| Nickel-cobalt?Ni-Co?alloy is an important transition metal alloy with good magnetic properties,hydrogen storage,wear resistance and chemical stability.Electrodeposition is often used in industrial production to prepare Ni-Co alloys.However,hydrogen evolution is serious during electrodeposition of Ni-Co alloys,which often leads to hydrogen embrittlement of the coatings,and secondary treatment of electrolytes is likely to cause secondary pollution.How to solve the above problems has been research focus.In this paper,Ni-Co alloy coatings were prepared by electrodeposition in choline chloride-urea,choline chloride-lactic acid,choline chloride-ethylene glycol and 1-butyl-2-methylimidazolium hexafluorophosphate.Determination of choline chloride-urea,choline chloride-lactic acid,choline chloride-ethylene glycol and 1-butyl-2-methylimidazolium hexafluorophosphate by Fourier transform infrared spectroscopy,ultraviolet-visible-near-infrared spectrophotometer,Raman spectroscopy,etc.The coordination structure of ionic liquid with nickel and cobalt ions showed that nickel ions are commonly coordinated in tetrahedral or octahedral structures in eutectic solvents.However,the structure is variable in the choline chloride-ethylene glycol solution,and there is also a planar structure,and it is also proved that urea and metal ions are complexed in the choline chloride-urea system.On this basis,the density functional theory is used to study the stable complex structure of Ni2+and Co2+and its frontier orbital information.The results show that the most active surface of the electrode is[NiCl5H2O]3-and[CoCl4]2-,it may be reduced at the cathode.The electrochemical behavior and electrocrystallization mechanism of nickel-cobalt alloy in four different ionic liquids were studied by cyclic voltammetry and chronoamperometry.The results show that the redox reaction of nickel-cobalt alloy in eutectic solvent system is under diffusion control and the process is an irreversible.The electrocrystallization process of nickel-cobalt alloy in the above four systems all follows three-dimensional instantaneous nucleation.The electrocrystallization process is also a three-dimensional instantaneous nucleation,in addition to the calculation of choline chloride-urea,choline chloride-lactic acid,choline chloride-ethylene glycol and 1-butyl2-methylimidazolium hexafluorophosphate.The diffusion constants of the binary alloy ions in the system are 3.018×10-8cm2s-1,3.997×10-9cm2s-1,3.957×10-8cm2s-1and2.267×10-7cm2s-1,respectively.The Ni-Co alloy in the BmimPF6 system is more easily reduced.The coordination structures of Ni2+and Co2+in different ionic liquid systems were estimated by FT-IR,UV-Vis and Raman spectroscopy.The results show that nickel ions are common in deep eutectic solvents which is tetrahedral or octahedra,however,the structure is variable in the CE solution,and there is also a planar structure,and it is proved that urea,water molecules and metal ions are complexed.On this basis,the density functional theory is used to study the stable complex structure of Ni2+and Co2+and its frontier orbital information.From the reduction activity,the most active surface of the electrode is[NiCl5H2O]3-and[CoCl4]2-,Most likely to be reduced at the cathode.The phase composition and content of the nickel-cobalt alloy coating were investigated by scanning electron microscopy?SEM?,electrochemical workstation,and X-ray diffractometry?XRD?.At the same time,the effects of main salt ratio,temperature,deposition time,current density and sodium citrate on the properties of the coating were studied.The optimal formula of the electrolyte was determined:?1?Choline chloride:urea=1:2,NiCl2·6H2O:CoCl2·6H2O=10:1,temperature is 50°C,deposition time 30 min,current density 1.8 A/dm2,0.04 g/L sodium citrate,nickel-cobalt alloy coating obtained at this time,corrosion potential Ecorr=-0.338 V,corrosion current Jcorr=1.675×10-8 A·cm-2,Rct=28100?·cm2;?2?Choline chloride:lactic acid=1:2,NiCl2·6H2O:CoCl2·6H2O=10:1.Temperature 55°C,deposition time 30min,current density 1.6 A/dm2,0.03 g/L sodium citrate,Ni-Co coating obtained at this time,corrosion potential Ecorr=-0.255 V,corrosion current Jcorr=2.172×10-66 A·cm-2,Rct=14000?·cm2;?3?The kinetic potential of-1.0 V in the choline chloride-glycol system can obtain the best corrosion-resistant nickel-cobalt alloy coating,corrosion The potential Ecorr=-0.277 V,the corrosion current Jcorr=1.73×10-66 A·cm-2,Rct=21155?·cm2;?4?The best corrosion resistance nickel can be obtained at a constant potential of-1.5 V in the BmimPF6 system,corrosion potential Ecorr=-0.268 V.The resulting Ni-Co alloy coating has a uniform and dense surface with an average grain size of 3.1 nm to 20.6 nm,and the Ni-Co alloy coating obtained by electrodeposition has a preferred orientation in the?200?direction. |
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