Adsorptive square-wave voltammetry of quasi-reversible electrode processes with a coupled catalytic chemical reaction

Abstract

There are several strategies for enhancing the sensitivity of electroanalytical methods. Usually, those strategies are based on the selection of the voltammetric technique, the inclusion of an accumulation step, and the eventual addition of a catalytic chemical reaction that regenerates the electroactive species. Square-wave voltammetry (SWV) is one of the most sensitive techniques. In the case of electroanalytical applications, it is typically preceded by an electrochemical or adsorptive pre-concentration step.

In this manuscript, the theory of SWV for a quasi-reversible electrode process coupled to a catalytic chemical reaction between an adsorbed reagent and a soluble product is presented. The dependences of the dimensionless net peak current and its peak potential on the value of the standard charge transfer rate constant are described. The variation of the SWV parameters such as frequency and potential pulse amplitude are discussed. The effect of the chemical and electrochemical kinetics on the voltammetric profile is analyzed.

Appendix

List of symbols and abbreviations
A	Electrode surface
a	Auxiliary variable of adsorption
c o	Concentration of oxidized electroactive species
${c}_o^{*}$	Bulk concentration of oxidized electroactive species
c r	Concentration of reduced electroactive species
${c}_r^{*}$	Bulk concentration of reduced electroactive species
D	Diffusion coefficient
δ	Time of a numerical integration step
dE	Potential increment
E sw	Square-wave amplitude
E(t)	Dimensioned square-wave potential function
E°′	Formal potential of the redox reaction
E p	Peak potential
F	Faraday constant
f	Square-wave frequency
Γ o	Surface concentration of oxidized species
${\varGamma}_o^{ini}$	Initial surface concentration of oxidized species
I(t)	Dimensioned current
ΔI p	Net peak current
K ad	Adsorption constant
k s	Standard charge transfer rate constant
k cat	Pseudo-first order catalytic rate constant
${k}_{\mathrm{cat}}^{'}$	Second order catalytic rate constant
n	Number of exchanged electrons
φ (t)	Dimensionless potential function
ϕ	Auxiliary concentration function
Ψ(t)	Dimensionless current
ΔΨp	Dimensionless net peak current
ΔΨ	Dimensionless net current
Ψ b	Dimensionless backward current
Ψ f	Dimensionless forward current
q	Number of subintervals in each wave
R	Gas constant
T	Temperature in Kelvin degrees
t	Time
θ	Auxiliary concentration function
x	Distance from the electrode surface