Oxidation Treatment And Catalytic Performance For Oxygen Reduction Reaction Of Boron-doped Amorphous Carbon Thin Films

The shortage of natural resources and the increase of air pollution have made people's demand for new energy sources more and more urgent.Fuel cells have received widespread attention in countries around the world due to their high energy conversion rate,environmental friendliness,simple equipment and convenient operation.From the introduction of the principle of fuel cell to today,it has been more than 200 years.However,it has not been commercialized on a large scale.The reason is that the fuel cell's power generation cost is too high,and the economic benefits are far less than the traditional thermal power generation.Among them,the catalyst cost accounts for one-third of the total cost.The fuel cell catalysts are divided into a cathode and an anode.The cathode catalyst is used in an amount five times that of the anode,and is also a controlling factor for the power generation efficiency of the fuel cell.Up to now,the commercial cathode catalyst is a platinum-based material.As a noble metal,platinum is not only costly,but also has poor stability and short service life.Therefore,finding a more suitable catalyst is the key to solve the fuel cell problem.Promising catalyst materials(boron-doped amorphous carbon films)were prepared by hot filament chemical vapor deposition,and the porosity and specific surface area of the carbon film were increased by air oxidation treatments.The effects of air oxidation process parameters on the physical structure and electrocatalytic properties of boron-doped amorphous carbon films were studied.The catalytic performance of boron-doped amorphous carbon films after air oxidation treatment was compared with commercial Pt/C catalysts.The main conclusions of this subject are as follows:(1)Carbon films prepared by hot filament chemical vapor deposition are formed with the cauliflower-like cytoplasm,and the surface structure is relatively complete.From the TEM and XRD analyses,the carbon species in the films are amorphous.The FT-IR and XPS measurements show that boron atoms have formed B-C with carbon and are incorporated into the carbon films in the form of valence bonds.(2)The porosity and specific surface area of the boron-doped amorphous carbon films can be increased by air oxidation treatments.When the boron-doped amorphous carbon films are subjected to air oxidation,cracks and holes appear on the surface of the films.It is known that the occurrence of gaps and pores in the cauliflower-like cytoplasm is related to air oxidation parameters,and the edge of the cytoplasm is more easily oxidized due to the presence of defects,eventually forming a porous boron-doped amorphous carbon films.Moreover,when the oxidation parameters are different,the porosity of the films exhibits a certain regularity.Oxidizing at 25-470 ? for 1 h,the porosity of the films increases first and then decreases with increasing oxidation temperature,reaching maximum at 450 ?;oxidizing at 450 ? for 15-75 min,the porosity of the film increases first and then decreases with increasing oxidation time and reaches a maximum at 45 minutes.Therefore,the optimum air oxidation parameter is oxidation at 450 ? for about 45 minutes.(3)In the electrochemical tests,the results of the cyclic and linear sweep voltammetry measurements show that the catalytic performance of boron-doped amorphous carbon catalysts has a certain relationship with the porosity.When the film was oxidized at 450 ? for 45 min,the catalytic performance was optimal and the oxygen reduction potential of the catalyst was at-0.286 V vs.Ag/AgCl,and the number of transferred electrons n was 3.24.This catalytic performance still has a certain gap with commercial platinum-based catalysts.(4)The boron-doped amorphous carbon catalysts exhibited excellent performance in the methanol resistance and stability tests.Compared with the commercial Pt/C catalysts,the boron-doped amorphous carbon catalysts have obvious advantages in methanol resistance,and the catalytic performance does not decrease significantly after adding methanol for 1200 s.Moreover,the boron-doped amorphous carbon catalysts only decreased by 10% after working for 30,000 s,which was much lower than 45% of the Pt/C catalyst,and showed good catalytic stability.