(362e) Multiscale Modelling of Backspillover Processes in Electrochemically Promoted Systems

Backspillover in catalysis, denotes a migration of one or more species from the support to the catalytic surface. This metal-support interaction in some cases is followed by a significant alteration and enhancement of the catalytic activity increasing the surface reaction rate by up to 1500%. In the 1980s, it was first observed by Stoukides and Vayenas [1] that the catalytic activity of a metal catalyst deposited on a solid electrolyte can dramatically be enhanced by applying potential between the catalyst and a reference electrode. Later, it was found by Nicole and Comninellis [2] that this effect can be extended to an oxide catalyst, whose activity can be increased by up to a factor of 10 via anodic polarization. This phenomenon is known as  Electrochemical Promotion of Catalysis (EPOC), also referred to as Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA) and is of increasing interest nowadays in the fields of modern electrochemistry and surface science [3,4]. Although this technology exhibits a great potential, it has still not found industrial applications, partly because the underlying phenomenon is not fully understood yet and cannot be modelled to allow robust system design.

Here, we propose an accurate multi-scale model for such a system, which in conjunction with high fidelity, purpose-designed experiments currently underway, will illuminate electrochemical promotion. The various and complex phenomena taking place are described in their characteristic length-scales and any interactions are explicitly considered. The proposed model couples a macroscopic model based on a CFD software implementing the Finite Elements Method (COMSOL Multiphysics) and an in-house developed efficient implementation of the kinetic Monte Carlo method (kMC) [5].

The macroscopic model is based on partial differential equations (PDEs) and is employed for the simulation of charge  transport throughout the cell as well as of the electrochemical phenomena taking place at the Triple Phase Boundaries (TPBs, where the gas phase is in contact with the catalyst and the support). The microscopic model is employed for the simulation of reaction-diffusion microprocesses on the catalytic lattice. The macro- and microscopic models are coupled via fluxes (from the support to the micro-lattice) of ''backspillover'' species at the anodic TPBs leading to an integrated multi-scale system which can efficiently be used for parameter estimation studies exploiting experimental data using appropriate optimisation techniques. The system considered comprises a Pt catalytic film (anode) deposited on an YSZ support and Au (cathode) reference/counter electrodes for the oxidation of carbon monoxide. The dimensions of both anodic and cathodic electrodes are in the order of nanometers, whereas the support is orders of magnitude larger.

 

References

[1] M. Stoukides, C.G. Vayenas, J. Catal. 1981; 70(1): 137-146.

[2] J. Nicole, C. Comninellis, Solid State Ionics. 2000; 136-137(1-2): 687-692.

[3] D. Poulidi, M.E. Rivas, I.S. Metcalfe, J. Catal. 2011; 281(1): 188-197.

[4] E.P.M. Leiva, C.Vazquez, M.I.Rojas, M.M. Mariscal. J.Appl.Electrochem. 2008; 38(8): 1065-1073.

[5] B. Hari, F. Goujon, C. Theodoropoulos. 2009; Integrated multi-scale models for microreactor simulation and design. In: S. Pierucci, ed. AIDIC Conference Series. pp 167-176 DOI: 10.3303/ACOS0909020