Dynamics of anion exchange membrane electrolysis: Unravelling loss mechanisms with electrochemical impedance spectroscopy, reference electrodes and distribution of relaxation times

In recent years, alkaline exchange membrane water electrolysis (AEM-WE) has attracted a lot of attention for its potential cost reduction compared to traditional electrolysis systems. Despite this promise, challenges related to efficiency and stability must be effectively addressed to fully realise the potential of AEM-WE. This paper presents a comprehensive investigation of an AEM-WE single-cell including electrochemical impedance spectroscopy (EIS) in conjunction with the equivalent circuit model (ECM). For the first time distribution of relaxation times (DRT) analysis is performed on an AEM-WE cell, employing a reversible hydrogen electrode (RHE) as a reference electrode. Half-cell EIS measurements and subsequent DRT spectra are presented, clearly indicating anodic and cathodic half-cell reactions. The DRT analysis reveals five distinct loss mechanisms in the AEM-WE system. These include the hydrogen evolution reaction, the oxygen evolution reaction, and ionic transport losses occurring within the catalyst layers. Through a systematic variation of the operating parameters we successfully allocate DRT peaks to their respective physicochemical origins. The findings contribute valuable insights into the electrochemical processes within the AEM-WE single-cell, offering a better understanding of the underlying mechanisms and facilitating the target-oriented development of enhanced membrane electrode assemblies.