Study of Synthesis and Performance of Carbon-based Electrocatalytic Materials for Triiodide Reduction Reaction in the Counter Electrode of Dye-Sensitized Solar Cells

Author:Jing Hong Yu

Supervisor:an yong lin shi yan tao hao ce


Degree Year:2019





Dye-sensitized solar cells(DSSCs)have broad prospects in application due to their high theoretical efficiency,simple process,low cost,and environmental friendliness.As a key component of DSSCs,the electrocatalytic process on the surface of the counter electrode(CE)has a critical impact on device performance.Conventional platinum(Pt)based CEs are expensive and susceptible to iodine corrosion in electrolytes.Therefore,designing non-Pt electrocatalytic materials with low-cost and outstanding performance has important practical significance and research value.Carbon materials are readily available and inexpensive,rich in structure,and diverse in morphology.To modulate the surface/interface structure and physicochemical properties of carbonaceous materials at different scales(from the atomici/molecular scale to nanoscale)l,construct a highly active center for electrocatalytic reaction on CE surface,and develop a green controllable synthesis method for carbon materials are important scientific issues facing the field of DSSCs today.Based on the most conmmon triiodide reduction reaction(IRR)occurring on the CE surface,this paper carried out research on IRR catalytic active center construction and material synthesis from the scale of atoms/molecules and nanometers.Meanwhile,we also systematically explored the structure-activity relationship between the elemental composition,microstructure structure,surface morphology of carbon-based CE material and IRR catalytic performance.Firstly,amino-functionalized graphene was prepared via a green and mild approach and successfully developed into a CE material in DSSCs.Studies have confirmed that ozone oxidation of graphite oxide(GO)in advance can significantly increase the number of oxygen-containing functional groups,facilitate the dispersion of GO in the aqueous phase.More importantly,the oxygen-containing functional groups can provide more anination sites,excess oxygen-containing functional groups can be removed by photoreduction(the resulting sample was labeled as AGO-hv).Electrochemical characterizations confirmed that AGO-hv has excellent catalytic properties for IRR,the DSSCs obtained a power conversion efficiency(PCE)of 7.51%,which was close to the Pt-based CE(7.79%)under the same conditions.In addition,the mechanism and regularity of the effects of different nitrogen doping types on the IRR electrocatalytic properties of graphene were studied using density functional theory(DFT)calculations,indicating that AGO-hv has a lower ionization energy,and the binding energy of the pyridine nitrogen on the AGO-hv to the I atom is moderate,which is more favorable for the electrocatalytic reaction.Secondly,a graphitized carbon matrix material containing the onion-like structure and amorphous SiO2 was prepared via high-temperature pyrolysis using natural brown coal as a self-sacrificing template.Meanwhile,the effects of annealing temperature and active components on the structural composition and electrocatalytic properties of coal-derived catalysts were studied.In this material,the nanostructure formed by the Ca-based particle coated with graphitized carbon layers has good chemical stability,when etched with hydrochloric acid,the Ca species contained in the onion-like carbon structure is hardly remoxved.In addition,the experi:mental results confirmed that S1O2 in the material has a promoting effect on IRR electrocatalytic performance.Using the prepared material as the CE of DSSC,the device achieved a PCE of 9.03%,which was significantly higher than Pt counterpart(8.24%).Thirdly,biomass carbon materials with high specific surface area,good porosity,and rich active components were prepared by activation and pyrolysis using pomelo peel as a carbon source.Studies have shown that as activation and templating agent in the pyrolysis process,zinc chloride(ZnCl2)can mainly increase the specific surface area and form an excellent pore structure,which is beneficial to increase the catalytic active sites and promote mass transfer.Meanwhile,this biomass-derived carbon is rich in heteroatoms,which helps to cause charge distribution on the surface of the carbon material to form a catalytically active center.The electrochemical characterization results confirmed that the carbon-based CE has an excellent electrocatalytic performance for IRR.The DSSC device yielded a PCE of 8.29%,which was comparable to the device performance using Pt-based CE(8.24%).Fourthly,a novel high-efficiency MOFs-derived carbon-based single-atom catalytic material was constructed.By taking advantage of ZIF-67 as a precursor,a supported catalytic material with atomically dispersed Co can be obtained by increasing the specific surface area of the carbon material and controlling the strong metal-support interactions.The advantages of using this strategy to prepare carbon-based single-atom catalyst are as follows:ZIF-67 has abundant metal coordination sites and ideal confinement space,its ligands can spatially separate metal nodes,making metal atom migration restricted,the self-agglomeration behavior betiween metal atoms is avoided to the utmost extent,thus the metal atom can be supported on the carbon matrix in a single atomic level.The research results indicated that the material has an excellent electrocatalytic activity for IRR.The corresponding assembled DSSC device achieved a PCE of 7.89%,which was better than Pt counterpart(7.76%).