Electrochemical Performance Of Heteroatom Doped Carbon Based For Oxygen Electrode Of Bifunctional Catalysts

Due to the climate change and the exhaustion of fossil fuel,the development ofsustainable energy is of vital importance for human beings.Many advancedtechnologies for clean energy conversion,such as fuel cells,water electrolysis,metal-airbatteries,become the subject of both extensive fundamental and utilitarian studies.Oxygen electrode electrocatalysts are among the main bottlenecks for the commercialization of fuel cells and water electrolysis technologies.At present,Pt and its alloys are still the irreplaceable electrocatalysts for oxygen reduction reaction(ORR)at the cathodes of the fuel cells,and RuO2 and Ir O2 are the best electrocatalysts for oxygen evolution reaction(OER)at the anodes of water electrolysis devices.At present,the best known catalysts are still precious metals,such as Pt-,Ru-,and Ir-based catalysts,but the high cost and scarcity prohibits their large-scale applications for the above mentioned technologies.Therefore,the development of oxygen electrodecatalysts with high activity,long-term stability,affordable cost and selectivity isbeneficial for the commercialization of clean energy facilities.In this regard,a series ofheteroatom-doped oxygen electrode catalysts which exhibit low cost,highcatalytic activity,as well as long durability were controlled synthesizedIn this thesis,we have prepared a series of doped carbon catalyst with melamine,dopamine and some nitrogen rich materials as precursors.And the catalyst structure and performance ofN-doped carbon metal-free catalyst,the catalyst structure and performance of N-and Co-doped carbon catalyst,the probable roles of Co and melamine to N-and Co-dopedcarbon catalyst,and the effect of late transition metals Co on the structureand performance of the doped carbon catalysts have been intensively investigated in bothexperimental and theoretical aspects.Firstly,an N-doped carbon metal-free catalyst is prepared by the pyrolysis ofthe hybrid precursor of urea and Thiourea in nitrogen atmosphere.The effects of pyrolysingtemperature,heat treatment method on the performance are investigated.And the catalysts arecharacterized by means of XRD,TEM,XPSand rotating disk electrode.The resultsshow that 800?is the optimal pyrolysis temperature.Andthe oxygen reduction on the catalyst follows a four-electron transfer mechanism.The N/S-C modified electrode shows a OER onset overpotential of only 231 mV which is close to the IrO2,when current density 10 mA/cm~2 Its potential is 1.49,Its ORR onset potential of 0.86 V,the limiting diffusion current density is about-5.83mA/cm~2.In methanol mixed solution,long durability is good.Secondly,High temperature pyrolysis of sodium alginate,melamine,six hydrated cobalt chloride complex to prepare the transition metal cobalt nitrogen doped carbon based catalyst,denoted as Co/N-C.The temperature and load were investigated and materials are characterized by XRD,SEM,BET,XPS,the experimental results show that the cobalt doped carbon based materials in nitrogen doped its good catalytic activity with high stability,OER onset overpotential of 190 mv,when the potential is 1.55 V when the current density is 30.2mA/cm~2,ORR onset overpotential of 0.88 V,the limiting diffusion current density of-6.01mA/cm~2 by 7h test the current density only decreased about 6%.Thirdly,The dopamine solution,mercaptan and configuration of the sodium alginate solution was prepared by mixing the nitrogen doped carbon and sulfur cobalt based catalyst denoted as N/S/Co-CAS,the formation of cobalt containing hydrogel after freeze drying after the formation of the aerogel,then calcined in a nitrogen atmosphere to form high carbon aerogels,N and S make it more active sites exposed,when added to the catalytic activity of transition metal cobalt can be improved,OER onset overpotential of 220 mv,when the current density is equal to 10mA/cm~2,the potential is 1.44 V,ORR onset overpotential of 0.89 V,the limiting diffusion current density is-5.9mA/cm~2.