Electron-deficient Cuδ+ stabilized by interfacial Cu-O-Al bonding for accelerating electrocatalytic nitrate conversion

Electrocatalytic nitrate reduction to NH3 not only enables the recycling of nutrients from nitrate wastewater but can also lead to complete nitrogen elimination when paired with an NH3 oxidation reaction to achieve innocuous N-2. Albeit electron-deficient copper (Cu delta+) is an active catalytic site for an electrocatalytic nitrate reduction reaction (ENRR), its stabilization under the reductive polarization potential of ENRR is challenging. Herein, we report the in-situ electroreduction of CuAl-mixed oxide to construct a Cu-Al2O3 interface with strong metal-support interactions (CuAl-LDO-r), which can form and stabilize Cu delta+ via Cu-O-Al bonds. The batch ENRR tests revealed that Cu52Al48-LDO-r delivers an NH3-N selectivity of 97.4%, stable specific activity of 661.6 mg-N m(-2)h(-1) for NH3-N production (faradaic current efficiency of 70.4%), and minimal Cu leaching when reducing 22.5 mg L-1 NO3--N at 1.10 V vs. Ag/AgCl, outperforming most of the reported catalysts under similar reaction conditions. Combined in-situ spectrometric analyses and theoretical calculations demonstrate that the robust performance of Cu delta+ originates from its substantial affinity toward the N-intermediates, which promotes molecule activation and prevents intercoupling to dinitrogen species. For nitrate elimination, the ENRR was coupled with an anode-driven breakpoint chlorination reaction, and the designed system enabled complete conversion of NO3--N (44.5 mg L-1) to N-2 with an electrical consumption of 1.82 kwh mol(N)(-1).

Automated summary

Electrocatalytic nitrate reduction is an important method for nutrient recycling and complete nitrogen elimination. The in-situ electroreduction of CuAl-mixed oxide can stabilize Cu delta+ and achieve good performance in electrocatalytic nitrate reduction. Furthermore, coupling ENRR with a breakpoint chlorination reaction enables complete conversion of nitrate.