Boron-Modified NiFe-MOF-74 Catalyst for the Oxygen Evolution Reaction in Anion Exchange Membrane Water Electrolyzers

Metal-organic frameworks (MOFs) and their derivatives have attracted considerable attention in the quest for highly active precious group metal-free (PGM-free) electrocatalysts for the oxygen evolution reaction (OER) as anodes in anion exchange membrane water electrolyzers (AEMWEs). However, their application in AEMWEs has been limited due to inherent challenges, such as low electrical conductivity and limited stability under high cell voltages. To address these issues, we present a novel approach involving the post-synthesis modification of NiFe-MOF-74 using sodium borohydride. This modification introduces boron into the ligand, resulting in an increased electron density at the metal centers, which optimizes the adsorption energies of oxygen intermediates. The modified catalyst (NiFe-MOF-74-B) was analyzed through XPS, XRD, SEM, and STEM, and a mechanism for the boron modification process was proposed. NiFe-MOF-74-B demonstrates enhanced activity and stability in a 1 M KOH solution. In AEMWE tests using a NiFe-MOF-74-B anode, current densities of 1 A cm⁻² and 2.0 A cm⁻² were achieved at 1.81 V and 2.12 V, respectively, with durability assessed over 100 h. These findings highlight the potential of rationally modifying and integrating MOF materials as OER catalysts in AEMWEs.