Titanium-based metal-organic framework, NH2-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 NH2-MIL-125(Ti) via impregnation of Co(NO3)2. The resulting Co@NH2-MIL-125(Ti) with embedded single-site CoII species, confirmed by XPS and XAS measurements, shows enhanced activity under visible light exposure. The increased H2 production is likely triggered by the presence of active CoI 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 H2 production. Via thorough 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 CoII sites. Overall, this straightforward manner of confinement of CoII cocatalysts within NH2-MIL-125(Ti) offers a highly stable visible-light-responsive photocatalyst.

In the version of this article, there were errors in Fig. 2a and d. In Fig. 2a, we have changed Cu2+ to Cu(0) in the revised version. While the two references cited in our paper used Cu2+ in their schematics,1,2 we believe that Cu(0) is the correct representation for the electrochemically mediated amine regeneration (EMAR)3. To be clear, the Cu metal anode is oxidized into cupric ions. The cupric ions then bind to the carbamate and displace the CO2 and form a copper–amine complex. The copper–amine complex is then reduced at the cathode where Cu metal is plated out. In Fig. 2d, we have changed the polarity of the cathode and anode in the revised version. A proton is released at the anode, while a hydroxide is released at the cathode. We have also simplified the quinone/hydroquinone chemistry in the revised version to be consistent with proton and hydroxide stoichiometry. The original and revised Fig. 2 images are shown below. The changes have been made to the html and PDF versions of the article.

Electrochemical CO₂ conversion into fuels or chemicals and CO₂ capture from point or dilute sources are two important processes to address the gigaton challenges in reducing greenhouse gas emissions. Both CO₂ capture and electrochemical CO₂ conversion are energy intensive, and synergistic coupling between the two processes can improve the energy efficiency of the system and reduce the cost of the reduced products, via eliminating the CO₂ transport and storage or eliminating the capture media regeneration and molecular CO₂ release. We consider three different levels to couple electrochemical CO₂ reduction with CO₂ capture: independent (Type-I), subsequent (Type-II) and fully integrated (Type-III) capture and conversion processes. We focus on Type-II and Type-III configurations and illustrate potential coupling routes of different capture media, which include amine-based solutions and direct carbamate reduction, redox active carriers, aqueous carbonate and bicarbonate solutions, ionic liquids CO₂ capture and conversion mediated by covalent organic frameworks. [Figure not available: see fulltext.]