Synthesize Of N,Fe Doped Carbon Based Material With Excellent Performance Towards Oxygen Reduction Reaction

In recent years,with the fast development of our society,the demand for traditional fossil energy are increase dramatically,which leads to two rigorous and unprecedented conundrums are before human beings that need to be addressed.On the one hand,fossil energy have been wide excavated and used for centuries since the invention of the steam engine,and now the limited and non-renewable source are reach to the edge of run out.That is to say,the fossil energy can no longer long term support the production and living needs of mankind.On the other hand,with the excessive use of fossil fuels,the living environment human being now is face to many serious problems,for instance,haze,acid rain and ozone hole.Therefore,it is an urgent need to develop an environment-friendly energy supply with high energy density and long term stability to replace the traditional fossil energy.Fuel cells are one of the most promising electrochemical energy conversion and storage devices by virtue of their low even no emissions and high energy conversion efficiency.And in Fuel cells,the oxygen reduction reaction in cathode plays a crucial role in the whole reaction.However,the kinetics of oxygen reduction reaction of fuel cell is very sluggish.As a consequence,the oxygen reduction reaction is often happened with the introduction of catalyst.Come so far,the main catalyst which used in fuel cells is still depending on platinum(Pt)based materials,the high loading of platinum in cathode and the high priced of Pt have become the inhibited factor for the commercial development of fuel cells.Therefore,it is a key element to develop a new type of catalyst with high efficiency and low cost to replace the traditional Pt-based catalyst so that promotes the commercialization of fuel cells.In this principle,a large and intensive research effort is devote to design and fabricate new catalyst.So far,carbon based materials and transition metal based materials have attracted much attention in the field of oxygen reduction reaction catalysts because of their low cost and good tolerance to methanol poisoning effects,which were considered to scalable materials to replace Pt.In this paper,we scientifically investigate the latest researches about the design route,preparation method and catalytic performance of carbon based and transition metal based materials in home and overseas.And on this basis,the carbon based and transition metal based catalysts toward oxygen reduction reaction were prepared by using a simple and efficient method.Varieties of test instruments have been carried out to exhibit the structural,morphologies,physical and chemical properties of these catalysts.And electrochemical measurements toward oxygen reduction were also studied to estimate the related catalytic properties of the prepared carbon based and transition metal based catalysts.The main exploits of this thesis can be summarized as follows:1.A new and simple strategy was demonstrated to prepare porous nanosheets composites(labled as N-BPDC-H3PO4)by reusing the waste banana peel as biomass derived carbon.The banana peel was mixed with the aqueous solution contains H3PO4 and transfer into an autoclave for hydrothermal processing.After freeze-drying,the sample was carbonized in the tube furnace under the atmosphere of ammonia.The typical product(N-BPDC-H3PO4-1000)has a content of 2.94 at.%nitrogen,and the specific surface area is as large as 1401 m~2/g.When N-BPDC-H3PO4-1000 is used as a catalyst for the oxygen reduction reaction,the RDE results show that the limiting diffusion current density of N-BPDC-H3PO4-1000 is 5.30 mA/cm~2,which is very close to the Pt/C(5.52 mA/cm~2).Interestingly,when the potential(vs.Hg/HgO)is between-0.591 V and-0.481 V,the diffusion current density of N-BPDC-H3PO4-1000 is even higher than that of Pt/C.More importantly,N-BPDC-H3PO4-1000 shows excellent tolerance to methanol poisoning effects and long term cycling stability both in alkaline medium and in acidic medium.Furthermore,this work demonstrates a good example for turning discarded rubbish into valuable functional products and addresses the disposal issue of waste biomass simultaneously for environment clean.2.We report a novel and simple method to prepare nitrogen(N)doped hierarchical porous carbon(HPC)/reduced graphene oxide(RGO)composites by reusing waste biomass(pomelo peel)and coupled with graphene oxide(GO).This method is low-cost and environmentally friendly for without using any acid or alkali activator in the preparation.The typical sample(N-HPC/RGO-1)has a 5.96 at.%content of nitrogen with a larger BET surface area(1194 m~2/g).The RDE tests show that N-HPC/RGO-1 exhibits not only a relatively positive onset potential and high current density,but also considerable methanol tolerance and long term durability in alkaline media as well as in acidic media.The electron transfer number is close to 4,which means that it is mostly via a four electron pathway toward oxygen reduction reaction.The excellent catalytic performance of N-HPC/RGO-1 is due to the synergistic effect of the inherent interwoven network structure of HPC,the good electrical conductivity of RGO,and the heteroatom doping for the composite.3.Melamine and ferrocene were used as raw materials,which act as carbon source,nitrogen source and iron source.The raw materials were dispersed into ethanol solution under the magnetic stirring,and after the solvent evaporated under a mild heating environment,the powders were carbonized in two-step to synthesize self-doped carbon nanotube composites(labled as Fe2.5C/N-CNT)with different content of N and Fe.Fe2.5C nanoparticles which protected by the graphitic carbon layers in the composites are effective active sites for the oxygen reduction reaction and can keep chemically stable both in acids or alkaline medium,which leading to a long term and effective catalytic performance toward oxygen reduction reaction.The electrochemical measurement results demonstrated that Fe2.5C/N-CNT-3 with the content of 8.28%nitrogen and 1.29%iron show the best catalytic performance toward oxygen reduction reaction,and the limiting diffusion current density can reach 6.69 mA/cm~2.Excitingly,after 30000 cycles accelerated durability test,the catalytic performance of Fe2.5C/N-CNT-3 toward oxygen reduction reaction only show 6%degradation,suggesting the excellent long term stability of the Fe2.5C/N-CNT-30 catalyst.