Practical operating flexibility of a bifunctional freestanding membrane for efficient anion exchange membrane water electrolysis across all current ranges

This study explores a symmetric configuration approach in anion exchange membrane (AEM) water electrolysis, focusing on overcoming adaptability challenges in dynamic conditions. Here, a rapid and mild synthesis technique for fabricating fibrous membrane-type catalyst electrodes is developed. Our method leverages the contrasting oxidation states between the sulfur-doped NiFe(OH)₂ shell and the metallic Ni core, as revealed by electron energy loss spectroscopy. Theoretical evaluations confirm that the S–NiFe(OH)₂ active sites optimize free energy for alkaline water electrolysis intermediates. This technique bypasses traditional energy-intensive processes, achieving superior bifunctional activity beyond current benchmarks. The symmetric AEM water electrolyzer demonstrates a current density of 2 A cm⁻² at 1.78 V at 60°C in 1 M KOH electrolyte and also sustains ampere-scale water electrolysis below 2.0 V for 140 h even in ambient conditions. These results highlight the system's operational flexibility and structural stability, marking a significant advancement in AEM water electrolysis technology.