tests. Furthermore, it was found that the temperature increase causes a perm-selectivity (H₂/N₂ and H₂/CO₂) decrease, while the transmembrane pressure increase involves a general improvement of the perm-selectivity.     

Graphite oxide/functionalized graphene oxide and polybenzimidazole composite membranes for high temperature proton exchange membrane fuel cells

Graphite oxide/polybenzimidazole synthesized by 3, 3′-diaminobenzidine and 5-tert-butyl isophthalic acid (GO/BuIPBI) and isocyanate modified graphite oxide/BuIPBI (iGO/BuIPBI) composite membranes were prepared for high temperature polymer proton exchange membrane fuel cells (PEMFCs). All membranes were loaded with different content of phosphoric acid to provide proton conductivity. The GO/BuIPBI and iGO/BuIPBI membranes were characterized by SEM which showed that the filler GO or iGO were well dispersed in the polymer matrix and had a strong interaction with BuIPBI, which can improve the chemical stability of BuIPBI membrane and support a higher acid content. The proton conductivities of the GO/BuIPBI and iGO/BuIPBI with high acid loading were 0.016 and 0.027 S/cm, respectively, at 140 °C and without humidity.     

Intercalating ionic liquid in graphene oxide to create efficient and stable anhydrous proton transfer highways for polymer electrolyte membrane

Approaches for constructing efficient and stable proton transfer highways in polymer materials are urgently desirable and required for elevated-temperature polymer electrolyte membrane fuel cell (PEMFC). Herein, ionic liquid intercalated GO (IGO) with acceptable fluidity is synthesized by a facile one-pot method and then utilized to construct anhydrous transfer highways in polymer-based composite membrane. The basic-imidazole-cation-containing ionic liquid (IL) increases the flexibility of IGO and meanwhile reinforces the interaction with acidic sulfonated poly(ether ether ketone) (SPEEK) matrix, thus yielding more proportion of perpendicularly oriented IGO and the subsequent formation of 3-D cross-linked IGO networks. The IL molecules act as effective proton carrier sites along IGO networks, and in this way, efficient and long-range transfer highways for “bulk in-plane” proton conduction are constructed. SP-(25I-GO)-10% achieves the maximum conductivity of 7.29 mS cm^?1 at 150 °C, 10 times higher than that of SPEEK control membrane. Meanwhile, the maximum current density and power density of SP-(25I-GO)-10% at 90 °C are 574.1 mA cm^?2 and 145.1 mW cm^?2, increased by 48% and 102% compared with that of SPEEK control membrane, respectively. Additionally, the nanoconfined effect of interlayer renders composite membrane enhanced IL retention ability through capillary force, consequently stable proton conduction and single cell behavior.