Efficient Photoelectrocatalytic Synthesis of Ammonia by Superionic Conductor with Mixed Ion/Electron Conduction

Photoelectrochemical (PEC) nitrate reduction shows substantial potential for solar-to-ammonia (NH₃) conversion. However, low electron density and disordered electron conduction of conventional catalysts result in limited performance and low Faraday efficiency. Herein, a FePS_2.66Li_0.87 superionic conductor (SIC) is developed by introducing lithium ions into van der Waals immobile layered of FePS₃ catalyst. This layered crystal framework facilitates high-concentration lithium ions confinement and long-range diffusion at room temperature, transitioning the conduction mechanism from electronic to mixed ionic/electronic. The typical nanofluidic ion transport leads to a high ionic conductivity of 16.4 mS cm⁻¹ at room temperature and enhanced electronic conductivity of 5 × 10⁻⁶ S cm⁻¹. Furthermore, mobile lithium ions within interlayers enhance the interaction between the low-lying 3d_yz orbitals of Fe interacting with 2a₂ empty antibonding orbitals of NO₃⁻. An excellent PEC ammonia production of 134.18 µmol cm⁻² h⁻¹ with 96.95% Faradaic efficiency is achieved, and the corresponding solar-to-NH₃ efficiency of 57.13% offers a promising pathway toward sustainable ammonia production.