Perry Samuel C, Al Shandoudi Laila M, Denuault Guy
Chemistry, University of Southampton , Highfield, Southampton, SO17 1BJ, U.K.
Anal Chem. 2014 Oct 7;86(19):9917-23. doi: 10.1021/ac502645e. Epub 2014 Sep 19.
In sampled-current voltammetry (SCV), current transients acquired after stepping the potential along the redox wave of interest are sampled at a fixed time to produce a sigmoidal current-potential curve akin to a pseudo steady state voltammogram. Repeating the sampling for different times yields a family of sampled-current voltammograms, one for each time scale. The concept has been used to describe the current-time-potential relationship at planar electrodes but rarely employed as an electroanalytical method except in normal pulse voltammetry where the chronoamperograms are sampled once to produce a single voltammogram. Here we combine the unique properties of microdisk electrodes with SCV and report a simple protocol to analyze and compare the microdisk sampled-current voltammograms irrespective of sampling time. This is particularly useful for microelectrodes where cyclic voltammograms change shape as the mass transport regime evolves from planar diffusion at short times to hemispherical diffusion at long times. We also combine microdisk sampled-current voltammetry (MSCV) with a conditioning waveform to produce voltammograms where each data point is recorded with the same electrode history and demonstrate that the waveform is crucial to obtaining reliable sampled-current voltammograms below 100 ms. To facilitate qualitative analysis of the voltammograms, we convert the current-potential data recorded at different time scales into a unique sigmoidal curve, which clearly highlights kinetic complications. To quantitatively model the MSCVs, we derive an analytical expression which accounts for the diffusion regime and kinetic parameters. The procedure is validated with the reduction of Ru(NH3)6(3+), a model one electron outer sphere process, and applied to the derivation of the kinetic parameters for the reduction of Fe(3+) on Pt microdisks. The methodology reported here is easily implemented on computer controlled electrochemical workstations as a new electroanalytical method to exploit the unique properties of microelectrodes, in particular at short times.
在采样电流伏安法（SCV）中，沿着感兴趣的氧化还原波改变电位后采集的电流瞬变在固定时间进行采样，以产生类似于伪稳态伏安图的S形电流-电位曲线。在不同时间重复采样会得到一系列采样电流伏安图，每个时间尺度对应一个。该概念已被用于描述平面电极上的电流-时间-电位关系，但除了在常规脉冲伏安法中（其中计时电流图被采样一次以产生单个伏安图）外，很少用作电分析方法。在这里，我们将微盘电极的独特性质与SCV相结合，并报告了一种简单的方案，用于分析和比较微盘采样电流伏安图，而无需考虑采样时间。这对于微电极特别有用，因为随着传质机制从短时间的平面扩散演变为长时间的半球形扩散，循环伏安图的形状会发生变化。我们还将微盘采样电流伏安法（MSCV）与一个调节波形相结合，以产生伏安图，其中每个数据点都是在相同的电极历史条件下记录的，并证明该波形对于获得低于100 ms的可靠采样电流伏安图至关重要。为了便于对伏安图进行定性分析，我们将在不同时间尺度记录的电流-电位数据转换为一条独特的S形曲线，这清楚地突出了动力学复杂性。为了对MSCV进行定量建模，我们推导了一个考虑扩散机制和动力学参数的解析表达式。该程序通过Ru(NH3)6(3+)的还原（一个典型的单电子外层球过程）进行了验证，并应用于推导Pt微盘上Fe(3+)还原的动力学参数。这里报道的方法很容易在计算机控制的电化学工作站上实现，作为一种利用微电极独特性质的新电分析方法，特别是在短时间内。
