Preparation Of Transition Metal Filled Nitrogen Doped Carbon Nanotubes By Molten Salt Method And Its Energy Conversion Application

Nano-carbon materials can be used as multi-functional scaffolds to build complex catalysts,which can promote electron and mass transport.Good contact with electrolytes can also lead to interfacial electron transfer,thereby adjusting the electronic structure of surface active sites and optimizing electrocatalytic activity.In particular,the strong coupling of metal compounds with nitrogen and the synergistic effect with nanocarbons make it possible for nanocarbons to replace precious metal catalysts.However,the synthesis process of nanocarbon/metal hybrids with good nanostructures and interfaces includes the synthesis of a nanocarbon matrix,the surface functionalization of nanocarbons,and the nucleation and growth of metal compounds.The preparation process is extremely complicated for the following reasons:the equipment is complicated,the precursor is expensive,the synthetic environment is corrosive,and the energy consumption is high.Therefore,developing a simple and low-cost method for manufacturing nano-carbon/metal hybrids is very important for large-scale applications of nano-carbon-based catalysts in electrocatalysis.In our previous work,several nitrogen-doped carbon networks with excellent oxygen reduction activity have been successfully prepared by a simple and controlled molten salt method.This method is simple and easy to operate,the structure is controllable,the specific surface area of the catalyst is large,the pore structure is rich,and the catalytic performance is high.Therefore,it is attractive to use the molten salt method to produce well-designed nano-carbon-based electrocatalysts.However,this requires improvements in both mechanism and methodology.In this paper,using melamine as the carbon source and nitrogen source,three differently-formed transition metal-filled nitrogen-doped carbon nanotubes were successfully prepared in CaCl₂+MCl_x（M=Fe、Co、Ni、Mn）molten salt system.This thesis consists of three part,the main contents are as follows:（1）Nitrogen-doped carbon nanotubes filled with pea pod-like Fe₃C were prepared in a CaCl₂+FeCl₃ molten salt system.The formation mechanism of carbon nanotubes was discussed by physical characterization,and the mechanism of catalytic activity was shown by DFT theoretical calculations.The obtained Fe₃C@NCNTs catalysts showed good catalytic activity and long-term stability in HzOR and ORR.（2）Nitrogen-doped carbon nanotubes filled with tubular Co in the tube were prepared in the CaCl₂+CoCl₂ molten salt system.The catalyst Co@N-CNTs-2 showed excellent bifunctional electrocatalytic activity of ORR and OER.（3）Spiral Mn-filled nitrogen-doped carbon nanotubes were prepared in CaCl₂+MnCl₂ molten salt system.The Mn@HNCNTs-2 catalyst prepared by this method has a higher surface area and higher ORR catalytic activity.