Facet-controlled palladium nanocrystalline for enhanced nitrate reduction towards ammonia.

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