Transforming NiFe layered double hydroxide into NiFePx for efficient alkaline water splitting

Developing high-performance alkaline water electrolyzers for efficient hydrogen production is a promising approach to achieving carbon neutrality. Herein, we converted a mixed cation NiFe layered double hydroxide (LDH) into a NiFePx electrocatalyst using a phosphidation process. The resulting NiFePx material showed significantly enhanced hydrogen evolution reaction (HER) performance compared to the NiFe LDH. Furthermore, the change in surface composition of the NiFePx during the oxygen evolution reaction (OER) process was investigated using in situ surface-enhanced Raman spectroscopy (SERS), which revealed that the real active sites were NiOOH species, thus providing direct evidence that phosphides are unstable for the OER. Finally, an anion-exchange membrane (AEM) electrolyzer with the NiFePx as the HER catalyst and the NiFe LDH as the OER catalyst was constructed, which showed a current density of 300 mA(-2) at an applied potential of 2.15 V with excellent stability for approximately 100 hours with no significant decrease in performance.