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 Cu 2 O (111), CuO (111), and Cu (111) at different pH. Cu 2 O (111), with abundant undercoordinated Cu atoms on the surface, shows easier adsorption of NO 3 - than Cu (111) or CuO (111). NRA on CuO (111) is hindered by the large Δ G of adsorption of NO 3 - and hydrogenation of *NO. Thus, Cu (111) and Cu 2 O (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 3 - , *NO → *NOH/*NHO, and *NH 3 desorption, as the three can be rate-determining steps depending on the local environment. Moreover, previous experimentally detected NH 2 OH on copper-based catalysts may come from the NRA on Cu 2 O (111) as the most probable pathway on Cu 2 O (111) is NO 3 - → *NO 3 → *NO 2 → *NO → *NHO → *NHOH → *NH 2 OH → *NH 2 → *NH 3 → *NH 3 (g). At high reduction potential, CuO x would be reduced into Cu, so the effective active substance for NRA in a strong reduction environment is Cu.