Surface-Modified Ultrathin Metal–Organic Framework Nanosheets as a Single-Site Iron Electrocatalyst for Oxygen Evolution Reaction

The development of heterogeneous catalyst with well-dispersed active metal sites is one of the hottest research topics. By properly choosing or designing the host material to stabilize the active sites, host-engineering strategy is commonly applied for the preparation of quasimolecular heterogeneous catalysts. Here, by doping the metal–organic framework (MOF) Co-BPDC with 4-(4′-formylphenyl)benzoic acid, ultrathin nanosheets with an aldehyde group-modified surface were facially produced. Upon the addition of ethylenediamine, the surface aldehyde group was converted into imine groups in situ. At this stage, the Co-BPDC nanosheet still had relatively poor catalytic activity in oxygen evolution reaction (OER). After metalation with Fe3+ under ambient conditions, the catalytic activity was greatly enhanced for the resulting nanosheet. With a surface Fe content of 2.87 wt %, the observed electrochemical overpotential and Tafel slope for the Co-BPDC nanosheet in OER decreased to 291 mV and 38 mV/decade, respectively. Meanwhile, the nanosheet catalyst also showed moderate catalytic stability. By taking advantage of the ultrathin nanosheet, the catalytic active Fe sites were immobilized on the nanosheet by the surface imine ligands. This strategy enables the economical and facial production of an atomically dispersed metal catalyst in a large scale under ambient conditions. With the easily accessible and modifiable large surface, the ultrathin MOF nanosheet is an ideal host material for anchoring active metal sites after surface modification.