We introduce a multiprobe platform for the investigation of single-walled carbon nanotubes (SWNTs) that allows the electrochemical response of an individual SWNT to be mapped at high spatial resolution and correlated directly with the intrinsic electronic and structural properties. With this approach, we develop a detailed picture of the factors controlling electrochemistry at SWNTs and propose a definitive model that has major implications for future architectures of SWNT electrode devices.

The scanning droplet-based technique, scanning electrochemical cell microscopy (SECCM), combined with electron backscatter diffraction (EBSD), is demonstrated as a powerful approach for visualizing surface structure effects on the rate of the oxygen reduction reaction (ORR) at polycrystalline platinum electrodes. Elucidating the effect of electrode structure on the ORR is of major interest in connection to 10 electrocatalysis for energy-related applications. The attributes of the approach herein stem from: (i) the ease with which the polycrystalline substrate electrode can be prepared; (ii) the wide range of surface character open to study; (iii) the possibility of mapping reactivity within a particular facet (or grain), in a pseudo-single crystal approach, and acquiring a high volume of data as a consequence; (iv) the ready ability to measure the activity at grain boundaries; and (v) an experimental arrangement (SECCM) that 15 mimics the three-phase boundary in low temperature fuel cells. The kinetics of the ORR was analyzed and a finite element model was developed to explore the effect of the three-phase boundary, in particular to examine pH variations in the droplet and the differential transport rates of the reactants and products. We have found a significant variation of activity across the platinum substrate, inherently linked to the crystallographic orientation, but do not detect any enhanced activity at grain boundaries. Grains with 20 (111) and (100) contributions exhibit considerably higher activity than those with (110) and (100) contributions. These results, which can be explained by reference to previous single crystal measurements, enhance our understanding of ORR structure-activity relationships on complex high-index platinum surfaces, and further demonstrate the power of high resolution flux imaging techniques to visualize and understand complex electrocatalyst materials.

Conducting carbon materials: A multi-microscopy approach shows that local heterogeneous electron-transfer rates at conducting diamond electrodes correlate with the local density of electronic states. This model of electroactivity is of considerable value for the rational design of conducting diamond electrochemical technologies, and also provides key general insights on electrode structure controls in electrochemical kinetics (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The characteristics of three different carbon electrodes, glassy carbon (GC), oxygen-terminated polycrystalline boron-doped diamond (pBDD) and "pristine" carbon nanotube networks (CNTN) as voltammetric sensors for detection of the neurotransmitter serotonin have been investigated. For each electrode, detection sensitivity was determined using cyclic voltammetry (CV), a technique often used to provide information on chemical identity in electrochemical assays. The CNTN electrodes were found to exhibit background current densities ca. two orders of magnitude smaller than the GC electrode and ca. twenty times smaller than pBDD, as a consequence of their "pristine" low capacitance and low surface coverage. This was a major factor in determining serotonin detection limits from CV, of 10 nM for the CNTN electrode, 500 nM for pBDD and 2 microM for GC. The two most sensitive electrodes (CNTN and pBDD) were further investigated in terms of resistance to electrode fouling. CV analysis showed that fouling was less on the pBDD electrode compared to the CNTN and, furthermore, for the case of pBDD could be significantly minimised by careful selection of the CV potential limits, in particular by scanning the electrode potential to suitably cathodic values after oxidation of the serotonin.