Trans.Nonferrous Met.Soc.China31(2021)832−841
Physicochemical properties of1,3-dimethyl-2-imidazolinone−ZnCl2
solvated ionic liquid and its application in zinc electrodeposition
Ai-min LIU1,Meng-xia GUO1,Zhong-ning SHI2,Yu-bao LIU3,
Feng-guo LIU1,Xian-wei HU1,You-jian YANG1,Wen-ju TAO1,Zhao-wen WANG1
1.Key Laboratory for Ecological Metallurgy of Multimetallic Mineral(Ministry of Education),
Northeastern University,Shenyang110819,China;
2.State Key Laboratory of Rolling and Automation,Northeastern University,Shenyang110819,China;
3.State Key Laboratory of Baiyunobo Rare Earth Resource Rearches and Comprehensive Utilization,
Baotou Rearch Institute of Rare Earths,Baotou014030,China
Received12April2020;accepted10November2020
Abstract:Zinc chloride(ZnCl2)was dissolved in the1,3-dimethyl-2-imidazolinone(DMI)solvent,and the metallic zinc coatings were obtained by electrodeposition in room-temperature ambient air.The conductivity(σ),viscosity(η), and density(ρ)of the DMI−ZnCl2solvated ionic liquid at various temperatures(T)were measured and fitted. Furthermore,cyclic voltammetry was ud to study the electrochemical behavior of Zn(II)in the DMI−ZnCl2solvated ionic liquid,indicating that the reduction
of Zn(II)on the tungsten electrode was a one-step two-electron transfer irreversible process.XRD and SEM−EDS analysis of the cathode product confirmed that the deposited coating was metallic zinc.Finally,the effects of deposition potential,temperature and duration on the morphology of zinc coatings were investigated.The results showed that a den and uniform zinc coating was obtained by potentiostatic electro-deposition at−2V(vs Pt)and353K for1h.
Key words:electrodeposition;zinc;1,3-dimethyl-2-imidazolinone;physicochemical properties;cyclic voltammetry
1Introduction
Zinc is usually deposited on the surface of steel materials to obtain a den and uniform coating with excellent adhesion.Zinc,ud as a sacrificial anode,can protect the steel materials against corrosion[1].Conditional production of zinc coatings was carried out with electrodeposition in the aqueous cyanide,basic non-cyanide,and chloride solutions.However,the electrodeposition of zinc in aqueous solutions has disadvantages such as hydrogen embrittlement,wastewater treatment, and low current efficiency[2,3].Thus,it is of significant direction to ek new solvents from which high-quality zinc coatings can be deposited without environmental pollution.
In recent years,the electrodeposition of zinc and its alloys in ionic liquids have attracted increasing attention from rearchers.Compared with aqueous solutions,ionic liquids have better thermal stability,lower vapor pressure,and wider electrochemical windows[4−6].LIN and SUN[7] reported that zinc could be electrodeposited from the ZnCl2−1-methyl-3-ethylimidazolium chloride (ZnCl2−MEIC with molar ratio of1:1)and ZnCl2−AlCl3−MEIC ionic liquid at potential of −0.8V(vs Al).HSIU et al[8]investigated the influence of electrolyte composition on the electrochemical window of the ZnCl2−1-ethyl-3-methylimidazolium chloride(ZnCl2−EMIC)ionic liquid,indicating that the electrochemical window
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Corresponding author:Zhong-ning SHI;Tel:+86-24-83686381;E-mail:**************.edu DOI:10.1016/S1003-6326(21)65542-5
1003-6326/©2021The Nonferrous Metals Society of China.Published by Elvier Ltd&Science Press
Ai-min LIU,et al/Trans.Nonferrous Met.Soc.China31(2021)832−841833
was−2V when the ZnCl2−EMIC ionic liquid was acidic,and zinc coating was able to deposit at −0.05V(vs Zn)and383K.DENG et al[9] electrodeposited zinc in the N-butyl-N-methyl-pyrrolidinium dicyandiamide(BMP-DCA)ionic liquid containing ZnCl2at−2.4V(vs Fc/Fc+)and 323K.Zn and Zn−Au a
lloy were obtained on a Au electrode by electrodeposition in the ZnCl2−1-butyl-3-methylimidazolium chloride(ZnCl2−BMIC with molar ratio of3:2)ionic liquid,while Zn−Co alloy was produced from the ZnCl2−BMIC ionic liquid containing1.16wt.%CoCl2[10,11]. However,above ionic liquids are expensive,and electrodeposition experiments should be performed in a glove box filled with inert gas becau the ionic liquids are nsitive to the air and water, which greatly limits their industrial application.
Deep eutectic solvents(DES),which were first described by ABBOTT in2003,have been widely studied for electrochemical application due to their low cost.XU et al[12]obtained Zn−Ti alloy by electrodeposition in the ZnCl2−urea(molar ratio of 3:1)DES containing0.27mol/L TiCl4at353K. YANG et al[13]prepared Zn−Ni alloy coating from the choline chloride−urea(ChCl−urea with molar ratio of1:2)DES containing0.1mol/L NiCl2 and0.4mol/L ZnCl2at343K,while CHU et al[14] prepared Zn−Co alloy coating from the DES containing0.11mol/L ZnCl2and0.01mol/L CoCl2. LI et al[15]added0.10g/L GO(graphene oxide)to the ChCl−urea DES containing0.2mol/L ZnCl2, and successfully produced a novel Zn−GO composite coating by pul electrodeposition. SANCHEZ et al[16]prepared Zn−Ce coating in the ChCl-urea DES containing0.3mol/L ZnCl2and 0.1mol/L CeCl3.LI et al[17]electrodeposited Zn−Ni alloy coatings with controllable components and excellent corrosion res
翻译 在线istance by adding5wt.% water to the ChCl−urea DES containing0.08mol/L NiCl2and0.4mol/L ZnCl2.BAO et al[18] explored the electrochemical deposition of Zn from lactate−ChCl(molar ratio of2:1)at a constant current density of10mA/cm2.BAKKAR and NEUBERT[19]obtained bulk Zn layers from the ChCl−urea−EG(ethylene glycol)DES(molar ratio of1:1.5:0.5)at potential ranging from−1.2to −1.5V(vs Ag).VIEIRA et al[20]investigated the electrochemical behavior of zinc in the ChCl−EG (molar ratio of1:2)DES containing ZnCl2on different electrodes including glassy carbon,stainless steel,Au,Pt,Cu and Zn.PEREIRA et al[21]prepared zinc from the ChCl−EG DES containing5×10−4mol/mL ZnCl2,and found that the additive of dimethyl sulfoxide(DMSO)could achieve grain refinement and produce zinc with a minimum grain size of31.7nm.ALESARY et al[22]obtained a bright zinc coating by adding nicotinic acid,boric acid,and benzoquinone to the ChCl−EG DES containing6×10−4mol/mL ZnCl2.
ENDO et al[23]found that a smooth aluminium film can be obtained by electrode-position in the1,3-dimethyl-2-imidazolidinone−AlCl3(DMI−AlCl3)ionic liquid at313K when the content of AlCl3was higher than50at.%.Recently, ZHANG et al[24]reported an exceptional organic solvent compod of DMI and LiNO3,and directly deposited a La film from LaCl3at−2.3V(vs Ag) and298K.It was found that the DMI solvent has good solubility and coordination ability for chlorides,and it has advantages i
crowdedncluding low cost, low melting point,being innsitive to water,and wide electrochemical window.In this work,ZnCl2 was dissolved in the DMI solvent for zinc electrodeposition.The conductivity,viscosity and density of the DMI−ZnCl2solvated ionic liquid at different temperatures were measured.Furthermore, the solubilities of ZnCl2in the DMI solvent at different temperatures were measured,and the electrochemical behavior of Zn(II)in DMI−ZnCl2 ionic liquid was investigated by cyclic voltammetry and potentiostatic electrodeposition.
2Experimental
Zinc chloride(ZnCl2,98%)and1,3-dimethyl-2-imidazolidinone(DMI,99%)were purchad from Shanghai Aladdin Bio-Chem Technology Co., Ltd.,China.The DMI−ZnCl2solvated ionic liquid was prepared by adding0.29g/mL ZnCl2to the DMI solvent and stirring on a magnetic heating plate in ambient atmosphere.The conductivity, viscosity,and density of the ionic liquid were measured bad on the fixed cell constant method, the rotation method,and the Archimede’s principle, respectively.Moreover,the solubilities of ZnCl2in the DMI solvent were measured by the equilibrium method.
Cyclic voltammetry was performed using a three-electrode system by a electrochemical workstation(CHI600E,Shanghai Chenhua
Ai-min LIU,et al/Trans.Nonferrous Met.Soc.China31(2021)832−841 834
Instrument,Shanghai,China).A tungsten wire (99.99%,diameter of1mm)was ud as the working electrode,while two platinum wires (99.99%,diameter of1mm)were ud as the counter electrode and the reference electrode, respectively.The surface of electrodes were polished with sandpapers,cleaned with ethanol and deionized water,and then dried before the measurement of cyclic voltammogram.The working electrode was immerd in the ionic liquid with depth of1.4cm.
Electrodeposition experiments were also carried out using a three-electrode system by the CHI600E electrochemical workstation.The working electrode was a tungsten sheet(99.99%, side area of1cm2),while the counter electrode and the reference electrode were platinum wires.After electrodeposition experiments,the surface of the working electrode was washed with acetone and distilled water,dried naturally and then stored in a glove box,in which the contents of water and oxygen were below1×10−6.X-ray diffraction(XRD, D8ADVANCE,Bruker,Germany)was ud to analyze the pha structure of the zinc deposited on tungsten substrates.In addition,the surface morphology and elemental composition of zinc coatings were studied by a scanning electron microscope(SEM,ULTRA PLUS,Zeiss Microscope,Germany)combined with X-ray dispersive energy spectrometer(EDS).
3Results and discussion
3.1Physical and chemical properties of DMI−
ZnCl2solvated ionic liquid
The relationship between the conductivities of the DMI−ZnCl2solvated ionic liquid and temperature(313−303K)is shown in Fig.1(a).It can be en that the conductivity incread from 0.571to0.932mS/cm when the temperature incread from313to363K.This was becau the increa of the temperature was beneficial to the diffusion of ions in the ionic liquid,which promoted the mass transfer rate and caud the incread of conductivity.However,the increa rate of conductivity was small at353−363K.
Fig.1Conductivities of DMI−ZnCl2solvated ionic liquid as function of temperature(a),relationship between lnσand T−1(b),viscosities of DMI−ZnCl2solvated ionic liquid as function of temperature(c)and relationship between lnηand T−1(d)
Ai-min LIU,et al/Trans.Nonferrous Met.Soc.China31(2021)832−841835
The conductivity of the DMI−ZnCl2solvated ionic liquid was of the same order of magnitude as that o
f some conventional ionic liquids ranging from0.1to10mS/cm[25].For example,the conductivity of the EMIC ionic liquid at298K was reported to be 3.43−3.71mS/cm[26].In comparison,the conductivity of the DMI−ZnCl2 solvated ionic liquid was much smaller than that of the aqueous solution containing3.7mol/L ZnCl2at 298K(107mS/cm)[27].However,the conductivity of the DMI−ZnCl2solvated ionic liquid was larger than that of the urea−ZnCl2(molar ratio of3:1) DES at298K(0.051mS/cm)[12],and the urea−ZnCl2(molar ratio of3.5:1)and ChCl−ZnCl2 (molar ratio of1:2)DES at315K(0.18and 0.06mS/cm,respectively)[28].As we know,the DMI solvent is an organic liquid with small conductivity.Therefore,it can be indicated that the conductivity of the DMI solvent was modified by the Lewis acidic cation Zn(II),and the DMI−ZnCl2 solvated ionic liquid that has similar characteristics as conventional ionic liquid was obtained.
In general,the relationship between the conductivity of ionic liquid and temperature can be expresd using the Arrehnius equation[25]:
lnσ=lnσ0−Eσ/(RT)(1) whereσis the conductivity(mS/cm),σ0is a pre-factor(mS/cm),Eσis the conductivity activation energy(kJ/mol),R is the ideal gas constant(8.314J·K−1·mol−1),and T is the temperature(K).As shown in Fig.1(b),there was a good linear relationship between lnσand T−1. Through linear fitting,the relationship between the conductivity of DMI−ZnCl2solvated ionic liquid and
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temperature can be expresd by Eq.(2),and the activation energy of the conductivity was determined to be9.387kJ/mol:
lnσ=3.095−1129.059/T(2) The high viscosity of ionic liquids is one of the bottlenecks preventing them from gaining large-scale industrial applications.In general,the viscosity of ionic liquid is determined by the internal van der WAALS force and the interaction of hydrogen bonds.Thus,suitable additives are added to the ionic liquid to reduce the viscosity.In this work,the viscosities of the DMI−ZnCl2 solvated ionic liquid at323−373K were measured by the rotation method.The relationship between the viscosities of the DMI−ZnCl2solvated ionic liquid and temperature is shown in Fig.1(c).The viscosity decread with increasing temperature becau the van der WAALS force and hydrogen bond strength within the system changed with temperature.Furthermore,the relationship between viscosity and temperature can be expresd by the Arrhenius formula[29]:
lnη=lnη0+Eη/(RT)(3) whereηis viscosity(mPa·s),η0is a pre-factor (mPa·s),and Eηis the activation energy of viscosity (kJ/mol).As shown in Fig.1(d),there was a good linear relationship between lnηand T−1.By linear fitting,the relationship between the viscosity of DMI−ZnCl2solvated ionic liquid and temperature can be expresd by Eq.(4),and the activation energy of the viscosity was determin
ed to be 8.364kJ/mol:
lnη=−0.033+1006.014/T(4) The densities of the DMI−ZnCl2solvated ionic liquid at313−373K were measured by the Archimede’s principle.The relationship between the densities of the DMI−ZnCl2solvated ionic liquid and temperature is shown in Fig.
ikala
2.
Fig.2Densities of DMI−ZnCl2solvated ionic liquid as function of temperature
It can be found from Fig.2that the density demonstrated a linear relationship with temperature. Besides,the density gradually decread from1.205 to1.163g/cm3with temperature increasing from 313to373K,and the trend was relatively flat.This is becau when the temperature incread,the migration rate and spacing of particles in the ionic liquid incread,which caud the expansion of volume.Since the number of particles per unit area was diminished at higher temperature,the density became smaller.Through linear fitting,the densities
Ai-min LIU,et al/Trans.Nonferrous Met.Soc.China31(2021)832−841 836
of the DMI−ZnCl2solvated ionic liquid at different
temperatures can be expresd using the following
equation:
ρ=−6.464×10−4T+1.406(5)tahina
whereρis the density(g/cm3).
The concentration of ZnCl2in the DMI−ZnCl2
solvated ionic liquid is an important parameter
during the process of zinc electrodeposition.Hence,
the effect of temperature on the solubilities of ZnCl2
in the DMI solvent was explored.The solubilities
of ZnCl2in the DMI solvent at313,333,353
and373K were determined to be0.29,0.32,0.45,
and 1.58g/mL,respectively.With temperature
increasing from313to353K,the solubility of
ZnCl2gradually incread from0.29to0.45g/mL.
It was worth noting that when the temperature
incread from353to373K,the solubilities of
ZnCl2significantly incread from0.45to
1.58g/mL.However,the ionic liquid at373K
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became very viscous,and eventually turned
into a transparent colloid which was no longer
suitable for zinc electrodeposition.Therefore,it was
not recommended to perform zinc electro-bops
deposition experiments with saturated ZnCl2
concentration,especially at temperature higher than 373K.Therefore,the measurement of physico-chemical properties and electrochemical experiments in this work were carried out in the DMI−ZnCl2 solvated ionic liquid containing0.29g/mL ZnCl2at 313−373K.
3.2Electrochemical behavior of Zn(II)in DMI−
ZnCl2solvated ionic liquid
The electrochemical behavior of Zn(II)ions in the DMI−ZnCl2solvated ionic liquid at313K was studied by cyclic voltammetry using a tungsten working electrode.It can be en from Fig.3(a)that the cyclic voltammetry curve from1to−3V(vs Pt) was a straight line,and the current was almost zero, indicating that the DMI solvent was stable within this potential range.When0.29g/mL ZnCl2was dissolved in the DMI solvent,a pair of redox peaks were found within the electrochemical window of the DMI solvent.Obviously,the reduction peak corresponds to the reduction of Zn(II)ions to metallic zinc,while the oxidation peak was related to the peeling of metal zinc from the electrode surface.The ont potential of the reduction of Zn(II)ions was−1.13V(vs Pt),and the potential of the oxidation peak was−0.13V(vs Pt).Fig.3Cyclic voltammetry curves on tungsten electrode in DMI solvent and DMI−ZnCl2solvated ionic liquid at 313K(scan rate of40mV/s)(a)and in DMI−ZnCl2 solvated ionic liquid at353K and different scan rates(b) As en in Fig.3(b),the current densities of
the oxidation peaks incread as the scan rate incread from20to100mV/s,and the potential of the oxidation peaks shifted to the more positive values.However,the scan rate had no obvious influence on the current density and potential of the reduction peak,indicating that the reduction reaction was not controlled by diffusion.Besides, only one reduction signal was obrved.Therefore, the reduction
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of Zn(II)was a one-step two-electron transfer irreversible reaction process.Moreover,it should be noted that a“nucleation loop”related to the nucleation of the deposited zinc was obrved.
拜拜的英文3.3Effect of deposition potential,temperature
and duration on zinc coatings
The process of metal electrodeposition includes the formation and growth of crystal nuclei, and overpotential is the driving force for nucleation. According to the analysis from the cyclic
