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Elucidation of interface reactions between water and electrode metal by large-scale simulation

Hidetoshi Kizaki

Graduate School of Engineering, Osaka University










First-principles simulations based on quantum mechanics, which make progress dramatically, have played a huge role in figuring out various phenomena in the field of materials science. Recently, first-principles simulations for mechanisms of electric chemical reactions have also made progress dramatically. Since we could not observe elementary steps of reactions directly in traditional experiments of electric chemical reactions, so far reactions mechanisms have been discussed by considering reaction kinetics between reactants and products. However, the dramatic progresses of first-principles simulations enable us to investigate elementary steps of reactions under atomic-scale criteria, traces of those on electrode interface and its dependence on electrode potentials and electrode metals.
For example, it is important to study the interface reactions between water and the electrode metal in the field of fuel cell. Therefore reaction simulations that take an influence of complicated water structures and electrode interfaces into account have been performed. As a result, the adsorption mechanism of H atom on a Pt surface in transferring electronic charge from hydronium ion, H₃O+, to Pt-electrode, which is Volmer mechanism as a first step of hydrogen generation reaction, has been reproduced. This enables us to obtain a significant key of solving the hydrogen generation reaction mechanism by investigating an interaction between H₃O+ and a metal surface and investigating H-adsorption dependence on behavior of water and electric potential.
However, due to the limitation of computational resources, the dependence on super cell size of periodic boundary conditions remains in the traditional simulations of electrode interface. Moreover, in order to take statistically adequate sampling of infinite geometry of metastable water and investigate the reaction path of H-adsorption dependence on the electric potential and the electrode metal, a large amount of calculation is required. To solve the problem, large-scale fast parallel computations are indispensable. By using the K computer and more realistic models, we aim to solve the whole electrode reactions of fuel cell.