Experimental and numerical model study of the limiting current in a channel flow cell with a circular electrode

Abstract

We describe first measurement in a novel thin-layer channel flow cell designed for the investigation of heterogeneous electrocatalysis on porous catalysts. For the interpretation of the measurements, a macroscopic model for coupled species transport and reaction, which can be solved numerically, is feasible. In this paper, we focus on the limiting current. We compare numerical solutions of a macroscopic model to a generalization of a Leveque-type asymptotic estimate for circular electrodes, and to measurements obtained in the aforementioned flow cell. We establish that on properly aligned meshes, the numerical method reproduces the asymptotic estimate. Furthermore, we demonstrate that the measurements are partially performed in the sub-asymptotic regime, in which the boundary layer thickness exceeds the cell height. Using the inlet concentration and the diffusion coefficient from literature, we overestimate the limiting current. On the other hand, the use of fitted parameters leads to perfect agreement between model and experiment.

Numerical calculation of the limiting current for a cylindrical thin layer flow cell

“…In order to interpret the experimental data, we used values for the diffusion coefficient D and the inlet concentration c in from two sources. From [17], values of D = 3 × 10 −9 m 2 /s and c in = 0.62 mol/m 3 can be obtained from a fit to limiting current data measured in a rectangular flow cell with circular catalyst spot for the temperature range 20-80 • C. The values D = 3.7 × 10 −9 m 2 /s and c in = 0.71 mol/m 3 have been established in [18] using a rotating disk experiment. Fig.…”

“…For a method to calculate this value based on a given discrete concentration distribution, see [17]. From the modeling point of view the most critical boundary conditions in our model are the boundary conditions at the inlet and the outlet.…”

“…Therefore, the outlet is So, we assume that the boundary = ∂ of the computational domain is subdivided into an inlet I , an outlet O , an anode A , and a symmetry boundary S . The rest of consists of inert, impermeable walls W [17]. The following boundary conditions are applied:…”

The Role of Reactive Reaction Intermediates in Two‐Step Heterogeneous Electrocatalytic Reactions: A Model Study

“…[16,17]. Due to the current state of the numerical code, it was not possible to model the surface reactions directly.…”

Numerical Partitioning Model for the Koutecký-Levich Analysis of Electrochemical Flow Cells with a Combined Channel/Wall-Jet Geometry

“…Regardless of their wide range of application and advantages over RDEs, flow cells often involve complex flow velocity profiles and, thus, analytical solutions for the mass transport limited current as a function of flow rate are available only for generalized systems. [31][32][33][34][35][36] While numerical methods can provide approximations for more complex cell designs, [37][38][39][40][41] the commonly applied Koutecký-Levich (K-L) analysis to derive kinetic information from RDE experiments * Electrochemical Society Member.…”