Abstract
We use a coordination-based kinetics model to look at the kinetics of the turnover frequency (TOF) for the oxygen reduction reaction (ORR) for platinum nanoclusters. Clusters of octahedral, cuboctahedral, cubic, and icosahedral shape and size demonstrate the validity of the coordination-based approach. The Gibbs adsorption energy is computed using an empirical energy model based on density functional theory (DFT), statistical mechanics, and thermodynamics. We calculate the coordination and size dependence of the Gibbs adsorption energy and apply it to the analysis of the TOF. The platinum ORR follows a Langmuir–Hinshelwood mechanism, and we model the kinetics using a thermodynamic approach. Our modeling indicates that the coordination, shape, and the Gibbs energy of adsorption all are important factors in replicating an experimental TOF. We investigate the effects of size and shape of some platinum polyhedra on the oxygen reduction reaction (ORR) and the effect on the mass activity. The data are modeled quantitatively using lognormal distributions. We provide guidance on how to account for the effects of different distributions due to shape when determining the TOF.
Highlights
There is a long history of speculation that catalytic reactions depend on structure and shape, and the coordination of the catalyst [1]
We model the kinetics (turnover frequency (TOF)) of surface sites showing that they strongly depend on the shape and structure of nanoclusters
density functional theory (DFT) has been combined with kinetic Monte Carlo methods to look at the TOF on platinum nanoclusters [9]
Summary
There is a long history of speculation that catalytic reactions depend on structure and shape, and the coordination of the catalyst [1]. Nanocluster synthesis has reached the stage where narrow particle size distributions of desired shapes of many elements and alloys may be achieved [3]. This allows experimentalists to fine-tune catalytic reactions so that specific shapes, sizes, and the coordination of the catalyst is known. We model the kinetics (turnover frequency (TOF)) of surface sites showing that they strongly depend on the shape and structure of nanoclusters. Rück, et al have determined the platinum ORR size dependence via density functional theory (DFT) [8]. We calculate the Gibbs energy using an established procedure [10]
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