Angstrom-Scale Confinement Activates O2 via Spin and Charge Reconfiguration.

First-principles calculations show that angstrom-scale slit confinement alone activates O2 via the coupled spin, charge, and bonding reconfiguration. Across electronically distinct walls (graphene, h-BN, and g-C3N4), reducing the gap drives a stepwise evolution from triplet O2 to superoxide-like and spin-quenched peroxo-like states, followed by O-O scission and surface chemisorption. A pressure-gap relation exhibits a sharp signature at the crossover, suggesting the confinement-driven generation of reactive oxygen species without dopants, photons, or external fields.