The Preparation Of Nitrogen Doped Carbons And Theirphotovoltaic Performances As Counter Electrode Materials

Due to the enriched N doping active sites,well-developed porous texture with high specific surface areas and high conductivity,N-doped porous carbons are promising electrode materials in dye-sensitized solar cells(DSSCs)and supercapacitors.So the synthesis of N-doped porous carbons from proper C and N sources and investigate the performances in DSSCs and supercapacitors are meaningful for the development of carbon-based energy materials.This thesis involves the synthesis of a series of N-doped porous carbons and graphenes,as well as the resultant electrochemical performances in DSSCs and supercapacitors.The main contents of the work are summarized as follows:(1)Activated N-doped porous carbons(a-NCs)were synthesized by pyrolysis and alkali activation of graphene incorporated melamine formaldehyde resin(MF).Under optimal activation temperature of 700℃,the afforded sample,labeled as a-NC700,possesses a specific surface area of 1302 m2 g-1,a N fraction of 4.5% and a moderate graphitization degree.When used as a supercapacitor electrode,a-NC700 offers a high specific capacitance of 296 F g-1 at a current density of 1 A g-1,an acceptable rate capability and a high cycling stability in 1 M H2SO4 electrolyte.The supercapacitor based on a-NC700 delivered energy densities of 5.0~3.5 Wh kg-1 under power densities of 83~1609 W kg-1.Moreover,a-NC700 also demonstrated high electrocatalytic activity for I3-reduction.When employed as a counter electrode(CE)of DSSCs,a power conversion efficiency(PCE)of 6.91% was achieved,which is comparable to that of the Pt CE based counterpart(7.10%),highlightingthe potential as low-cost while efficient catalytic CE material.(2)Nitrogen doped graphenes(NGs)were synthesized by pyrolysis of graphene polypyrrole composites(G-PPys),the as-preparedNGs demonstrated mesoporous texture with large specific surface areas,high N doping levels with homogeneous distribution,superiorwettabilities and moderate graphitization phase,therefore are capable of offeringhigh electroactive surface areas,high electrode/electrolyte compatibility and well conductivities.When used as CEs of DSSCs,a PCE of 6.89% was yielded,which is comparable to that of Pt CE(7.08 %).Meanwhile,superior photovoltaic stabilities and reliabilities could also be achieved.(3)S,N co-doped porous carbonsembedded with CoxNiy alloy(CoxNiy@NSCs)were synthesized by high temperature pyrolysis of dry gel,which was fabricatedusing starch and gelatin as carbon,nitrogenand sulfur sources whereas metal nitrate as alloy precursors.The afforded composites are featured by rapid charges and electrolyte ions transfer rates,high conductivities and electrocatalytic activity for I3-reduction,moderate N,S doping levels and graphitization degree,mesopores texture and superhydrophilic surface.When employed as a CE of DSSCs,a PCE of 7.58% was finally achieved,which is superior to that of the Pt CE based counterpart(7.10%).