Voltammetric scanning electrochemical cell microscopy: Dynamic imaging of hydrazine electro-oxidation on platinum electrodes

Voltammetric scanning electrochemical cell microscopy (SECCM) incorporates cyclic voltammetry measurements in the SECCM imaging protocol, by recording electrochemical currents in a wide potential window at each pixel in a map. This provides much more information compared to traditional fixed potential imaging. Data can be represented as movies (hundreds of frames) of current (over a surface region) at a series of potentials and are highly revealing of subtle variations in electrode activity. Furthermore, by combining SECCM data with other forms of microscopy, e.g. scanning electron microscopy and electron backscatter diffraction data, it is possible to directly relate the current-voltage characteristics to spatial position and surface structure. In this work we use a "hopping mode", where the SECCM pipet probe is translated toward the surface at a series of positions until meniscus contact. Small amounts of residue left on the surface, upon probe retraction, demark the precise area of each measurement. We use these techniques to study hydrazine oxidation on a polycrystalline platinum substrate both in air and in a deaerated environment. In both cases, the detected faradaic current shows a structural dependence on the surface crystallographic orientation. Significantly, in the presence of oxygen (aerated solution) the electrochemical current decreases strongly for almost all grains (crystallographic orientations). The results highlight the flexibility of voltammetric SECCM for electrochemical imaging and present important implications for hydrazine electroanalysis.