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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• 作者：Guofeng Cui ; Hong Liu ; Gang Wu ; Jianwei Zhao ; Shuqin Song ; Pei Kang Shen
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：March 27, 2008
• 年：2008
• 卷：112
• 期：12
• 页码：4601 - 4607
• 全文大小：342K
• 年卷期：v.112,no.12(March 27, 2008)
• ISSN：1932-7455

文摘

In this work, the oxidation mechanism of hypophosphite anion ( H₂PO₂^- ) in acidic and alkaline media in thepresence of Ni(II) specie was investigated by using electrochemical impedance spectroscopy (EIS) and densityfunctional theory (DFT). In EIS, three major electrochemical processes in the electroless deposition processwere found, when the solution pH ranged from 5.5 to 9.5. To understand the microscopic mechanisms involved,all participate species in the reaction pathways were calculated by the DFT method along with a natural bondorbital (NBO) analysis. Two emulating reactions were demonstrated: Path (I) passes through a primarydehydrogenation (D-RP), and Path (II) includes a primary addition of OH^- (A-RP) on the hypophosphiteanion. By comparison of the energy levels of all species, it can be concluded that Path (II) is energeticallyfavorable under both acidic and alkaline conditions. The DFT and NBO analysis can provide strong evidencefor the loops detected in the EIS, especially especially for the inductive loop (IL-M) in the medium-frequencydomain that is caused by the formation of [Ni^I-H₃PO₂(OH)] and the capacitive loop (CL-L) in the low-frequency domain by [H₂PO₂(OH)]. The combination of electrochemical analysis (EIS) and first principletheory (DFT) analysis proves that it is helpful to explore the nature of the interaction between anodic andcathodic reactions in the electroless deposition process.