(434d) Modelling of Varying Length-Scaled Catalytic Films in Electrochemically Promoted Systems

Authors: 
Fragkopoulos, I. S., University of Manchester
Theodoropoulos, C., The University of Manchester



Electrochemical Promotion of Catalysis (EPOC) is the enhancement of the catalytic activity when potential or current is applied in systems where a metal catalyst is deposited on a solid electrolyte. Due to this application, a symbloc of species [Oδ- - δ+] known as ‘backspillover’ species are generated at the Triple Phase Boundaries (TPBs, places where the electrolyte, the gas phase and the metal meet) and spill over the catalytic film producing an effective double layer. It has been found that the effective double layer affects the binding strength of catalytic surface adsorbates, resulting in a dramatic enhancement of the catalytic activity [1,2]. EPOC effect also referred to as Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) was found that can also be extended to oxide catalysts, whose activity can be increased by up to a factor of 10 via anodic polarization [3]. Although EPOC exhibits a great potential nowadays in the fields of modern electrochemistry [4,5], it has still not found industrial applications, mainly because the underlying phenomenon is not fully understood yet and cannot be modelled to allow robust system design [6] and control.

In this work we first study the behaviour of supported catalysts of varying nano-structured length scales under open circuit and high pressure conditions in order to get a better understanding on the catalyst-support boundary and its effect on the catalytic activity and the surface reaction rates. We propose an in-house developed efficient implementation of the kinetic Monte Carlo method (kMC) [7] for the simulation of reaction-diffusion micro-processes on the catalytic films and in conjunction with relevant experimental data (Prof Ian Metcalfe’s group) we obtain insights of this open circuit ''enhancement'' phenomenon as well as reliable  estimates of the surface reaction kinetics.

We subsequently exploit the obtained kinetic parameters to construct an accurate multi-scale framework [8] for the same nano-structured systems to quantify the Electrochemical Promotion effect under closed circuit conditions. The multi-scale framework couples a 3-D macroscopic model based on partial differential equations (PDEs) simulating charge transport as well as electrochemical phenomena at the TPBs implemented through commercial software (COMSOL Multiphysics) and the 2-D kMC simulator described above. Dynamic coupling of macro- and microscopic models at the TPBs leads to the construction of an integrated multi-scale system. Moreover, due to computationally extensive ‘large’ kMC simulations, the catalytic surface is split into a number of smaller “representative” lattices whose total area is only a fraction of the actual catalytic area and intelligent interpolation techniques [9,10] are employed to simulate the interactions between the lattices including lateral (lattice-to-lattice) transport through diffusion. The system considered in this study comprises of a thin Pt catalytic film on an YSZ support and Au reference/counter electrodes for the oxidation of carbon monoxide.

References

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