Spectroscopic and electrochemical studies of iodine coordinated to noble-metal electrode surfaces

Abstract

The kinetics of redox processes of unadsorbed species at noble-metal electrodes are altered to varying degrees by pretreatment of the electrode surface with a full monolayer of iodine. For example, the rate of the quinone/hydroquinone redox couple at pH 4 is increased significantly at Rh, Pd, Ir, and Pt but decreased slightly at Au after these electrodes were coated with iodine. These observations provided the motivation to pursue a comparative study of the surface electrochemical properties of iodine coordinated to these metals and their bimetallic alloys. Experimental measurements were based upon thin-layer electrochemistry, low-energy electron diffraction, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The findings accumulated to date indicate the following: (i) Iodine is spontaneously and oxidatively chemisorbed as iodine atoms on these metals, (ii) I is covalently bonded to the surface metal atoms; that is, only little or no ionic character exists in the I-metal chemical bond, (iii) Adsorbate-adsorbate interactions within the close-packed I layer are negligible with respect to the I-metal bond, (iv) I can be reductively eliminated from the surface either by exposure to electrogenerated hydrogen or by application of sufficiently negative potentials, (iv) The surface binding strength of I at the subject electrodes decreases in the order Ag > Au > Pt > Ir. (v) The close-packed I layer is not insulating; electron transfer can occur directly from the I adatom, (vi) The conductivity of an I-coated surface is slightly lower than that for a surface which does not contain any chemisorbed material, (vii) The profound dependence of the surface electrochemical properties of I on the surface composition of the metal electrodes makes it a suitable electrochemical tracer in the study of mixed-metal interfaces.

Development of a New System for Photocatalytic Water Splitting into H2 and O2 under Visible Light Irradiation

“…Soriaga et al have reported that I ¹ anions in aqueous solution were spontaneously and oxidatively chemisorbed as zero-valent I atoms on a Pt polycrystalline electrode and formed a stable monolayer on the Pt surface. 176 The binding energies of I 3d 5/2 and I 3d 3/2 observed over the PtTiO 2 were in fair agreement with those over the Pt polycrystalline electrode. As shown in Figure 17, the pressure of a gas mixture of H 2 and O 2 rapidly decreased in the case of the fresh PtTiO 2 due to the water formation from H 2 and O 2 on naked Pt surface.…”

“…They also reported that the iodine could be reductively eliminated from the surface either by exposure to electrogenerated H 2 or by application of sufficiently negative potentials. 176 Therefore, the following two mechanisms can be suggested for the H 2 production over I-adsorbed Pt surface:…”

Gold nanoparticle bioconjugates labelled with 211At for targeted alpha therapy

“…31 We believe, that due to the similarity between iodine and astatine adsorption of 211 At undergoes according to the same reaction. Because of the increasing tendency of halides from F À to I À to form covalent bond with gold surface we expect that chemisorption of At will be the strongest in the halogen group.…”

Freestanding Nanosheets from Crosslinked Biphenyl Self‐Assembled Monolayers

“…[26] The iodine (I 3d) doublet appears with the I 3d 5/2 peak centered at 618.4 eV, which is the chemical shift typical for iodine adsorbed on a Au(111) surface. [27] An analysis of the attenuation of the Au 4f XPS signal shows that the increase in film thickness after iodine treatment is about 3 Å, which is close to the van der Waals' diameter of iodine (4.3 Å). Integration of the iodine 3d 5/2 peak intensity and comparison to the carbon C 1s intensity using a two-layer model for the attenuation of iodine by the crosslinked SAM yields an average of 1.2 iodine atoms per biphenyl unit.…”