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

Abstract

We present numerical studies of the flow profile and electrode currents for the hydrogen oxidation and oxygen reduction reactions in an electrochemical flow cell. Koutecký-Levich type equations are obtained by partitioning the electrode surface into flow profile regimes and their correlation to idealized wall-jet and channel electrode geometries. The precision of several Koutecký-Levich type equations is evaluated and it is shown that differences between the most commonly applied equations are negligible within the range of flow rates studied and are surpassed by experimental errors.

Fundamental insight into enhanced activity of Pd/CeO2thin films in hydrogen oxidation reaction in alkaline media

“…The Koutecky–Levich equation was used to estimate the number of transferred electrons ( n ):where , and where j is the current density, j k is the kinetic current density, j lim is the diffusion-limited current density, ω is the rotation rate in rpm, F is the Faraday constant (96 485 C mol −1 ), D H 2 is the diffusion coefficient of H 2 in water (4.58 × 10 −5 cm 2 s −1 at 20 °C), 30 ν is the kinematic viscosity (0.01 cm 2 s −1 ) 30 and C H 2 is the bulk concentration of H 2 in the solution (1 × 10 −6 mol cm −3 ). 31 The constant 0.2 is used as the rotation rate is in rpm. 23 The Koutecky–Levich plots were plotted using current densities measured at 0.8 V RHE .…”

A Modular Double Electrode Flow Cell with Exchangeable Generator and Detector Electrodes

“…Multiphysics finite-element simulations were performed to initially check the applicability of the analytical calculations above, to gain further insight into the mass transport in the DEFC and to elucidate possible wall effects. Previously, simulations were used to understand mass transport in macrofluidic cells of various configurations [22,44,45] and microfluidic cells, particularly those with same width of the electrode and channel. [23][24][25][26] Identical parameters were used in the analytical calculations and our simulations (Table 2).…”

A highly flexible electrochemical flow cell designed for the use of model electrode materials on non-conventional substrates

“…More likely, the overall diffusion limited current is governed by several aspects as outlined by Fuhrmann et al 23 As a result, none of the already established relationships can be used directly to describe our setup with sufficient accuracy. Whereas preliminary numerical simulations revealed a scaling of I lim with V 4/5 , further studies 24 are being pursued in this direction.…”

“…For the presented cell, such numerical correlation/expression is currently under investigation. 24 Nevertheless, since the ORR is a highly irreversible reaction, which renders determination of catalyst activity in form of the exchange current density i 0 unpractical, ORR catalyst activity is conventionally determined at 0.9 V. 4,29 At this potential, usually the measured currents are low and only a small fraction of the diffusion limited current (e.g., below 1/10 for a flow rate of 1 ml min −1 in Figure 5) and direct determination of kinetic currents at 0.9 V from polarization curves without correction for mass-transport is feasible without imposing significant errors. As a first approach, the specific activity i spec (Equation ( 2)), defined as the current I at 0.9 V at 1 ml min −1 divided by the geometric area and the roughness factor (Equation ( 1)), was determined for the same Pt samples prepared on various substrates, which were already used for validating the mass-transport control properties of the flow cell by comparing the obtained limiting current,…”