Disk-Generation/Ring-Collection Scanning Electrochemical Microscopy:  Theory and Application

Abstract

The potential of ring-disk ultramicroelectrodes (RD UMEs) as probes for scanning electrochemical microscopy (SECM) was investigated both theoretically and experimentally. In particular, the disk-generation/ring-collection (DG/RC) mode of operation was considered. In this case, the interaction of two species with the substrate under investigation can be followed simultaneously from single tip current-distance measurement (approach curve) to the substrate. Theoretical approach curves for DG/RC were calculated by numerical methods. Such approach curves to both insulating and conducting substrates indicate a strong tip response dependence on the ring radius while the response was relatively insensitive to ring thickness and overall tip radius. The RD tip was characterized by fitting experimental approach curves recorded at insulating and conducting substrates to simulated curves for a given tip geometry. DG/RC SECM was then applied to investigate the partitioning of iodine across a liquid-liquid interface.

Microjet ring electrode (MJRE): Development, modelling and experimental characterisation

“…A value of D = 7.7 · 10 À6 cm 2 s À1 was obtained, which compares reasonably with literature values [60,61]. Armed with a knowledge of the diffusion coefficient and the inner radius of the rings (a = 108.5 lm) from optical microscopy, the current measured by LSV could be compared to that expected, given d = 1 lm for the epoxy-sealed electrode (estimated by optical microscopy) and d = 0.35 lm for the glass-sealed electrode (electron microscopy).…”

Theoretical evaluation of the collection efficiency at ring-disc microelectrodes

“…Electrode coupling between the ring and the disc, known as the collector-generator technique, has predominantly been used to study mass transport effects such as diffusion in scanning probe electrochemical microscopy (SECM) [11,12] and convection with impinging jet flow [13]. Macro ring-disc electrodes were extensively used to probe reaction kinetics [14], although micro ring-discs have yet to be used for this purpose.…”

Diffusional interactions at dual disk microelectrodes: comparison of experiment with three-dimensional random walk simulations

“…Because of the asymptotic nature of the working curve, Eqs. (11) and (12) will be most useful for smaller values of g K 10), where there is an appreciable change in S for a given change in g.…”

“…In each of these applications, it is critical to understand the diffusional interaction between the individual electrodes so that crosstalk can be minimized (when making independent measurements) or maximized (for electrochemiluminescence and diffusion layer titrations). For some types of multi-electrode probes, such as the dual microband [5][6][7]9,10] and microringdisk [11,12] electrodes, diffusional interactions have been modeled using computer simulations because their geometry can be reduced to two dimensions. However, many other probes lack this symmetry and therefore, modeling the diffusional interaction must be done in three dimensions.…”