Depletable peroxidase-like activity of FeO nanozymes accompanied with separate migration of electrons and iron ions.

As pioneering FeO nanozymes, their explicit peroxidase (POD)-like catalytic mechanism remains elusive. Although many studies have proposed surface Fe-induced Fenton-like reactions accounting for their POD-like activity, few have focused on the internal atomic changes and their contribution to the catalytic reaction. Here we report that Fe within FeO can transfer electrons to the surface via the Fe-O-Fe chain, regenerating the surface Fe and enabling a sustained POD-like catalytic reaction. This process usually occurs with the outward migration of excess oxidized Fe from the lattice, which is a rate-limiting step. After prolonged catalysis, FeO nanozymes suffer the phase transformation to γ-FeO with depletable POD-like activity. This self-depleting characteristic of nanozymes with internal atoms involved in electron transfer and ion migration is well validated on lithium iron phosphate nanoparticles. We reveal a neglected issue concerning the necessity of considering both surface and internal atoms when designing, modulating, and applying nanozymes.