Electrochemical Impedance Spectroscopy and First-Principle Investigations on the Oxidation Mechanism of Hypophosphite Anion in the Electroless Deposition System of Nickel

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1、J.Phys.Chem.C2008,112,4601-46074601ElectrochemicalImpedanceSpectroscopyandFirst-PrincipleInvestigationsontheOxidationMechanismofHypophosphiteAnionintheElectrolessDepositionSystemofNickelGuofengCui,*,²HongLiu,²GangWu,³JianweiZhao,*,§ShuqinSong,

2、andPeiKangShen

3、Sch

4、oolofChemistryandChemicalEngineering,SunYat-senUniVersity,Guangzhou510275,China,DepartmentofChemicalEngineering,UniVersityofSouthCarolina,Columbia,SouthCarolina29208,DepartmentofChemistry,NanjingUniVersity,Nanjing210093,China,andStateKeyLaboratoryofOptoelectroni

5、cMaterialsandTechnologies,SchoolofPhysicsandEngineering,SunYat-senUniVersity,Guangzhou510275,ChinaReceiVed:October4,2007;InFinalForm:December13,2007Inthiswork,theoxidationmechanismofhypophosphiteanion(H2PO2-)inacidicandalkalinemediainthepresenceofNi(II)speciewas

6、investigatedbyusingelectrochemicalimpedancespectroscopy(EIS)anddensityfunctionaltheory(DFT).InEIS,threemajorelectrochemicalprocessesintheelectrolessdepositionprocesswerefound,whenthesolutionpHrangedfrom5.5to9.5.Tounderstandthemicroscopicmechanismsinvolved,allpar

7、ticipatespeciesinthereactionpathwayswerecalculatedbytheDFTmethodalongwithanaturalbondorbital(NBO)analysis.Twoemulatingreactionsweredemonstrated:Path(I)passesthroughaprimarydehydrogenation(D-RP),andPath(II)includesaprimaryadditionofOH-(A-RP)onthehypophosphiteanio

8、n.Bycomparisonoftheenergylevelsofallspecies,itcanbeconcludedthatPath(II)isenergeticallyfavorableunderbothacidicandalkalineconditions.TheDFTandNBOanalysiscanprovidestrongevidencefortheloopsdetectedintheEIS,especiallyespeciallyfortheinductiveloop(IL-M)inthemedium-

9、frequencydomainthatiscausedbytheformationof[NiI-H3PO2(OH)]andthecapacitiveloop(CL-L)inthelow-frequencydomainby[H2PO2(OH)].Thecombinationofelectrochemicalanalysis(EIS)andfirstprincipletheory(DFT)analysisprovesthatitishelpfultoexplorethenatureoftheinteractionbetwe

10、enanodicandcathodicreactionsintheelectrolessdepositionprocess.1.Introductionisstillpoorlyunderstood.15-17Touhamifirstusedelectrochemi-calimpedancespectroscopy(EIS)toi