Synthesis Of Carbon-based Transition Metal Catalysts And Their Electrocatalysis Research

Energy is one of the most important material basis for the survival and development of humankind.Till now,fossil energy has always been the main energy source for mankind.With the continuous consume of fossil fuels and the aggregated environmental pollution,the development of clean and renewable energy becomes the top priority.In recent years,the emergence of fuel cells and hydrogen energy provide new ideas and new directions for solving the energy crisis.The fabrication of highly active catalysts becomes the core techniques toward efficient fuel cells and electrocatalytic hydrogen production.Till now,the noble platinum or platinum alloys are the most widely used catalysts.However,the high cost and low resistance to methanol severely restrict its large scale commercial applications.Therefore,it is of great significant to develop inexpensive,easily available non-noble metal catalysts with high performance and good durability.In this paper,we synthesized three kinds of carbon-based transition metal catalysts via high temperature calcination and solvothermal method.The structure,morphology,and composition of the catalysts were examined by a series of characterization technologies including scanning electron microscope(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS)and so on.In addition,the electrocatalytic performance(eg:oxygen reduction reaction,hydrogen evolution reaction),stability and durability of the catalysts were examined.The results showed that the obtained catalysts exhibited excellent catalytic performance and good stability.This could be ascribed to their unique structure and heteroatom nitrogen-doping.The main contents of this study include the following three sections:(1)The preparation of metal-organic framework derived Co-N-C catalysts and their catalytic performance for oxygen reduction reactionsIn this experiment,cobalt-containing MOFs precursors(Co-MOFs)were prepared by hydrothermal reaction using Hip(1 H-Imidazo[4,5-f][1,10]phenanthroline)and anhydrous CoCl2 as the raw materials.Then the obtained Co-MOFs was subjected to calcination under N2 protection at 700,800 and 900 ?,respectively,the samples were denoted as Co-N-C-700,Co-N-C-800 and Co-N-C-900.The obtained materials were applied as catalysts for the oxygen reduction reaction(ORR).The results showed that the Co-N-C-800 exhibited the best catalytic performance among the three catalysts and better stability and methanol resistance as compare to the commercial Pt/C catalysts,demonstrating the great application potential of the Co-N-C-800 catalyst.(2)Fabrication of cobalt-doped bamboo-like carbon nanotubes(Co-bCNTs)and their catalytic performance for oxygen reduction reaction.The precursor was prepared by self-assemble of melamine(M),cyanuric acid(CA)polyethyleneimine(PEI)in aqueous solution.The obtained precursor nanoplates were denoted as PEI-MCA.After that,the precursor was mixed with anhydrous CoCl2 and grind into fine powder.The mixed powder was subjected to calcination under N2 atmosphere at temperature of 800 ?.The black cobalt doped bamboo-like carbon nanotubes(Co-bCNTs)were obtained.The Co-bCNTs showed excellent ORR catalytic activity with 4 electrons pathway.The Co-bCNTs also exhibited better stability and methanol resistance as compared with commercial Pt/C catalysts.(3)Synthesis of molybdenum sulfide/onion-like carbons composites for hydrogen evolution reactionIn this study,candle soot was collected using glass slide as the collector.For the preparation of the onion-like carbons(OLCs),the crude candle soot was subjected to calcination at 800 ? for 2 h under a N2 flow.After cooling to room temperature,OLCs were obtained.This method provides a cost-effective approach toward OLCs,making it as low-cost and easily-available supporting materials.For the preparation of MoSx/OLCs composites,ammonium tetrathiomolybdate((NH4)2MoS4)and OLCs were dispersed in N,N-dimethyl formamide(DMF)and subjected to hydrothermal treatment.The obtained MoSx/OLCs composites exhibited many active surface sites with wrinkled edge and abundant unsaturated sulfur atoms.In addition,the supporter OLCs exhibited good conductivity which is facilitated for electrons transfer and charges transport.The MoSx/OLCs composites also exhibited high HER performance in 0.5 M H2SO4 solution with a low overpotential and a small Tafel slope of 57 mV dec-1 as well as good stability.