Local Chemical Environment Dependent Nitrate-Reduction-to-Ammonia Performance on Cu-Based Electrocatalysts.

The active component of copper-based materials for electrocatalytic nitrate reduction to ammonia (NRA) remains unclear due to the susceptibility of oxidation of copper. Using density functional theory calculations, NRA pathways are evaluated on low-index crystal surfaces CuO (111), CuO (111), and Cu (111) at different pH. CuO (111), with abundant undercoordinated Cu atoms on the surface, shows easier adsorption of NO than Cu (111) or CuO (111). NRA on CuO (111) is hindered by the large Δ of adsorption of NO and hydrogenation of *NO. Thus, Cu (111) and CuO (111) contribute most to the NRA activity while CuO (111) is inert. Three key steps of NRA on copper-based catalysts are identified: adsorption of NO, *NO → *NOH/*NHO, and *NH desorption, as the three can be rate-determining steps depending on the local environment. Moreover, previous experimentally detected NHOH on copper-based catalysts may come from the NRA on CuO (111) as the most probable pathway on CuO (111) is NO → *NO → *NO → *NO → *NHO → *NHOH → *NHOH → *NH → *NH → *NH(g). At high reduction potential, CuO would be reduced into Cu, so the effective active substance for NRA in a strong reduction environment is Cu.