Application Of Functionalized Carbon Nanotubes In Counter Electrodes Of Dye-Sensitized Solar Cells

Dye-sensitized solar cells?DSSCs?,as representative of new thin-film solar cells,have attracted much attention due to their simple preparation process,environmental friendliness,high energy conversion efficiency and relatively low cost.DSSCs are usually composed of a photoanode?a TiO₂ porous film adsorbed with dye?,a counter electrode,and an electrolyte containing a redox couple?I₃^-/I^-?.Among them,the counter electrode,as one of the key parts of DSSCs,has the function of collecting external circuit electrons and catalyzing the redox I₃^-/I^-electric pair.The conventional counter electrode material,platinum?Pt?,although it has excellent catalytic activity,is expensive and has limited reserves due to its noble metal,and is easily corroded by electrolytes,thereby limiting its further large-scale application.Therefore,it is extremely urgent to develop cost-effective,high-efficiency,abundant-volume and corrosion-resistant non-platinum catalytic materials.Carbon nanotubes?CNTs?dominated by sp² hybridization,as a typical representative of the carbon material family,have attracted wide attention from researchers due to their excellent mechanical,electrical and chemical properties.In this thesis,carbon nanotubes were used as the research object.The morphology,structure,composition and electrochemical properties of CNTs were prepared and optimized by microwave heat treatment.The results were applied to the I₃^-reduction system and the common effect relationship was revealed.The main research contents are as follows:The morphology,structure,composition and surface chemistry of CNTs were optimized by oxygen plasma surface treatment with carbon nanotubes as the precursor.The effect of plasma treatment time on the surface properties of carbon nanotubes was investigated.It was found that plasma-treated carbon nanotubes?P-CNTs?inherit the one-dimensional linear structure characteristics of the original carbon nanotubes,and the length of the carbon nanotubes is cut from a few micrometers into short tubes of several hundred nanometers.P-CNTs have abundant active edge sites and oxygenated species,which activates the sidewalls and open ends of carbon nanotubes.Electrochemical experimental data and theoretical analysis results show that the proper amount of oxygen species on the CNT surface helps to improve the electrocatalytic performance of CNTs.The P-CNTs with a plasma treatment time of 3 minutes exhibited superior I₃^-reduction performance than the original CNT and the commercial Pt counter electrode,and the photoelectric conversion efficiency reached 8.35%.Density functional theory calculations show that the hydroxyl groups and carbonyl groups on the surface of carbon nanotubes can greatly reduce the ionization energy of the reaction and accelerate the transfer of electrons from the external circuit to I₃^-,which helps to enhance the electrocatalysis.Cobalt nanoparticle-carbon nanotube composites were prepared by rapid microwave heat treatment with carbon nanotubes as carbon source and cobalt nitrate hexahydrate as cobalt source.The effect of the mass ratio of cobalt to carbon nanotubes on its electrocatalytic activity were studied.It is found that with the increase of the mass ratio of cobalt to carbon nanotubes,the I₃^-reducing ability of the composites increases first and then decreases.When the mass ratio of cobalt to carbon nanotubes is 10%,the composite exhibits optimal catalysis performance,and its photoelectric conversion efficiency reached 8.12%,higher than 7.76% of Pt.Continuous impedance tests show that Rct of Co/CNTs-10 does not change with the number of scans,indicating its higher electrochemical stability.On this basis,the effects of different transition metals?nickel and iron?on the catalytic properties of the composites were investigated.It was found that the introduction of cobalt and nickel is beneficial to improve and enhance the catalytic activity of carbon nanotubes compared with metallic iron.The photoelectric conversion efficiency is about 8% or more.