N-doped bamboo-like carbon nanotube-encapsulated CuNi alloy to enrich nitrate and boost electrochemical ammonia synthesis

Ammonia plays an irreplaceable role in agricultural production and also is an important chemical raw material and energy carrier. Developing a catalyst for the electrochemical NO₃⁻ reduction reaction (NO₃RR) to synthesize ammonia is crucial for energy, food security and pollution control. Herein, by adjusting the Cu/Ni ratio, we report a simple impregnation and calcination method to synthesize a N-doped bamboo-like carbon nanotube (CNT)-encapsulated CuNi alloy catalyst (Cu₇Ni₃-CNT). Cu₇Ni₃-CNT reveals an excellent ammonia synthesis performance, which has the highest Faraday efficiency (FE, 99.18%) at −0.8 V vs. reversible hydrogen electrode (RHE), along with an ammonia production rate of 20.90 mg·cm⁻²·h⁻¹. In addition, the highest ammonia production rate of Cu₇Ni₃-CNT can reach 23.21 mg·cm⁻²·h⁻¹, with a high FE (90.80%) at −1.0 V vs. RHE. At the same time, the electrocatalyst displays exceptional stability, which can operate steadily for 400 h at 300 mA·cm⁻². The high catalytic activity and excellent stability derive from catalyst structure and the synergistic effect between Cu₇Ni₃ alloy and encapsulating bamboo-like CNT. The incorporation of Ni enhances the intrinsic activity of Cu for NO₃RR. CNT endows the catalyst with a larger specific surface area, more exposed active sites to further improve the apparent activity, and higher stability. The internal cavity of CNT also contributes to the enrichment of nitrate. Furthermore, in-situ Raman spectroscopy and density functional theory (DFT) calculations reveal that Cu in the alloy can effectively adjust the adsorption energy of *NO₃ by Ni element and increase the activity of *H as the reduction driving force, thereby improving the intrinsic activity of NO₃RR.