CIQTEK EPR200M with 3D-Printed Electrolytic Cell Enables Operando Detection of Radical Intermediates
Understanding the formation of radical intermediates is key to controlling electrochemical reaction rates and selectivity. These short-lived species at the electrode interface dictate outcomes, and relying solely on final products can lead to speculative mechanisms. With operando EPR using CIQTEK benchtop EPR200M, researchers can directly capture radicals in situ, mapping their formation sequence and structural fingerprints for robust mechanistic evidence. A recent collaboration between Beijing University of Technology (Sun Zaicheng / Liu Yichang), Tsinghua University (Yang Haijun), and Wuhan University (Lei Aiwen) introduced a novel 3D-printed electrolytic cell tailored for in situ EPR. Fabricated with high-precision digital light processing (DLP), this flat cell enables reproducible integration with electrochemical systems. Their results, published in Chemical Engineering Journal under the title Bespoke electrolytic cell for operando EPR tests: Revealing the formation and accurate structures of amino and phenolic radicals, demonstrate the workflow’s ability to uncover radical structures across representative reactions. Methodological Breakthrough: 3D-Printed Flat Electrolytic Cell for Reproducible Operando EPR High-dielectric solvents commonly used in electrochemical cells reduce EPR signal-to-noise, making radical detection challenging. The flat cell design mitigates dielectric losses and enhances the resonator’s Q factor, improving operando EPR performance. Beyond physics, the cell is engineered for reproducibility. Using DLP 3D printing, electrode channels, positioning structures, and short-circuit protection are fixed during fabrication. This eliminates manual variability, reduces system resistance, and improves signal quality, while maintaining mechanical strength, solvent compatibility, and cost efficiency. This approach transforms operando EPR into a workflow of "standardized structural component + reproducible procedure", enabling cross-team and cross-system reproducibility and mechanistic comparison. Time-Resolved Evidence Tracks Radical Formation in C–N Coupling In situ EPR with time-resolved acquisition allows mapping radicals in real-time, showing which species appear first and how they evolve. This provides a reproducible evidence chain at the intermediate level, moving mechanistic understanding beyond product-based inference. Cycloaddition Intermediates Reveal Reaction Selectivity By comparing substrate-specific spectra and calculating spin density, EPR signals are directly translated into radical structural fingerprints. This forms a closed-loop framework for explaining regio- and chemo-selectivity in (3+2) cycloaddition reactions. Solvent Effects Guide C–O Coupling Design In situ EPR shows that the same radical exhibits distinct spectra in MeCN versus HFIP. Combined with NMR, the study links solvent, radical structure, and reaction selectivity, providing an experimental evidenc...
