Stabilizing copper nanoparticles for electrochemical nitrate reduction via encapsulation inside carbon nanotubes

Abstract

Electrochemical nitrate reduction is an attractive pathway to synthesize ammonia from abundant nitrate sources. Copper (Cu) is an active catalyst for this transformation; however, its stability is often compromised by oxidation and leaching during electrocatalysis. Herein, we investigated the encapsulation of Cu nanoparticles inside carbon nanotubes (Cu-in-CNT), which significantly enhances both their structural and electrochemical stability compared to Cu nanoparticles supported on the outer surface (Cu-on-CNT). Encapsulation provides a protective environment that preserves the structure of the catalyst. Post-catalysis analysis reveals that Cu-in-CNT retains its metallic state, whereas Cu-on-CNT undergoes transformation to and CuO to Cu and Cu₂O. After 12 hours of continuous nitrate reduction, Cu-in-CNT exhibits much less Cu leaching (5.3 wt%) compared to Cu-on-CNT (20.5 wt%). Furthermore, Cu-in-CNT maintains a stable faradaic efficiency for nitrite and ammonia combined (∼80%), in contrast to significant declined observed for Cu-on-CNT (∼40%).