Direct eight-electron NO3−-to-NH3 conversion: using a Co-doped TiO2 nanoribbon array as a high-efficiency electrocatalyst

Abstract

Electrochemical nitrate (NO₃⁻) reduction is promising for simultaneously removing NO₃⁻ and producing high-value-added ammonia (NH₃). This process, however, requires efficient catalysts to enable direct eight-electron NO₃⁻-to-NH₃ conversion. Herein, the Co-doped TiO₂ nanoribbon array supported on a Ti plate (Co-TiO₂/TP) is developed as a highly active electrocatalyst for NO₃⁻ reduction to NH₃, achieving a large NH₃ yield of 1127 μmol h⁻¹ cm⁻² and high faradaic efficiency of 98.2% in 0.1 M NaOH with 0.1 M NO₃⁻, superior to its TiO₂/TP counterpart (88.5 μmol h⁻¹ cm⁻²; 35.1%). It also shows strong electrochemical stability. Theoretical calculations further reveal that Co doping can effectively increase the content of oxygen vacancies in TiO₂, thus improving the electrocatalytic performance of Co-TiO₂/TP for NO₃⁻ reduction to NH₃.