Abstract:

Electrocatalytic nitrate reduction reaction (NO₃RR) has been capturing immense interest in the industrial application of ammonia synthesis, and it involves complex reaction routes accompanied by multi-electron transfer, thus causing a challenge to achieve high efficiency for catalysts. Herein, we customized the Cu-O-Ti-O_v (oxygen vacancy) structure on the Cu/TiO₂ catalyst, identified through density functional theory (DFT) calculations as the synergic active site for NO₃RR. It is found that Cu-O-Ti-O_v site facilitates the adsorption/association of NO_x^- and promotes the hydrogenation of NO₃^- to NH₃ via adsorbed ^*H species. This effectively suppresses the competing hydrogen evolution reaction (HER) and exhibits a lower reaction energy barrier for NO₃RR, with the reaction pathways: NO₃^* → NO₂^* → HONO^* → NO^* → ^*NOH → ^*N → ^*NH → ^*NH₂ → ^*NH₃ → NH₃. The optimized Cu/TiO₂ catalyst with rich Cu-O-Ti-O_v sites achieves an NH₃ yield rate of 3046.5 μg h^-1 mg_cat^-1 at -1.0 V vs. RHE, outperforming most of the reported activities. Furthermore, the construction of Cu-O-Ti-O_v sites significantly mitigates the leaching of Cu species, enhancing the stability of the Cu/TiO₂ catalyst. Additionally, a mechanistic study, using in situ characterizations and various comparative experiments, further confirms the strong synergy between Cu, Ti, and O_v sites, which is consistent with previous DFT calculations. This study provides a new strategy for designing efficient and stable electrocatalysts in the field of ammonia synthesis.

Key words: Electrocatalytic nitrate reduction, Ammonia synthesis, Cu-O-Ti-O_v site, Synergic catalytic effect, Cu/TiO₂ catalyst