From Operando Investigations to Implementation of Ni-MOF-74 Oxygen Evolution Electrocatalysts

Metal-organic frameworks (MOFs) as electrocatalysts for the alkaline oxygen evolution reaction (OER) show promising catalytic activity by offering great variability and high surface areas, enabling performance optimization and mechanistic studies. However, their stability during reaction and the structure-performance relationship defining the origin of the high OER activity, are still vigorously debated. Herein, operando X-ray absorption spectroscopy and operando X-ray diffraction are applied to unveil the structural and electronic transformations of Ni-MOF-74 during OER. The irreversible destruction of the MOF-74 crystal into a highly OER active, amorphous NiOOH-metal organic compound is identified. Based on these findings, an amorphous Ni metal organic compound (Ni-MOC*) is proposed for achieving high current densities both in a three-electrode cell (14 A g_Ni⁻¹ at 1.5 V_RHE) and in an anion exchange membrane water electrolyzer (AEM-WE) with a stable AEM-WE performance exceeding 100 h at 500 mA cm⁻².