Electrochemical nitrate reduction to ammonia using Fe-doped TiO2 nanoparticles as electrocatalysts: The synergistic contribution from Fe and oxygen vacancy

Electrocatalytic nitrate reduction offers a sustainable approach to ammonia synthesis while simultaneously addressing nitrate contamination. Electrocatalysts with high activity, long durability and affordable cost are essential for advancing this field. This study demonstrates that Fe-doped TiO 2 nanoparticles synthesized by a simple hydrothermal route exhibit competitive electrocatalytic performances for nitrate-to-ammonia conversion. A faradaic efficiency (FE) of 82.3 %, an ammonia yield of 5.953 mg·cm −2 ·h −1 , and a selectivity of 85 % can be achieved and maintained in 10 cycles with a total duration of 60 h in alkaline electrolyte. These metrics substantially outperform the pristine TiO 2 . Defect chemistry analysis and DFT calculations reveal that Fe doping creates oxygen vacancies, and introduces impurity energy levels in the bandgap to improve the electrical conductivity of TiO 2 . Fe and oxygen vacancies synergistically modulate the nitrate adsorption energy, and the Fe active site further reduces the energy barrier for the rate-limiting step and suppresses the competing reactions, thereby effectively promoting ammonia synthesis.