Preparation And Property Of Nitrogen-doped Porous Carbon Based Counter Electrode For Dye-sensitized Solar Cells

State-of-the-art dye-sensitized solar cells(DSSCs)have drawn wide attention owing to their low cost,simple fabrication processes,high power conversion efficiencies and environmental friendly characteristics.In a typical DSSC device,the counter electrode(CE)plays an irreplaceable role in transferring electrons to triiodide(I3-)through external circuit and catalyzing the reduction of the redox couple.The structure and properities of CEs are main factors that affect the performance of DSSCs.So far,platinum(Pt)is the most extensively studied counter electrode for DSSCs.However,the massive utilization of Pt is restricted by its high cost and inferior stability.Therefore,carbon materials are expected to replace noble metal Pt as a new generation of electrode materials because of good electrical conductivity,low price,excellent stability,their easily changing surface chemical properties and pore structure.However,the lower electrocatalytic activity limits the application of carbon materials in DSSCs.How to design the structure and chemical composition,improve the electrocatalytic activity of carbon materials is the key to CEs.Effective measure should be taken to improve electrocatalytic activity of the carbon materials.High added value utilization of coal resources is the inevitable choice for the sustainable energy development in China.Coal tar pitch has the advantages of abundant reserves,low price and high carbon residue rate.The main work of this thesis is to prepare nitrogen doped porous carbon materials using coal tar pitch and synthetic pitch as carbon precursor,and to study the electrocatalytic performance of counter electrode for DSSCs.The main results of this paper are as follows:Coal pitch based nitrogen-doped porous carbon material(NPC)was prepared using coal tar pitch as carbon source,melamine as nitrogen source and MgO as hard template.The successful introduction of nitrogen species improve the electrocatalytic activity of carbon materials,the high aromaticity of coal tar pitch can improve the conductivity of carbon materials.In the process of preparation,pre-oxidation operation plays an important role in increasing the nitrogen content of NPC.When the carbonization temperature is 800 oC and the ratio of raw material is 6:1:2,the nitrogen content of NPC is 4.29 wt.%,the specific surface area can reach up to 651 m2 g-1,the electrocatalytic performance of the material is the best and photoelectric conversion efficiency of 8.19% can be achieved.Nitrogen-doped 3D hollow porous graphene balls(NHPGB),with well-balanced electrical conductivity and electrocatalytic activity were synthesized from nitrogen-riched pitch by hard-template method,photoelectric conversion efficiency of 8.75% and high electrochemical stability were achieved.3D porous structure ensures sufficient exposure of electrocatalytic active sites and avails full contact with triiodide/iodide electrolyte.In this study,the effects of different carbonization temperature,different material ratio,different pore structure and different carbon precursors on the photoelectric conversion efficiency were also investigated.When carbonization temperature is 900 oC and the ratio of raw material is 6:1,the nitrogen content of NHPGB can reach up to 7.11 wt.%.Besides,the proportion of the pyridinc nitrogen and graphitized nitrogen is 89.1%,which plays a key role in improving the photoelectric conversion efficiency of NHPGB.