Sher Anna A, Bond Alan M, Gavaghan David J, Harriman Kathryn, Feldberg Stephen W, Duffy Noel W, Guo Si-Xuan, Zhang Jie
Oxford University Computing Laboratory, Wolfson Building, Parks Road, Oxford, OX1 3QD, United Kingdom.
Anal Chem. 2004 Nov 1;76(21):6214-28. doi: 10.1021/ac0495337.
Large-amplitude sinusoidal ac voltammetric techniques, when analyzed in the frequency domain using the Fourier transform-inverse Fourier transform sequence, produce the expected dc and fundamental harmonic ac responses in addition to very substantial second, third, and higher ac harmonics that arise from the presence of significant nonlinearity. A full numerical simulation of the process, Red right arrow over left arrow Ox + e(-), incorporates terms for the uncompensated resistance (R(u)), capacitance of the double layer (C(dl)), and slow electron transfer kinetics (in particular, the reversible potential (E degrees ), rate constant (k(0)), and charge transfer coefficient (alpha) from the Butler-Volmer model). Identification of intuitively obvious patterns of behavior (with characteristically different sensitivity regimes) in dc, fundamental, and higher harmonic terms enables simple protocols to be developed to estimate R(u), C(dl), E degrees , k(0), and alpha. Thus, if large-amplitude sinusoidal cyclic voltammograms are obtained for two concentrations of the reduced species, data obtained from analysis of the recovered signals provide initial estimates of parameters as follows: (a) the dc cyclic component provides an estimate of E degrees (because the R(u) and k(0) effects are minimized); (b) the fundamental harmonic provides an estimate of C(dl) (because it has a high capacitance-to-faradaic current ratio); and (c) the second harmonic provides an estimate of R(u), k(0), and alpha (because the C(dl) effect is minimized). Methods of refining the initial estimates are then implemented. As a check on the fidelity of the parameters (estimated on the basis of an essentially heuristic approach that solely utilizes the dc, fundamental, and second harmonic voltammograms), comparison of the predicted simulated and experimental third (or higher) harmonic voltammograms can be made to verify that agreement between theory and experiment has been achieved at a predetermined level. The use of the heuristic pattern recognition approach to evaluate the oxidation of ferrocene at a platinum electrode (a reversible process) in the very high resistance solvent dichloromethane (0.1 M Bu(4)NPF(6)) and the reduction of Fe(CN(6))(-) at a glassy carbon electrode (a quasi-reversible process) in much lower resistance but higher capacitance conditions found in aqueous (0.5 M KCl) media is described and verifies the inherent advantages of employing large-amplitude sinusoidal techniques in quantitative studies of electrode processes.
当使用傅里叶变换 - 逆傅里叶变换序列在频域中分析大振幅正弦交流伏安技术时，除了由于显著非线性的存在而产生的非常可观的二次、三次及更高次交流谐波外，还会产生预期的直流和基波交流响应。对氧化还原过程（Red右箭头在左箭头Ox + e(-)之上）进行完整的数值模拟，纳入了未补偿电阻（R(u)）、双层电容（C(dl)）以及缓慢电子转移动力学（特别是巴特勒 - 伏默模型中的可逆电位（E°）、速率常数（k(0)）和电荷转移系数（α））等项。识别直流、基波和更高次谐波项中直观明显的行为模式（具有特征性不同的灵敏度范围），使得能够开发简单的协议来估计R(u)、C(dl)、E°、k(0)和α。因此，如果针对还原态物质的两种浓度获得大振幅正弦循环伏安图，从对恢复信号的分析中获得的数据可按如下方式提供参数的初始估计值：(a) 直流循环分量提供E°的估计值（因为R(u)和k(0)的影响最小化）；(b) 基波谐波提供C(dl)的估计值（因为它具有高电容与法拉第电流比）；(c) 二次谐波提供R(u)、k(0)和α的估计值（因为C(dl)的影响最小化）。然后实施改进初始估计值的方法。作为对参数保真度的检验（基于一种本质上启发式的方法进行估计，该方法仅利用直流、基波和二次谐波伏安图），可以比较预测的模拟和实验三次（或更高次）谐波伏安图，以验证理论与实验之间在预定水平上达成了一致。描述了使用启发式模式识别方法评估在高电阻溶剂二氯甲烷（0.1 M Bu(4)NPF(6)）中铂电极上二茂铁的氧化（一个可逆过程）以及在水相（0.5 M KCl）介质中较低电阻但较高电容条件下玻碳电极上Fe(CN(6))(-)的还原（一个准可逆过程），并验证了在电极过程定量研究中采用大振幅正弦技术的固有优势。
