Dynamic Generation of Fe0 Nanoparticles From an Unconventional FeO6 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.