Fabrication Of Graphene Based Composites And Their Applications In Hydrogen Generation

Graphene, which is a planar monolayer of sp2-bonded carbon atoms tightly packed into a two-dimensional honeycomb lattice, has drawn tremendous attention since it was isolated in2004. Owing to the unique two-dimensional (2D) structure and excellent physical and chemical properties, such as excellent heat conduction, mechanical properties, chemical stability, and large specific surface area, researchers have made intensive efforts in investigating graphene and its functionalized derivatives in recent years. It can be applied in nanoelectronics, sensors, nanocomposites, batteries, super capacitors, hydrogen storage, et al. Here, we mainly focus on the synthesis of different graphene composites which can be used as efficient catalysts in hydrogen production.In this thesis, cobalt/graphene sheets (Co/GRs) nanocomposites, which are highly efficient catalysts, have been prepared using a one-step solvothermal method in ethylene glycol. Co2+salts were converted to Co nanoparticles, which were simultaneously inserted into the graphene layers with the reduction of graphite oxide sheets to GRs. The as-synthesized samples were characterized by X-ray diffraction, Raman spectroscopy, Transmission electron microscopy, High-resolution transmission electron microscopy and Vibrating sample magnetometer. The maximum saturation magnetization value reached80.8emu·g-1. The catalytic activity of the composite was investigated by the hydrolysis of sodium borohydride in aqueous solution both with and without a GRs support. It was found that the high electronic conductive GRs support increased the hydrogen generation rate (about two times) compared with pure cobalt. The improved hydrogen generation rate, low cost and uncomplicated recycling makes the Co/GRs nanocomposites promising candidates as catalysts for hydrogen generation.A novel fiber catalyst, cobalt/graphene sheets nanocomposite anchored on polyacrylonitrile fibers (Co/GRs-PANFs), which can be easily recycled and used in any reactor with different shapes, was synthesized by anchoring cobalt/graphene (Co/GRs) on Polyacrylonitrile fibers coated with graphene (GRs-PANFs) at low temperature. Co nanoparticles were well dispersed on the surface of GRs-PANFs. The catalytic activity of the catalyst was investigated by the hydrolysis of NaBH4in aqueous solution with GRs-PANFs, GRs powders and Co powders as control groups. It was found that both GRs and fiber are contributed to the hydrogen generation rate of Co/GRs-PANFs (3222mL·min-1·g-1Co/GRs-PANFs) compared with cobalt powders (915mL·min-1·g-1Co) and Co/GRs (995mL·min-1·g-1Co/GRs)-The improved hydrogen generation rate, low cost and uncomplicated recycling makes the Co/GRs-PANFs promising candidate as catalysts for hydrogen generation. Meanwhile, the single graphene-PAN fiber was placed in a circuit and the LED lamp was lit which implied that there was current through the circuit and the single graphene-PAN fiber can be used as an electrical wire.Although it is an efficient way to generate hydrogen form the hydrolysis of sodium borohydride, it still exists several disadvantages such as high cost of sodium borohydride. recycle of sodium metaborate, et al. A series of N-doped graphene/P25(N-GRs/P25) nanocomposites were synthesized by solvothermal and characterized by X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of as-prepared N-GRs/P25for hydrogen production from water under ultraviolet light irradiation was investigated. The results show that N-GRs/P25nanocomposites have a higher photocatalytic activity than pure P25. N-GRs as a cocatalyst is a more promising candidate for development of high-performance photocatalysts in the photocatalytic H2production.