Synthesis, Characterization And Electrocatalytic Properties Of Heteroatom-Doped Graphene

Heteroatom doping has been an effective way to tailor the properties of graphene and greatly broadened the application areas of graphene, and opens up a new field of research in carbon materials. In this thesis, we choose graphene oxide (GO) as precursors to prepare heteroatom doped graphene by different methods, and systematically studied their structures and properties. The dissertation is mainly focussed on:(1) Synthesis of nitrogen-doped graphene (nG) and its electrocatalytic properties. A series of nGs with different electrocatalytic abilities toward oxygen reduction reaction(ORR) were prepared via a two-steps pyrolysis method by controlling a reaction temperature on the physical mixture of graphene oxide and urea. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) displayed nG with highly wrinkled and overlapping structures. X-ray photoelectron spectroscopy (XPS) showed that nitrogen was successfully doped in graphene with the formation of pyridinic N, pyrrolic N and graphitic N, and the maximum nitrogen content was6.6at%. Cyclic voltammogram and rotating disk electrode measurement showed that nGs exhibited high electrocatalytic activity with an onset potential of0.1V in an acid electrolyte. Moreover, the nGs catalyzed oxygen reduction revealed a favorable formation of water via a four-electron pathway and excellent stability over the commercial Pt/C catalyst. Furthermore, the nG obtained at200℃in the first pyrolysis step displayed the best catalytic performance.(2) Synthesis of sulfur-doped graphene (S-RGO) and its electrocatalytic properties. A series of S-RGOs with different ORR electrocatalytic activities were prepared via a hydrothermal reaction method by controlling the reaction temperature on Na2S as a reductant and dopant with GO. Fourier transformation infrared spectroscopy (FTIR), Raman spectroscopy and Thermogravimetric analysis (TGA) results revealed that with the increase of hydrothermal reaction temperature, the reduction degree and thermal stability of graphene increased. TEM and SEM displayed that S-RGO had more wrinkles and overlaps. XPS demonstrated that the sulfur content in S-RGO-180was4.19at%, and sulfur was successfully doped in graphene with the formation of C-S-C. Electrochemical tests showed that with the increase of hydrothermal reaction temperature, the conductivity and electrocatalytic activity of RGO and S-RGO gradually enhanced. Furthermore, S-RGO-180behaves the best reversibility, the highest electrochemical activity and ORR electrocatalytic ability.