Biradical-mediated synergistic electrocatalysis using metal-free redox molecular catalysts

Nature’s redox enzymes achieve remarkable selectivity by organizing active sites with precise spatial control, an ability difficult to replicate in synthetic systems. Inspired by this, we report a class of stable, metal-free bicarbenium-based molecular catalysts that undergo electrochemical two-electron reduction to form biradical intermediates. These radicals are confined within a rigid xanthene bridge (~4.3 Å), creating a spatially defined pocket that engages paramagnetic substrates like O₂ and NO. This biradical-mediated synergistic catalysis enables highly selective two-electron oxygen reduction (99.3% H2O2 selectivity, 96.8% Faradaic efficiency, 2.21 mol g⁻¹cat h⁻¹ productivity) and three-electron nitric oxide reduction (NH₂OH as major product, 87.2% Faradaic efficiency, 1.68 mol g-¹cat h-¹ productivity). Experimental and computational studies confirm sustained redox cycling supported by favorable spin-pairing and substrate binding geometries, which enhance catalytic selectivity and efficiency. This work demonstrates a blueprint for pathway-specific, radical-mediated catalysis and offers new design principles for metal-free electrocatalytic platforms exploiting open-shell reactivity.