Cascade Electrocatalytic Nitrate Reduction Reaching 100% Nitrate-N to Ammonia-N Conversion over Cu2O@CoO Yolk–Shell Nanocubes

The electroreduction of nitrate to ammonia via a selective eight-electron transfer nitrate reduction reaction offers a promising, low energy consumption, pollution-free, green NH3 synthesis strategy alternative to the Haber–Bosch method. However, it remains a great challenge to achieve high NH4+ selectivity and complete conversion from NO3––N to NH4+–N. Herein, we report ingredients adjustable Cu2O@CoO yolk–shell nanocubes featured with tunable inner void spaces and diverse activity centers, favoring the rapid cascade conversion of NO3– into NO2– on Cu2O and NO2– into NH4+ on CoO. Cu2O@CoO yolk–shell nanocubes exhibit super NH4+ Faradaic efficiencies (>99%) over a wide potential window (−0.2 V to −0.9 V versus RHE) with a considerable NH4+ yield rate of 15.27 mg h–1 cm–2 and fantastic cycling stability and long-term chronoamperometric durability. Cu2O@CoO yolk–shell nanocubes exhibited glorious NO3–-N to NH4+–N conversion efficiency in both dilute (500 ppm) and highly concentrated (0.1 and 1 M) NO3– electrolytes, respectively. The nitrate electrolysis membrane electrode assembly system equipped with Cu2O@CoO yolk–shell nanocubes delivers over 99.8% NH4+ Faradaic efficiency at cell voltages of 1.9–2.3 V.