Durability and Performance Improvement of Anion Exchange Membrane Water Electrolysis with High Ionic Strength Anolyte

Green hydrogen is emerging as a cornerstone of the global energy transition, providing a pathway to decarbonize industries that are otherwise difficult to electrify, such as chemical production, heavy transportation, and steel manufacturing. Water electrolysis, especially when powered by renewable energy sources, has been considered a cost-effective method for green hydrogen generation. Anion exchange membrane water electrolyzers (AEMEL) are a promising technology that combines the advantages of conventional liquid water alkaline electrolyzers (AEL) and proton exchange membrane water electrolyzers (PEMEL). The alkaline operation environment allows the use of earth-abundant catalysts for the oxygen evolution reaction (OER) and non-perfluorinated polymer membranes, while the compact design of AEMEL reduces the device cost compared to AEL. However, long-term durability of AEMEL still remains challenging under high-pH electrolytes (pH>13) and high current density (>1A/cm²) due to the degradation concerns. While low hydroxide concentration is desirable for improved chemical stability, increased cell overpotential in low-pH environments has been observed, compromising the overall efficiency of the system.

This study presents high ionic strength anolyte as a promising strategy to improve the performance of AEMEL operating at a low hydroxide concentration. The research delves into the mechanisms behind these improvements, particularly addressing the cathode hydration issues associated with low pH alkaline anolytes in a dry-cathode AEMEL configuration. The findings demonstrate that cations in the high ionic strength anolyte significantly reduce the cathode overpotential by enhancing water transport from the anode to the cathode via cation migration and diffusion through the AEM. This approach allows for the use of neutral salts as the main cation source, which effectively reduces the anolyte alkalinity and mitigates the potential degradation of cell parts. Different alkali cation species and concentrations were tested consistently in a membrane electrode assembly. The result shows that the improvement on the overpotential depends on the mobility and dynamic ionic radius of the cation. With the implementation of the optimized low-pH high ionic strength anolyte, the AEMEL achieved durable and energy-efficient performance at 60°C and 1A/cm² for over 1,000 h.