Defect-engineered TiO2 nanotube cathode for nitrate reduction to ammonia and upcycling into (NH4)2SO4 in the paired electrolysis system

Wastewater contains significant amounts of NO3 that can be directly electrochemically upcycled into the valuable ammonia products. In this study, based on the density functional theory, a defect-engineered TiO2 nanotube array cathode (Co-BTNA) was developed for NO3 reduction and further upcycling into (NH4)2SO4 in the paired electrolysis system. The doped cobalt and oxygen vacancy defects in the Co-BTNA synergistically facilitated the electrons transfer to NO3 with high selectivity of NH3. Meanwhile, the acid anolyte produced via the electrochemical half-reaction at anode was used to trap NH3 for (NH4)2SO4 production. At a current density of 18 mA & BULL;cm- 2, 100 % of NO3 removal efficiency and 93.0 % of NH3 selectivity were achieved with NH3 recovery rate of 182.25 g-(NH4)2SO4 & BULL;d- 1 & BULL;gcat-1 at energy consumption of 27.1 kWh & BULL;kg- 1(NH4)2SO4. In general, this study proposed a sustainable and efficient approach for upcycling wasted NO3 into ammonia fertilizer without external acid and alkali addition.