Preparation And Properties Of Metal-ion-doped Co₃O₄ Nanoarray Electrodes For Oxygen Evolution Reaction

With the rapid increase of distributed power generation technologies such as wind and solar power plants,the storage of massive excess electricity derived from these intermittent energies is becoming a prominent problem.Electrochemical water splitting for the renewable hydrogen production from these intermittent energies is considered as one of the most promising methods to solve this problem.In this paper,carbon fibre paper(CFP)possesses three-dimensional(3D)macroporous structure,excellent electrical performance and high stability,which is employed as the substrate material.Doped-metal-ions Co_xM_3-xO₄(M=Fe?Ni?Mn and Ce)nanoarrays grown on CFP are successfully fabricated by using the facile methods of hydrothermal synthesis and thermal decomposition.The morphologies,structure,ingredient and performances of Co₃O₄ nanoarray electrodes for OER(oxygen evolution reaction)were investigated by FESEM(field emission scanning electron microscopy),XRD(X-ray diffraction),TEM(transmission electron microscopy),XPS(X-ray photoelectron spectroscopy)and related electrochemical techniques.Studies have shown that the architectures of homogeneous Co_xFe_3-xO₄nano-arrays are vertically grown on CFP by a facile method of hydrothermal and heat treatment.Co₃O₄-NWs/CFP,Co_2.7Fe_0.3O₄-NWs/CFP and Co_2.3Fe_0.7O₄-NSs/CFP nanoarray electrodes were prepared by controlling the Fe³⁺concentration in the hydrothermal fluid.When the Fe³⁺concentration was set to zero and 0.1 M,the resultant Co_xFe_3-xO₄ maintained the morphology of nanowire.When the Fe³⁺concentration was increased to 0.3 M in the hydrosolvent,the morphology of Co_xFe_3-xO₄ changed from nanowires to nanosheets.Tafel slopes of Co_2.7Fe_0.3O₄-NWs/CFP and Co_2.3Fe_0.7O₄-NSs/CFP nanoarray electrodes in the alkaline solutions are 41.2 m V dec^-1 and 34.3 m V dec^-1,respectively,which is less than that of pure Co₃O₄-NWs/CFP electrode(188.7 m V dec^-1).The OER potential of the Co_2.3Fe_0.7O₄-NSs/CFP composite electrode has a very small fluctuation during the60000 s electrolysis at the different current densities(20-500 m A cm^-2).The Co_2.3Fe_0.7O₄-NSs/CFP composite electrode exhibited a remarkable stability at the current density of 1000 m A cm^-2 for>100 h without a morphology change.Motivated by the mechanisms of Fe³⁺deped Co₃O₄,doped Co_xM_3-xO₄ nanoarray electrodes with different metal ions of Ni,Mn and Ce were prepared on CFP by the methods of hydrothermal and subsequent heat treatment.All Co Ni O-NWs/CFP,Co Mn O-NWs/CFP,and Co Ce O-NWs/CFP nanoarray electrodes exhibited uniform nanowire architectures that is consistent with Co₃O₄-NWs/CFP.The doping of Ni,Mn,and Ce ions has not change the crystal structure of Co₃O₄.THe OER overpotentials of Co O-NWs/CFP,Co Ni O-NWs/CFP,Co Mn O-NWs/CFP and Co Ce O-NWs/CFP nanoarray electrodes at a current density of 10 m A cm^-2 in 1 M KOH 401 m V and 357m V,357 m V and 597 m V,respectively,indicating that the incorporation of Ni and Mn into the pristine Co₃O₄ nanowires can improve the electrocatalytic activities.The Co Ni O-NWs/CFP nanoarray electrode at a current density of 1000 m A cm^-2 achieved high OER stability of approximately 130 h,which is higher than that of pristine Co₃O₄,Co Mn O-NWs/CFP and Co Ce O-NWs/CFP nanoarray electrodes.