ADVANCED ELECTROCHEMICAL IMPEDANCE ANALYSIS OF POLYMER ELECTROLYTE MEMBRANE-BASED WATER ELECTROLYZERS

Abstract

This thesis reports an in-depth exploration of polymer electrolyte membrane water electrolyzer (PEMWE) operation for green hydrogen production using advanced electrochemical impedance spectroscopy (EIS) techniques. Unique methods were developed to decouple the cathode and anode operation, enabling individualized EIS analysis of the electrodes. Physicochemical models of cell operation were developed to extract crucial physical properties from EIS analysis. This work improves upon conventional in situ voltage analyses by developing novel in operando EIS methods that offer critical insights into PEMWEs, improving cell prototyping and diagnostic methods. To start, a specialized cell configuration tailored to analyze hydrogen evolution in the absence of water oxidation was developed, allowing resistances and physical parameters associated with hydrogen transport, ionic transport, and electrode kinetics to be determined. These insights provided conditions to minimize the cathode impedance, which were used to allow analysis of the anode in PEMWE. Critical parameters such as the anode capacitance, kinetic parameters, contact impedance, and ionic conductivity were determined and monitored for various operating conditions. These analyses were then extended to alternative cell designs and conditioning protocols, unveiling the impact the operational profile has on cell performance and stability. Finally, a reproducible three-electrode configuration was developed based on finite element simulations of PEMWE operation, enabling direct measurement of the cathode and anode contribution to the cell voltage and impedance. A comprehensive analysis of the electrode processes and thermodynamic relations is provided and was used to develop a modified EIS model for two-electrode PEMWE analyses. These studies shed light on the complexity of PEMWE operation and provide valuable approaches to interpret this complex process using advanced EIS analyses. The findings presented here will significantly impact the development of PEMWE-based green hydrogen plants, providing methods to rapidly diagnose cells, prototype novel designs, and improve cell efficiency.