Ligand-engineered Ni-based metal-organic frameworks for electrochemical oxygen evolution reaction

Regulating morphology and crystal structure of metal-organic frameworks (MOFs), as well as fabricating bimetallic MOFs have been widely proposed to optimize the electronic structure of MOFs and thus enhance electrochemical oxygen evolution reaction (OER) activity. Distinguish from these conventional and complex strategies, this work mainly focuses on the convenient ligand-engineering strategy to optimize the electronic structure of Ni-MOFs. Specifically, the electron-rich ferrocene (Fc) unit is linked into the ligand of Ni-MIL-53-NH2 by the stable covalent bond on the basis of Schiff-base reaction. Noticeably, the resulting Ni-MIL-53-Fc exhibits significantly enhanced OER activity compared to parent Ni-MIL-53-NH2, achieving 6.6-times improvement of TOF value from 0.19 to 1.25 s-1 at the overpotential of 350 mV. Further characterizations confirm that the incorporation of Fc unit can enhance the charge transfer, which induces more electrons aggregated in the Ni active sites and thus improves the intrinsic activity of Ni sites toward OER activity. This ligand-engineering strategy can be extended to fabricate highly active and stable catalysts toward other electrocatalytic reactions.