Impact of the Assembly Method on the Surface Area-to-Volume Ratio and Electrochemical Oxidation Potential of Metal Nanospheres

Abstract

Here we report that the peak oxidation potential (Ep,ox) of electrode-attached Au nanospheres (NSs) in anodic stripping voltammetry (ASV) experiments depends on the electrochemically measured surface area-to-volume ratio (SA/V). The SA/V in turn depends on the method of NS assembly onto the electrode, which results in different Ep,ox values for the same-sized Au NSs that are assembled in different ways onto the same electrode material. The assembly methods tested on indium tin oxide-coated glass electrodes (glass/ITO) include electrostatic attachment to an amine-functionalized silane linker, electrophoretic deposition (EPD), direct drop-cast deposition, and drop-cast deposition after mixing with carbon black. The measured SA/V of same-sized NSs follows the order of silane linker > EPD > drop-cast with carbon black > direct drop-cast. The Ep,ox decreases as the SA/V increases as controlled by the assembly method. The measured Ep,ox for the Au NSs correlated to the measured SA/V better than the actual NS diameter. These findings reveal important information about what ultimately controls the oxidative stability of metal NSs and can help to explain previously described electrode effects on metal NS oxidation potentials. These results also provide guidelines for choosing an assembly method that optimizes the SA/V for performance and stability against oxidation or ripening (size increase).