Studies On The Preparation Of Noble-metal-free Supported Porous Graphene And Their Application In Cathode Of Low Temperature Fuel Cell

As the most fundamental driving force,energy has been the material basis for the survival of human society,and developing renewable energy conversion technology is of great significance for promoting the sustainable development of human society.Among them,low temperature fuel cell is considered as the most promising energy conversion device in 21^stt Century.However,the overall performance of the fuel cells is mainly limited by speed of the cathodic oxygen reduction reaction（ORR）.Recently,the development and research on carbon-based noble-metal-free catalysts which can solve the problems of cost and life fundamentally,has become one of the most active and competitive subjects among the scientific community.In this thesis,we used graphene as carbon-based support and synthesized porous graphene utilizing low temperature self-assembly and carbonthermal reaction processes.As a result,we have prepared a series of transition metal supported heteroatoms-doped porous graphene-based catalysts,meanwhile,the relationship of the structure characterization、composition、and electrocatalytic performance have been carefully discussed.The main work contents and conclusion as follows:（1）We obtained Fe₂O₃ NPs supported sulfur-doped graphene aerogels（Fe₂O₃/S-GAs）through an one-step in situ reduction procedure at 90℃under atmospheric pressure,during the process,we applied dithiothreitol as reduction reagent and sulfur precursors without any crosslinking agent.The results of materials characterization showed that Fe₂O₃/S-GAs possessed a mesoporous and macroporous structure with uniform distribution of NPs.Electrochemical measurements revealed that the resulting mesoporous carbons exhibited apparent electrocatalytic activity for oxygen reduction reactions（ORR）,and Fe₂O₃/SGAs was the best among the series,with a more positive onset potential（+0.95 V vs RHE）,higher selectivity（3.75 of electron transfer number at 0.2 V vs RHE）,better stability,and stronger tolerance against methanol crossover than commercial Pt/C catalysts in a 0.1 M KOH solution.We found that the remarkable ORR performance was attributed to the abundant channel which was beneficial to the flow of electrolytes and electron,and the multiple valence states of transition metal.（2）A hybrid of N-doped porous graphene/Co-encapsulated carbon nanotubes（NPG/Co-CNTs）was successfully prepared by a facile carbonthermal reduction etching process combining with a CVD method.During the fabrication process,we utilized ammonium molybdate(（NH₄）₆Mo₇O₂₄·4H₂O)as etching agent,cobaltous nitrate（Co（NO₃）₂·6H₂O）as a cobalt precursor,and melamine as a dual precursor for nitrogen and CNTs.With a series of chemical characterization,we found that graphene and（NH₄）₆Mo₇O₂₄·4H₂O react readily to produce MoC_x、CO₂ and NH₃ under high temperature.Among them,MoC_x served as efficient acidic removable templates and was responsible for the formation of mesoporous structure within both sides of carbon base.CNTs,synthesized by chemical deposition,were in charge for preventing the channels from collapse.Electrochemical detection results show that the catalyst exhibited enhanced catalytic performances for ORR via a dominated four-electron pathway in0.1 M KOH solution,when compared to commercial Pt/C catalyst,its catalytic ORR activity was comparable to Pt/C,as well as superior long-term stability and even better tolerance to methanol crossover than that of Pt/C.We supposed that the excellent electrocatalytic activity may be attributed to Metal-N/C active sites、porous graphene as carbon base and 3D hybrids nanostructure combing 2D graphene and 1D nanotubes.