Insights into the design of homogeneous electrocatalytic flow sensor via a rotating disc electrode system

Abstract

Homogeneous electrocatalytic reaction has been extensively applied in electrochemical flow sensors especially for the detection of non-electroactive species. Herein, homogeneous electrocatalytic reaction is studied on a rotating disc electrode (RDE) system to mimic the forced convection in flow sensors in both experiments and theory. The experimental RDE voltammogram reveals a pre plateau feature under the rotation frequency of 25 rpm and the corresponding theoretical current–potential curves generated by 2D axisymmetric electrochemical analysis model is in good consistency with the experimental voltammetric responses. Based on the same model, mediator and substrate concentration distributions and the diffusion layer thicknesses are discussed in detail. Moreover, the interference of direct electrochemical oxidation of the substrate is investigated via the homogeneous electrocatalytic reaction between 1,1′-ferrocenedicarboxylic acid and L-cysteine and the corresponding second-order rate constant (372 (mol m−3)−1 s−1) is shown by the modified model. Also, the influence of substrate diffusion coefficients in homogeneous electrocatalytic reaction is analyzed and the obtained transition point indicates the specific critical second-order rate constant for both ferroceneacetic acid (106.02 (mol m−3)−1 s−1) and 1,1′-ferrocenedicarboxylic acid (105.36 (mol m−3)−1 s−1) as the mediator. At last, the design principle of homogeneous electrocatalytic flow sensor is summarized.