Electrocatalytic Performance Of Nitrogen-doped Graphene And Mo₂C/Graphene Nanocomposite

Since graphene was successful prepared by mechanical cleavage from graphite in2004by Geim and coworkers, such paradigm two-dimensional (2D) material has rapidly risen to be one of the hottest stars in materials science due to its many exciting and unusual characteristics. Graphene,2D honeycomb network with monolayer structure of sp2hybridized carbon atoms packed in a hexagonal lattice, exhibits remarkable electronic, optical, thermal and mechanical properties, including high Young’s modulus, robust fracture strength, high thermal conductivity, fast charge mobility, large specific surface area, high chemical stability and unique optical transmittance. Therefore, graphene has shown great potentials in wide application fields, such as biomedicine, reinforced composite, sensors, catalysis, energy conversion and storage device.In search of new properties and applications, researchers are devoting their attention into designing and constructing graphene-based functional materials with hierarchical structure and multifunctional properties. Heteroatom-doped graphene and graphene nanocomposite are two typical types of graphene-based functional materials. In-situ growth and post-treatment strategy have been applied for the synthesis of doped graphene. As for graphene-based nanocomposites, graphene oxide (GO) nanosheets are used as a platform for the deposition of diverse nano-objects, including metal, semiconductor and polymer, etc, through various strategies, such as covalent and noncovalent methods, hydrothermal and solvothermal approach, electrochemical and electrophoresis deposition, photochemical reaction. In this dissertation, we have designed and synthesized two kinds of graphene-based functional materials, i.e., nitrogen-doped graphene and Mo2C/graphene nanocomposite, which exhibit enhanced electrocatalytic performances for fuel cell. The main results can be summarized as following:1. A new kind of nitrogen-doped graphene electrocatalyst with well-defined mesoporous structure has been fabricated by a scalable and templateless technique of directly annealing of pre-synthesized GO-polydopamine (GO/PDA) nanocomposites. Although with the high-temperature treatment, the obtained nitrogen-doped graphene nanosheets in well-dispersed state are possessed with well-defined mesoporous architecture and large specific surface area owing to the pre-polymerization of dopamine on the GO nanosheets as the spacing. Furthermore, the prepared nitrogen-doped graphene as the electrode material with a four-electron pathway exhibits more positive onset potential and larger current density than the controlled samples in alkaline solution, indicating an enhanced oxygen reduction reaction (ORR) activity.2. A facile and scalable method in combination of hydrothermal technique and high-temperature process has been reported for the synthesis of Mo2C/graphene nanocomposite by using ammonium molybdate and graphene oxide as precursors. GO sheets play dual roles of the loading platform and carbon source in the formation of Mo2C/graphene nanocomposite. During the annealing process, the produced Mo2C nanoparticles by the decomposition of ammonium molybdate as the spacing effectively avoid the reaggregation of graphene nanosheets. The obtained nanocomposites show remarkable hydrogen evolution reaction (HER) electrocatalytic activity.