A Construction Of Novel Carbon-Based Electrocatalysts Based On Transition Metal-Organic Ligand Complexation

The utilization of fossil fuels has brought great development to mankind,but also caused serious energy and environmental crises.As a result,the usage of clean energy and renewable resources has become particularly important.Zinc-air batteries（ZABs）are very different from the conventional batteries,which employ the zinc plate as the anode electrode,the air electrode as cathode electrode and potassium hydroxide as the electrolyte.ZABs have high theoretical energy density,but the kinetic process of oxygen reduction reaction（ORR）on the air electrode of ZABs is sluggish,requiring efficient catalysts to accelerate the reaction.At present,platinum and its alloys are considered as the most efficient the electrocatalysts for oxygen reduction reaction.However,the demerits of these noble metals such as high cost and poor stability hinder the commercial application of ZABs.Developing alternative materials of noble metal catalysts with low price,high activity and good stability is the key to the large-scale commercialization of ZABs.Based on this,three kinds of effective Fe/N-C catalysts were prepared by the complexation strategy of transition metals with organic ligands.The compositions,and morphological and structural properties of the prepared catalysts were characterized by scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）,transmission electron microscopy（TEM）and Raman spectroscopy.The electrocatalytic properties of the prepared composites were tested by electrochemical methods such as cyclic voltammetry（CV）,linear scanning voltammetry（LSV）,accelerated durability test（ADT）and chronoamperometry（i-t）.In addition,the zinc-air batteries were also assembled with the as-obtained catalysts as the air cathode and the battery performance was tested.Many meaningful results are obtained,which are summarized as follows.First,novel iron coordinated nitrogen-doped carbon materials,named Fe-N-C-T（where T represents the pyrolysis temperature）was prepared by pyrolysis of iron-terpyridine complex-embedded ZIF-8.The effect of reaction conditions such as organic ligand,pyrolysis temperature on the composition,morphology,structure and electrocatalytic performance of the as-prepared catalysts was studied.The optimized Fe-N-C-900 showed excellent electrocatalytic activity for ORR,with more positive onset potential（0.99 V vs.RHE）and half-wave potential（0.87 V vs.RHE）and larger limiting current density(7.5 m A cm^-2)when compared to other contrast materials.The zinc-air battery assembled with the as-obtained Fe-N-C-900 catalyst as the air cathode achieved larger specific capacity and better rate performance than the commercial Pt/C assembled zinc-air battery.Second,Fe₃N loaded nitrogen-doped carbon microspheres（N-CMSs）,labelled as Fe₃N/N-CMSs-T（where T stands for pyrolysis temperature）were prepared by pyrolysis of glucose microspheres adsorbing 1.10-phenanthroline-iron complex and dicyandiamide.The as-prepared Fe₃N/N-CMSs-900 has high graphitization degree,large electrochemical active specific surface area and high active Fe₃N site,showing excellent oxygen reduction electrocatalytic performance.A zinc-air battery was assembled with the as-synthesized catalyst as the air cathode,which showed higher power density and better rate performance than Pt/C based battery.Third,nitrogen-doped porous carbon supported Fe₃C nanoparticles were obtained by pyrolysis of the PVP aerogel containing 2-aminoterephthalic acid-iron complex,labeled as Fe₃C/N-C-T（where T denotes the pyrolysis temperature）.The influencing law of the composition,morphology and structure of the materials on the electrocatalytic performance of the as-obtained catalysts were summarized.The optimized Fe₃C/N-C-800 material showed excellent ORR electrocatalytic activity and good stability in alkaline solution.The zinc-air battery assembled with Fe₃C/N-C-800as the zinc-air cathode showed larger peak power density,higher specific capacity and better rate performance than the commercial Pt/C catalyst-based zinc-air battery.