Low Temperature Plasma Modified Fe/Co/N Doped Hollow Graphene Spheres Loaded Platinum-Nickel Alloy Catalyst And Its Application In Direct Methanol Fuel Cells

With the progress of society and the development of industry,the global energy crisis caused by the depletion of traditional fossil fuels and environmental pollution is imminent,which prompted people to look for possible renewable and clean energy,such as fuel cells and water electrolytic devices.Direct methanol fuel cell（DMFC）is an important part of the fuel cell,methanol oxidation reaction（MOR）and oxygen reduction reaction（ORR）are the key reactions on the anode and cathode of the fuel cell,respectively.However,the electrode reaction faces the problems of slow electrocatalytic reaction kinetics,high price of commercial catalysts and poor stability.In addition,hydrogen evolution reaction（HER）,as an important semi-reaction for the cathode of water electrolytic device,also faces the problems of expensive and unstable commercial catalysts.Therefore,the development of efficient,stable and economical new electrocatalysts for ORR/MOR/HER is an important link to achieve their large-scale application.As an effective means of material modification,the low-temperature plasma technology can achieve etching,doping,reduction and oxidation of catalysts,thus generating more defects and surface functional groups,so as to adjust the chemical structure and electronic structure of the materials surface,increase the exposure of electrical conductivity and active sites,and improve the electrocatalytic activity of materials.In addition,the low temperature plasma reaction system can make the chemical reaction with high activation energy occur under relatively mild conditions,which has the advantages of wide application range,short action time,environmental protection and low cost.Based on the technical advantages of the low temperature plasma,the high efficiency and low platinum electrocatalyst was prepared by the modification of Fe/Co/N co-doped hollow graphene spheres by low temperature radio-frequency（RF）plasma and loaded with platinum-nickel nanoparticles.And the platinum-nickel core-shell electrocatalyst was prepared by low temperature RF plasma reduction.In addition,the catalysts are further applied to direct methanol fuel cells to realize the application of energy devices.The main contents and achievements of this paper are as follows:（1）Fe/Co/N co-doped hollow graphene spheres（FCNHGS）was prepared and treated by low temperature RF plasma under Ar,Ar/NH₃,Ar/H₂,N₂and O₂atmosphere,which effectively regulated the surface electronic and chemical structure of the FCNHGS.The suitable conditions were created for the deposition of platinum nickel alloy（Pt₁Ni₂）nanoparticles（NPs）.The results show that the plasma treatment under specific atmosphere has different effects on the surface of the prepared FCNHGS,such as O₂plasma（etching and oxidation）,N₂plasma（etching and doping）,Ar plasma（etching）,Ar/H₂plasma（etching and reduction）,Ar/NH₃plasma（etching,doping and reduction）.Therefore,the plasma treatment atmosphere can effectively adjust the surface electronic and chemical structure of the FCNHGS,making it rich in defects and specific surface functional groups,and provide enough anchoring sites for the deposition of Pt₁Ni₂NPs.Due to the synergistic effect between Pt₁Ni₂NPs and FCNHGS,the Pt₁Ni₂@Ar/NH₃-FCNHGS showed the best bifunctional catalytic activity and the highest Pt utilization for both ORR and HER.In addition,the Pt₁Ni₂@Ar/NH₃-FCNHGS is applied to DMFC cathode,it exhibits good open-circuit voltage,power density and stability,which is superior to the commercial Pt/C catalyst.This work not only used the low temperature plasma technology to prepare efficient and stable catalysts,but also was an environmentally friendly and efficient preparation technology,which had more far-reaching applications in fuel cells and other fields.（2）The Fe/Co/N co-doped hollow graphene spheres loaded with Pt@Pt Ni core-shell structure（Pt₁Ni₂@P-FCNHGS-200P）were successfully synthesized by two times of argon-ammonia radio-frequency plasma treatment.This catalyst has better MOR and ORR properties than commercial Pt/C catalyst.The line-scan EDS spectra showed that Pt₁Ni₂@P-FCNHGS treated by plasma at different temperatures（25℃,100℃,200℃,300℃and 400℃）showed different structures of Pt₁Ni₂NPs.At 200℃,the Pt₁Ni₂NPs showed a high catalytic activity and stability of the Pt@Pt Ni core-shell structure（Pt shell/Pt Ni core）,while the Pt₁Ni₂NPs without plasma treatment showed a disordered structure,indicating that the plasma treatment can accelerate the atomic diffusion of Pt₁Ni₂NPs at a specific temperature to form a core-shell structure.In addition,the results show that plasma treatment can produce more defects and Fe/Co-N non-noble metal active sites on the FCNHGS to increase the specific surface area of the active site and electrochemical active,thus further improving the catalytic activity of the catalyst in the target reaction.In particular,the Pt₁Ni₂@P-FCNHGS-200P was applied to DMFC cathode,which showed the superior power density and stability to commercial 20wt.%Pt/C.In this study,the Pt-based alloy structure was modified by the plasma technology to improve the catalytic performance and stability,and reduce the cost of precious metals.To sum up,this paper aims to prepare the efficient,low-cost and stable bifocal catalysts and improve the electrocatalytic performance of oxygen reduction/hydrogen evolution reaction（ORR/HER）and methanol oxidation/oxygen reduction reaction（MOR/ORR）.By using the low temperature plasma,the surface modification and regulation of the catalysts structure were carried out to generate defects and functional groups to anchor and disperse nanoparticles.In addition,the low temperature plasma reduction treatment is applied to construct core-shell structure of nanoparticles and expose more electrochemical active sites,thus enhancing electrocatalytic activity and stability.This paper provides a theoretical reference for the design and preparation of the new bifunctional catalysts with high efficiency,stability and low-cost.In addition,the further application of the low temperature plasma technology in electrocatalytic surface modification and synthesis is realized.