Size-induced d band center upshift of copper for efficient nitrate reduction to ammonia.

Electrocatalytic nitrate reduction (NORR) technique has emerged as a hotspot in NH production, for its practicability, and a series of advanced electrocatalysts with high activity and robust stability needed to be constructed in today's era. In this work, size-tunable Cu nanoparticles on porous nitrogen-doped hexagonal carbon nanorods (Cu@NHC) were reasonably designed and served for catalyzing NORR in neutral media. Especially, Cu@NHC demonstrated a remarkable electroactivity for NH production as it showed a suitable grain size with massive catalytic centers and favorable d band structure with faster *NO-to-*NO catalytic dynamics. As expected, Cu@NHC (3628.28 µg h mg) had a much higher NH yield than those for Cu@NHC (1268.42 µg h mg) and Cu@NHC (725.03 µg h mg). And those collected NH products indeed derived from NORR process revealed by N isotope-labeling and systemic control tests. Moreover, Cu@NHC was also durable for NORR bulk electrolysis with minor loss in activity. This work offered an effective modifying tactics to boost NORR catalysis and could guide the design of other advanced electrocatalysts via size-induced surface engineering.