Particle array modelling

Oxide surfaces, and in particular oxide films, are versatile substrates for the preparation of model catalysts. Quite a few of these systems show nanoscale reconstructions, which can be employed as templates for the growth of ordered model catalysts of reduced complexity. In order to efficiently control the growth of nanostructured metal particle arrays, two conditions have to be met. First, the template must provide sites of high interaction energy that trap the deposited metals. Second, the kinetics of the growth process must be carefully controlled by choosing... 

The Diffusion Domain Approach The so-called diffusion domain approach was first proposed by Amatore et al. [36], and has proved highly useful in several theoretically based reports on this subject to model the diffusion current at those randomly distributed spherical micro- (or nano-) particle arrays [35, 37-39]. 

A two-dimensional model of circular particles has been developed to describe the liquid redistribution behaviors, which assumes that the chemical potential of the liquid in all the pores in a given particle array is the same at equilibrium [84]. When an atom is located under the surface of a liquid-vapor meniscus, with an average radius of curvature r, its chemical potential is given by... 

The composition of the dense systems that have been simulated up to now is summarized in Table 1. The polymer chains are modeled as unbranched sequences of 100 isodieimetric units connected by links of length <7, while the filler particles are modeled as spherical entities with diameter a/. The simulated systems consist of three-dimensionally periodic arrays of cubic cells of edge 40 a containing Np polymer chains and Nf filler particles. The polymer units interact through a 12 — 6 Lennard-Jones potential Euu = — 2((r/ruu) ], where Tuu is the distance be-... 

Fig. 8. Steady-state model for the earth s surface geochemical system. The kiteraction of water with rocks ki the presence of photosynthesized organic matter contkiuously produces reactive material of high surface area. This process provides nutrient supply to the biosphere and, along with biota, forms the array of small particles (sods). Weatheriag imparts solutes to the water, and erosion brings particles kito surface waters and oceans.

Summing up this section, we would like to note that understanding size effects in electrocatalysis requires the application of appropriate model systems that on the one hand represent the intrinsic properties of supported metal nanoparticles, such as small size and interaction with their support, and on the other allow straightforward separation between kinetic, ohmic, and mass transport (internal and external) losses and control of readsorption effects. This requirement is met, for example, by metal particles and nanoparticle arrays on flat nonporous supports. Their investigation allows unambiguous access to reaction kinetics and control of catalyst structure. However, in order to understand how catalysts will behave in the fuel cell environment, these studies must be complemented with GDE and MEA tests to account for the presence of aqueous electrolyte in model experiments. 

As shown in Fig 1. the model is a one-dimensional array of equal mass, hard-point particles, the even-numbered particles form a set of... 

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