Cuni Carbon Brush Synthesis Assisted by Polyphenol for Efficient Nitrate Electroreduction to Ammonia: Performance and Mechanism Based on Dft Calculation

Abstract

Electrocatalysis can reduce nitrate in wastewater to ammonia, a high-value product. However, the rapid NO3- reduction in a neutral environment with low-electrolyte concentration faces significant challenges. This study prepared a three-dimensional (3D) carbon brush electrode loading with CuNi alloy nanoparticles with the help of polyphenol. The 3D structure significantly increased the efficiency for NO3- reduction. In a neutral solution with Na2SO4 of only 0.05 M, the nitrate removal and ammonia yield rate reached 98.8 ± 1.1% and 206.9 ± 6.7 μg h-1 cm-2. The two values were 25 and 147 times higher than those of a two-dimensional CuNi carbon paper. Additionally, Ni doping in the CuNi catalyst reduced the accumulation of NO2- by 40% and increased the ammonia yield by 70%. DFT calculations gave us a novel perspective on the mechanism behind this electrocatalysis. Compared to single Cu, a shift of the d-band center toward the Fermi level was likely the fundamental reason for the enhanced activity of the CuNi catalyst. This shift greatly reduced the O-N-O bond angle of *NO2, an essential intermediate, making hydrogenation reaction much easier. These findings offer broad prospects of efficient nitrate electroreduction to ammonia by the novel 3D electrode.

Keywords: Electrocatalysis, nitrate electroreduction, Ammonia synthesis, CuNi catalyst, three-dimensional electrode, density functional theory