Co-adsorbtion of Cu and Keggin type polytungstates on polycrystalline Pt: interplay of atomic and molecular UPD

Abstract

Second harmonic generation (SHG), electrochemical quartz microbalance (EQCM), and cyclic voltammetry are applied to clarify the structure and properties of Cu adlayers formed in the presence of Keggin polytungstate anions. For 0.02-10 mM CuSO4 solutions, no pronounced suppression of underpotential copper deposition (Cu UPD) by 0.1-10 mM H3PW12O40 (PW12) or H4SiW12O40 (SiW12) is observed in electrochemical experiments. Moreover, coadsorption with polyanions results in an increase of charge in the Cu UPD region. EQCM data demonstrate high surface coverage with polytungstate in the overall potential range and their pronounced co-adsorption with Cu2+ cations under open circuit. The unusual potential dependence of EQCM response of polytungstates is discovered and discussed in terms of anion interactions with adsorbed hydrogen. The SHG response of Cu UPD demonstrates a non-linear dependence on Cu surface coverage, which is interpreted in terms of discontinuous submonolayers consisting of 2D Cu islands. The additives of PW12 or SiW12 decrease copper SHG response at low and high CuSO4 concentrations, with minor effect for a mid range of concentrations. In all mixed solutions, the potential dependence of the SHG response remains typical for Cu UPD, not for polytungstates. SHG transients measured under potential step mode demonstrate that the initial non-steady-state SHG behavior of the adlayer is more close to the behavior of polytungstates, but typical copper features appear at longer wavelength. These facts favor the hypothesis of Cu adatom penetration through anionic adlayers and formation of a metal submonolayer at the vacant areas between large quasi-spherical polyanions, with subsequent transformation into a Pt/Cu/polytungstate layered structure.

Electrocatalytic and Photoelectrochemical Reduction of Carbon Dioxide at Hierarchical Hybrid Films of Copper(I) Oxide Decorated with Tungsten(VI) Oxide Nanowires

“…5A). During such preconditioning, the Cu(I) and Cu(II) sites are expected to interact, 62 form insoluble species, 63 or to get intercalated within tungstate units of WO 3 . The excess of copper ions (unbound to WO 3 ) is removed (stripped) from the electrode surface to solution in the initial 2-3 scans.…”

Toward Effective CO2 Reduction in an Acid Medium: Electrocatalysis at Cu2O-Derived Polycrystalline Cu Sites Immobilized within the Network of WO3 Nanowires

“…SEM of the initially deposited bilayer film composed of Cu 2 O nanostructures over-coated with WO 3 nanowires is illustrated in the Supporting Information as Figure S3. Later, the film has been subjected to conditioning by voltammetric cycling in the potential range from 1 to −0.25 V. Under such conditions, Cu(I) and Cu(II) ionic sites are expected to interact, 88 form insoluble species, 89 undergo reduction to Cu 0 , and get intercalated within tunnels existing in hexagonal WO 3 . It is apparent from Figure 5A that the excess of copper ions (unbound to WO 3 ) is removed (stripped) from the electrode surface to solution in the initial positive-going scans.…”

Traditional and Novel Platinum/Conducting Oxide Electrocatalysts: Trends and Promise

“…The majority of experimental illustrations are related to Pt coexisting with tungsten, molybdenum, tin, and vanadium oxide. Some representative original publications [1][2][3][4][5][6][7][8][9][10] are mentioned below in respect to the following aspects addressed in the report.…”

“…(5) Model 2D materials (modified electrodes) useful to clarify various mechanistic aspects for electrocatalysis; e.g. these materials can be prepared by means of molecular modification of the platinum metal surfaces, with the use of highly symmetric polyoxometalates as analogues of oxides [3,7,10].…”