On the Occurrence of Competitive Adsorption at the Platinum−Acetonitrile Interface by Using Surface-Enhanced Raman Spectroscopy

Abstract

Surface-enhanced Raman scattering (SERS) from the platinum electrode−acetonitrile interface in the presence of iodide, the lithium cation, water, and pyridine was analyzed as a function of applied potential. It was found that the typical Raman band of cyanide species by the dissociation of the solvent acetonitrile upon adsorption onto highly roughened platinum electrode surfaces was detectable for all of the systems that were studied. However, the onset potential of the dissociation reaction of acetontrile differed for the four systems. We assume that competitive adsorption may exist between each of the above four species and the solvent acetonitrile molecule, especially at the dissociation reaction−active sites of the Pt surface. This competitive adsorption therefore significantly inhibits the decomposition reaction of acetonitrile. The interactions of these adsorbates with Pt are assumed to weaken in the sequence pyridine > I- > water ≈ Li+ on the basis of the observations of different negative shifts of the onset potential of acetonitrile decomposition. For the system with water or iodide, double-band character for the CN band was also detected. It is assumed to be due to the existence of two types of adsorbed ion pairs at the Pt surface: CN-···CH3CN and CN-···Li+/Na+.

The hydrogen evolution reaction: from material to interfacial descriptors

“…87 Moreover, measuring the 1 H NMR spectra of H 2 O in these electrolytes helped reveal the role of alkali cations in the proton acidication following the strength of the cation-water interaction, Li + being the strongest. 84 As previously discussed, in situ techniques such as sum frequency generation 88 (SFG), Raman spectroscopy, 89,90 FTIR spectroscopy, 85,86 or surface X-ray diffraction 91 (XRD) are currently employed to appreciate how these constraints on the water structure in the bulk of the electrolyte translate to the electrochemical interface. While all these techniques converge to the fact that polarizing the electrode negatively results in an enrichment of water at the interface, some discrepancies about the role of the cation, 85,88 or water orientation 88,91 remain.…”

The Crucial Role of Water in the Stability and Electrocatalytic Activity of Pt Electrodes

“…Acetonitrile, found in the first group, is often used as a solvent for fundamental reactivity studies due to its simple chemical structure, wide electrochemical stability window, good miscibility with water, relatively good conductivity, and capability to solvate ions (ε r = 37.5). ,,− Different analysis tools like in situ infrared spectroscopy, ,, surface-enhanced Raman spectroscopy, , and surface X-ray diffraction were used to investigate the adsorption behavior, decomposition, and influence of water on the acetonitrilePt interaction. It has been shown that acetonitrile chemisorbs at the Pt surface, being able to displace water and undergo oxidation and reduction without being desorbed from the surface within a wide potential range. , Baldelli et al showed using sum-frequency generation that acetonitrile undergoes a reorientation on Pt at the potential of zero charge (pzc).…”

“…It is well-known from the literature that the addition of water decreases the electrochemical stability window, although the reductive decomposition was investigated in more detail compared to oxidative decomposition. The reductive decomposition of acetonitrile on roughened Pt was reported to result in adsorbed CN and CH 3 groups. , It was also found that acetonitrile can undergo a reductive dimerization and trimerization reaction, leading to cyclic products like 4-amino-2,6-dimethyl­pyrimidine or 2,4,6-trimethyl-1,3,5-triazine, but methane was also described as reduction product. , For anodic degradation, it was found that upon the addition of water the potential window is decreased and anodic acetonitrile decomposition is induced by water oxidation forming H 2 O •+ . H 2 O •+ can react with acetonitrile to form acetamide, which can further decompose to CO, CO 2 , methanol, methane, acetic acid, and formic acid.…”

Ordered Structures and Morphology-Induced Phase Transitions at Graphite–Acetonitrile Interfaces

“…The intermolecular forces between ACN molecules are mainly dipole–dipole interactions . Thin films of ACN vapor-deposited at a cryogenic temperature in ultrahigh vacuum (UHV) allow studies of solid–ACN interfaces without the interference of water forming hydrogen bonds with ACN. , Previous reports showed that the chemisorbed layer of ACN displayed an “end-on” or “side-on” orientations on metal − and semiconductor surfaces. − With respect to physisorption, it was found by XRD that thick ACN films exhibit a high-temperature α phase at 115 K instead of the more stable β phase observed in the bulk. , It is, therefore, important to conduct a thorough study of ACN on graphite due to the seeming inconsistency and the multiple structural possibilities as well as the relevance to potential applications.…”