Promoting Photocatalytic Activity of NH<sub>2</sub>-MIL-125(Ti) for H<sub>2</sub> Evolution Reaction through Creation of Ti<sup>III</sup>- and Co<sup>I</sup>-Based Proton Reduction Sites
Vitalii Kavun, Evgeny A. Uslamin, Bart van der Linden, Stefano Canossa, Andrey Goryachev, Emma E. Bos, Jara G. Santaclara, Grigory Smolentsev, Eveliina Repo, Monique A. Van Der Veen
Abstract
High Resolution Image Download MS PowerPoint Slide Titanium-based metal–organic framework, NH 2 -MIL-125(Ti), has been widely investigated for photocatalytic applications but has low activity in the hydrogen evolution reaction (HER). In this work, we show a one-step low-cost postmodification of NH 2 -MIL-125(Ti) via impregnation of Co(NO 3 ) 2 . The resulting Co@NH 2 -MIL-125(Ti) with embedded single-site Co II species, confirmed by XPS and XAS measurements, shows enhanced activity under visible light exposure. The increased H 2 production is likely triggered by the presence of active Co I transient sites detected upon collection of pump-flow-probe XANES spectra. Furthermore, both photocatalysts demonstrated a drastic increase in HER performance after consecutive reuse while maintaining their structural integrity and consistent H 2 production. Via through characterization, we revealed two mechanisms for the formation of highly active proton reduction sites: nondestructive linker elimination resulting in coordinatively unsaturated Ti sites and restructuring of single Co II sites. Overall, this straightforward manner of confinement of Co II cocatalysts within NH 2 -MIL-125(Ti) offers a highly stable visible-light-responsive photocatalyst.