Performance And Mechanism Study Of Functionalized Carbon Nanotubes And The Composite With Sulfide For Electrocatalytic Oxygen Evolution Reaction

Carbon nanotubes have good electrical conductivity,high specific surface area,excellent chemical stability and other properties.The tunable structure of carbon nanotubes provides the possibility to improve the electrocatalytic activity and reveal the relationship between structure and performance,so they are used in OER catalysis.The poor hydrophilicity of the original carbon nanotubes directly affects their application.Therefore,functionalization of the carbon nanotubes can not only improve the hydrophilicity of the carbon nanotubes,but also change the electronic distribution of the surrounding carbon atoms,so that the carbon nanotubes can have excellent OER catalytic performance.In addition,when functionalized carbon nanotubes are combined with transition metal sulfide,the carbon nanotubes can prevent the aggregation of sulfide to obtain fast kinetics and good stability of the catalyst.Moreover,the high electron transfer rate between carbon nanotubes and sulfide can further improve the catalytic performance.Based on the above discussion,this thesis uses functionalized carbon nanotubes as transition metal sulfide carrier and independent catalyst for OER catalysis respectively.The details are as follows:Functionalized carbon nanotubes are able to accelerate the electron transport rate of composites as carriers.In this work,the OER catalyst Co_1.5Mo_1.0S/o-MWNTs is prepared by the composite of cobalt-molybdenum bimetallic sulfide and oxidized multi-walled carbon nanotubes.Mo S₂has a large surface area and more active sites.The electronic structure of the catalyst can be adjusted by doping Co.During OER catalysis,the Co ion loses the electrons and becomes more electrophilic.More Co³⁺can adsorb OOH to form Co OOH,which is an intermediate of the OER reaction and facilitate the OER reaction as the active site.Co_1.5Mo_1.0S/o-MWNTs has excellent catalytic performance as the OER catalyst,and the water splitting device assembled by Co_1.5Mo_1.0S/o-MWNTs has a voltage of only 1.60 V at the current density of 10 m A cm^-2,and the stabilization time of more than 10 h.Cobalt and nickel-based materials have high OER catalytic activity.In this paper,the synergistic effect between nickel-cobalt bimetallic sulfide and functionalized carbon nanotubes was used to synthesize the highly efficient and durable Co Ni bimetal sulfide and o-MWNTs complex for OER catalysis by simple hydrothermal method.Metal loading on carbon-based nanomaterials with excellent electrical conductivity can not only improve the electron transfer rate of the composite,but also avoid the negative influence of metal phase dissolution and aggregation on the catalytic activity during OER catalytic oxidation process.During OER catalysis,as metal ions are oxidized in Co Ni₂S₄/o-MWNTs to form a high oxidation state Ni/Co OOH,which is capable of efficient OER catalysis as an intermediate in OER catalysis.In addition,both the water splitting device assembled by Co Ni₂S₄/o-MWNTs and the charge-discharging zinc-air battery have good performance and lengthy life span.Functionalized carbon materials have been used in some electrochemical reactions for a long time,but the catalytic mechanism is unknown.In this paper,we use the coaxial structure of double walled carbon nanotubes（DWNTs）to introduce the carboxyl group into the outer wall.The inner wall can still provide a continuous conductive path after the outer wall is functionalized.P-DWNTs-3 is obtained by treating DWNTs with plasma for 3 min.As an OER catalyst,P-DWNTs-3 has good catalytic performance in 1.0 M KOH.In addition,this paper focuses on the study of the carboxyl group involved in the catalytic mechanism of OER as an active site:the carboxyl group on P-DWNTs-3 surface promote OER catalytic reaction through the formation and hydrolysis of lactone,and return to its initial state at the end of the cycle.The study of this carboxyl catalyst provides a feasible strategy to develop carbon-based catalysts for energy conversion and storage systems in alkaline medium.