Interfacial Screening in Ultrafast Voltammetry: A Theoretical Study of Redox-Active Monolayers.

The impact of interfacial screening on electron transfer (ET) at ultrashort time scales is theoretically investigated on redox active monolayers by linear sweep voltammetry (LSV). The charging current associated with the nanosecond screening process is an important experimental determinant in finding both the reorganization energy (λ) and electronic coupling (|M|) through ultrafast methods. On the one hand, time dependent decay of the charging current mitigates its impact on the current contribution from faradaic processes, while on the other hand, allowing substantial decay translates into a reduced upper-bound of applicable scan rates, which are crucial for ultrafast characterization. Analysis of the decay in the charging current suggests that the desired screening may be achieved for relatively weakly coupled systems within the charging time constant. For weakly coupled systems, the scan rate corresponding to nanoscale charging time constants appears to be suitable for the ultrafast investigation of ET characteristics. Moreover, the level of screening achieved at nanosecond decay times is shown to change with the coverage of electrode surface by monolayers; which appears to be accompanied by sharp drops in the time constant during successive saturation of interfacial layers by supporting ions (SI). These observations are expected to help design electrochemical device systems with interfaces capable of high faradaic efficiency at ultrafast limits.