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Water splitting based on first‐row transition metal (3d) photocatalysts is a cost‐effective technology for the conversion of abundant solar energy into useful energy on a large scale. The catalytic core of photosynthetic enzymes is a cubic CaMn4O5 cluster. Illuminated by natural photosynthesis, artificial solar water splitting photocatalysts composed of metal clusters are now being designed and tested. Ideally, such photocatalysts composed of atomically precise metal clusters with regular crystal structures are promising model catalysts that can be used to study structure–performance relationships. Recent advances based on metal cluster designs have improved our understanding of photoinduced charge separation and catalytic water redox reactions. This Minireview summarizes the recent advances in 3d metal cluster photocatalysts with well‐defined structures for photocatalytic water splitting and focuses on different clusters with tunable structures that are capable of achieving better photocatalytic properties. [ABSTRACT FROM AUTHOR]

Heterometallic lanthanide–transition‐metal (4f–3d) clusters with well‐defined crystal structures integrate multiple metal centers and provide a platform for achieving synergistic catalytic effects. Herein, we present a strategy for enhanced hydrogen evolution by loading atomically precise 4f–3d clusters Ln52Ni56 on a CdS photoabsorber surface. Interestingly, some Ni2+ ions in the clusters Ln52Ni56 were exchanged by the Cd2+ to form Ln52Ni56−xCdx/CdS composites. Photocatalytic studies show that the efficient synergistic multipath charge separation and transfer from CdS to the Eu52Ni56−xCdx cluster enable high visible‐light‐driven hydrogen evolution at 25 353 μmol h−1 g−1. This work provides the strategy to design highly active photocatalytic hydrogen evolution catalysts by assembling heterometallic 4f–3d clusters on semiconductor materials. Assembling lanthanide–transition‐metal (4f–3d) clusters Ln52Ni56 (Ln=Eu, Pr, Nd and Gd) onto CdS composites achieved enhanced photocatalytic H2 production. Some Ni2+ ions in the clusters were exchanged by Cd2+ to form Ln52Ni56−xCdx/CdS composites. An Eu52Ni56−xCdx/CdS species shows the highest activity of 25 353 μmol h−1 g−1 and an apparent quantum efficiency of 42.4 %. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) provide a tunable platform for hierarchically integrating multiple components to effect synergistic functions that cannot be achieved in solution. Here we report the encapsulation of a Ni-containing polyoxometalate (POM) [Ni4(H2O)2(PW9O34)2]10− ( Ni4P2) into two highly stable and porous phosphorescent MOFs. The proximity of Ni4P2 to multiple photosensitizers in Ni4P2@MOF allows for facile multi-electron transfer to enable efficient visible-light-driven hydrogen evolution reaction (HER) with turnover numbers as high as 1476. Photophysical and electrochemical studies established the oxidative quenching of the excited photosensitizer by Ni4P2 as the initiating step of HER and explained the drastic catalytic activity difference of the two POM@MOFs. Our work shows that POM@MOF assemblies not only provide a tunable platform for designing highly effective photocatalytic HER catalysts but also facilitate detailed mechanistic understanding of HER processes. [ABSTRACT FROM AUTHOR]

A photoactive MOF-based composite with simultaneously incorporated Ru-photosensitizer and Ni(II) molecular catalyst via a "ship-in-a-bottle" synthetic strategy, exhibits highly active, selective and robust, for photocatalytic CO 2 to CO conversion under visible-light illumination. Photocatalytic reduction of CO 2 to CO is a promising strategy for reducing atmospheric CO 2 levels and storing solar radiation as chemical energy. Here, we demonstrate that a molecular catalyst [NiII(bpet)(H 2 O) 2 ] successfully encapsulated into a highly robust and visible-light responsive metal–organic framework (Ru-UiO-67) to fabricate composite catalysts for photocatalytic CO 2 reduction. The composite Ni@Ru-UiO-67 photocatalysts show efficient visible-light-driven CO 2 reduction to CO with a TON of 581 and a selectivity of 99% after 20-h illumination, because of the facile electron transfer from Ru-photosensitizer to Ni(II) active sites in Ni@Ru-UiO-67 system. The mechanistic insights into photoreduction of CO 2 have been studied based on thermodynamical, electrochemical, and spectroscopic investigation, together with density functional theory (DFT) calculations. This work shows that encapsulating molecular catalyst into photoactive MOF highlights opportunities for designing efficient, stable and recyclable photocatalysts. [ABSTRACT FROM AUTHOR]