Ultrafast Electrochemical Techniques

Abstract

Ultrafast electrochemical techniques provide information about the kinetics and thermodynamics of redox processes that occur at submillisecond or even nanosecond timescales. This short timescale is achieved either by making very rapid transient measurements or by using ultrasmall probes to achieve very high rates of diffusion under steady‐state conditions. Microelectrodes (i.e. electrodes with critical dimensions in the micrometer range) play pivotal roles in both approaches. Electrochemistry has several advantages over spectroscopy in that it provides direct information about electron transfer (E) and coupled chemical (C) reactions. Ultrafast electrochemical techniques now allow it to do so at times as short as 10 ns. In transient measurements, decreasing the lower accessible timescale depends critically on fabricating ultramicroelectrodes that continue to respond ideally as their critical dimension (e.g. the radius of a microdisc) decreases. It is now possible to assemble microelectrodes that respond to changes in applied potential within less than a few nanoseconds. In steady‐state approaches, ultrasmall probes are required to make short timescale measurements and various approaches that yield nanodes (i.e. electrodes of nanometer dimension) have been proposed. However, beyond the need for smaller probes and faster instrumentation, the continued development of new theory describing electron transfer is essential, where the dimensions of the zone that is depleted of reactant because of a Faradaic reaction and the electrochemical double layer become comparable.

Marcus theory of outer-sphere heterogeneous electron transfer reactions: High precision steady-state measurements of the standard electrochemical rate constant for ferrocene derivatives in alkyl cyanide solvents

“…Achievement of the desired mass transport to the electrode necessary for the measurement of fast kinetics at steady-state requires the use of either diffusion to ever decreasingly sized ''nanodes'' or hydrodynamic methods incorporating high flow velocities over microelectrodes [25]. Kinetic analysis via diffusion only methods is compromised by the necessity to record very smooth voltammetry on a sub-nanoamp scale using electrodes which have to be precisely engineered to a known geometry.…”

3D Fuzzy Graphene Microelectrode Array for Neurotransmitter Sensing at Sub-cellular Spatial Resolution

“…(Taylor et al 2017;Yang et al 2017) This is likely due to the small size of the miniaturized electrode that allows for a more rapid response to changes in the applied potential. (Forster 1994(Forster , 2006 Smaller RC cell time constants and significantly reduced ohmic (iR) drop have been observed for miniaturized microelectrodes, making them very attractive for investigating high speed electrontransfer reactions.…”

3D Fuzzy Graphene Microelectrode Array for Neurotransmitter Sensing at Sub-cellular Spatial Resolution

“…allows for a more rapid response to changes in the applied potential. (Forster 1994(Forster , 2006 Smaller RC cell time constants and significantly reduced ohmic (iR) drop have been observed for miniaturized microelectrodes, making them very attractive for investigating high speed electrontransfer reactions.…”