Kinetic Monte Carlo Studies of Enhanced Chemical Reactions on Nanoporous Electrodes
Nanoporous electrodes have the effect of enhancing kinetically-limited electrochemical reactions due to the enlargement of electrode surface area. It has recently been reported that the confinement effect of reactants in the pores plays an important role for the enhancement of the reactions[1, 2]. By using these catalytic effect of nanoporous electrodes, the application to nonenzymic sensor (ex. glucose) has been explored. The purpose of the present work is to study the effects of nanoporous electrodes on the enhanced chemical reactions on an atomic length scale by the kinetic Monte Carlo (KMC) simulation. We focus our attention on the confinement effect of reactants as well as the enlargement of the electrode area. We have developed a combination of KMC and grand canonical Monte Carlo (GCMC) for the multiscale simulation of the reactions and the mass transport in solution.
We have performed a series of KMC-GCMC simulations to study the correlation between the porous structures (cylindrical, random) and the enhancement of the reactions. The simulation system is a three-dimensional square lattice consisting of electrode, solution and replenishing region. Figure-1 is a schematic diagram of this system. Reactant particles are distributed in solution and their diffusion is simulated by random walk. The upper part of the solution is a replenishing layer to supply the reactant particles when the concentration becomes low as a result of the surface reactions. We consider a simple electrode reaction. It is assumed that reactants are removed on the electrode with a given rate constant. We consider two types of pore structures; cylindrical pore and random pore. The diffusion and reaction of the particles are simulated by KMC method. The replenishing layer is simulated by GCMC method.
We first confirmed that nanoporous electrodes enhance slow reactions compared to flat electrodes. The influence of the pore structures on the reaction mechanism is studied in detail. We also study the reaction of the mixture of slow and fast reactant particles as an application to the sensors.
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