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Over the past few decades the popularity of carbon as an electrode material has increased dramatically. The fact that so many different types of carbon materials are commercially available has led to their use in a wide range of applications. [1] However, despite the large amount of research conducted with carbon electrodes, there still remains uncertainty about the individual roles of the edge-plane and basal-plane regions in the electrochemical response of a graphite surface. Herein, we address this fundamental problem and introduce a novel approach to investigate the source of the electrochemical reactivity of graphite.A good way to understand the electrochemical properties of graphite electrodes is to study the voltammetry of welldefined graphite surfaces. For this reason, basal-plane highly ordered pyrolytic graphite (HOPG) is an attractive material; the surface consists of atomically flat basal-plane graphite terraces separated by steps and defects which expose extremely thin bands (multiples of 0.335 nm) of edge-plane graphite.[1, 2] Accordingly, the voltammetric characteristics of basal-plane HOPG electrodes in simple redox couples are well-documented. [1,3,4] HOPG cyclic voltammograms provide relatively poor fits to linear diffusion simulations and display an increased peak-to-peak separation, indicative of slow electron-transfer kinetics relative to other electrode materials. [1,[3][4][5] These characteristics become more pronounced if fewer defects are present on the surface. [6][7][8] With the aid of a 2D simulation approach that allowed us to take the actual size and separation of surface defects into account, we recently demonstrated that the characteristics of HOPG cyclic voltammograms are consistent with the voltammetry of a macroarray of nanobands (edge-plane steps). [9,10] In other words, for the range of redox couples considered, the basal plane was effectively inert (Supporting Information). Given that edge-plane steps can make up less than 0.5 % of the total electrode area, and heterogeneous electron-transfer electrons are known to occur at basal-plane terraces as well as edge-plane steps, [11,15] the suggestion that basal-plane graphite makes no contribution to HOPG voltammograms is quite controversial.For the work reported herein, we sought to prove beyond any doubt that the cyclic voltammetry response of basal-plane HOPG is solely due to the edge-plane steps present as defects on the electrode surface by selectively blocking the basalplane terraces to leave only the edge-plane defects uncovered; covering the basal-plane terraces with inert material should make no difference to the observed voltammetry. Although heterogeneous electron-transfer reactions occur at basal-plane terraces, a combination of nonlinear diffusion and the large difference in reactivity between basal-and edgeplane graphite gives cyclic voltammograms in which the basalplane terraces appear to be inert. For example, a previous study in which we compared experimental and simulated cyclic voltammograms for the oxidation of...

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In-situ AFM has been used to directly study the growth of individual lead nuclei on a highly boron doped diamond electrode and the rates at which they appear as a function of time and overpotential. This method represents a new approach to the study of these processes, previously only possible indirectly via comparison of potentiostatic current transients with models such as that of Scharifker and Mostany (Journal of Electroanalytical Chemistry, 1984, 177, 13). It therefore allows the assumptions made by these models to be tested in an independent manner. At high overpotentials, it is found that the growth rate of the nuclei is close to that predicted assuming diffusion control, a result representing the first direct verification that this is in fact the case using a method independent of current transient analysis. A re-expression for the Scharifker and Mostany equation for the current density, an improvement in that it allows less equivocal interpretation of the results, is suggested, and the nucleation rate derived from it compared with that determined directly by AFM. A very good agreement is found, demonstrating the validity of the in-situ AFM approach in this case, and also suggesting that the assumptions made by the Scharifker and Mostany model are substantially correct.