The micro-optical ring electrode Part 2: Theory for the transport limited, steady-state photocurrent

Abstract

The Micro-Optical Ring Electrode (MORE) is a photoelectrochemical device based on a ring microelectrode that uses the insulating material interior to the ring electrode as a light guide. In this paper, we derive asymptotic analytical expressions for the steady state, transport limited photocurrent generated at MOREs with thin microrings ((ring inner radius)/(ring outer radius) values > 0.99) for two general types of photoelectrochemical system (a) the PE (Photophysical-Electrochemical) system, wherein the photoexcited species itself is directly detected on the ring; and (b) the PCE (Photophysical-Chemical-Electrochemical) system, wherein the photoexcited species undergoes a homogeneous electron transfer reaction prior to electrochemical detection.

Microelectrode systems for the study of photochemical processes in solution

“…(12) and (14) supply expressions for [ * Ru 2+ ] ss and [Ru 3+ ] ss in terms of constants so that only MV Å+ needs to be treated. Eq.…”

“…[ * Ru 2+ ] ss and [Ru 3+ ] ss were defined in Eqs. (12) and (14), respectively. Note that the kinetic term only applies to the region of solution in which the photochemical reaction occurs (defined by the fibre core and indicated by the dashed lines for each of the three geometries in Fig.…”

“…Notably, an optoelectrochemical probe consisting of an optical fibre coated in metal to form a ring ultramicroelectrode (UME) was introduced by Kuhn and Weber for the electrochemical detection of photogenerated species in solution [8]. This type of optical ring electrode was successfully developed further for imaging purposes [9,10] and kinetic studies of photochemical processes [11][12][13]. For example, the micro-optical ring electrode (MORE) was used to detect electro-active species with lifetimes <9 Â 10 À5 s [11] and to study photoelectrochemical kinetics [12].…”

“…This type of optical ring electrode was successfully developed further for imaging purposes [9,10] and kinetic studies of photochemical processes [11][12][13]. For example, the micro-optical ring electrode (MORE) was used to detect electro-active species with lifetimes <9 Â 10 À5 s [11] and to study photoelectrochemical kinetics [12]. Ring electrodes are characterised by well-defined mass-transport in quiescent solution [14][15][16][17][18] and this is a particularly attractive feature of MOREs.…”

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

“…This was developed further by both Smyrl et al [45,46] for imaging purposes and Boxall and O'Hare [47,48] for kinetic studies of photochemical processes. More recently, Lee and Bard [49] combined scanning electrochemical microscopy (SECM) and optical microscopy (OM) using a ring UME that acted as both an optical and electrochemical probe for imaging microstructures.…”