Probing the Accelerated Electron Transfer from Co to Fe within a Cyanide Framework Using Electrochemiluminescence...

The coordination environment of metal centers is pivotal to the catalytic performance of heterogeneous catalysts, including Prussian blue analogues. However, elucidating the structure-activity relationship at the single-particle level under operando electrochemical conditions remains a significant challenge. Here, we employ electrochemiluminescence microscopy (ECLM) in combination with density functional theory (DFT) calculations to investigate for the first time the exceptional catalytic activity of CoFe-PBA at the single-particle level. DFT calculations reveal that Co doping effectively reduces the energy gap (ΔE) between the occupied N 2p orbitals and the unoccupied metal 3d orbitals, facilitating electron transfer from Co to Fe via the cyanide bridges. Under electrochemical bias, this configuration enables Co centers to dramatically accelerate interfacial electron transfer and consequently lead to valence-state transitions of metal ions. This rapid charge transfer activates an efficient Fenton-like reaction at the Co sites, which catalyzes the continuous generation of radical oxygen species from H₂O₂. These radicals subsequently trigger intense electrochemiluminescence emission of luminol. Leveraging this Co-enabled signal amplification mechanism, we achieve exceptionally bright and stable single-particle ECLM imaging of CoFe-PBA. Moreover, we develop a highly sensitive ECLM-based detection platform for alkaline phosphatase, demonstrating its potential for practical analytical applications. This work highlights the critical role of engineered metal-center kinetics in advancing the ultrasensitive ECLM.