A Robust n-n Heterojunction: CuN and BN Boosting for Ambient Electrocatalytic Nitrogen Reduction to Ammonia

An n-n type heterojunction comprising with CuN and BN dual active sites is synthesized via in situ growth of a conductive metal-organic framework (MOF) [Cu₃ (HITP)₂ ] (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) on hexagonal boron nitride (h-BN) nanosheets (hereafter denoted as Cu₃ (HITP)₂ @h-BN) for the electrocatalytic nitrogen reduction reaction (eNRR). The optimized Cu₃ (HITP)₂ @h-BN shows the outstanding eNRR performance with the NH₃ production of 146.2 µg h^-1 mg_cat ^-1 and the Faraday efficiency of 42.5% due to high porosity, abundant oxygen vacancies, and CuN/BN dual active sites. The construction of the n-n heterojunction efficiently modulates the state density of active metal sites toward the Fermi level, facilitating the charge transfer at the interface between the catalyst and reactant intermediates. Additionally, the pathway of NH₃ production catalyzed by the Cu₃ (HITP)₂ @h-BN heterojunction is illustrated by in situ FT-IR spectroscopy and density functional theory calculation. This work presents an alternative approach to design advanced electrocatalysts based on conductive MOFs.