Stabilizing Copper Nanoparticles for Electrochemical Nitrate Reduction via Encapsulation Inside Carbon Nanotubes

Abstract

Electrochemical nitrate reduction is an attractive pathway to form ammonium from abundant nitrate sources. Copper is an active catalyst for this transformation, but their stability often during electrocatalysis suffers due to its oxidation and leaching. Herein, we investigated the encapsulation of copper nanoparticles inside carbon nanotubes (Cu-in-CNT), which significantly enhances both their structural and electrochemical stability compared to copper nanoparticles supported on the outer surface of the CNT (Cu-on-CNT). Encapsulation creates a protective environment that helps preserve the intrinsic nature of the catalyst. Post-electrochemical X-ray analysis reveals that Cu-in-CNT retains its metallic state, whereas Cu-on-CNT undergoes phase transformation from Cu and CuO to Cu and Cu 2 O. After 12 hours of continuous nitrate reduction, Cu-in-CNT exhibits minimal copper leaching (5.3 wt%) compared to substantial metal loss observed in Cu-on-CNT (20.5 wt%). Furthermore, Cu-in-CNT maintains a more stable faradaic efficiency for nitrite and ammonium combined (~80%) than Cu-on-CNT (~40%) in 12 h electrolysis.