Specific Adsorption of a Bisulfate Anion on a Pt(111) Electrode. Ultrahigh Vacuum Spectroscopic and Cyclic Voltammetric Study

Abstract

We addressed in this study the process of specific adsorption of anions at the metal/solution interface. We focused on the nature of the surface chemical bond that accounted for the phenomenon of adsorption specificity in the context of bisulfate coverage and structural information. While we limited our investigations to bisulfate adsorption on the Pt(111) electrode in sulfuric and mixed sulfuric/perchloric acid media, our conclusions have general significance in explaining ionic adsorption events in electrochemistry. We used core-level electron energy loss spectroscopy, auger electron spectroscopy, low energy electron diffraction, and cyclic voltammetry. Our findings show that in the studied range of sulfuric acid concentration (10-4−10-1 M) the maximum anion coverage is 0.34 ± 0.02 monolayer (ML) and that this coverage corresponds to a highly ordered Pt(111)(√3 × √3)R30° surface structure. S2p core-level and LMM Auger electron spectra indicate that the chemical state of bisulfate sulfur is +6, as in the sulfate anion in a sulfate salt matrix. However, the electron density on the adlattice sulfur is higher than in the salt, evidently due to back-donation of electrons from the substrate to the adsorbate. We conclude that backdonation plays a major role in binding the anions to the surface. Further, the plot of the back-donated electron density vs electrode potential assumes a distorted parabolic shape. The descending parabola branch covers the potential range where bisulfate adsorption increases with potential, and a flat minimum coincides with the double layer potential range. When OH adsorption and platinum oxidation begin, a 2D compressive effect of the O-type adsorbates causes the bisulfate−platinum O−Pt bond to be sequentially cleaved. The “flow” of metal electrons to the adsorbate is therefore reduced, and the S2p loss energy approaches the level characteristic of sodium sulfate unperturbed by surface interactions. Loss spectra from Pt4f7/2 confirm that the oxidized surface is emersed to vacuum but in the double layer potential range fail to respond to either the electrode potential change or the bisulfate adsorption.

Remarkably Durable High Temperature Polymer Electrolyte Fuel Cell Based on Poly(vinylphosphonic acid)-doped Polybenzimidazole

“…Cyclic voltammogram (CV) measurements on the PVPA-wrapped and non-wrapped composites were carried out in 0.1 M HClO 4 aqueous solutions3132. The electrochemical surface area (ECSA) of the Pt nanoparticles of the MWNT/PVPA-PyPBI/Pt was evaluated to be 40.2 m 2 /g, which is lower than that 51.6 m 2 /g of the MWNT/PyPBI/Pt23 (see Supplementary Information, Fig.…”

Adsorption of Iodide and Bromide on Au(111) Electrodes from Aprotic Electrolytes: Role of the Solvent

“…Due to the stripping of the solvation shell upon discharge and formation of the bond with the surface, there is an activation barrier for this process leading to a limited rate of this process. Examples are the adsorption of iodide, bromide and sulfate on Pt and Au single crystal electrodes [17,18,22,23,28,40,[76][77][78][79] Also upd systems and proton adsorption e. g. on Pt belong to this category. The potential dependence leads to adsorption peaks in cyclic voltammograms (or capacitance peaks in AC-voltammetry), the peaks of which shift by ca.…”

Interfacial effects on the catalysis of the hydrogen evolution, oxygen evolution and CO2-reduction reactions for (co-)electrolyzer development

“…Cation/anion effects.─ Electrolyte components can significantly influence the activity of a given electrocatalyst, even if they are seldom regarded as being directly involved in the catalytic process of interest. As an example, the influence of cations and anions on the oxygen reduction activity of Ptelectrodes has been widely studied [169][170][171], but equivalent studies dealing with their effects on the OER-kinetics are still rare. Ganassin et al [172] grew Ir-oxide films on Ir(111) and observed a decrease of their OER performance upon transitioning from 0.1 M HClO 4 to 0.05 M H 2 SO 4 ; the authors related this behavior to a delay in the oxidation of the metallic surface and a corresponding shift of the OER towards more positive potentials, induced by the presence of HSO 4 -/ SO 4 2anions.…”