Cu/Cu_xO/Graphdiyne Tandem Catalyst for Efficient Electrocatalytic Nitrate Reduction to Ammonia

The electrocatalytic reduction reaction of nitrate (NO₃ ^-) to ammonia (NH₃) is a feasible way to achieve artificial nitrogen cycle. However, the low yield rate and poor selectivity toward NH₃ product is a technical challenge. Here a graphdiyne (GDY)-based tandem catalyst featuring Cu/Cu_xO nanoparticles anchored to GDY support (termed Cu/Cu_xO/GDY) for efficient electrocatalytic NO₃ ^- reduction is presented. A high NH₃ yield rate of 25.4 mg h^-1 mg_cat. ^-1 (25.4 mg h^-1 cm^-2) with a Faradaic efficiency of 99.8% at an applied potential of -0.8 V versus RHE using the designed catalyst is achieved. These performance metrics outperform most reported NO₃ ^- to NH₃ catalysts in the alkaline media. Electrochemical measurements and density functional theory reveal that the NO₃ ^- preferentially attacks Cu/Cu_xO, and the GDY can effectively catalyze the reduction of NO₂ ^- to NH₃. This work highlights the efficacy of GDY as a new class of tandem catalysts for the artificial nitrogen cycle and provides powerful guidelines for the design of tandem electrocatalysts.