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

Abstract

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.

Synthesis and Optimization of Zeolitic Imidazolate Frameworks for the Oxygen Evolution Reaction

“…The ZIF‐8 exhibits a negligible OER activity compared with a high current response from ZIF‐67. A potential of approximately 1.72 V (vs. reversible hydrogen electrode (RHE) with onset potential being close to 1.6 V) to reach an impressive benchmark current density of 10 mA cm −2 in ZIF‐67 is comparable to many of the carbon‐based nanostructures reported [35, 37–39] …”

“…Here, it is worth noting that this OER activity is comparable to or better than the many carbon‐based nanostructures including MOF and ZIF‐derived metal‐incorporated carbons produced by extensive chemical treatment (Figure 3 e). [27, 35, 37–40] For example, the OER performance of ZIF‐67 and other carbon nanostructures produced at elevated temperatures, that is, between 700–1100 °C from the inorganic, MOF, polymeric, graphene‐oxide precursors and templates, and in their heteroatom doping and metal/metal oxide grafting states, is summarized in Table S3 (in the Supporting Information). The OER activity is also higher than the commercial Pt/C, and approaching the benchmark material, IrO 2 /C (Figure 3 e).…”

Recent advances in vacancy engineering of metal‐organic frameworks and their derivatives for electrocatalysis

“…[142][143][144][145] Recently, the plasma technology is used to create the vacancies on the surface of electrocatalysts due to its strong etching effect. For instance, MOFs with abundant vacancies were 146 As shown in Figure 9, the engraved CUMSs generated on the surface of Co-MOF-74 by plasma engraving. The high-density electrons bombardment of plasma can break the coordinated bonds between metal cluster and organic ligand to introduce the CUMSs without the destruction of its phase integrity.…”

“…The Jiang group reported a novel fabrication of microwave‐induced plasma engraving to endow Co‐MOF‐74 with abundant missing linkers under controlled conditions 146 . As shown in Figure 9, the engraved CUMSs generated on the surface of Co‐MOF‐74 by plasma engraving.…”

“…Schematic diagram of the preparation of catalysts by plasma engraving. Reproduced with permission from Ref [146]…”