Electrode surface reconstruction platinum surfaces

We have also discussed two applications of the extended ab initio atomistic thermodynamics approach. The first example is the potential-induced lifting of Au(lOO) surface reconstmction, where we have focused on the electronic effects arising from the potential-dependent surface excess charge. We have found that these are already sufficient to cause lifting of the Au(lOO) surface reconstruction, but contributions from specific electrolyte ion adsorption might also play a role. With the second example, the electro-oxidation of a platinum electrode, we have discussed a system where specific adsorption on the surface changes the surface structure and composition as the electrode potential is varied. 

The interaction of iodine with palladium and platinum electrodes was studied in different electrolyte solutions and on single crystals with electrochemical techniques and UHV spectroscopic ex situ measurements [111]. The chemisorption of atomic iodine on palladium researched extensively because of its ability to protect the surface from air and water interactions. Moreover, it is able to induce a surface reconstruction from a stepped surface to a (1 x 1) unreconstructed one. 

In electrochemical experiments, LEED is used to define the structure of a single-crystal electrode surface [e.g., the (100) face of platinum] before its use in a cell, and to monitor changes that may have taken place upon immersion or electrochemical treatment. One often finds, for example, that a single-crystal surface will reconstruct, to yield a new surface arrangement, upon contact with an electrochemical medium at certain potentials (e.g., see Figure 13.4.7) (113, 116). 

Time-resolved measurements can be made at storage rings with high flux insertion devices that use a quick-scanning mode of operation of the monochromator [574]. In a reported study, products of Mo corrosion in KOH solution could be identified and quantified [578]. Application of time-resolved dispersive high-energy X-ray absorption fine structure (DXAFS) measurements on platinum nanoparticles in a fuel electrode have been described [575]. Results indicate severe surface reconstruction of the nanoparticle surface, showing at least three types of Pt-0 bonds (adsorbed OH, adsorbed atomic O and amorphous PtOx) under oxidative conditions. 

The application of time-resolved high energy X-ray diffraction on platinum nanoparticles in fuel electrodes has been described [28]. Results indicate severe surface reconstruction of the nanoparticle surface showing at least three types of Pt-0 bonds (adsorbed OH, adsorbed atomic O and amorphous PtO ) under oxidative conditions. 

Temporary performance losses have been observed in PEFCs after long galvanostatic or potentiostatic experiments (Uribe and Zawodzinski 2002 Jarvi et al. 2003 Eickes et al. 2006 Donahue et al. 2002). All of these researchers found that this decay could be recovered by lowering the potential of the air electrode below approximately 0.6 V. Much of this decay has beeu attributed to oxidation of platinum, and reconstruction of these oxides, causing a reduction in catalytic activity for the ORR. Although recoverable decay cau be problematic, especially for devices intended to operate at relatively high potentials for long times, it is a lesser concern than permanent loss of platinum surface area... 

Heterogeneous nucleation on active sites Real surfaces, for instance obtained with melt-grown gold, silver, or platinum single-crystal electrodes, exhibit various sites and structural imperfections of different dimensionahty, such as kinks, vacancies, monatomic steps, reconstructed surface domains, 2D islands, and holes [2, 129, 130]. Defining the number of active sites S under particular experimental conditions as No, one may consider the heterogeneous nucleation process as the successive incorporation of monomers Ml into site-confined clusters S — Mi... 

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