Efficient electrocatalytic nitrate reduction via boosting oxygen vacancies of TiO2 nanotube array by highly dispersed trace Cu doping

Nitrate pollution of water bodies is a serious global-scale environmental problem. The electrocatalytic nitrate reduction reaction (NO3RR) using Cu-based electrodes allows excellent nitrate removal; however, its long-term operation results in copper leaching, leading to health risks. This study proposes a strategy for efficient nitrate removal through the activation of oxygen vacancies on a highly dispersed Cu-doped TiO2 nanotube array (Cu/TNTA) cathode via electrodeposition. The mechanism underlying the activation of oxygen vacancies and enhancement in charge transfer at the cathode–pollutant interface upon trace (0.02 wt%) Cu doping is elucidated by electron paramagnetic resonance analysis, UV–visible diffuse reflection spectroscopy, and Raman spectroscopy. The Cu/TNTA-300 exhibits a nitrate removal rate of 84.3% at 12 h; the electrode activity did not decrease after 10 cycles, and no Cu2+ was detected in the solution. Electrochemical characterization and density functional theory calculations demonstrate that Cu doping promotes efficient charge transfer between nitrate and the electrode and reduces the energy barrier of the nitrate reduction reaction. This work provides a platform for novel design of cathodes for use in efficient and safe electrocatalytic nitrate reduction in environmental water bodies. [Display omitted] •Cu/TNTA-300 exhibits good electro-NO3RR efficiency by trace (0.02%) Cu doping.•Morphology of Cu/TNTA-300 is unchanged in 10 cycles and no Cu leaching.•The ECSA of the Cu/TNTA-300 is 2.4 times higher than the TNTA before Cu doping.•This work reveals activation mechanism of nitrate reduction by oxygen vacancies.•A promotion effect of Cu doping on NO3RR is revealed from the orbital perspective.