High-Index Surface Structure Engineering of Au–Pd Concave Triple-Octahedrons for Boosting Electrocatalytic Nitrate Reduction to Ammonia

Nitrate reduction to ammonia (NRA) is of extreme significance in the ammonia synthesis, wastewater remediation, and nitrogen cycle. However, NRA seriously suffers from slow kinetics and low selectivity due to its eight-electron transfer process and the complex reaction intermediates. Herein, concave triple-octahedral Au–Pd alloy nanocrystals (NCs) with {331} high-index facets (HIFs) are proposed for NRA, exhibiting excellent activity and selectivity with high NH3 yield rate (4591.71 μg h–1 mgcat–1) and Faraday efficiency (61.96%) at −1.15 V vs SCE under ambient circumstance, because of the abundant low-coordinated stepped sites and the alloying electronic structure of Au–Pd. Theoretical calculation shows that the Pd modified Au(331) stepped surface endows the adsorption of NO3– and N–O bond breaking with high reactivity, which boosts the activity and selectivity of NRA.