A Cyclone Flow Cell for Quantitative Analysis of Kinetics at Porous Electrodes by Differential Electrochemical Mass Spectrometry

Abstract

In this work the scope of differential electrochemical mass spectrometry (DEMS) is extended towards quantitatively identifying kinetics of electrochemical reactions in porous electrodes by dynamic measurements. The method is demonstrated by analyzing the kinetics of CO oxidation on a carbon supported Pt/Ru catalyst using a cyclone flow DEMS cell, which allows online studies of porous electrodes. The cyclone flow cell generates a rotating flow field above the stationary electrode. Experimentally validated CFD simulations show that the constructed cell features a homogeneous concentration boundary layer over approximately 75% of the electrode surface area, and that the diffusion limited current density is proportional to flow rate to the power of two third, which is characteristic for turbulent flows. Calibration experiments are performed, and a physical model including mass transfer and reactions inside the porous electrode as well as information about the concentration boundary layer from the CFD results is set up. By matching simulation results and experimental data for CO oxidation, kinetic parameters are determined. With DEMS, not only current and potential but also the CO2 production rate can be observed with a high time resolution which allows to conduct quantitative macrokinetic analysis and to identify parameters quite reliably with a low number of dynamic experiments.