Enrichment of Active Hydrogen at Amorphous CoO/Cu ₂ O Heterojunction Interfaces Enhances Electrocatalytic Nitrate Reduction to Ammonia

Abstract

The reduction of nitrate into valuable ammonia via electrocatalysis offers a green and sustainable synthetic pathway for ammonia. The electrocatalytic nitrate reduction reaction (NO₃RR) encompasses two crucial reaction steps: nitrate deoxygenation and nitrite hydrogenation. Notably, the nitrite hydrogenation reaction is regarded as the rate-determining step of the process. Herein, the amorphous CoO support introduced for the construction of the a-CoO/Cu₂O tandem catalyst provides sufficient active hydrogen and synergistically catalyzes the NO₃RR. The a-CoO/Cu₂O catalyst showed excellent performance with a maximum NH₃ Faradaic efficiency of 95.72% and a maximum yield rate of 0.96 mmol h^-1 mg_cat ^-1 at -0.4 V. In the flow cell, the maximum NH₃ yield rate of 12.14 mmol h^-1 mg_cat ^-1 is achieved at -800 mA. The high NO₃RR activity of a-CoO/Cu₂O is attributed to the synergistic cascade effect of amorphous CoO and Cu₂O at the heterojunction interface, where Cu₂O serves as the adsorption site for NO₃ ^-, while the accelerated active hydrogen generation of amorphous CoO promotes the nitrite hydrogenation reaction. This work provides a strategy for designing multi-site cascade catalysts centered on amorphous structures to achieve efficient NO₃RR.