Low Temperature Plasma Assisted Synthesis Of Graphene-based Composites And Their Electrochemical Performance

The development of efficient,environmentally friendly,and safe energy storage and conversion devices is an enduring thesis in the field of energy and materials.Supercapacitors as an energy storage device and direct methanol fuel cells as an energy conversion device have received widespread attention.Efficient electrode materials and catalyst materials have become the key issue to research.Studies have shown that the doping of heteroatoms for graphene is an effective electrode material and an excellent choice for catalyst supports.Various preparation methods such as hydrothermal method,high temperature calcination method,and electrochemical method are used to prepare the heteroatoms doping graphene.However,almost of these methods require multi-step chemical reactions,high temperature,and toxic doping reagents,which are not conducive to material performance and environment protection.There are a few reports about the method of low temperature plasma technology to prepare the doped graphene.The method is environmentally friendly,efficient and energy-saving,but the research on the specific preparation mechanism and optimization of the preparation process is not systematic enough and has great exploration value.Based on the characteristics of low-temperature plasma technology,this paper develops a new doped graphene preparation strategy,explores the possible mechanism and existing advantages of plasma in the material preparation process,and further analysis of the superiority of the corresponding materials in supercapacitors performance and catalytic methanol oxidation reaction performance.The research contents are as follows:(1)Using graphene oxide and thiourea as precursors,nitrogen and sulfur co-doped graphene were prepared by hydrogen and argon mixture inductively coupled plasma discharge and hydrothermal method respectively.The possible reaction mechanism in plasma treatment was analyzed by optical emission spectrometry,and the best discharge parameters were discussed.The results show that the plasma treatment can effectively reduce graphene oxide,achieve higher content of doping than hydrothermal method.The plasma treatment can also reduce the stacking of graphene sheets,effectively adjust pore size distribution and obtain larger specific surface area than hydrothermal method.The electrochemical tests also show that the plasma treatment sample has the higher specific capacitance,superior rate performance and cycle stability.As electrode materials of supercapacitors,materials prepared by plasma-assisted method exhibited superior specific capacitance,rate performance,and cycle stability in the three-electrode system and two-electrode supercapacitor devices compared with the material prepared by hydrothermal methods.(2)Nitrogen-doped graphene-loaded Pt and Ni nanocomposites were prepared by H2 and N2 mixed low-temperature plasma discharge based on an inductively coupled plasma source.Compared with single H2 plasma,H2 and N2 mixed plasma discharge has more advantages.First,while reducing graphene oxide and metal ions,it can effectively dope nitrogen into the graphene framework,thereby creating more defects and providing more active sites to promote the uniformity of the catalyst particles dispersion.Secondly,the enhanced physical bombardment of the N2 plasma significantly reduces the catalyst particle size.In addition,compared with traditional wet chemical methods,this gas-phase synthesis strategy is simple,energy-saving and environmentally friendly.Compared with non-nitrogen-doped samples and commercial Pt/C catalysts,the prepared catalysts showed better catalytic activity,stability and anti-poisoning ability for methanol oxidation reaction.Therefore,this novel low-temperature plasma assisted technology provides a new way to synthesize catalysts with the required performance.