Reference-Electrode Configuration in CO2 Electrolysis (CO2E) and Anion-Exchange Membrane Water Electrolysis (AEMWE) Cells for Degradation and Stability Evaluation

Abstract

CO2 electrolysis (CO2E) and anion-exchange membrane water electrolysis (AEMWE) have both been identified as promising technologies for reducing emissions from the industrial and energy sectors in pursuit of achieving net-zero goals.1,2,3,4 Recent developments of electrocatalysts, membranes, and electrolyser cell design have resulted in rapid progress of CO2E and AEMWE, achieving high current densities and faradaic efficiencies at the laboratory scale.1,2 However, the long-term stability of these technologies requires improvement if they are to be deployed at commercially relevant scales.2,5 Unfortunately, degradation phenomena such as; cathode flooding6, 10, catalyst degradation7, membrane instability8,9, and salt precipitation10 are difficult to diagnose electrochemically, without the ability to decouple resistance contributions in-situ.We have therefore developed a 3-electrode technique and explored protocols that allow for the decoupling of cathode and anode overpotentials during long-term stability measurements.By using an edge-type reference electrode connected to the membrane through a liquid electrolyte bridge, we successfully demonstrate the ability to assess the performance of individual components within different membrane-electrode assembly (MEA) configurations. We highlight instabilities with using edge-type reference electrodes such as changes in the pH of the electrolyte bridge, and discuss efforts to mitigate these issues to permit long-term stability testing. We then demonstrate how this method can be used to provide more insights into degradation phenomena in both CO2 and AEM water electrolyser cells, showing early diagnosis - up to 7 hours before detection from a conventional 2-electrode set-up - of failure mechanisms during stability testing.The proposed 3-electrode technique is capable of separating anode and cathode overpotentials over the course of extended testing periods and provides a platform to study the electrochemical response of individual electrolyser components to various degradation phenomena, and the durability of CO2E and AEMWE materials. Critical gaps in knowledge surrounding these issues can be better understood, which will enable these technologies to advance to the next stages of development.