Department of Chemistry, University of Washington , Seattle, Washington 98195-1700, United States.
J Am Chem Soc. 2016 Aug 24;138(33):10605-10. doi: 10.1021/jacs.6b05848. Epub 2016 Aug 12.
Colloidal semiconductor nanocrystals offer a unique opportunity to bridge molecular and bulk semiconductor redox phenomena. Here, potentiometric titration is demonstrated as a method for quantifying the Fermi levels and charging potentials of free-standing colloidal n-type ZnO nanocrystals possessing between 0 and 20 conduction-band electrons per nanocrystal, corresponding to carrier densities between 0 and 1.2 × 10(20) cm(-3). Potentiometric titration of colloidal semiconductor nanocrystals has not been described previously, and little precedent exists for analogous potentiometric titration of any soluble reductants involving so many electrons. Linear changes in Fermi level vs charge-carrier density are observed for each ensemble of nanocrystals, with slopes that depend on the nanocrystal size. Analysis indicates that the ensemble nanocrystal capacitance is governed by classical surface electrical double layers, showing no evidence of quantum contributions. Systematic shifts in the Fermi level are also observed with specific changes in the identity of the charge-compensating countercation. As a simple and contactless alternative to more common thin-film-based voltammetric techniques, potentiometric titration offers a powerful new approach for quantifying the redox properties of colloidal semiconductor nanocrystals.
胶体半导体纳米晶体为连接分子和体相半导体氧化还原现象提供了独特的机会。在这里，我们展示了电势滴定法作为一种定量测量自由-standing 胶体 n 型 ZnO 纳米晶体的费米能级和充电电位的方法，这些纳米晶体每个纳米晶体具有 0 到 20 个导带电子，对应于载流子密度在 0 到 1.2×10(20)cm(-3)之间。胶体半导体纳米晶体的电势滴定以前没有被描述过，而且类似的涉及如此多电子的任何可溶性还原剂的电势滴定也几乎没有先例。对于每个纳米晶体的集合，费米能级与载流子密度的线性变化都可以观察到，斜率取决于纳米晶体的尺寸。分析表明，集合纳米晶体的电容受经典表面电双层的控制，没有表现出量子贡献的证据。费米能级也随着电荷补偿抗衡离子的特定变化而发生系统的位移。作为比更常见的基于薄膜的伏安技术更简单和非接触的替代方法，电势滴定为定量测量胶体半导体纳米晶体的氧化还原性质提供了一种强大的新方法。
