| With the development of society, the demand for energy and environment has been urgently increased. However, it is a horrendous waste if the precious fossil resources (such as petroleum, coal, natural gas and so on) are just employed as fuel, and that would cause serious environmental pollution. Therefore, it is very important to develop and utilize new clean energy. The new clean energy forms including wind,solar, tide etc have attracted much attention and showed great potential in practical application, while they still suffer from the problems of circumscribed region, treacherous climate and so on. To solve the above problems, we must novel energy storage and conversion devices, improve the utilization efficiency. For these devices, the fuel cell and metal-air batteries are the two important forms, but the high price of precious metal catalysts hinders their popularization and application. As a consequence,developing the non-precious catalyst with high efficiency is a critical way to promote the practical application of them.In this thesis, the nanocarbons including carbon nanotubes and graphene were employed as based material to synthesize a series of composites with different components and structure; and the obtained non-precious materials showed well performance in ORR, OER and/or HER. Besides, the strategies to prepare well-performance carbon based composite could provide valuable reference for the studies in electrochemical catalysis. The thesis would be presented in the following four aspects:1. Bamboo-like nitrogen-doped carbon nanotubes with embedded cobalt nanoparticles (Co@NCNTs) was fabricated by the pyrolysis of Co2+ and dicyandiamide. Test results demonstrated that the optimized electrocatalyst showed well performance in ORR and OER. The major factors that influenced the performance were discussed and the nitrogen chemical state and metal element play important roles. Moreover, the catalyst showed good activity and stability in rechargeable zinc-air batteries, which indicated their potential applications.2. A novel bifunctional catalyst by coating CoOx nanoarrays with a porous nitrogen-doped carbon (NC) through the carbonation of a PVDF and dicyandiamide membrane was reported. The porous NC not only provides a conductive coating to benefit the charge transfer and retains the channels for electrolyte diffusion, but also greatly enhanced the electrochemical surface area, which endow the materials higher activity for both ORR and OER. When employed as air cathode in rechargeable zinc-air batteries, the electrode showed durable performance superior to Pt/C and IrO2/C, which demonstrated the potential of the electrodes and also the efficiency of the constructing strategy.3. Nickel-cobalt oxides supported on Co/N decorated graphene were prepared by introducing nickel in a zeolitic imidazolate framework-67(ZIF-67) as the precursor, which showed improved OER performance due to the as-derived NixCoyO4, and maintained the ORR performance of Co/N doped carbon at the same time. Meanwhile, graphene was utilized to further enhance the electrochemical surface area and charge transfer efficiency. The resulting composite showed good performance and well stability in ORR and OER, demonstrating the great potential of the composite in metal-air batteries.4. The organic molecule with C/N was introduced when the ZIF-67 template was pyrolysis under Ar atmosphere; a phosphorization process was subsequent conducted. The final product was consisted of Co, CoP and hierarchical carbon; in which the Co nanoparticles were encapsulated in carbon nanotubes and the CoP distributed on polyhedral carbon shell.The CNTs enhanced the conductivity and electrochemical surface area,resulting in better ORR, OER and HER performance than the samples without CNTs. |
