Study On Large-scale Preparation And Catalytic Performance Of Several Nitrogen-doped Porous Carbon Materials For Oxygen Reduction

The development of green clean energy is extremely urgent to deal with the increasingly serious energy crisis and environmental problems.In some alternative energy,fuel cell because it has many advantages,such as high power density,no pollution and low noise,is considered to be a very promising clean energy to replace the traditional fossil fuels.Oxygen reduction reaction(ORR)as an important process of fuel cells has received extensive attention for many researchers.However,its reaction rate is quite slow in the absence for effective catalysts,which impedes large-scale commercial application of fuel cells.At present,platinum-based materials as the most effective ORR catalysts have been recognized to accelerate the reaction rate for ORR.Unfortunately,scarce platinum resources and its high cost also hindered the commercial application for this metal.Therefore,finding non-precious metal or metal-free materials as ORR catalysts to replace the current Pt/C has become a hot research field.Using the rich resources,cheap raw materials and simplify the experimental operation for large-scale preparation of ORR catalysts by the reasonable design is the crux,although the researchers have made important progress for developing these materials.In this dissertation,we will focus on the large-scale synthesis and performance of a series of nitrogen-doped porous carbon materials based on rational use of cheap raw materials or natural wastes,different chemical reactions,and improving its catalytic performance for ORR in terms of current density,onset potential,half-wave potential,electrochemical stability and methanol tolerance.Four kinds of nitrogen-doped carbon materials,such as nitrogen-doped porous carbon particles derived from "black bread reaction",combustion approach synthesis of porous carbon foam and further derived the nitrogen-doped porous carbon material,nitrogen-doped nanoporous carbon and nitrogen-doped nanoporous carbon sheets derived from waste pomelo peel and bagasse were successfully prepared,respectively.Under the best preparation condition,the products have some useful features,and show excellent electrochemical performance.The main research contents and results of this dissertation are as follows:1.Fluffy carbon network were successfully prepared using low-cost sucrose and concentrated sulfuric acid as raw materials.The inspiration comes from the concentrated sulfuric acid carbonized sucrose in the high school textbooks."Black bread reaction" experiment principle is that the concentrated sulfuric acid has a strong dehydration properties,which could make H and O two elements in the sucrose removed in accordance with the molar ratio of 2:1 in the form of dehydration and carbon generated.The remaining concentrated sulfuric acid could react with carbon to produce carbon dioxide and sulfur dioxide,resulting in the formation of fluffy carbon network.This reaction is very quickly and suitable for large-scale synthesis of porous carbon.Finally,the precursor was heated in tube furnace(NH3 atmosphere)for obtaining the final product.Electrochemical tests show that the onset potential and current density(at 0.055 V,vs.RHE)of typical product(N-PCPs-800)are about 750 mV(vs.RHE)and 4.2 mA cm-2,exhibiting excellent electrochemical stability and methanol tolerance in alkaline media.N-PCPs-800 also has excellent catalytic performance for ORR in acidic media,which may be attributed to the high BET specific surface area of product generated by "black bread reaction" and effective nitrogen-doping by high temperature heat treatment in NH3 atmosphere.2.The experiment of "Pharaoh’s snake" is a very famous expansion reaction,and often used as an interesting experiment to inspire the enthusiasm in chemistry for people.Inspired by this,we successfully prepared the porous carbon foam by meticulously reasonable design about the similar expansion reaction,namely lit the mixture of ethanol,sodium bicarbonate and sucrose.The ethanol burning can make sucrose carbonized as well as the sodium bicarbonate thermally decomposed to produce a mass of carbon dioxide,which result in the formation of porous carbon foam.This reaction is simple and cheap,suitable for mass production.We found that different temperatures have great influence on the performance of the products.Electrochemical performance tests show that typical product(NCM1000)presents the best catalytic activity for ORR in terms of more positive onset potential in both alkaline and acidic media,is about 10 mV(vs.Hg/HgO)and 390 mV(vs.Ag/AgCl),which may be due to the "combustion reaction" to produce this unique foam structure with high BET specific surface area,as well as a large number of active sites created by nitrogen-doping.In addition,this novel combustion method is expected to be applied for other materials in the field of synthesis.3.Nature can provide a lot of biomass resources to satisfy people’s various demand.However,if we do not have the ability to deal with the biomass wastes generated in the production and living,which will pollute our environment.Therefore,the reasonable utilization of these environmental wastes as raw materials for the synthesis of valuable products will be a good choice.Based on this,we successfully prepared the nitrogen-doped nanoporous carbon by hydrothermal and post-processing method using the recycling pomelo peel as the raw material.The typical product(N-PC-1000)prepared under the best experimental conditions showed better catalytic activity for ORR in terms of more positive onset potential and higher current density,the values are about 10 mV(vs.Hg/HgO)and 4.60 mA cm-2(-0.8 V,vs.Hg/HgO),respectively.After 2000 continuous cycles,N-PC-1000 displayed weak loss in activity,presenting excellent electrochemical stability.The test results also exhibited that N-PC-1000 has excellent tolerance to methanol poisoning effects.Therefore,N-PC-1000 may be a promising catalyst for ORR.In addition,the use of environmental waste to prepare valuable energy materials not only reflects the idea of turning waste into treasure,but also plays a role in purifying environment with great significance.4.The structure and performance of products can be easily affected by different raw materials,synthesis methods and conditions.It is very important to simplify the experiment procedure and decrease cost for the quantity production of products.We successfully synthesized nitrogen-doped nanoporous carbon sheets by one-step heat treatment method using the bagasse as precursor based on the above two principles.The results show that the product is mainly composed of amorphous carbon with nitrogen-doping and possesses high BET specific surface area(up to 1284 m2 g-1).More importantly,the onset potential,half-wave potential and current density of typical product(N-NCS-1000)is about 0.010 V,-0.100 V and 5.21 mA cm-2(-0.8 V,vs.Hg/HgO)in alkaline media,and about 0.430 V,0.250 V,4.09 mA cm-2(-0.2 V,vs.Ag/AgCl)in acidic media,respectively,suggesting that N-NCS-1000 has excellent catalytic performance for ORR.In addition,the one-step synthesis method for nitrogen-doped nanoporous carbon sheets is a very simple,easier to scale up and environmental friendly.