Au/UiO-66-Zr nanohybrids: boosting the yield rates of electrochemical ammonia synthesis with the sacrificial effects of faradaic efficiencies

Abstract

This work has developed two series of catalysts for nitrogen reduction reaction (NRR), i.e., xAu/UiO-66-NaBH₄ and xAu/UiO-66-N₂H₄ nanohybrids, where UiO-66-Zr is loaded with Au nanoparticles. NH₃ yield rates (r_NH3) are greatly boosted owing to the sacrificial effects of a few faradaic efficiencies (FEs), which is due to different influences of the loaded Au or closely-related lost-linker defects on the electrochemically active surface areas and charge transfer efficiencies and further on r_NH3 and FEs, respectively. The optimal 5Au/UiO-66-NaBH₄ has a high r_NH3 of ∼163.33 μg mg_cat⁻¹ h⁻¹ but only a moderate FE of ∼55.52% due to the sacrificial effects of FEs. Furthermore, the loading features of Au nanoparticles and the structures of UiO-66-Zr supports in xAu/UiO-66-NaBH₄ are more favourable than those for xAu/UiO-66-N₂H₄ because NaBH₄ is a stronger reducing agent and a more powerful destroyer of UiO-66-Zr supports in comparison with N₂H₄·H₂O, which endow them the generally higher r_NH3 and higher FE.