Application Of Plasma Synthesis And Modification Of Nitrogen-Doped Carbon Nanotubes Based Electrocatalytic Materials In Direct Methanol Fuel Cell

In recent years,with the social progress and the growing demand for energy,a power generation device direct methanol fuel cell（DMFC）,which directly converts chemical energy into electrical energy,has emerged.Due to its many advantages,such as abundant fuel sources,low prices,high energy conversion efficiency,and pollution-free,it has attracted widespread attention from scientists.Developing new,efficient,and structurally stable catalysts for oxygen reduction reaction（ORR）and methanol oxidation reaction（MOR）is crucial,but highly challenging.At present,commercial Pt based catalysts have high costs,poor stability,and slow catalytic reaction kinetics,which restrict their practical application.The research and preparation of new high-efficiency electrodes is an important component of the development of DMFC technology.Plasma technology is widely used in the synthesis and modification of materials due to its simple operation,high efficiency,green environmental protection,and low cost.In order to realize the high utilization rate,high activity and stability of Pt based catalysts for DMFC,two new methods for preparing flexible DMFC integrated electrodes were developed in this thesis,including DC plasma magnetron sputtering（DC-PMS）technology and plasma enhanced chemical vapor deposition（PECVD）technology.The main research content and achievements of this thesis are as follows:（1）Successfully deposited platinum（Pt）onto nitrogen doped carbon nanotubes coated with CoFe alloy by using DC-PMS technology under argon atmosphere（Pt-CoFe@NCNT/CFC）.This fabricated electrode catalyst exhibits ultra-high ORR,MOR,and hydrogen precipitation（HER）performance,which are superior to commercial Pt/C catalysts.Inductively coupled plasma emission spectroscopy（ICP-OES）shows that the content of Pt nanoparticles（NPs）deposited on carbon nanotubes is 2.32 wt%,which indicates that DC-PMS technology can effectively reduce the actual load of Pt in the process of precious metal deposition,while improving its dispersion,so as to achieve the goal of low cost and high activity.In addition,it was found that the loaded Pt mainly exists in the form of Pt⁰,which can effectively enhance the catalytic activity of the catalyst for the target reaction.Moreover,DC-PMS technology is single atom deposition,thus can maintain the highly conductive structure of the carrier.This study opens up a new approach for using DC-PMS technology to load precious metals on the surface of heterostructure carrier,which can greatly improve the electrochemical performance and significantly reduce the costs of the synthesized electrode material.（2）Paste Ru target onto the surface of Pt target,and use DC-PMS technology to deposit RuPt alloy NPs onto CoFe@NCNT/CFC surface.A nitrogen doped carbon nanotube based catalyst coated with CoFe alloy rich in defects and low content of RuPt alloy NPs was prepared using plasma enhanced chemical vapor deposition（PECVD）technology（P-RuPt-CoFe@NCNT/CFC）,demonstrating excellent MOR performance and high resistance to CO poisoning.The ICP-OES result shows that the content of Ru NPs and Pt NPs deposited on carbon nanotubes is 0.11 wt.%and 0.73 wt.%,respectively,indicating a lower loading capacity of precious metals.Raman spectroscopy shows that after PECVD plasma treatment the I_D/I_G value of P-RuPt-CoFe@NCNT/CFC is 0.971,which is significantly higher than that of untreated ones RuPt-CoFe@NCNT/CFC（I_D/I_G=0.890）,indicating that PECVD plasma discharge treatment in Ar/NH₃atmosphere can not only increase the content of zero valent noble metals,but also strengthen the defects of NCNTs,increase the active site,and greatly improve the catalytic activity of the catalyst.This work provides valuable insights for the development of defect rich,low-cost precious metal alloy catalysts.In summary,the aim of this thesis is to improve the electrocatalytic performance of ORR/MOR through the design of electrode catalysts.By using DC-PMS technology,precious metals can be distributed evenly on the substrate surface with low content,high density,and high activity,achieving the goal of low cost and high activity of electrocatalysts.PECVD plasma technology is used to enrich the exposure of electrochemical active site through the micro design and adjustment of the electronic and chemical structure of the catalyst surface,and the manufacture of surface defects.This thesis is related to the research of new efficient and low-cost catalysts,providing basic data and theoretical reference for the design and development of highly stable catalysts,and promoting the wider application prospects of plasma technology in material synthesis and surface modification.