Facet-controlled palladium nanocrystalline for enhanced nitrate reduction towards ammonia

Electrochemical nitrate reduction reaction (NO 3 − RR) is considered an appealing way for producing ammonia (NH 3 ) under ambient conditions and solving environmental problems caused by nitrate, whereas the lack of adequate catalysts hampers the development of NO 3 − RR. Here, we firstly demonstrate that the Pd nanocrystalline with a well-desired facet can act as a highly efficient NO 3 − RR electrocatalyst for ambient ammonia synthesis. Pd (1 1 1) exhibits excellent activity and selectivity in reducing NO 3 − to NH 4 + with a Faradaic efficiency of 79.91% and an NH 4 + production of 0.5485 mmol h −1 cm −2 (2.74 mmol h −1 mg −1 ) in 0.1 M Na 2 SO 4 (containing 0.1 M NO 3 − ), which is 1.4 times higher than Pd (1 0 0) and 1.9 times higher than Pd (1 1 0), respectively. Density functional theory (DFT) calculation reveals that the superior NO 3 − RR activity of Pd (1 1 1) originates from its optimized activity of NO 3 − adsorption, smaller free energy change of the rate-limiting step (*NH 3 to NH 3 ), and poorer hydrogen evolution reaction activity (HER, competitive reaction). This work not only highlights the potentials of Pd-based nanocatalysts for NO 3 − RR but also provides new insight for the applications in NO 3 − RR of other facet-orientation nanomaterials.