Here we report the electrochemical determination of the surface-area-to-volume ratio (SA/ V) of Au nanospheres (NSs) attached to electrode surfaces for size analysis. The SA is determined by electrochemically measuring the number of coulombs of charge passed during the reduction of surface AuO following Au NS oxidation in HClO, whereas V is determined by electrochemically measuring the coulombs of charge passed during the complete oxidative dissolution of all of the Au in the Au NSs in the presence of Br to form aqueous soluble AuBr. Assuming a spherical geometry and taking into account the total number of Au NSs on the electrode surface, the SA/ V is theoretically equal to 3/radius. A plot of the electrochemically measured SA/ V versus 1/radius for five different-sized Au NSs is linear with a slope of 1.8 instead of the expected value of 3. Following attachment of the Au NSs to the electrode and ozone treatment, the plot of SA/ V versus 1/radius is linear with a slope of 3.5, and the size based on electrochemistry matches very closely with those measured by scanning electron microscopy. We believe the ozone cleans the Au NS surface, allowing a more accurate measurement of the SA.

Here we describe the electrochemical size stability of 1.6, 4.1, and 15.1 nm diameter Au nanoparticles (NPs) supported on indium tin oxide-coated glass electrodes (glass/ITO). Anodic stripping voltammetry (ASV) and the electrochemically-measured total surface area-to-volume ratio (SA/V) provide the NP size following surface oxidation-reduction cycling from −0.2 to 1.6 V (vs Ag wire) in 0.1 M HClO 4 . After 1000 oxidation-reduction cyclic voltammetry (CV) scans, the relative size increases by a factor of 12, 7, and 2 for the 1.6, 4.1, and 15.1 nm diameter Au NPs, respectively. The relative size increase is largest for the smallest NPs, also confirmed by electron microscopy, indicating their lower size stability towards surface oxidation-reduction cycling. The size increase is fastest within the first 200 cycles, which decreases with a further increase in the number of cycles until the Au NP diameter stabilizes. The size transformation is more dramatic at higher Au NP electrode coverage and 30%-100% of the Au dissolves during cycling, depending on the coverage and NP size. Various potential cycling and holding profiles show that the Au NP size increases during reduction of the oxide layer, consistent with an electrochemical Ostwald ripening mechanism.

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We describe the electrooxidation and size stability of 0.9 nm average diameter triphenylphosphine monosulfonate (TPPS)‐stabilized Au nanoclusters (NCs) as compared to 1.6 nm tetrakis(hydroxymethyl)phosphonium chloride (THPC)‐stabilized Au NCs and 4.1 nm citrate (Cit)‐stabilized Au nanoparticles (NPs). The potential for oxidative dissolution in KBr follows the order of TPPS Au0.9nm NCs (0.219 V)

Here we report that the peak oxidation potential (E p,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 E p,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 E p,ox decreases as the SA/V increases as controlled by the assembly method. The measured E p,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).