Synthesis Of Multiple Doped 3D Ordered Mesoporous Carbon Materials And Their Electrocatalytical Performance

The excessive use of fossil fuels has caused global environmental pollutions.Green and clean energy conversion technologies,such as fuel cells,have attracted much attention.However,the slow kinetics of the oxygen reduction reaction(ORR)at the cathode of the fuel cell,and its high overpotential have hindered its large-scale application.Therefore,the goal of scientific research is to improve its working efficiency.In order to simplify the synthesis procedure for ORR electrocatalysts,enhance active site density,and decrease cost,this thesis explores the preparation of non-noble metal electrocatalysts supported on heteroatom-doped ordered mesoporous carbon materials by using a solvent-free nano-confined method.The obtained electrocatalysts possess highly dispersed and easily accessible active sites after optimizing their structures and electronic structure.Various characterization methods are used to investigate the catalyst morphology,structure and compositions.The relationships between the electrocatalytic activity and material structures are also explored.The major contents of the thesis are as follows.(1)The thesis proposes a simple solvent-free nano-confined preparation method to solve the issues of weak precursor interactions,easy agglomeration of metal species under high temperatures,and complicated synthetic process.The large surface area,high pore volume and N and S coordination of ordered mesoporous carbon are designed to disperse Fe species and optimize their electrocatalytic activity.Methionine(Met),FeC13 and mesoporous silica template KIT-6 can be well-mixed after grinding.The N,S co-doped 3D ordered mesoporous carbon with atomic dispersion of FeNx can be obtained after high temperature pyrolysis and template removal.Through a series of control experiments,an in-depth study on the calcination temperature,different templates and key active sites has been conducted.The optimized sample possesses a high surface area of 890 m2/g,a pore volume of～1.25 cm3/g,high N and content of 7.36 wt.%,a high density of FeNx and C-S-C sites.It presents superior ORR performance with a half-wave potential of 0.92 V and 0.76 V in 0.1 M KOH and 0.5 M H2SO4 respectively.Moreover,the sample also has an excellent methanol tolerance and stability.Besides,the experimental results demonstrate that the synergistic effects between N,S and FeNx sites can enhance the catalytic activity significantly.(2)The preparation of solvent-free nano-confined method can be further explored to the synthesis of bifucntional electrocatalysts.In order to address the issues of MoS2 nanosheets in HER,including easy stacking,low edge active site exposure and low conductivity,bifunctional electrocatalysts with FeNx and ultra-thin MoS2 sites supported on ordered mesoporous carbon supports have been synthesized.The loading of composite precursors FeCl3,MoCl5 and Met into the mesopores of the KIT-6 template,the metal-confined conversion and the carbonization can be completed in a one-step high-temperature calcination process.After template removal by HF,electrocatalysts with Fe-doped MoS2 nanosheets supported on heteroatom-doped ordered mesoporous carbons can be obtained.The optimized sample possesses a high surface area of 900 m2/g,a pore volume of～1.4 cm3/g,a high density of FeNx sites,as well as highly dispersed and ultrathin MoS2 nanosheets.It exhibits good bifunctional electrocatalytic potential.The half-wave potential of the optimized sample reaches～0.92 V in the alkaline ORR tests,and the HER performance in the acidic electrolyte with a low overpotential of 220 mV at a current density of 10 mA/cm2.