Study On Preparation And Photoelectrochemical Properties Of Graphitic Carbon Nitride Thin Films With Different Thicknesses

Photoelectrocatalytic technology has been considered to be the most promising hydrogen production approach for the future application,to explore superior photoelectrode materials is of great significance for further improving the performance.Graphite carbon nitride（g-CN）is one of the most attractive photocatalysts because of its appealing band structures,excellent chemical stability and environmental friendliness.It is a key point to construct high-quality g-CN thin-film photoelectrodes,and to push forward the practical application in g-CN-based photoelectrocatalysis.In this thesis,we developed the thermal evaporation technology to prepare g-CN thin films,and controlled the thickness of the deposited thin films by changing the loading amounts of the precursor.Subsequently,the effects of the thickness of the g-CN thin films on their photoelectrochemical properties have been systematically studied.Two series of g-CN thin films were fabricated by the conventional one-step thermal evaporation method and the improved two-step technique,respectively.The thickness of the thin films was controlled by changing the loading amounts of the precursors.The optical morphology and light transmittance of the deposited g-CN thin film have been compared,and the results showed that the thin films synthesized by the improved two-step thermal evaporation deposition method possessed better uniformity and light transmittance.The structure,surface morphology,thickness,chemical bonding characteristics,light absorption and photoluminescence properties of the g-CN thin films have been studied.It is found that by increasing the loading amounts of the precursor,the thickness of the deposited thin films gradually increased,and leading to a continuously enhanced light absorption capacity.Meanwhile,the deposited g-CN thin films maintained good transparency and uniformity.We studied and determined the most suitable testing parameters for measuring the photoelectrochemical properties of g-CN thin films.In order to record stable photoelectrochemical results,the prepared g-CN thin film needed to be stored in a dry dish.The thickness of the g-CN thin films showed a notable effect on their photoelectrochemical properties.When the thickness of the thin film increased,the corresponding photoelectrochemical performance gradually decreased.This is because the thicker thin film increased the transport distance for the photogenerated charge carriers from the thin film to the FTO conductive layer,leading to greater transport loss and reducing the photocurrent density.When 2g of the precursor was loaded for thin film deposition,the g-CN photoelectrode showed best photoelectrochemical performance,the photocurrent density reached 20μAcm^-2 under an AM1.5 illumination and 1.23V/RHE bias.The above results indicate that a precise control on the thickness of g-CN thin film is expected to further improve its photoelectrochemical properties,thereby providing a new idea to promote the photoelectrocatalytic application of g-CN materials.