Ti‐Substituted Keggin‐Type Polyoxotungstate as Proton and Electron Reservoir Encaged into Metal–Organic Framework for Carbon Dioxide Photoreduction

Abstract A key challenge for photocatalystic CO 2 reduction is the design and synthesis of photocatalyst with remarkable performance in visible‐light absorption, CO 2 adsorption, and electron‐coupled proton transfer. Here a visible light–driven hybrid photocatalyst Au@NENU‐10, consisting of Au nanoparticles (NPs), Ti‐substituted keggin‐type polyoxometalate [PTi 2 W 10 O 40 ] 7− (PTiW), and HKUST‐1, is synthesized by the one‐pot method at atmosphere condition where PTiW acts as both electrons' and protons' reservoir, and a reactive active center is encaged into HKUST‐1 to boost CO 2 reduction, HKUST‐1 as a microreactor to concentrate CO 2 molecules, and Au NPs harvesting visible light. Notably, compared to [PW 12 O 40 ] 3− ‐encaged HKUST‐1 (NENU‐3) with an octahedron shape, the Ti‐substituted counterpart of NENU‐10 shows a cube shape with a little corner cut, which is ascribed to the higher net charge on terminal oxygen atoms of PTiW, slowing down the crystal growth along the 〈100〉 direction. Moreover, PTiW always exposes on {100} plane of HKUST‐1 in the synthesis process, stabilizing Au NPs and thus being dispersed evenly in NENU‐10. Owing to the stronger protonation of TiO and TiOW, Au@NENU‐10 shows higher CO 2 reduction activity and selectivity under visible‐light irradiation (λ > 420 nm), about 85.3‐fold and 5.2‐fold enhancement, respectively, corresponding to the CO 2 ‐to‐CO and CO 2 ‐to‐H 2 conversion in contrast to Au@NENU‐3.