On Pt-based electrode

Dunietz BD, Markovic NM, Ross Jr PN, Head-Gordon M. 2004. Initiation of electro-oxidation of CO on Pt based electrodes at full coverage conditions simulated by ah initio electronic structure calculations. J Phys Chem B 108 9888-9892. 

These fuel cell results, completed by the different spectroscopic and chromatographic results, allowed us to propose a detailed reaction mechanism of ethanol oxidation, involving parallel and consecutive oxidation reactions, on Pt-based electrodes, where the key role of the adsorption steps was underlined. 

Table 1. Activities of a number of hydrocarbon fuels (including hydrogen) on Pt-based electrodes In basic media.

Fig. 1.28 Effect of perfluorocarbon additives on the kinetics of oxygen reduction on Pt-based electrodes. Characteristics of flooded cell.

Investigation of the Effect of Superacid Imide Electrode Coatings Upon the Rate of Cathodic Electro-reduction of Oxygen on Pt-based Electrodes. 

Fig. 1.23 Evaluation of perfiuorooctanes as electrode coatings for oxygen reduction on Pt-based electrodes at 25 C. 

In a staged multi-scale approach, the energetics and reaction rates obtained from these calculations can be used to develop coarse-grained models for simulating kinetics and thermodynamics of complex multi-step reactions on electrodes (for example see [25, 26, 27, 28, 29, 30]). Varying levels of complexity can be simulated on electrodes to introduce defects on electrode surfaces, composition of alloy electrodes, distribution of alloy electrode surfaces, particulate electrodes, etc. Monte Carlo methods can also be coupled with continuum transport/reaction models to correctly describe surfaces effects and provide accurate boundary conditions (for e.g. see Ref. [31]). In what follows, we briefly describe density functional theory calculations and kinetic Monte Carlo simulations to understand CO electro oxidation on Pt-based electrodes. 

Gas-phase quantum chemistry (QC) calculations of CO and OH adsorption on Pt-based anodes provide valuable information on structure and energetics of adsorbates (for e.g. see [15, 19, 21]). A detailed review of CO adsorption calculation was presented by Fiebelman and co-workers [15]. Detailed CO and OH adsorption calculations on Pt-based electrodes have also been reported (for e.g. see [19] and references therein). Potential effects on CO binding energy and frequency have been discussed in detail by Koper and coworkers [20]. However, these calculations do not attempt to investigate the mechanism of the CO electrooxidation. Anderson and co-workers have used first-principle QC chemistry and semi-empirical calculations to understand the effect of potential on fuel cell electrochemistry in general, and CO oxidation electrochemistry in particular [16, 32, 33]. 

This bifunctional mechanism is typically invoked to explain CO oxidation on Pt-based alloys as well. While this model has been successful in describing several experimental results on Pt-based electrodes, a complete first-principle theoretical evidence to this mechanism does not exist. 

For details on the potential energy surface (PES) for CO oxidization, the reader is referred to Ref. [18]. In what follows, we describe the second stage of our Multi-scale approach. We show results of our Monte Carlo simulations, to elucidate the CO electrooxidation kinetics on Pt-based electrodes. 

This chapter discusses a staged multi-scale approach for understanding CO electrooxidation on Pt-based electrodes. In this approach, density functional theory (DFT) is used to obtain an atomistic view of reactions on Pt-based surfaces. Based on results from experiments and quantum chemistry calculations, a consistent coarse-grained lattice model is developed. Kinetic Monte Carlo (KMC) simulations are then used to study complex multi-step reaction kinetics on the electrode surfaces at much larger lengthscales and timescales compared to atomistic dimensions. These simulations are compared to experiments. We review KMC results on Pt and PtRu alloy surfaces. 

Methanol Fuel Cells The electrooxidation and dissociation of small organic molecules such as methanol on Pt-based electrodes is one of the most extensively studied systems in terms of both fundamental and applied research in surface (interfacial) electrochemistry (see also Chapter 3.5). It involves a very complex reaction occurring in many steps and various kinds of surface (interfacial) species, including reactants, intermediates, poisons, supporting electrolytes and even solvent... 

Concerning methanol oxidation on Pt-based electrodes in acidic media, much effort was done during the last decades. For a detailed discussion, the reader is referred to several literature reviews (Iwasita, 2002 Koper et al, 2009 Markovic et al, 2002 Watanabe andUchida, 2009). To summarize, the mechanism for methanol oxidation involves two main steps ... 

Saravanan, C., Dunietz, B. D., Markovic, N. M., Somorjai, G. A., Ross, P. N., and Head-Gordon, M. (2003). Electro-oxidation of CO on Pt-based electrodes simulated by electronic structure calculations. J. Electroanal. Chem. 554-555 459-465 Schiraldi, D. A. (2006). Perfluoiinated polymer electrolyte membrane durability. Polym. Rev. 46(3) 315... 

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