Metal-organic framework encapsulated single-atom Pt catalysts for efficient photocatalytic hydrogen evolution

Abstract

Atomically dispersed metal catalysts have emerged as a new research frontier in the catalytic community due to the utmost atom efficiency and tunable functionality in a wide variety of catalytic reactions. In the present work, a general operable synthetic platform for stable and well-defined positioned single-atom metal catalysts encapsulated in metal-organic framework (MOF) architecture was developed. Using the MOF-808 based single ion trap method, single metal ions were effectively captured by ethylenediaminetetraacetic acid (EDTA) ligands, which were exchanged with the original formate ligands anchored at the Zr6 cluster metal nodes. Upon activated in hydrogen atmosphere at 200 °C, the stable MOF-808-EDTA encapsulated single-atom metal catalysts with well-defined atomic positions were synthesized. The synthesized single-atom metal catalysts were confirmed using various experimental characterization techniques including high-angle annular dark-field scanning transmission electron microscope, extended X-ray absorption fine structure spectroscopy analysis, and diffuse reflectance infrared Fourier transform, as well as theoretical density functional theory calculations. As a demonstration case, it has been found that the as-synthesized MOF-808-EDTA encapsulated single-atom Pt catalyst shows the excellent photocatalytic hydrogen evolution activity (68.33 mmol g−1 h−1) and high stability. The apparent quantum efficiency reaches up to 67.6% at 420 nm. This work not only provides a general and effective synthesis approach for preparing stable, uniformly distributed, MOF encapsulated single-atom metal catalysts such as Pd, Rh, Ru, Cu, Co, and Ni, but also sheds new insights into single-atom metal catalysts for photocatalytic water splitting for hydrogen production.