Design and resistance analysis of a co-electrolysis cell through impedance spectroscopy

Abstract

CO2 capture is a key component of the ecological transition towards achieving carbon neutrality. The direct CCE project (direct Carbon Capture and Electrolysis) aims to develop a system capable of chemically absorbing CO2 emitted by a waste treatment plant in Vienna and converting this absorbed CO2 into syngas, specifically reducing it to H2 and CO. This reduction process takes place in an electrochemical cell, known as a Co-Electrolyzer, where a voltage is applied to drive the reaction. However, the energy supplied to the electrolyzer can not be used to full extent, as several components of the cell contribute to energy losses by imposing resistance to charge transport. This thesis focuses on impedance measurements under varying design parameters to evaluate the different sources of energy losses in each case. Additionally, it explores the feasibility of detecting CO2 reduction through impedance spectroscopy.The three main topics of this thesis include: 1. Stabilizing the impedance spectroscopy signal by minimizing noise to ensure consistent measurements. A solution was also implemented to amplify the voltage delivered to the electrolyzer using the PSM3750 spectrometer in combination with the Solartron device. 2. Conducting spectroscopic measurements on a 100 cm2 active area Co-Electrolyzer under varying experimental conditions using four different absorption fluids for CO2 capture. 3. Designing a new electrolyzer with a smaller 16 cm2 active area optimized for impedance spectroscopy measurements.The impedance spectroscopy results from the 100 cm2 cell revealed that the cell’s response varies depending on the CO2-absorption fluid. For some catholytes (electrolyte on the cathode side), such as KOH, the charge transfer resistance associated with CO2 reduction could be identified, while in other cases, this identification proved more challenging. The design of a smaller electrolyzer will enable localized impedance spectroscopy measurements at the electrode level, facilitated by the inclusion of a reference electrode. This approach allowed the separation of resistances from the two reactions in the Nyquist diagrams obtained through impedance spectroscopy. Understanding and evaluating the various sources of potential losses in the cell provides a clearer insight into its behavior and helps identify areas for improvement.