MIL-53(Fe) Nanosheet Arrays with Coordinatively Unsaturated Metal Sites as an Electrocatalyst for Oxygen Evolution Reaction

The design and synthesis of metal–organic frameworks (MOFs) for direct use as electrode materials are crucial for enhancing the electrocatalytic oxygen evolution reaction (OER). Herein, the ultrathin MIL-53(Fe) nanosheet arrays with enriched coordinatively unsaturated metal sites (denoted as MIL-53(Fe)/NF-B0.2-2) are obtained under the inhibition and modulation of benzoic acid (BA) ligands via a substitution-suppression process. The results confirm that this unique ultrathin structure effectively increases the electrochemical active surface areas (ECSA) and exposes the coordinatively unsaturated metal sites. More importantly, the enriched coordinatively unsaturated metal sites acting as active sites facilitate the adsorption of OH– during the OER process. Additionally, MIL-53(Fe)/NF-B0.2-2, with its optimized energy band structure, exhibits superior charge transfer ability and diffusion processes, significantly improving the reaction kinetics in alkaline electrolytes. As a result, the MIL-53(Fe)/NF-B0.2-2 electrode only requires extremely low overpotentials of 190 and 229 mV to reach current densities of 10 and 100 mA cm–2 for OER, respectively. This research not only proposes a novel strategy for designing efficient electrocatalysts but also provides insights into the structure–activity relationship, advancing the rational design of MOFs as effective electrode materials.