Self-shuttle-mediated electron transfer to boost photocatalytic hydrogen production of Co–Zn bimetallic MOF

Abstract

A Co–Zn bimetallic metal–organic framework with exceptional water- and photo-stability was demonstrated as an active photocatalyst for the hydrogen evolution reaction (HER) from water, outperforming monometallic analogues. The synergistic electronic coupling between electron-deficient Co(II) and electron-rich Zn(II) is key to allow charge migration from Zn toward Co for highly active reduction sites. The coupling also suppresses framework decomposition via Co(II)/Co(III) redox and enables photocatalytic HER activity through UV-driven ligand-to-metal charge transfer. With the addition of a fluorescein sensitizer, CoZn MOFs exhibit remarkable UV-visible performance, achieving an H₂ production rate of 16 700 μmol g⁻¹ h⁻¹ over an extended period, which is the highest rate among cocatalyst-free bimetallic MOFs. The system exhibits an impressive apparent quantum efficiency of 17.7% at 254 nm and 3.3% at 456 nm. Our bimetallic strategy paves the way to design photoactive MOFs and overcome their instabilities, especially under harsh photochemical processes for water splitting.