Molecular-Level Models

Molecular-level SOFC models aim to understand (i) the kinetics of the reaction at the interface between electrode and electrolyte, (ii) the conduction process in the electrolyte, and (iii) the conduction process in the electrodes. Catalytic activity at TPB, activation energy for oxygen ion transport, and surface exchange current are application examples for such models. 

Within the last two decades, enormous progress has been achieved in the ability to calculate the structures, the properties (e.g., thermodynamic, mechanical, transportation properties), and the reactivity of solids starting from atomistic approaches. The molecular-level models can be classified into three categories. 

With the improvement in hardware and software tools, the ab initio electronic structure calculations will gain importance because they can deal with increasingly complex systems and yield higher precision in the result. Along with this trend, the hybrid techniques will grow in relevance. It is expected that the hybrid methods will play an important role in the molecular-level modelling of SOFCs in the near future. 

Netherlands, Appendix The electrode configuration of a three-electrode cell (1995), pp. 167-183. 

Ivers-Tiffee, in Solid Oxide Fuel Cells VI, eds. S. C. Singhal 

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However, one should keep in mind that simplified models of the actual physical systems are routinely used and that molecular-level modeling techniques involve various levels of approximations. In principle, computational chemistry can only disprove, and never prove, a particular reaction mechanism. In practice, however, a computational investigation may still, in many cases, be a useful guide as to the likeliness of a given reaction pathway. Comparison to experimental information and to computational studies of alternative reaction mechanisms will help establish the kind of trust (or lack thereof) that should be put into a particular reaction mechanism obtained by computational chemistry. 

Classical molecular simulation methods such as MC and MD represent atomistic/molecular-level modeling, which discards the electronic degrees of freedom while utilizing parameters transferred from quantum level simulation as force field information. A molecule in the simulation is composed of beads representing atoms, where the interactions are described by classical potential functions. Each bead has a dispersive pair-wise interaction as described by the Lennard-Jones (LJ) potential, ULj(Ly) ... 

This section deals with multi-scale models for the PEFC and consists of three subsections, 4.1,4.2, and 4.3, that relate to molecular-level models, bridging models between scales and device/process level models, respectively. The objectives of these subsections are to survey the development and application of these models. 

A predictive molecular thermodynamics approach is developed for microemulsions, to determine their structural and compositional characteristics [3.7]. The theory is built upon a molecular level model for the free energy change. For illustrative purposes, numerical calculations are performed for the system water, cyclohexane, sodium dodecyl sulfate as surfactant, pentanol as cosurfactant and NaCl as electrolyte. The droplet radius, the thickness of the surfactant layer at the interface, the number of molecules of various species in the droplets, and the distribution of the components between droplets and the continuous phase are calculated. The theory also predicts the transition from a mi-... 

Molecular-Level Modeling of the Structure and Proton Transport within the Membrane Electrode Assembly of Hydrogen Proton Exchange Membrane Fuel Cells... 

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