Zoski Cynthia G, Luman Charles R, Fernández José L, Bard Allen J
Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, USA.
Anal Chem. 2007 Jul 1;79(13):4957-66. doi: 10.1021/ac070021c. Epub 2007 May 26.
We discuss SECM tip voltammetry, where a UME tip is held above a conductive substrate within about a tip radius and a tip voltammogram is recorded as its potential is slowly scanned while the substrate is held at a fixed potential. When the potential of the substrate is changed, the series of steady-state tip voltammograms provide information about the reactants and products. When the potential of the substrate, ES, is set so that the reaction at the substrate is opposite to that at the tip (the usual SECM conditions), a total positive feedback (tpf) tip voltammogram is recorded. When the substrate potential is set to values where the reaction at the substrate is the same as that occurring on the tip, the tip is shielded from the species in the bulk solution. Depending upon the substrate potential, this can cause total shielding (ts) or a voltammogram that is the result of partial feedback/partial shielding (pf-ps). The result is a series of tip voltammograms that are characterized by tpf, pf-ps, or ts, depending upon ES. Experimental tip voltammograms resulting from the reversible reduction of TCNQ and oxidation of ferrocene in MeCN are reported. These are compared with those from simulations and approximate equations developed to describe the features of the tip voltammograms generated under tpf, ts, or pf-ps conditions. The effect of the diffusion coefficient ratio on the ability of the UME tip to reach a true steady state is also addressed and possible applications, e.g., obtaining information about the reversibility of an electrochemical reaction, the product of an electrochemical reaction, the stability of that product, or the diffusion coefficients of the electroactive species, are discussed.
我们讨论扫描电化学显微镜（SECM）尖端伏安法，其中超微电极（UME）尖端在导电基底上方约一个尖端半径内保持，在基底保持固定电位时，随着其电位缓慢扫描记录尖端伏安图。当基底电位改变时，一系列稳态尖端伏安图提供有关反应物和产物的信息。当将基底电位ES设置为使得基底上的反应与尖端上的反应相反（通常的SECM条件）时，记录到总正反馈（tpf）尖端伏安图。当将基底电位设置为基底上的反应与尖端上发生的反应相同的值时，尖端被与本体溶液中的物质屏蔽开。根据基底电位，这可能导致完全屏蔽（ts）或由部分反馈/部分屏蔽（pf-ps）产生的伏安图。结果是一系列根据ES以tpf、pf-ps或ts为特征的尖端伏安图。报道了在乙腈中TCNQ的可逆还原和二茂铁的氧化所产生的实验尖端伏安图。将这些与模拟结果以及为描述在tpf、ts或pf-ps条件下产生的尖端伏安图特征而开发的近似方程的结果进行了比较。还讨论了扩散系数比对于UME尖端达到真正稳态能力的影响，并讨论了可能的应用，例如获取有关电化学反应的可逆性、电化学反应的产物、该产物的稳定性或电活性物质的扩散系数的信息。
