CuNi nano-alloy loading on three-dimensional electrode for efficient nitrate electroreduction to ammonia: Performance and mechanism based on DFT calculation

Recovery of nitrogen from industrial wastewater through electrochemically reducing nitrate to ammonia attracts increasing research interest. However, conventional two-dimensional (2D) planar substrates limit the catalyst activity. Loading catalysts on three-dimensional (3D) electrodes with high specific surface area is an effective way to enhance electrode catalytic activity. In this work, we fabricated a 3D carbon brush electrode loaded with CuNi nano-alloy (CuNi/CB). The CuNi/CB achieved ammonia yield rate (NH3-Nyr) of 479.1 ± 5.3 μg h−1 cm−2 within 0.5 h, with a Faraday efficiency of 73.4 %. Compared with CuNi supported on carbon paper (CP), carbon felt (CF) and carbon cloth (CC), the NH3-Nyr of CuNi/CB were higher by 114.7, 35.2, and 26.8 times, respectively. The outstanding performance of CuNi/CB benefited from the higher specific surface area of the 3D carbon brush. Additionally, Ni doping in the CuNi catalyst reduced the accumulation of NO2− by 39.7 % and increased the NH3-Nyr by 82.9 %. Density functional theory (DFT) revealed that a shift of the d-band center toward Fermi level was likely the fundamental reason for the enhanced activity of the CuNi catalyst, comparing with single Cu catalyst. These findings offer broad prospects of efficient nitrate electroreduction to ammonia by the novel 3D electrode.