Real-time convolutional voltammetry enhanced by energetic (hot) electrons and holes on a surface plasmon waveguide electrode

TL;DR

This paper presents a real-time optical method using surface plasmon polaritons to monitor electrochemical reactions, revealing how energetic carriers enhance current and optical signals on a waveguide electrode.

Contribution

It introduces a theoretical model validated experimentally that links optical response to electrochemical current, especially under high SPP power where energetic carriers dominate.

Findings

Optical response proportional to convolution of current density.

High SPP power creates energetic electrons and holes.

Enhanced electrochemical current due to energetic carrier transfer.

Abstract

Surface plasmon polaritons (SPPs) propagating along a waveguide working electrode are sensitive to changes in local refractive index, which follow changes in the concentration of reduced and oxidised species near the working electrode. The real-time response of the output optical power from a waveguide working electrode is proportional to the time convolution of the electrochemical current density, precluding the need to compute the latter a posteriori via numerical integration. The theoretical optical response of a waveguide working electrode is derived, and validated experimentally via chronoamperometry and cyclic voltammetry measurements under low power SPP excitation, for various concentrations of potassium ferricyanide in potassium nitrate electrolyte at various scan rates. Increasing the SPP power induces a regime where the SPPs no longer act solely as a probe of electrochemical activity, but also as a pump creating energetic electrons and holes via absorption in the working electrode. In this regime the transfer of energetic carriers (electrons and holes) to the redox species dominates the electrochemical current density, which becomes significantly enhanced relative to equilibrium (low SPP power) conditions. In this regime the output optical power remains proportional to the time convolution of the current density, even with the latter significantly enhanced by the transfer of energetic carriers.