Preparation And Electrochemical Application Of High Purity Carbon

Since the industrial revolution in the 19th century,in order to maintain social economic development and rapid population growth,non-renewable energy sources（coal,crude oil,oil shale,natural gas,etc.）as the main energy sources have been consumed in large quantities.However,the storage of non-renewable energy is limited,and excessive exploitation and utilization will seriously pollute the environment and harm the survival and development of human beings.Therefore,the research and development of efficient,clean and renewable energy is an effective way to solve the energy crisis and achieve sustainable development.Hydrogen is considered as one of the most promising renewable energy sources because of its clean and recyclable properties.Among many hydrogen production methods,water electrolysis is regarded as the most promising technology for high purity hydrogen production due to its advantages of cheap raw material and simple preparation equipments.However,oxygen evolution reaction（OER）,as a semi-reaction of water electrolysis,has a slow reaction kinetics,which hinders the improvement of hydrogen production efficiency from water electrolysis.In addition,although precious metals such as iridium and ruthenium have high OER electrocatalytic activity,their high price and low content in the earth’s crust hinder their large-scale commercial application in OER electrocatalysts.Carbon materials（such as carbon nanotubes,graphene,carbon nanofibers,etc.）have the advantages of high specific surface area,high electrical conductivity,high mechanical elasticity and low density,and can have high OER electrocatalytic activity after heteroatom（such as nitrogen,sulfur and boron）doping.Therefore,they are widely used in the preparation of OER electrochemical catalysts.In this thesis,a simple method was used to prepare free-standing carbon nanofibers networks.Then,the carbon nanofiber networks were further annealed in ammonia to obtain nitrogen-doped carbon nanofibers,and their OER electrocatalytic performance was studied.The main research contents and results are as follows:1)Firstly,we fabricated free-standing carbon nanofiber networks,by loading copper nitrates on Al foils,performing chemical vapor deposition（to grow carbon nanofiber networks）,and finally etching the Al foils using sodium hydroxide aqueous solution.The free-standing carbon nanofiber networks were porous,hydrophobic and highly flexible.2)The free-standing carbon nanofiber networks could absorb various oils and organic solvents,and their absorption capacity was 70-250 times their own weight.Furthermore,after removing the absorbed oils and organic solvents via burning or distillation,the free-standing carbon nanofiber networks exhibited superior recyclability.3)After further annealing the free-standing carbon nanofiber networks in ammonia,the obtained nitrogen doped carbon nanofibers（NCNFs）demonstrated high electrocatalytic activities and super stability for OER.Their overpotential at current density of 10 m A cm^-2was 450 m V,and their Tafel slope was 90 m V dec^-1.In addition,OER activity of the NCNFs was remarkably higher than that of the CNFs,confirming the vital role of nitrogen doping in the improvement of OER activity of the CNFs.