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 ( ), and topothesy length ( 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 τ or decrease in ). The onset and offset of the anomalous regime is controlled by τ and , 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.

Mechanistic Insights for Low-Overpotential Electroreduction of CO2 to CO on Copper Nanowires

“…A series of peaks appear in the anodic scans prior to the onset of irreversible oxidation at ∼0.5 V. The peaks at ca. 0.36, 0.4–0.42, and 0.44–0.46 V can be assigned to the OH ad features associated with the (100), (110), and (111) facets of face-centered-cubic (fcc) Cu, respectively. , The slight shifts in peak positions among the different types of Cu nanowires are likely a result of the varying surface roughness factors and/or the capacitance effect. , In addition to these three peaks, two other peaks were observed at ∼0.1–0.15 and ∼0.32–0.34 V, which were not reported in the previous studies of extended surfaces . In particular, the peak at ∼0.32–0.34 V (denoted as * in Figure a and the following discussion) was found to become more pronounced for the Cu nanowires prepared at higher temperatures.…”

Influence of Geometry on Thin Layer and Diffusion Processes at Carbon Electrodes

“…Carbon materials exhibit complex surface structures due to the type of carbon, its shape, the interfacial structures, and the surface functional groups. , Most studies have explored the effects of the surface chemical structures of carbon electrodes, aiming to promote electrocatalytic effects and adsorption. , Recently, more studies are addressing how three-dimensional geometric structure affects electrochemistry. − Kant et al developed the theory regarding random surface roughness of electrodes and demonstrated that the surface roughness or morphology can affect amperometry, , voltammetry, − and electrochemical impedance responses. , In particular, when the size of the geometric structure matches the thickness of the diffusion layer, the geometric structure confines the analyte within the rough surface, resulting in thin layer electrochemical behavior. , Thin layer electrochemistry affects the redox products observed; for example, under thin layer conditions, there are enhanced cyclization reactions of catecholamines. , The Compton group developed thin layer theory for several carbon geometric structures, including arrays , and porous structures. − Thin layer phenomena were observed in porous materials or in those with cavities for solution confinement, such as vertically aligned multiwall carbon nanotubes, carbon nanotube yarns, and carbon nanopipets. ,,− However, both diffusion and thin layer electrochemistry contribute to the electrode response, but results are often simplified to consider only one effect at a time. , Systematic experiments with simulations that explain the effects of various carbon electrode geometries would provide a comprehensive understanding of how surface structure affects the contributions of diffusion and thin layer processes to electrochemical behavior.…”

Differential Square-Wave Voltammetry

“…At solid electrodes differential pulse voltammetry can be even more analytically effective than SWV, due to the ability for providing lower background current by adjusting the ratio between the potential step and pulse duration . Parveen and Kant studied extensively the properties of arbitrary pulse voltammetries, − considering in particular the role of the solid electrode roughness and unequal diffusivity. On the other hand differential pulse voltammetry is inferior in providing mechanistic information on the electrode reaction compared to SWV.…”