Cascade Electrocatalytic Nitrate Reduction Reaching 100% Nitrate-N to Ammonia-N Conversion over CuO@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 NH synthesis strategy alternative to the Haber-Bosch method. However, it remains a great challenge to achieve high NH selectivity and complete conversion from NO-N to NH-N. Herein, we report ingredients adjustable CuO@CoO yolk-shell nanocubes featured with tunable inner void spaces and diverse activity centers, favoring the rapid cascade conversion of NO into NO on CuO and NO into NH on CoO. CuO@CoO yolk-shell nanocubes exhibit super NH Faradaic efficiencies (>99%) over a wide potential window (-0.2 V to -0.9 V versus RHE) with a considerable NH yield rate of 15.27 mg h cm and fantastic cycling stability and long-term chronoamperometric durability. CuO@CoO yolk-shell nanocubes exhibited glorious NO-N to NH-N conversion efficiency in both dilute (500 ppm) and highly concentrated (0.1 and 1 M) NO electrolytes, respectively. The nitrate electrolysis membrane electrode assembly system equipped with CuO@CoO yolk-shell nanocubes delivers over 99.8% NH Faradaic efficiency at cell voltages of 1.9-2.3 V.