Fine-Tuning the Coordinatively Unsaturated Metal Sites of Metal-Organic Frameworks by Plasma Engraving for Enhanced Electrocatalytic Activity.

Metal-organic frameworks (MOFs) have recently emerged as promising electrocatalysts because of their atomically dispersed metal sites and porous structures. The active sites of MOF catalysts largely exist as coordinatively unsaturated metal sites (CUMSs). In this study, facile microwave-induced plasma engraving is applied to fine-tune the CUMSs of cobalt-based MOF (Co-MOF-74) without destroying its phase integrity by controlling the plasma-engraving species, intensity, and duration. The electrochemical activity of the engraved MOF is found to be quantitatively correlated to the coordination geometry of the metal centers corresponding to CUMSs. Specifically, the hydrogen plasma-engraved Co-MOF-74 shows an enhanced catalytic activity of oxygen evolution reaction, which exhibits a low overpotential (337 mV at 15 mA cm-2), high turnover frequency (0.0219 s-1), and large mass activity (54.3 A g-1). The developed CUMS control strategy and the revealed CUMSs activity correlation can inspire the further microstructure tuning of MOFs for various applications.