Potential-dependent insights into the origin of high ammonia yield rate on copper surface via nitrate reduction: A computational and experimental study

• DOI: 10.1016/j.jechem.2024.04.039
• Publication Date: 2024-05-10T16:32:01Z
• Authors: Yangge Guo; Nannan Sun; Liuxuan Luo; Xiaojing Cheng; Xueying Chen; Xiaohui Yan; Shuiyun Shen; Junliang Zhang
• Keywords: Experimental validation; Density functional theory; Nitrate reduction to ammonia; Copper surface; Constant electrode potential method

Focusing on revealing the origin of high ammonia yield rate on Cu via nitrate reduction (NO3RR), we herein applied constant potential method via grand-canonical density functional theory (GC-DFT) with implicit continuum solvation model to predict the reaction energetics of NO3RR on pure copper surface in alkaline media. The potential-dependent mechanism on the most prevailing Cu (1 1 1) and the minor (1 0 0) and (1 1 0) facets were established, in consideration of NO2−, NO, NH3, NH2OH, N2, and N2O as the main products. The computational results show that the major Cu (1 1 1) is the ideal surface to produce ammonia with the highest onset potential at 0.06 V (until −0.37 V) and the highest optimal potential at −0.31 V for ammonia production without kinetic obstacles in activation energies at critical steps. For other minor facets, the secondary Cu (1 0 0) shows activity to ammonia from −0.03 to −0.54 V with the ideal potential at −0.50 V, which requires larger overpotential to overcome kinetic activation energy barriers. The least Cu (1 1 0) possesses the longest potential range for ammonia yield from −0.27 to −1.12 V due to the higher adsorption coverage of nitrate, but also with higher tendency to generate di-nitrogen species. Experimental evaluations on commercial Cu/C electrocatalyst validated the accuracy of our proposed mechanism. The most influential (1 1 1) surface with highest percentage in electrocatalyst determined the trend of ammonia production. In specific, the onset potential of ammonia production at 0.1 V and emergence of yield rate peak at −0.3 V in experiments precisely located in the predicted potentials on Cu (1 1 1). Four critical factors for the high ammonia yield and selectivity on Cu surface via NO3RR are summarized, including high NO3RR activity towards ammonia on the dominant Cu (1 1 1) facet, more possibilities to produce ammonia along different pathways on each facet, excellent ability for HER inhibition and suitable surface size to suppress di-nitrogen species formation at high nitrate ...