Preparation Of Heteroatom-doped Carbon Based Materials And Their Electrocatalytic Performances

As a kind of clearn energy conversion device production facility,fuel cells can transform chemical energy to electrical energy and have attracted much attention due to their high specific energy density,high efficiency,and low pollution output.As one of the cleanest fuels,hydrogen has attracted worldwide attentions.Consequently,as the most efficient technology for hydrogen production,water electrolysis has become a research hotspot in the field of clean energy production.However,cathodic oxygen reduction reaction(ORR)has been a limit step for improving the whole efficiency of fuel cells due to its sluggish kinetics.Electrolysis of water is also limited by high overpotential of hygrogen evolution reaction(HER)and oxygen evolution reaction(OER)and the resulted high energy consumption.So,it is significant important to develop non-precious metal catalysts with low cost,high activity and high stability for ORR,HER and OER.Among various catalysts,heteroatom doped carbon materials have been considered as good candidates due to their high electron conductivity and fruitful active sites.This thesis aims at development of high efficient heteroatoms doped carbon materials based electrocatalysts for ORR,HER and OER,and the following three parts of work were carried out:(1)The N,P dual-doped hierarchically porous graphitic biocarbons were prepared via a simple pyrolysis method using biomass chitosan as C and N sources,triphenyl phosphine(P(Ph)3)as P source and Zn Cl2 as activating agent.The added amount of P(Ph)3 was optimized and the as-prepared samples were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and N2adsorption-desorption methods.The electrocatalytic activities of the as-prepared samples were evaluated for oxygen reduction reaction(ORR)in alkaline media.The results showed that the catalytic properties of N,P dual-doped samples were greatly enhanced compared with the phosphine free ones.The optimized catalyst with addition of 0.75 g P(Ph)3 exhibited nearly equivalent catalytic performances to the commercial Pt/C(20%)with respect to onset potential,halfwave potential and limit current density.The catalyst also exhibited superior long-term stability and methanol resistence than commercial Pt/C(20%).(2)N-doped carbon spheres were prepared using ionic liquid as carbon and nitrogen source by co-calcination the mixture of ionic liquid and silica spheres in N2 followed by etching with HF.The hollow/solid carbon spheres can be selectively obtained by using water/enthanol as solvent.The as-prepared samples were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS)and N2 adsorption-desorption methods.The as-prepared samples exhibited prominent performances as bifunctional electrocatalysts for oxygen reduction reaction(ORR)and hydrogen evolution reaction(HER).Especially,the hollow carbon spheres derived from 1-butyl-3-methylimidazolium chloride has shown superior and comparable catalytic activity to commercial Pt/C(20%)for ORR in alkaline and acid media,respectively.It also exhibited most high catalytic performance for HER in0.5M H2SO4 and 247 m V and 112 m V/dec for overpotential at 10 m A/cm2 and Tafel slope was obtained,respectively.Furthermore,the catalyst has shown much higher long-term stability and tolerance for methanol.(3)Nitrogen doped carbon wrapped Cox P catalysts were prepared by pyrolysis of the precursorformed by self-assembly of cobalt salt,terephthalic acid and PVP followed by phosphatization in the presence of sodium hypophosphite.The temperature for phosphatization was optimized and the catalysts were characterized by SEM,TEM,XRD,X-ray photoelectron spectroscopy(XPS)and N2adsorption-desorption methods.The electrocatalytic activity tests showed that the catalyst phosphated at 420 °C exhibited the highest catalytic activities for ORR and OER under alkaline condition and for HER under acidic condition.Besides,the catalyst has shown better stability and methanol resistence than commercial Pt/C(20%).