Dynamic Generation of Fe 0 Nanoparticles From an Unconventional FeO 6 Single‐Atom Site Embedded in 3D‐Opened Multiscale S‐Doped Porous Carbon for High‐Efficiency Ammonia Electrosynthesis

The development of dynamic electrocatalysts whose active sites evolve under operating conditions represents a frontier in catalysis. An important challenge is to identify suitable pre‐catalytic sites and supports that direct dynamic processes toward highly active species while stabilizing them. Here we embed atomically dispersed six‐coordinate FeO 6 sites in a 3D‐opened multiscale S‐doped porous carbon, serving respectively as pre‐catalytic sites and supports for electrochemical nitrate reduction to ammonia. During repeated voltammetric scans, the current density increases continuously, revealing dynamic transformation of the FeO 6 sites into residual single‐atom sites and newly formed Fe 0 nanoparticles. Integrated in situ and theoretical studies elucidate a dissolution‐migration‐reduction pathway: deeply embedded FeO 6 single‐atom sites dissolve and migrate through interconnected pore channels and are electrochemically reduced to Fe 0 nanoparticles stabilized by the S‐doped surface. The dynamically generated Fe 0 nanoparticles show higher nitrate reactivity than the single‐atom Fe moieties. Further analysis reveals a crossover mechanism merging the normal and hydroxylamine pathways, accounting for the high ammonia electrosynthesis performance. These findings establish a design principle for dynamic electrocatalysis by pairing a metastable pre‐catalytic site with a hierarchically porous sulfur‐doped carbon support, converting site evolution from an uncontrolled process into a controllable route for generating and stabilizing highly active species.