High Performance Carbon Oxygen Reduction Catalysts Derived From Ionic Liquid

Oxygen reduction reaction(ORR)plays important roles in many energy conversion devices and the ORR process directly determines the efficiency of these devices.Since the kinetics of ORR is sluggish,highly efficient ORR catalyst are usually required in practical applications of these devices.Precious metal such as Pt is widely used for efficient catalysis of ORR.However,these catalysts suffer from their high cost and poor durability,and are therefore not suitable for large-scale application.Heteroatom doped carbon catalysts are featured by their low cost,excellent stability and high ORR activity.Owing to these characteristics,they were considered to be promising alternatives to precious metal based ORR catalysts.The type and concentration of the heteroatom in the doped carbon catalysts significantly influences its ORR catalyst.In this thesis,ionic liquid,which has a low melting point,is utilized as precursor to generate a series of carbon catalysts doped with heteroatoms.The structure,composition and morphology of these catalysts are systematically investigated.The catalytic activity and electrochemical stability of these catalysts are also studied.In addition,the factors affecting the activity of the catalysts are surveyed as well.The detailed content of the thesis can be summarized as follows:1.A new ionic liquid containing N and S was prepared and used as precursor for carbonization synthesis of N and S co-doped carbon materials.To introduce three-dimensional ordered macroporosity into the product,silica templates were used.The results show that the carbon catalyst synthesized at 1100°C(3DOM NS-C-1100)exhibited enhanced ORR performance compared to commercial 20% Pt/C catalyst in alkaline condition.Durability tests demonstrate that 3DOM NS-C-1100 possess excellent stability in alkaline condition and good tolerance to methanol poisoning.SEM,TEM,Raman tests indicate that the excellent ORR performance of 3DOM NS-C-1100 is originated from its well-ordered hierarchical pore structure,which greatly enhances the mass transfer in the catalytic process.In addition,the high graphitization degree and high graphite N content in 3DOM NS-C-1100 also partly accounts for its high activity.2.A new ionic liquid,containing Fe and N,is synthesized.A highly efficient Fe and N co-doped ORR catalyst is obtained by direct carbonization of the ionic liquid without using any template.Characterization results reveal that the catalyst obtained at 800°C(Fe-N-C-800)exhibited comparable ORR performance,while much higher OER activity than commercial Pt/C catalyst.Superior durability of Fe-N-C-800 is also show.A large Fe and N content and high graphitization degree of Fe-N-C is demonstrated to be responsible for its excellent catalytic activity.