Nucleation of Pt Monolayers Deposited via Surface Limited Redox Replacement Reaction

Abstract

The study of Pt nucleation on Au(111) deposited via surface limited redox replacement of underpotentially deposited Cu monolayer is presented. Series of Pt deposition experiments were performed where starting coverage of an underpotentially deposited Cu monolayer varied from 0 to 1. Exsitu Scanning Tunneling Microscopy and statistical image processing are used to characterize the morphology of deposited Pt monolayers. The Pt nucleation density and the average size (area) of Pt nanoclusters is used as the main descriptors of Pt monolayer morphology. Results are discussed within the framework of analytical model developed to describe qualitatively our data. The relevance of our work for design of Pt monolayer catalyst is illustrated studying the CO electrosorption on Pt monolayers with different nucleation densities and average size of Pt nanoclusters.

Recent Advances in the Growth of Metals, Alloys, and Multilayers by Surface Limited Redox Replacement (SLRR) Based Approaches

“…Cyclic voltammetry and scanning tunneling microscopy ( Fig. 4) used to monitor the growth clearly show a "quasi-perfect," twodimensional growth of up to 35 monolayers of Ag on Au (111). A complementary kinetic study of Pb and Tl UPD layer stability at open-circuit potential identifies the oxygen reduction reaction as key oxidative competitors of Ag in the proposed displacement protocol [33].…”

“…Proposed early on by Brankovic et al [27] without detailed experimental description the shuttling approach inspired the development of setups with (111). Reproduced from Ref.…”

“…The protocols employed in these techniques assume either co-deposition of the growing metal (Ag or Cu) with a reversibly deposited mediator metal (typically Pb 2+ ) (DMG) [7,9] or use of pre-deposited submonolayer of a "surfactant" metal (Pb 2+ ) (SMG) [8] that floats on the top of the depositing metal and facilitates the 2D growth. The applicability of these methods employing underpotentially deposited (UPD) [10][11][12] mediators was successfully demonstrated by growth of both "perfect 2D" monolayer to bilayer Ag films [13] and commercially thick Ag and Cu epitaxial deposits on Au (111) substrates [7][8][9]. The surfactant mediation of Pd deposition by H UPD layers was used recently for the growth of one dimensional nanostructures [14] Although results of structural characterization and elemental analysis suggest smooth and inclusion free epitaxial films grown by DMG and SMG [7][8][9]13], these methods are still subject to some limitations and practical inconvenience that need to be addressed.…”

Polarization-dependent Total Reflection Fluorescence X-ray Absorption Fine Structure (PTRF-XAFS) Studies on the Structure of a Pt Monolayer on Au(111) Prepared by the Surface-limited Redox Replacement Reaction

“…8 Brankovic et al systematically studied the reaction mechanism of SLRR to replace the UPD Cu with Pt. They proposed a kinetic model, 16 based on the stoichiometry of SLRR, 6 and also proposed the nucleation mechanism of the Pt monolayer clusters, 17 and the UPD procedure on the Pt monolayer modified surface. 9,15 However, some aspects remain unclear.…”

Electrocatalysts Prepared by Galvanic Replacement

“…For example, from the reactions presented in Table 1 the two most favorable reactions would be the deposition of Au on freshly reduced Cr or Al with the simultaneous oxidation of the latter into Cr(OH) 3 or Al(OH) 3 , since the combination of the relevant half-cell reactions have a potential difference of +1.002 − (−1.126) = +2.128 V vs. SHE (Standard Hydrogen Electrode) and +1.002 − (−2.300) = +3.302 V vs. SHE respectively. It is obvious that before embarking on thermodynamic calculations that provide an estimate of the tendency of a galvanic replacement/deposition reaction to occur one should take into consideration the following: (i) the Pourbaix diagram of the metal M that is tested for replacement, to identify the forms in which it may exist under the given pH and aeration conditions and the corresponding standard potentials (for example, in aerated neutral solutions Cr should be present as Cr 2 O 3 [5] rendering galvanic deposition of Ag simply via reaction (9) impossible to take place on defect-free chrome surfaces); (ii) standard potentials should be corrected to their equilibrium values, taking into account the exact metal ions concentration [6]; and (iii) the possibility of metal complexation, depending on the presence of ligands, which should be taken into account when considering the half reactions since this may not only affect the corresponding potential but also the valence of the metals and the stoichiometry of the reaction (as pointed out by Brankovic and co-workers [6,7], who provided evidence that, in the absence of any other than Cl − ligands, reaction (4) above may be replaced by one involving the replacement of four Cu atoms by one Pt with the formation of the stable Cu(I) complex of CuCl 2 − ). Indeed, one has to stress that some of the reduction potentials tabulated in the right-hand columns of Table 1 may decrease significantly in the presence of strongly complexing ligands (see, for example, the case of the Cu(I)/Cu couple in the presence of Cl − ).…”