Adsorption of pyrazine at the Au(111) | aqueous solution interface

The importance of grand-canonical quantum mechanical methods to describe the effect of electrode potential on the stability of intermediates involved in both electrochemical CO2 reduction and hydrogen evolution

Grand canonical quantum mechanics was employed to investigate intermediates of CO₂ER under constant potential instead of constant charge.

Effects of Polarization on the Extents and Kinetics of Adsorption of Ionic and Neutral Aromatic Heterocyclics Exhibiting Orientation Transitions at a Porous C Electrode

Comparative investigations of the adsorption and electrosorption of the heterocyclic compounds, pyridine, 1,4-pyrazine and 1-quinoline, and their orientation behaviours in an high specific-area C-cloth/H2O interphase, directly related to the replacement of preadsorbed and field-oriented solvent (H2O) molecules by oriented adsorbates themselves, have been carried out by means of in situ UV spectrophotometry conducted under positive or negative electric polarization at the C-cloth as an electrode. Surface charge, dipole moment of the adsorbate, polarization mode, acidity of the solution (leading to cation formation) and hydrophilic/hydrophobic properties of the adsorbed molecules in relation to the solvent (H2O vs. non-aqueous) are found to have important influences on these processes and hence govern the experimentally measurable extents and rates of their adsorption. The adsorption and orientation effects were indicated by evaluation of surface-dipole potential changes represented by Esin and Markov (EM)-type effects. Different adsorption and orientation processes amongst the three adsorbates, together with the possible rearrangement of the adsorbed molecules, were revealed by changes of the observed EM effects. The preferred adsorption/electrosorption behaviour arises by either “combined adsorption” (CAD) (i.e. combination of adsorption on open-circuit with electrosorption upon subsequent polarization) or by “alternate polarization electrosorption” (APE) (i.e. electrosorption by periodically reversed direction of polarization, between positive and negative, in one adsorption experiment). Negative-current polarization in a single transient also led to similar results for effective adsorptive removal of 1-quinoline from aqueous solution. Major differences of adsorption arise between neutral pyridine and its cation in acidic solution, including the effect of electrode polarization.

Orientation Change of Adsorbed Pyrazine on Roughened Rhodium Electrodes as Probed by Surface-Enhanced Raman Spectroscopy

A surface-enhanced Raman spectroscopic (SERS) study of pyrazine adsorbed on roughened Rh electrodes was performed. Potential and concentration effects on the adsorption behavior of pyrazine were investigated. The SER spectra display four pairs of overlapping bands with the relative intensity of each pair being highly potential dependent, which has not been observed on other metals. The orientation change of the adsorbed pyrazine from the end-on to N/pi bonded edge-on configuration is proposed to account for this potential-dependent relative intensity change. This hypothesis is further supported by the SERS results obtained at different pyrazine concentrations. In conjunction with the orientation effect, the interaction of Rh with hydrogen and oxygen generated at different potentials has a great influence on the adsorption configuration of pyrazine.

A reversibly switching surface

We report the design of surfaces that exhibit dynamic changes in interfacial properties, such as wettability, in response to an electrical potential. The change in wetting behavior was caused by surface-confined, single-layered molecules undergoing conformational transitions between a hydrophilic and a moderately hydrophobic state. Reversible conformational transitions were confirmed at a molecular level with the use of sum-frequency generation spectroscopy and at a macroscopic level with the use of contact angle measurements. This type of surface design enables amplification of molecular-level conformational transitions to macroscopic changes in surface properties without altering the chemical identity of the surface. Such reversibly switching surfaces may open previously unknown opportunities in interfacial engineering.