Flow, Transport, and Reactions in a Thin Layer Flow Cell

The performance of fuel cells depends on the rate parameters of the kinetic reactions between the involved species, among other conditions. The determination of these parameters is crucial for the understanding of the functionality of fuel cells. Differential electrochemical mass spectroscopy in thin layer flow cells is used as a tool to gain improved understanding of the heterogeneous catalytic reactions taking place in fuel cell catalytic layers. In this paper, we focus on the description of thin layer cells by numerical models based on partial differential equations and the extraction of kinetics parameters by inverse modeling. For the model setup, various software tools are used. The simulation of laminar free flow is performed by the commercial code COMSOL. A finite volume code is used for the simulation of the reactive transport. The latter is coupled with a Levenberg–Marquardt algorithm for the determination of kinetic constants. Two designs of thin layer flow cells are considered: a cylindrical and a rectangular design. A drawback of the cylindrical cell design is the highly inhomogeneous velocity field leading to spatial variations of the conditions for electrode reactions. In contrast, the rectangular cell design shows a homogeneous flow field in the vicinity of the catalyst. The rectangular cell design has the additional advantage that flow is essentially two dimensional and can be computed analytically, which simplifies the numerical approach. The inverse modeling procedure is demonstrated for a hydrogen-carbon monoxide system.