|Other Abstract||Fuel cells are considered as one of the most promising energy and power systems of the 21st century. However, the slow reaction rate and high overpotential of the oxygen reduction reaction on cathode are the main factors to impede the energy conversion efficiency in fuel cells. Presently, the platinum group metals are the most popular catalysts for oxygen reduction reaction, but the resources are very scarce and expensive. Thus, researchers have adjust their interests to the abundant transition metal resources. Nanocomposite catalysts could be obtained by combining the transition metal/metal oxides with porous carbon materials which have excellent electron transport properties, and they have drawn a lot of attention because they can accelerate the oxygen reduction reaction dramatically. In this thesis, we have prepared nitrogen-doped mesoporous carbon and the related nanocomposites containing cobalt-cobalt oxides particles through one-pot method, followed by characterization and analysis of their morphology, physical and chemical properties. Then, their electrocatalytic performances for oxygen reduction reaction have been studied.
Firstly, in aqueous solution, with 3-aminophenol as carbon and nitrogen sources, we chose the triblock copolymer F127 as a template, formaldehyde slowly generated from the decomposition of hexamethylenetetramine, reacted with 3-aminophenol to form aminated polymer under the catalyst of ammonia. Nitrogen-doped mesoporous carbon (NMC) was obtained after the calcination of the aminated polymer. After treating at 600 °C, the material containing 9.1 wt % nitrogen content, exhibits a specific surface area of 410.8 m2 g-1, a total pore volume of 0.297 cm3 g-1. This material tended to catalyze the oxygen reduction reaction mainly in a two-electron reaction pathway, and the onset potential was about -0.25 V in oxygen-saturated 0.1 M KOH with a scan rate of 10 mV s-1 and a rotational speed of 1600 rpm.
Secondly, Co(NO3)2·6H2O was introduced to the above one-pot reaction system. The nitrogen-doped mesoporous carbon supported cobalt-cobalt oxide nanocomposites (Co-CoOx/NMC) was obtained after calcination. It was found that the mesoporous structure was maintained. The sample calcinated at 600 °C showed a specific surface area of 423.7 m2 g-1 and a total pore volume of 0.314 cm3 g-1. In the composite system, cobalt presented in the forms of Co0、Co2+ and Co3+, and the cobalt-based particles (Co-CoOx) with the size of 6-20 nm, were well distributed in the nitrogen-doped mesoporous carbon matrix. This material tended to catalyze the oxygen reduction reaction mainly in a four-electron reaction pathway, and performed much better with the increasing amount of the cobalt into the reaction system. The onset potential was around -0.11 V in oxygen-saturated 0.1 M KOH with a scan rate of 10 mV s-1 and a rotational speed of 1600 rpm.
In this thesis, using 3-aminophenol as the precursor, the amino groups in the obtained polymers could interacts with the cobalt precursor, resulting in the uniform dispersion of the cobalt-cobalt oxide particles in the composites. The study showed that the introduction of cobalt species into the nitrogen-doped mesoporous carbon matrix could dramatically improve the electrocatalytic performances of oxygen reduction reaction, with increased current density and decreased overpotential.|