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

Abstract

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 NiFeP_x electrocatalyst using a phosphidation process. The resulting NiFeP_x material showed significantly enhanced hydrogen evolution reaction (HER) performance compared to the NiFe LDH. Furthermore, the change in surface composition of the NiFeP_x 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 NiFeP_x 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.