Synthesis Of Metal-free Se/C Catalyst And Its Performance For Oxygen Reduction Reaction

In today's environment pollution and energy crisis,foel cells have attracted much attention because of their environmental friendliness and high energy conversion rate In the fuel cell system,the oxygen reduction reaction occurring in the cathode is the most critical factor that restricts the performance of the fuel cell.At present,the most suitable material for cathodic oxygen reduction catalyst is still platinum-based catalyst However,the high price of platinum,the low storage capacity of the earth and the'vulnerability to methanol poisoning have limited the large-scale application,which has hindered the commercialization of fuel cells.Therefore,it is important to find a cheap and widely sourced oxygen reduction catalyst to replace platinum for the development of fuel cells.Among many non-noble metal catalysts,metal-free heteroatom-doped carbon materials have attracted more and more attention.However,most of the carbon-based catalysts have good oxygen reduction activity and stability under alkaline conditions.Under acidic conditions,the stability of materials is very poor and the two-electron reaction pathway is mostly carried out during the oxygen reduction process,resulting in the production of a large number of intermediate products,hydrogen peroxide.This not only reduces the efficiency of oxygen reduction,but also destroys the catalyst seriously by the free radicals produced by the decomposition of hydrogen peroxide,resulting in poor stability.Glutathione peroxidase in organisms can decompose hydrogen peroxide very efficiently,and its active center is selenium atom.Inspired by this,a new type of non-metallic catalyst,Se/C,was prepared by pyrolysis.It can reduce oxygen to water through four electron processes.The main results are as follows:(1)Se/C oxygen reduction catalyst was synthesized from selenium powder and carbon black by ball milling and high temperature heat treatment.Under acidic conditions,although the activity and stability of Se/C catalyst are not high,the yield of hydrogen peroxide is very low.The yield of hydrogen peroxide measured at 0.5 V(vs.RHE)is only 0.039%,which is much lower than that of commercial platinum carbon(2.6%)(2)The theoretical calculation shows that the ultra-low hydrogen peroxide yield of Se/C catalyst originates from the O-O bond breaking of*OOH,the intermediate of oxygen reduction,after the Se atom doped with carbon,which makes it impossible to desorb to produce hydrogen peroxide.Reduction of graphene oxide(RGO)by Se vapor treatment showed that carbon carriers with graphene structure were more conducive to the formation of Se/C active sites.(3)The effects of different carbon carriers on the synthesis of Se/C catalysts were investigated.It was found that KJ-600 carbon black with large specific surface area,many defect sites and strong chemical reaction activity was the most suitable carbon carrier,and the Se/C catalyst prepared had the best activity.In this paper,a new type of non-metallic Se/C catalyst for oxygen reduction was prepared by heat treatment of selenium powder and carbon materials.It showed high selectivity of four-electron reaction pathway in the process of oxygen reduction,which provided a reference for the preparation of non-noble metal catalysts instead of noble metal platinum-based catalysts in the future.