Interface-Engineered Iron-Zirconium Bimetallic Fumaric Acid MOF Intercalated on Boron Nitride Nanosheets: Mechanistic Insights into Enhanced Electrochemical Water Splitting.

Efficient and robust electrocatalysts are essential for advancing electrochemical water splitting (EWS) as a sustainable hydrogen production technology. Herein, we report a bimetallic iron-zirconium fumaric acid metal-organic framework (FZ-MOF) intercalated on boron nitride nanosheets (BNNs) as a high-performance catalyst for overall water splitting. The FZ-MOF offers a high density of molecularly dispersed active sites, while the fumaric acid linker ensures structural stability and optimal spatial exposure of these sites. Integration of BNNs significantly improves the conductivity and surface area, facilitating rapid charge transfer and efficient mass transport. Mechanistically, the Fe and Zr centers synergistically promote water molecule adsorption and activation, lowering the overpotentials for both the hydrogen and oxygen evolution reactions. The heterointerface between the MOF and BNNs further accelerates the reaction kinetics by providing abundant catalytic sites and efficient electron pathways. Electrochemical studies performed in 1 M KOH reveal excellent bifunctional performance: the hybrid catalyst exhibits overpotentials of 380 mV and 156 mV at 10 mA/cm for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The system exhibits superior kinetics, which is evidenced by low Tafel slopes and minimum charge-transfer resistance accessed by electrochemical impedance spectroscopy (EIS). Additionally, a two-electrode electrolyzer built on symmetric FZ-MOF@BNNs electrodes displays overall water splitting at a 1.86 V (10 mA/cm) cell voltage, including exceptional stability. This hybrid catalyst demonstrates low overpotentials, high current densities, and excellent durability, underscoring the potential of interface-engineered MOF composites for next-generation water-splitting applications.