Preparation And Oxygen Electrocatalytic Performance Of PPy-derived Carbon Fiber/tube Supported Electrocatalysts

Faced with increasingly severe energy shortages and environmental pollution,it is imperative to develop clean and sustainable electrochemical energy conversion technologies.Electrocatalysts play a vital role in the conversion and utilization of new energy sources.Therefore,the search for cheap,efficient,and stable electrocatalytic materials has always been the focus of research in the field of new energy sources.In recent years,cheap nitrogen-doped carbon（referred to as nitrogen-carbon）supported transition metal（Fe,Co,Ni,etc.）systems have shown great potential in the field of electrocatalysis and have become a research hotspot.This thesis focuses on polypyrrole（PPy）-derived carbon,based on the preparation and research of the electrocatalytic performance of supported catalysts based on PPy-derived carbon fibers/tubes,and explores its potential applications in the field of zinc-air batteries.The specific research content is as follows:Using PPy fiber as the precursor,the M/N-CF（M=Co,Cu,Mn,Fe,Ni）catalyst was prepared by a high-temperature gas-phase reduction strategy.The rich nitrogen defects and pore structure of PPy-derived carbon fibers are conducive to the capture and highly stable dispersion of metal precursors.The obtained M/N-CF electrocatalyst has a transition metal nanocrystal size of about 5nm and is highly dispersed,with a specific surface area of 730 m² g^-1.When used in oxygen reduction reaction,the half-wave potential of Mn/N-CF reached 0.87 V vs.RHE.In addition,Co/N-CF has excellent dual functions of Oxygen Evolution Reaction-OER(overpotential of 380 m V at 10 m A cm^-2)and Oxygen Reduction Reaction-ORR（half-wave potential of 0.85 V vs.RHE）,as the air cathode of zinc-air battery,with a maximum power density of 163 m W cm^-2.Indicating that M/N-CF catalyst has potential application prospects in energy conversion and storage systems.In order to further improve the OER performance of the catalyst,the P-modified hollow structure PPy tube was used as the carbon source,and the Co2P/NPC catalyst was prepared by one-step high-temperature pyrolysis.In this material,the hollow structure can effectively improve the mass transfer and interface electron transfer speed,and the co-doping of heteroatoms with N and P can effectively adjust the charge distribution of the carbon carrier.In addition,there is a strong electronic coupling between the NPC carrier and the Co2P particles.Their synergy makes the half-wave potential of Co2P/NPC 0.84 V vs.RHE,and the OER overpotential at 10 m A cm^-2 is 320 m V.As the air cathode of zinc-air battery,the maximum power density is 154 m W cm^-2.In order to further improve the dual functions（ORR and OER）of the catalyst,Co/N-CZn was successfully prepared by using PPy fibers modified with cobalt ammonium salt and zinc chloride as a source,through a high-temperature gas phase reduction strategy.The treatment of zinc chloride provides more defects for the carrier to capture metal molecules,effectively increases the micro mesoporous structure,and increases the specific surface area.The cobalt ammonium salt is also easier to be captured and reduced by the carrier during the high temperature process,and is beneficial to the generation of Co-N active sites.When used in oxygen reduction reactions,the half-wave potential of the prepared Co/N-CZn catalyst reaches0.88 V vs.RHE,which is very close to commercial Pt/C,and its kinetic current density at 0.85V vs.RHE（Jk）reached 36.6 m A cm^-2,exceeding Pt/C.When used in the oxygen evolution reaction,the overpotential at 10 m A cm^-2 is 280 m V.As the cathode of the zinc-air battery,the maximum power density reaches 195 m W cm^-2.Using PPy as the precursor,a novel Sb-N-C single-atom catalyst was prepared.Characterization methods such as spherical aberration electron microscopy,XPS and XANES proved that Sb was supported on the PPy-derived carbon carrier in the form of a single atom.In addition,due to the low melting point of Sb element（630 ^oC）,part of the Sb atoms will also volatilize during the high-temperature pyrolysis process,and at the same time increase the porosity of the N-C matrix,thereby enhancing the reaction substrate and catalytic products on the electrode interface the mass transfer rate.In an alkaline environment,the half-wave potential of Sb-N-C is as high as 0.90 V vs.RHE,and the kinetic current density（Jk）at 0.85 V vs.RHE also reaches 72 m A cm^-2,which far exceeds commercialization Pt/C.In addition,Sb-N-C also shows better ORR performance in acid electrolytes.