Uniform octahedral ZrO₂@C from carbonized UiO-66 for electrocatalytic nitrogen reduction

The electrochemical ammonia synthesis under ambient conditions is a promising process instead of the energy-intensity Haber-Bosch process with the release of huge greenhouse gases. But it still faces sluggish catalytic kinetics owing to difficulty of N₂ adsorption and N≡N bond cleavage. Herein, the uniform ZrO₂@C with octahedral structure is synthesized via two-step annealing treatment of UiO-66. The formation of ZrO₂ originates from Zr and O elements in UiO-66, and the grain size is confined by the produced carbon matrix from the carbonization of the organic ligand, resulting in more exposure of the active sites. ZrO₂@C obtained at 650 °C presents excellent electrocatalytic nitrogen reduction performance with a NH₃ yield rate of 6.72 μg h⁻¹ mg_cat.⁻¹ and a Faradaic efficiency of 2.68% at −0.6 V versus reversible hydrogen electrode (RHE). This work provides a strategy to design metal oxide@C from metal-organic frameworks for nitrogen fixation.