Collective\nEffect in Hierarchical Porous MOFs Combining\nSingle Atoms and Nanoparticles for Enhanced CO<sub>2</sub> Photoreduction\nto CO

Reasonable construction of atomically accurate photocatalysts\nis\nthe key to building efficient photocatalytic systems. Herein, we propose\na collective effects strategy that enables the consolidation of both\ncobalt single atoms (Co<sub>SAs</sub>) and nickel nanoparticles (Ni<sub>NPs</sub>) in hierarchical porous MOFs for the foundational features\nfor the preparation of high-performance photocatalysts. Among them,\nthe optimal sample Co<sub>SAs</sub>/Al-bpydc/Ni<sub>NPs</sub> achieved\na CO generation rate of 12.8 mmol·g<sup>–1</sup>·h<sup>–1</sup> and selectivity of 91% in 4 h. According to the experiment\ncharacterizations and theoretical simulations, we found that Co<sub>SAs</sub> facilitate CO<sub>2</sub> adsorption and activation, while\nNi<sub>NPs</sub> promote hydrogen spillover and transfer of hydrogen\nprotons to Co<sub>SAs</sub>, highlighting the collective effect of\nthe catalytic system with multiple active sites. Most importantly,\nas a proof of concept, this performance enhancement strategy can also\nbe applied to other hierarchically porous MOF photocatalysts, such\nas Al-bpdc, DUT-4, and UiO-67. This work provides new insight into\nthe development of performance optimization of CO<sub>2</sub> conversion\nphotocatalysts through the ingenious design of collective catalytic\nsites.