Synthesis Of Transition Metal-nitrogen Co-doped Carbon-Based Catalyst And Its Catalytic Activity For Oxygen Reduction

Fuel cells are considered to be the most promising energy conversion devices due to their high energy conversion efficiency.The oxygen reduction reaction?ORR?that occurs at the cathode of a fuel cell is an important part of a fuel cell,but because the reaction is so slow that an electrocatalyst is needed to catalyze it.Platinum-based precious metal materials are the most mature catalysts at present,but their high price,rare reserve,and sensitivity to methanol poisoning limit the development of commercialization.Therefore,the development of low-cost,high-efficiency and methanol-resistant non-precious metal catalyst materials is of great significance for the commercial application of fuel cells.This paper aims to develop a transition metal-nitrogen co-doped carbon-based catalyst material that is more efficient and stable than commercial Pt/C catalysts.The catalyst is prepared by simply pyrolyzing a mixture of a novel metal precursor,nitrogen source and conductive carbon black.The microstructure and internal structure of the catalyst materials were analyzed by means of SEM,HRTEM,XRD,XPS,Raman,BET,etc.Electrochemical testing techniques were used to study the catalytic properties of oxygen reduction,methanol resistance and stability.The main work is as follows:?1?In this paper,a low-cost and novel metal precursor?-nitroso-?-naphthol iron,nitrogen source urea and carrier conductive carbon black are used for heat treatment to prepare a highly efficient and stable Fe,N co-doped carbon-based catalyst?Fe/Fe₃C@C/N?,which solves the problems of high production cost and insufficient activity of the catalyst.A series of characterization results confirmed that the graphite layer-coated Fe/Fe₃C nanoparticles were supported on the nitrogen-doped carbon-based material.Due to the large number of active sites provided by this particular structure,the catalyst exhibits superior oxygen reduction catalytic performance,methanol resistance and stability in alkaline media over commercial Pt/C catalysts.It is worth noting that after nitrogen doping,the encapsulation structure in the Fe/Fe₃C@C/NC is more resistant to acid corrosion than that of Fe/Fe₃C@C/NC?undoped-nitrogen?,which is due to the co-bonding of Fe/Fe₃C and nitrogen in the encapsulation structure to provide additional protection.Thus,the catalyst also exhibits good oxygen reduction catalytic performance and excellent stability under acidic media.?2?In this paper,Cu,N co-doped carbon-based catalysts?Cu-N-KB?were prepared by heat treatment of?-nitroso-?-naphthol copper,melamine and conductive carbon black.The characterization results confirmed that Cu and N are uniformly distributed in the carbon support,in which copper exists in the form of crystalline copper particles and amorphous Cu-N_x,which effectively solves the agglomeration of the metal in the catalyst and the uneven structure and composition of the materials.The high specific surface area of the catalyst combined with the mesoporous structure ensures a large number of active sites and rapid mass transfer efficiency.The obtained catalyst exhibited superior oxygen reduction catalytic performance,methanol resistance and stability in a basic medium than a commercial Pt/C catalyst.The doping of copper is critical to the catalyst.After copper doping,not only the total nitrogen content of the catalyst is increased,but also the electrochemical impedance of the catalyst is lowered to improve the conduction efficiency and mass transfer efficiency of the electron.It is worth noting that the acid leaching of copper particles significantly reduces the performance of the catalyst.