Compositional And Structural Regulation Of Metallic Macrocyclic Compounds-derived Novel Electrocatalysts

In recent years,human society is facing a serious energy shortage.It is of great importance to develop green and sustainable energy.One of the most effective ways to alleviate the energy crisis is to make efficient and rational use of renewable clean energy resources,for example,the fuel cells,metal-air batteries and water splitting cells.The activity of catalysts plays a decisive role in above-mentioned energy storage and conversion techniques,accelerating the electrode reaction kinetics and decreasing the overpotentials of involved electrochemical reactions including oxygen reduction reaction,oxygen evolution reaction and hydrogen evolution reaction.At present,Pt group metals are the most active catalysts for these reactions.However,the high cost,low reserves and poor stability of these precious metals limits their large-scale applications.Therefore,it is very important to develop non-noble metals-based catalysts with low cost and high activity.In this paper,three novel transition metal-based hybrid materials which derived from metal macrocyclic compounds are planned and synthesized,which act as non-noble metal electrocatalysts for oxygen reduction,hydrogen evolution and oxygen evolution reactions.The morphology and structure of the catalysts were characterized by scanning electron microscopy（SEM）,high-angle circular dark-field scanning transmission electron microscopy（HAADF-STEM）,X-ray fine absorption spectroscopy（XANES）and X-ray photoelectron spectroscopy（XPS）.Electrochemical methods such as linear sweep voltammetry（LSV）,rotating disk electrode（RRDE）and stability test（I-T）were used to study the electrocatalytic performance of catalysts.Many significant results were obtained as follows:Firstly,dual metallic Fe/Ni-coordinated tetrapyridinylporphyrin embedded NH₂-MIL-101-Zn was synthesized by a facile solvothermal method by adding Fe/Ni-coordinated tetrapyridinylporphyrin into the reaction system used for preparation of NH₂-MIL-101-Zn.Subsequently,a novel Fe Ni alloy nanoparticles-loaded nitrogen-doped carbon material,named（Fe,Ni）/N-C,was successfully prepared by direct pyrolysis of the hybrid including Fe/Ni-coordinated tetrapyridinylporphyrin and NH₂-MIL-101-Zn at inert atmosphere.The（Fe,Ni）/N-C catalyst showed high electrocatalytic activity and good stability.Secondly,for further improving the atomic utilization efficiency,a novel single-atom Fe-N-C electrocatalyst was designed and synthesized by pyrolysis of co-assembly of Fe-functionalized tetrapyridinylporphin and ZIF-8 at 900oC.The as-obtained Fe-N-C possessed highly dense Fe-N₄active sites,and therefore showed remarkable electrocatalytic activity for ORR,with an onset potential of 0.999 V vs.RHE and a positive half-wave potential of 0.86 V vs RHE,and a large limiting current density of 6.7 m A cm^-2,superior to the benchmark Pt/C catalyst.When Fe/N-C-900was used as air catalyst for air zinc-air battery,the peak power density of the battery reached 166.0 m W cm^-2,which exceeded the valuable Pt/C-based zinc-air battery.Thirdly,in order to extend the application of transition metal-functionalized tetrapyridinylporphin,an efficient overall water splitting catalyst was synthesized by in situ growth of Co-coordinated Fe-functionalized tetrapyridinylporphin on the nickel foam（NF）and using PVP as the morphological tuning agent,followed by low-temperature phosphatizing treatment of the as-prepared hybrid,termed as PVP-NF@（Fe,Co）PP-P.The as-fabricated material displayed excellent electrocatalytic performance for both OER and HER in alkaline medium,with a small overpotential of290 m V at 10 m A cm^-2for OER and a small overpotential of 110 m V at 10 m A cm^-2for HER.The assembled water electrolyzer with PVP-NF@（Fe,Co）PP-P as both anode and cathode just needed a small cell voltage of 1.57 V to achieve the current density of10 m A cm^-2,superior to the cell with Pt/C as the cathode and Ru O₂as the anode.