Single potential step chronoamperometry for EC′ reaction at rough electrodes: Theory and experiment

Abstract

• Rough electrode shows anomalously enhanced current response. • Intermediate time regime has anomalous power-law relationship. • Enhancement is observed both in transient and steady-state time regimes. • Steady-state response is dependent on rate constant and RMS roughness. • Diffusion and diffusion-kinetics lengths govern roughness influence. The theory is developed for the chronoamperometry of first order homogeneous catalytic chemical reaction coupled with electron transfer ( EC ′ ) on a rough electrode. We obtained a solution for the diffusion problem on an arbitrary and random topography of the electrode to generalize Danckwerts’ equation. Derived equation of random electrode roughness is used for developing theory of (statistically isotropic) self-affine fractal on limited length scales. The characteristics fractal morphological parameters, viz. D H , ℓ and ℓ τ , are varied for detailed analysis of current transient. The current transient shows anomalously enhanced response for a rough electrode. Our theoretical results explain both transient and steady-state behavior of the current response under the influence of roughness. The anomalous enhancement of steady-state current is only observed when RMS roughness is greater than bulk reaction–diffusion length ( L k ). Finally, the theory is compared and validated with experimental data of ferrocyanide and ascorbic acid coupled system on rough Pt electrodes.