Theory for cyclic staircase voltammetry of two step charge transfer mechanism at rough electrodes

Abstract

We have developed theory for cyclic (staircase) voltammetry (CSCV) of a two step reversible charge transfer (EE) mechanism for redox species with unequal diffusion coefficients at rough electrodes. The various surface microscopies provide details of random morphology of the electrode which is characterized through the power spectrum in our theory. For the finite fractal electrode model, anomalous enhancement and scan rate dependence of the CSCV or CV response is caused by fractal dimension (D_H), lower length scale of fractality (ℓ), and topothesy length (ℓ_τ). The peak current corresponding to both charge transfer steps is enhanced with an increase in roughness of the fractal electrode (through increase in D_H or ℓ_τ or decrease in ℓ). The onset and offset of the anomalous regime is controlled by (ℓ_τ and ℓ, respectively. Results show that the electrode roughness has the potential to enhance the sensitivity of CSCV as an analytical technique. This is due to a decrease in the difference between the peak currents of two charge transfer steps and an increase in the ratio of the peak to the valley (minimum existing between the two peaks) current in the presence of roughness. Finally, we show that not accounting for roughness in data analysis may cause errors in estimation of composition, diffusion coefficient, improper assignment of electrode mechanism, and so forth.