Design Of Three-dimensional Nonprecious Metal-based Catalysts For Oxygen Evolution Reaction And Their Electrocatalytic Performance Studies

Current global economic development and human activities depond on energy more intimately than ever before.Conventional fossil fuels,however,is not renewable and causes serious environmental problems during their use.This leads to an urgent demand for clean energy and efficient energy-storage systems.Hydrogen features a high energy density with no pollution and is regared as one of the most promising clean energy sources.A facil and efficient method to produce hydrogen is electrochemical water splitting.However,the kinetics of oxygen evolution reaction?OER?on anode is usually more sluggish than that of hydrogen evolution reaction on cathode,leading to high overpotentials and low efficiency for electrochemical systems.On the other hand,metal-air battery as a promising energy storage system also involves OER on its cathode during charging process,and the slow kinetics of OER induces the capacity decay,low coulombic efficiency,and short lifetime.Therefore,efficient and stable OER catalysts are vital for both electrochemical water splitting systems and metal-air batteries.Presently,commercial OER catalysts are mainly Ir/Ru-based materials,while the shortage and the high cost of Ir and Ru signigicantly limit the large-scale industrial application of the Ir/Ru-based catalysts.Therefore,the development of efficient,stable and low-cost catalysts for OER is urgent.Herein,we focus on studying non-precious metal-based catalysts.Through morphological structure design and electronic structure modulation,we can increase the number of active sites and/or improve the intrinsic activities of the active sites,and thus enhance the OER activities of the catalysts.The main contents of this thesus are shown as below:?1?Design of Co carbonate hydroxide-based catalysts and their electrocatalytic performance studies.Carbon coated N and Fe modified Co carbonate hydroxide nanoneedle arrays grown on carbon cloth?C@NFe₁Co₁CH/CC?as OER catalysts was prepared by hydrothermal reaction and annealing at low tempreture.N and Fe co-modification is applied to improve OER acticity of Co CH.Metal-N-C species introduced by Fe and N modifcation change the rate determining step of OER and thus obviously improve the electrocatalytic activity of C@NFe₁Co₁CH/CC.Meanwhile,the carbon coating and continuous conductive carbon cloth backbones guarantee fast and stable electron transfer on its surface.As a result,the C@NFe₁Co₁CH/CC catalyst exhibits a low overpotential of 235 m V at 10 m A cm^-2 and a high mass activity of 681.4 A g^-1in alkaline solution.And the OER activity of C@NFe₁Co₁CH/CC is superior to those of other prepared Co CH-based catalysts and many reported Co-based catalysts.Moreover,a series of experiments demonstrate that the metal sites contribute more to activities of catalysts than the N-C sites,while the metal-N sites outperform the metal-O sites.?2?Design of Fe Ni metal-organic framework?Fe Ni MOF?and their electrocatalytic performance studies.Ultrasmall Ce O₂ nanoclusters?5 nm?were introduced onto Fe Ni MOF nanosheets by electrodeposition.The OER activity of MOFs is enhanced by constructing the interfaces between metal oxides and MOFs.The doping of Ce O₂ clusters and the strong interfacial electronic interaction between Ce O₂ and Fe Ni MOF can not only tune the electronic structures of Fe and Ni sites in Fe Ni MOF and thus improve their activities,but also accelerate the electron transfer rate and thus enhance the intrinsic activity of Ce O₂/Fe Ni MOF.In 1 M KOH solution,Ce O₂/Fe Ni MOF exhibits a much better OER activity than Fe Ni MOF and other reported MOF-based catalysts.And this catalyst only needs overpotentials of 220 m V and 233 m V to achieve current densities of 50 m A cm^-2 and 100 m A cm^-2,respectively.Besides,Ce O₂/Fe Ni MOF presents an outstanding stability over 50 h at 50 m A cm^-2.?3?Investigation of structure evolutions of Fe Ni MOF and Fe Ni layered double hydroxide?Fe Ni LDH?during OER process,design of Fe Ni-based hydroxide catalysts and their electrocatalytic performance studies.The evolution mechanisms of Fe Ni MOF and Fe Ni LDH during OER process were studied by in-situ and ex-situ Raman spectroscopy as well as X-ray diffraction.We found that both Fe Ni MOF and Fe Ni LDH finally evolved into metal?oxy?hydroxides?MOOH,M=Fe and Ni?during OER process,but the transformation kinetics of Fe Ni MOF is faster than Fe Ni LDH.Based on this finding,we designed and synthesized a novel nickel foam supported MOOH/Fe Ni LDH nanosheet arrays as OER catalyst.This MOOH/Fe Ni LDH catalyst owns a higher catalytic activity than many reported Fe Ni-based hydroxide catalysts.And low overpotentials of218 m V and 250 m V are required for MOOH/Fe Ni LDH to afford the current density of 50 m A cm^-2 and the mass activity of 244.9 A g^-1,respectively.In addition,MOOH/Fe Ni LDH exhibits an excellent stability over 50 h at 50 m A cm^-2.