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 FePS2.66Li0.87 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 3dyz 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.