Single-Atom Electronic Bridge Facilitates Cascade Charge Transfer from Encapsulated Polyoxometalate to Metal-Organic Framework for Efficient Photocatalytic CO2 Conversion

The POM@MOF system, combining the outstanding properties of polyoxometalates (POMs) and metal-organic frameworks (MOFs), demonstrates significant catalytic potential. However, the lack of stable and well-defined electron transfer pathways between the two components limits the efficiency of charge separation and transfer, thereby constraining its catalytic capability. Herein, we successfully constructed Ni single-atom electronic bridge (SAEB) between POM and MOF, based on our previously-reported PMo₁₁W@rht-MOF-1 composite. Spherical aberration-corrected transmission electron microscopy and X-ray absorption fine structure data indicated not only the hierarchical dispersion among single-atom Ni, POM and MOF, but also the Ni chemical binding between POM and MOF. This well-designed Ni-SAEB facilitated cascade electron transfer from encapsulated PMo₁₁W to rht-MOF-1 framework, confirmed by femtosecond transient absorption spectroscopy and in situ X-ray photoelectron spectroscopy. Further analysis revealed that the SAEB/POM@MOF system simultaneously harnessesed the electronic sponge effect of POM as well as the CO₂ enrichment and conversion capability of MOF. As a result, the Ni-SAEB/PMo₁₁W@rht-MOF-1 composite achieved a photocatalytic CO₂-to-CO conversion rate of 3 mmol g^-1 h^-1, far surpassing the PMo₁₁W@rht-MOF-1 without Ni-SAEB. In this study, the SAEB strategy expands our understanding of the catalytic functionality, which can not only serve as “surficial” catalytic center but also as cascade electronic bridges within “interface”, carrying scientific significance.