In Situ STM Revelation of the Adsorption and Polymerization of Aniline on Au(111) Electrode in Perchloric Acid and Benzenesulfonic Acid

Abstract

In situ scanning tunneling microscopy (STM) was used to study the adsorption and polymerization of aniline on Au(111) single-crystal electrode in 0.1 M perchloric acid and 0.1 M benzenesulfonic acids (BSA) containing 30 mM aniline, respectively. At the onset potential of aniline's oxidation, approximately 0.8 V [vs reversible hydrogen electrode], aniline molecules were adsorbed in highly ordered arrays, designated as (3 x 2 square root(3)) and (4 x 2 square root(3)) in perchloric acid and BSA, respectively. These structures consisted of intermingled aniline molecules and perchlorate or BSA(-) anions zigzagging in the <110> directions in HClO(4) and in the <121> directions in BSA. The coverage of aniline admolecule on Au(111) was lower in BSA than in HClO(4). Raising the potential to 0.9 V or more positive values triggered the oxidation and polymerization of aniline. With aniline molecules arranging in a way similar to the backbone of PAN in HClO(4), they readily coupled with each other to produce linear polymeric chains aligned predominantly in the 110 directions of the Au(111). Compared with the results observed in H(2)SO(4) (Lee et al. J. Am. Chem. Soc. 2009, 131, 6468), the rate of polymerization was slower in HClO(4) and the produced PAN molecules tended to aggregate on the Au(111) electrode. PAN molecules generated in HClO(4) were anomalously shorter than those formed in H(2)SO(4). In 0.1 M BSA, PAN molecules produced by small overpotential (eta < 100 mV) could assume linear chains or 3D aggregates, depending on [aniline]. These results revealed molecular level details in electropolymerization of aniline, highlighting the important role of anion in controlling the conformation of PAN molecules and the texture of PAN film.

Adsorption and Electrochemical Polymerization of Pyrrole on Au(100) Electrodes as Examined by In Situ Scanning Tunneling Microscopy

“…Adsorbed bisulfate anions arrange in an orderly fashion on Au(100) at 0.35 V, but in a disordered manner on Au(111) at E < 0.75 V . This is compared with the aniline adsorbed on the Au(111) electrode, , where a highly ordered aniline structure forms. This contrast might stem from the different basicities of Py and aniline.…”

STM Characterization of Self-Assembled Monolayers of Cysteine Betaine on Au(111) Electrode in Perchloric and Sulfuric Acids

“…The very different structures seen in these two media clearly reflect the marked influence of anions (ClO 4 – , HSO 4 – , and SO 4 2– ) on the spatial arrangement of Cys-b cations on Au(111). The coadsorption scheme involving a cation and anion is well-established in the modern study of interfacial electrochemistry, as exemplified by the underpotential deposition systems, where deposited metal cations are accompanied by anions on Au and Pt electrodes. , Meanwhile, molecular cations such as aniline and pyrrole are coadsorbed with anions of bisulfate, perchlorate, and chloride on the Au(111) electrode. − Similarly, this ionic interaction can hold for organosulfur compounds with terminal groups of −SO 3 – , −COOH, or cysteine on a gold electrode, where an adsorbate can arrange in different spatial structures in different electrolytes. ,,, …”

In situ scanning tunneling microscopy of 5-(Dodecyloxy)-2-(5-(4-(pentyloxy)phenyl)-1H-pyrazol-3-yl)phenol adsorbed on Au(111) electrode

“…Meanwhile, a number of studies have addressed the effect of potential on molecular adsorption on gold electrodes. Results most relevant to this study include heterocyclic aromatic molecules of pyridine [32,46], aniline [47], benzonitrile [48], uracil [31], bipyridine [20,34,35], etc. Typically, these molecules are not adsorbed at E < 0.2 V, but begin to interact with gold electrode as the potential is made more and more positive.…”