Study On Heat And Mass Transfer Enhancement And Catalytic Reaction Improvement Of Vertical Graphene

Attributed to the special vertical structure,vertically-oriented graphene（VG）not only gives full play to the graphene properties such as high in-plane thermal conductivity,high carrier mobility and high ductility,but also has great potential in heat and mass transfer and catalytic adsorption through abundant channels and edge structures between the lamellar.Plasma enhanced chemical vapor deposition（PECVD）is the main method for preparing VG.In this thesis,the effects of different growth temperature,radio frequency power,deposition time and the ratio of carbon source gas to carrier gas on the structure of VG prepared using PECVD were investigated.Various characterization techniques were employed to investigate the structure of the as-prepared VG.Based on the outstanding performance of vertical graphene,its applications in the field of heat and mass transfer enhancement and energy catalytic conversion were explored.Firstly,the enhancement effect of vertical graphene coating on corrosion resistance and heat dissipation of zirconium alloy was studied,and the mechanism of VG enhanced corrosion resistance and heat transfer was revealed.Then,the performance of VG supported MOS₂ catalyst for synthesis of ammonia fuel was studied,and the promotion mechanism of vertical graphene for catalytic reaction was analyzed.The results show that.1)The effects of growth temperature and radio frequency power on the growth of vertical graphene mainly reflect that it is difficult to achieve sufficient pyrolysis of C₂H₄ molecules at low temperature and low radio frequency power.High temperature and high radio frequency power will increase energy consumption and damage the substrate.The deposition time and carbon source ratio mainly affect the structure and defect formation of vertical graphene.Short deposition time and too low carbon source ratio cannot obtain uniform vertical graphene structure.Long deposition time and high carbon source ratio are easy to introduce large amount of surface defects.It was found that the quality and uniformity of vertical graphene structure were higher when the growth temperature was 700℃,the radio frequency power was 150 W,the deposition time was60 min,and the carbon source ratio was 10%.2)Composite materials（VGZA）were prepared by growing vertical graphene on zirconium alloy surface by PECVD process.According to the results of static contact angle and electrochemical corrosion experiment,the maximum static contact Angle of VGZA is 144.41°,the lowest self-corrosion current is 5.3407×10^-6 A/cm²,and the corresponding corrosion rate is0.1217 mm·a,indicating that the corrosion resistance of VGZA is significantly improved.According to the experiments of laser thermal conductivity meter and infrared thermal imaging technology,it is found that the presence of vertical graphene coating effectively enhances the thermal diffusion coefficient and heat transfer performance,especially at high temperature.3)Vertical graphene Mo S₂ composite was prepared by PECVD method.Vertical graphene can provide plenty of pores through its special structure to promote mass transfer,and rich edge structure can effectively improve the number of catalytic adsorption sites and catalyst cycle stability.Electrochemical results show that the working electrode with obvious vertical structure has better catalytic effect.The vertical graphene Mo S₂ composite electrode maintains stable performance after several cycles at the optimal operating voltage of 0.1 V vs.RHE.The ammonia synthesis rate is about 14.5μg/(h·mg_cat),and the faraday efficiency is 35%.