Quantitative Analysis of Cyclic Voltammetry of Redox Monolayers Adsorbed on Semiconductors: Isolating Electrode Kinetics, Lateral Interactions, and Diode Currents

Abstract

The design of devices whose functions span from sensing their environments, to convert light into electricity or to guide chemical reactivity at surfaces, often hinges around a correct and complete understanding of the factors at play when charges are transferred across an electrified solid/liquid interface. For semiconductor electrodes in particular, published values for charge transfer kinetic constants are scattered. Furthermore, received wisdom suggests slower charge transfer kinetics for semiconductor than for metal electrodes. We have used cyclic voltammetry of ferrocene-modified silicon photoanodes and photocathodes as the experimental model system, and described a systematic analysis to separate charge transfer kinetics from diode effects and interactions between adsorbed species. Our results suggest that literature values of charge transfer kinetic constants at semiconductor electrodes are likely to be an underestimate of their actual values. This is revealed by experiments and analytical models, showing that the description of the potential distribution across the semiconductor/monolayer/electrolyte interface has been largely oversimplified.

Exploiting the versatile alkyne-based chemistry for expanding the applications of a stable triphenylmethyl organic radical on surfaces

“…S2b †) enabled us to determine the apparent rate constant for electron transfer at the bound PTM center, k et,ap , using the recent theoretical model developed by Vogel et al accounting for semiconductor diode effects. 46 A value of 90 AE 20 s À1 was estimated, in accordance with the literature data reported for other silicon electrodes modied with electrochemically reversible systems. 29,46 The surface coverage of attached PTM moieties was electrochemically estimated from CVs of illuminated SAM-1-Rad-Si (eqn S1 †).…”

“…46 A value of 90 AE 20 s À1 was estimated, in accordance with the literature data reported for other silicon electrodes modied with electrochemically reversible systems. 29,46 The surface coverage of attached PTM moieties was electrochemically estimated from CVs of illuminated SAM-1-Rad-Si (eqn S1 †). Indeed, anodic charge integration at several scan rates (between 0.4 and 1 V s À1 ) resulted in an average value of (8.5 AE 0.3) Â 10 À11 mol cm À2 , very close to the analogous SAMs on Au (see Section 2.2.2).…”

Static Electrification of Plastics under Friction: The Position of Engineering‐Grade Polyethylene Terephthalate in the Triboelectric Series

“…Samples of PET (Ertalyte®, Dotmar Engineering Plastic Products, Australia), PTFE (McMaster‐Carr, CAT# 8545K26), poly(dimethylsiloxane) (silicone, McMaster‐Carr, CAT# 87315K65), PVC (McMaster‐Carr, CAT# 87545K521), nylon (nylon‐66, 514‐607, RS Components Australia), acrylic (PMMA, McMaster‐Carr, CAT# 8560K358), and PC (McMaster‐Carr, CAT# 85585K102) were cut to sheets of 2 × 2 cm in size and ≈0.3 cm in thickness. Deposition of a 1 μm‐thick layer of intrinsic amorphous silicon on prime‐grade 100‐oriented (⟨100⟩ ± 0.5°, n‐type, 8–12 Ω cm) silicon wafers (Siltronix, S.A.S, Archamps, France) followed a previously reported procedure [15b]. Amorphous silicon samples were cut to 1 × 1 cm in size and cleaned using the same procedures as for the plastic samples.…”

“…In an attempt to convert the XPS atomic percentage into a surface density number, we have compared the XPS‐derived elemental silver atomic percentage obtained on Ertalyte® with that measured on tribocharged intrinsic amorphous silicon samples that underwent the same charging/discharging procedure. Silver elemental intensities are roughly of the same order of magnitude on both samples (Figure a), with the advantage that intrinsic amorphous silicon is a perfect insulator in the dark, can be tribocharged, but still allows for scanning electron microscopy (SEM) measurements of sufficiently high quality (Figure b). Using a previously reported procedure,[11b] we estimate that ≈10 15 cm −2 atoms of silver were discharged on the Ertalyte® sample.…”

Reconsidering X-ray Photoelectron Spectroscopy Quantification of Substitution Levels of Monolayers on Unoxidized Silicon Surfaces

“…The attenuation length of C 1s electrons in an alkyl monolayer on gold is given by (12) The attenuation length of F 1s electrons in an alkyl monolayer on gold is given by (13) At this point, we have calculated the attenuation length for C (in the form of the alkyl chains) on silicon, . equals the attenuation length of carbon on gold, (a constant), multiplied by the ratio of the atomic density of carbon on gold to the atomic density of carbon on silicon, ,…”