Single-atom Electronic Bridge Facilitates Cascade Electron Transfer From Encapsulated Polyoxometalate to...

The POM@MOF system, integrating the exceptional properties of polyoxometalates (POM) and metal-organic frameworks (MOF), exhibits considerable catalytic potential. However, the absence of stable and well-defined electron-transfer pathways between the two components hampers charge separation and transport, thereby limiting its catalytic efficiency. Here, we constructed a 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 spectroscopy analyses revealed not only the hierarchical dispersion of single-atom Ni, POM, and MOF, but also the formation of chemical bonds between Ni and both POM and MOF. This precisely engineered Ni-SAEB facilitated cascade electron transfer from the encapsulated PMo₁₁W to rht-MOF-1 framework, as confirmed by femtosecond transient absorption spectroscopy and in situ X-ray photoelectron spectroscopy. Further investigations demonstrated that the Ni-SAEB/POM@MOF system simultaneously harnessed the "electronic sponge" effect of POM and the CO₂ adsorption-conversion capability of MOF. Consequently, the Ni-SAEB/PMo₁₁W@rht-MOF-1 composite achieved a CO₂-to-CO photocatalytic conversion rate of 3 mmol g^-1 h^-1, markedly surpassing that of PMo₁₁W@rht-MOF-1 without Ni-SAEB. This work establishes the SAEB strategy as a versatile catalytic concept, where single atoms serve as both surface catalytic centers and interfacial cascade electron mediators, with broad scientific significance.