Electrochemical Kinetics of AgAg+ and TMPDTMPD+ in the Room-Temperature Ionic Liquid [C4mpyrr][NTf2]; toward Optimizing Reference Electrodes for Voltammetry

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• 作者：Emma I. Rogers ; Debbie S. Silvester ; Sarah E. Ward Jones ; Leigh Aldous ; Christopher Hardacre ; Angela J. Russell ; Stephen G. Davies ; Richard G. Compton
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：September 20, 2007
• 年：2007
• 卷：111
• 期：37
• 页码：13957 - 13966
• 全文大小：208K
• 年卷期：v.111,no.37(September 20, 2007)
• ISSN：1932-7455

文摘

The voltammetry and kinetics of the AgAg⁺ system (commonly used as a reference electrode material inboth protic/aprotic and RTIL solvents) was studied in the room-temperature ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C₄mpyrr][NTf₂] on a 10 m diameter Pt electrode.For the three silver salts investigated (AgOTf, AgNTf₂, and AgNO₃, where OTf^- = trifluoromethanesulfonate,NTf₂^- = bis(trifluoromethylsulfonyl)imide, and NO₃^- = nitrate), the voltammetry gave rise to a redox couplecharacteristic of a "deposition/stripping" process at the platinum electrode surface. Using potential stepchronoamperometry, the diffusion coefficients of AgOTf, AgNTf₂, and AgNO₃ were found to be 1.05, 1.17,and 5.00 × 10^-11 m² s^-1. All three voltammograms were theoretically modeled to reveal surprisingly slowstandard electrochemical rate constants, k⁰, of 2.0, 1.5, and 0.19 × 10^-4 cm s^-1 respectively for the Ag⁺Ag⁰couple. As a potentially faster alternative to the AgAg⁺ system, the voltammetry and kinetics of theTMPDTMPD⁺ system (where TMPD = N,N,N ',N'-tetramethyl-p-phenylenediamine) was also studied, usingneutral TMPD and two TMPD radical cation salts, with BF₄^- and NTf₂^- counter anions. Diffusion coefficientsfor TMPD, TMPD⁺BF₄^-, and TMPD⁺NTf₂^- were calculated to be 1.84, 1.35, and 1.43 × 10^-11 m² s^-1respectively, and a k⁰ value of 2.6-2.8 × 10^-3 cm s^-1 was obtained from theoretical fitting of the cyclicvoltammetry. This number is an order of magnitude larger than that for the AgAg⁺ system, allowing for thesuggestion that the TMPDTMPD⁺ system may be more suitable than the AgAg⁺ system as a redox couplefor use in reference electrodes for ionic liquids.