Ligand defect engineered NH2-MIL-88B(Fe) for efficient oxygen evolution reaction in alkaline seawater†

Abstract

Rational design of viable routes to develop affordable and efficient oxygen evolution reaction (OER) catalysts is essential for advancing electrochemical water splitting, yet significant challenges remain, particularly in seawater. Here, we propose a ligand defect engineering strategy to modify the electronic structure of NH₂-MIL-88B(Fe) using a monodentate ligand (acetic acid, AcOH), inducing ligand vacancies in NH₂-MIL-88B(Fe) for oxygen evolution in an alkaline seawater electrolyte, thereby improving the performance of the electrocatalysts. The resulting defective MOFs (denoted as NH₂-MIL-88B(Fe)-x) exhibited exceptionally high catalytic activity for OER, requiring low overpotentials of 313 and 329 mV at a current density of 100 mA cm⁻² in 1 M KOH and simulated seawater (1 M KOH + 0.5 M NaCl) solutions, respectively. Experimental analyses revealed that the introduction of AcOH can modulate the d-band center of active sites in NH₂-MIL-88B(Fe)-x and play a critical role in alleviating chloride ion (Cl⁻) corrosion, thereby enhancing catalytic stability in seawater. When directly used as an OER catalyst in an alkaline electrolyte, wind and solar power were harnessed to operate the NH₂-MIL-88B(Fe)-x || Pt/C configuration to drive the electrolytic water reaction. Thus, the ligand defect strategy can be employed to design and prepare high-performance OER electrocatalysts, particularly for generating H₂ through water electrolysis powered by renewable energy sources.