Ti3+ redox dynamics enabling efficient nitrate reduction to ammonia on Ti2O3

The electrochemical nitrate reduction reaction (NO3-RR) demonstrates significant promise as a sustainable pathway for ammonia (NH3) synthesis and regulating the Earth's nitrogen cycle. However, its advancement is currently hindered by low catalytic activity, particularly limited by the sluggish rate-determining step of NO2- formation. Herein, we capitalize on the highly active and versatile redox properties of Ti3+ in Ti2O3, exploiting its spontaneous reduction of NO3- to NO2- to overcome the sluggish rate-determining step. Subsequently, the electrochemical reduction process continuously reduces the generated high valence titanium species back to Ti3+, creating a redox closed loop, and enabling the continuous NH3 synthesis. The catalyst achieves an outstanding NH3 production rate of 19.04 mg h(-1) mg(cat)(-1) with a Faradaic efficiency of 97.8 %. Using in-situ electrochemical electron paramagnetic resonance technology, we explored dynamic changes of Ti3+ in Ti2O3 during the process, while in-situ electrochemical infrared spectroscopy provided insights into intermediates' evolution. Density functional theory calculations confirmed Ti2O3 ' s highly active NO3- RR.