Synthesis And Study Of Carbon-based Transition-metal(Fe、Co、Ni)Electrocatalysts

More and more energy has been consumed to meet the high speed development of our society.Fossil fuels still occupy the main position in current energy structure,however,the non-renewable of fossil fuels restricts them unable for unlimit exploition.Moreover,the excess utilization of fossil fuels also have aroused many severe environmental pollution issues,affecting our daily life.Therefore,the development of new clean and renewable energy technologies to replace the traditional fossil fuels has attracted great research attention in the fields of science and technology.Fuel cells,metal-air batteries and hydrogen from water splitting are the storages of clean and renewable energy with the clean and environmentally friendly properties.As we know,oxygen reduction（ORR）and oxygen evolution（OER）are two critical reactions during the charge and discharge processes of fuel cells and metal-air batteries,while hydrogen evolution reactions（HER）and OER are two important reactions during water spllitting.However,the performances of the above mentioned reactions are highly dependent on ORR/OER/HER active electrocatalysts,which are highly desirable for developing high performance clean and renewable energy devices.This thesis work is mainly focused on the synthesis of carbon-based transition-metal（Fe,Co,Ni）electrocatalysts and their applications as ORR/OER/HER electrocatalysts for fuel cells,metal-air batteries and and full water splitting to generate H2/O2.In detail,this thesis work includes three parts of contents:Fristly,Fe/Fe2O3 nanoparticles embedded into Fe-N doped graphitic carbon composites were successfully synthesized by pyrolyzing the mixtures of Fe precursor and shrimple shell-derived N-doped carbon nanodots at the pyrolysistemperatures of 800℃\900℃、1000℃、1000℃ in N2 atmosphere.The XRD and TEM results demonstrate that Fe/Fe2O3 nanoparticles are uniform Ly embedded into porous graphitic carbon structure.As electrocatalyst,Fe/Fe2O3@Fe-N-C composite obtained at 1000℃（Fe/Fe2O3@Fe-N-C-1000）exhibits the best ORR/OER activities among all investigated catalysts.Detailedly,Fe/Fe2O3@Fe-N-C-1000 indicates superior bifunctional electrocatalytic activities toward ORR and OER in alkaline media,and its ORR activity is comparable to that of commercial Pt/C.Moreover,Fe/Fe2O3@Fe-N-C-1000 also indicates good ORR activity in acidic media.As air cathodic material,Fe/Fe2O3@Fe-N-C-1000 was assembled into a rechargeable Zn-air battery,exhibiting an open-circuit voltage of 1.3 V and a discharge power of 200 mW·cm^-2 with high charge and discharge cycling stability.Secondly,Ni3N/Ni nanosheet composites were obtained using metal-organic frameworks（Ni-BTC）as precursors by high temperature pyrolysis approach（600 ℃、700℃、800℃）in a NH3 atmosphere.The electrocatalytic measurements demonstrate that the as-prepared Ni3N/Ni-700 obtained at 700 ℃ exhibits high OER activity with an overpotential of 290 mV at current density of 10 mA·Ccm^-2 in the alkaline electrolyte,comparable to that ofthe commercial RuO2 electrocatalyst.The OER stability of Ni3N/Ni-700 can keep over 90%after 4000 cycles,indicating its high durability.Thirdly,Ni/Co alloy nanoparticles with different molar ratios of Ni to Co surported on the commercial activated carbon layers were successfully synthesized in a pyrolysis temperature of 1000℃ with a flowing N2 using Ni2+/Co2+-adsorbed activated carbon as precursor for electrocatalysis applications.The results demonstrate that the as-prepared NiCo alloy nanoparticles@activated carbon composites with different molar ratios of Ni to Co possess trifunctional electrocatalytic activities toward ORR/OER/HER.Among all catalysts investigated,Ni1Co3@C exhibits the highest ORR/OER activities and Ni3Co1@C displays the best HER activity in alkaline media.Based on the above results,Ni1Co3@C was utilized as air cathodic material to assemble a rechargeable Mg-air battery with an open-circuit voltage of 1.7 V and a discharge power of 30 mW·cm^-2.The home-made LED pattern and low-power fan can be readily driven using the constructed Mg-air battery.Further,a self-powered electrochemic water-spilliting system was built by employing the home-made Mg-air battery as the power,Ni1Co3@C and Ni3Co1@C as the anode and cathode materials,respectively.The results indicate that 8 mL of H2 can be collected after 3 h of the self-powered water splitting reaction with nearly unity Faradic efficiencies of H2（100%）and O2（100%）.