Research On The Preparation And Electrocatalytic Performance Of Transition Metal-based Hybrid Materials

Along with the increasing aggravation of energy and environmental problems,the demand and utilization of renewable energy have aroused enormous interest.Zn-air batteries and the overall water splitting has been showing huge advantages in the areas of the energy conversion and storage.Currently,the noble platinum-/iridium-/ruthenium-based materials are best catalysts for oxygen reduction reaction（ORR）,oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）.However,the low abundance and high cost of these noble metals limit their large-scale applications.Therefore,it is of crucial importance to develop nonprecious metal catalysts with low cost,high reserves and outstanding electrocatalytic activity.Herein,a series of transition metal-based electrocatalysts have been prepared by novel methods.The scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction spectroscopy（XRD）and X-ray photoelectron spectroscopy（XPS）are used to analyze the morphology,crystal phase,element composition and chemical valence of these as-prepared catalysts.The electrocatalytic performance of catalysts are characterized by various electrochemical testing methods such as cyclic voltammetry（CV）,linear scanning voltammetry（LSV）and chronoamperometric current-time（i-t）test.Many meaningful results are obtained,which are summarized as follows:1.Novel electrocatalytically-active hybrid materials comprised of dual-metal Mn-Cu cluster-loaded N-doped carbon-coated carbon nanotubes,named CNTs@（Mn,Cu）PPc-T（where T means the heat-treating temperature in °C）,are developed by heat-treating Mn/Cu polyphthalocyanine-encapsulated carbon nanotubes（CNTs）and subsequent acid leaching.The hybrid materials have high catalytic activity for both oxygen reduction（ORR）and oxygen evolution reaction（OER）.Among them,CNTs@（Mn,Cu）PPc-900 exhibits remarkable electrocatalytic performance for ORR with an onset potential of 0.930 V vs.RHE,and for OER with a low overpotential of 375 m V at 10 mA cm^-2.At the same time,when it is employed as a bifunctional air electrode in a rechargeable zinc-air battery,CNTs@（Mn,Cu）PPc-900 results in a high peak power density(158.5 m W cm^-2),excellent rate performance and good long-term cycling stability.2.Fe-coordinated polyphthalocyanine（Fe PPc）is successfully loaded on nickel foam（NF）by a facile solvothermal synthesis method,and FeS₂/Ni₃S₂/NF is obtained after sulfuration of the as-generated Fe PPc/NF.The FeS₂/Ni₃S₂/NF catalyst has excellent catalytic activity for both OER and HER.FeS₂/Ni₃S₂/NF only needs an overpotential of 277 m V to afford the current density of 10 mA cm^-2 for OER,and an overpotential of 58 m V to achieve the current density of 10 mA cm^-2 for HER.Using FeS₂/Ni₃S₂/NF as the anode and the cathode,respectively,the assembled water electrolyzer drives the overall water splitting at a current density of 50 mA cm^-2 with a cell voltage of 1.75 V,along with good long-term stability.3.An evaporative drying method with combination of phosphorization is used to prepare a bimetallic phosphide（Co Ni P/NF）catalyst supported on NF by using phytic acid as a phosphorus source.The as-obtained Co Ni P/NF catalyst shows good catalytic activity for both OER and HER in 1 M KOH electrolyte.It only needs the overpotentials of 260 and 70 m V to reach the current density of 10 mA cm^-2 for OER and HER,respectively.The assembled water electrolyzer employing Co Ni P/NF as the cathode and anode drives the overall water splitting at a current density of 10 mA cm^-2 with a cell voltage of 1.64 V,along with outstanding durability.