<i>In Situ</i> Probing Two Radicals in Halogenation Couplings from Photoanodic Single-Atom Catalysis

Photoelectrocatalysis (PEC) has emerged as a transformative heterogeneous protocol for oxidative organocatalytic synthesis, offering remarkable yield, selectivity, and stability. However, its mechanistic advantages over conventional methods remain unclear, largely due to the limitations of current techniques in uncovering the complexity of PEC systems. In this study, as a state-of-the-art advancement, a single-atom nickel oxide anchored BiVO₄ photoanode was developed for the halogenation of (hetero)arenes, with the bromination of anisole serving as a model reaction, achieving 88% yield and 94% selectivity. Notably, a suite of <i>in situ</i> techniques, including <i>in situ</i> Raman spectroscopy and online atmospheric pressure glow discharge mass spectrometry, was adapted to PEC systems to identify active sites and capture reactive intermediates in real time, respectively. These data, combined with time-resolved Fourier transform infrared spectroscopy and density functional theory simulations, revealed a diradical coupling mechanism driving the halogenation process. Furthermore, the photoanode demonstrated remarkable long-term stability for the bromination of anisole over 160 h, with nearly stoichiometric hydrogen evolution at the cathode, emphasizing its advantages for sustainable synthesis and green energy in practical scale-up applications. This work integrates multiple innovative <i>in situ</i> spectroscopic techniques, providing a universal method to uncover the inherent advantages of the PEC system in organic transformations.