Construction Of Electron-deficient Cu^δ+ Catalyst And Its Electrocatalytic Reduction Of Nitrate Nitrogen

Nitrate（NO₃^-）is a stable oxygen anion pollutant in water bodies.It is also the major cause of eutrophication in lakes,posing public health risks to neighbouring mammals and residents.Among these methods,the selective electrocatalytic nitrate reduction to NH₃（ENRR）,powered by renewable electric energy,is believed to be a promising alternative to traditional methods because of substantial nitrate removal capacity,mild reaction conditions,and minimal daily maintenances.Albeit electron-deficient copper(Cu^δ+)is an active catalytic site for an electrocatalytic nitrate reduction reaction（ENRR）,the negative polarization potential of ENRR can promote Cu^δ+to Cu~0 conversion.Therefore,the stabilization of Cu^δ+is highly important for an efficient ENRR reaction.Herein,we propose a facile strategy to form and stabilize the Cu^δ+by constructing the Cu-O-Al bonds and Cu-O-Ti bonds at the interface of Cu-Al₂O₃ and Cu-Ti O₂,respectively.The Cu^δ+-ENRR performance relationship and the reaction pathway for the conversion of NO₃^--N to NH₃-N on the catalyst surface were then investigated.The conclusions are as follows:（1）The in-situ electroreduction of Cu Al-mixed oxide,a Cu-Al₂O₃ interface with strong metal-support interactions can be formed(marked as Cu_xAl_100-x-LDO-r),at which the Cu^δ+is stabilized via the Cu-O-Al bond.The batch ENRR tests reveal the Cu₅₂Al₄₈-LDO-r delivers an NH₃ selectivity of 97.4%,stable specific activity of 661.6 mg-N m^-2h^-1 for NH₃ production（faradaic current efficiency of 70.4%）and little Cu leaching when treating 22.5 mg L^-1 NO₃^--N at-1.10 V vs.Ag/Ag Cl.Combined in-situ spectrometric analyses and theoretical calculations demonstrate the robust performance of Cu^δ+origins from its larger affinity with the N-intermediates,which promotes the molecule activation and prevents their intercoupling to dinitrogen species.For the purpose of nitrate elimination,the ENRR is coupled with an anode-driven breakpoint chlorination reaction,and the designed system enables a complete conversion of NO₃^--N(44.5 mg L^-1)to N₂with an electrical consumption of 1.82 kwh mol _N^-1.（2）Ti O₂-Cu was synthesized by a surfactant-free wet chemical reduction method,followed by an electrochemical activation step to induce the formation of Cu-O-Ti bonds at the interface as well as the stabilization of Cu^δ+.The batch ENRR tests find the Ti O₂-Cu-r delivers an NH₃ selectivity of 88.7%,stable specific activity of 377.8 mg-N m^-2h^-1for NH₃ production（faradaic current efficiency of 62.1%）when treating 22.5 mg L^-1 NO₃^--N at-1.00 V vs.Ag/Ag Cl.The durability of the Ti O₂-Cu-r was evaluated through a continuous-flow reaction cell,and the results demonstrate that the catalyst can confirm its high selectivity and stability in ENRR.¹⁵N isotope labeling experiments（DEMS）proved that ammonia originated from nitrate reduction and explored the intermediates and the reaction pathway.For the purpose of nitrate elimination,the ENRR is also coupled with a breakpoint chlorination reaction,and the designed system enables a complete conversion of NO₃^--N(44.5 mg L^-1)to N₂ with an electrical consumption of 1.78 kwh mol _N^-1.This work provides new ideas to further explore the role of Cu-based catalysts in the ENRR reaction and improve its reduction performance,and paves the way to the application of electrocatalytic reduction technology in environmental treatment.