Molecular Engineering at Electrode Interface Enables Efficient Catalytic Nitrogen Reduction

Molecular catalysts are promising for nitrogen (N 2 ) fixation due to their well‐defined sites and tunable coordination, yet most molecules in homogeneous systems reside in the bulk solution, leading to poor catalyst utilization. Here, we introduced a molecular engineering strategy by assembling a functionalized molecular molybdenum complex (PyMoBr 3 PNP) on graphdiyne (GDY) through π–π interactions. The resulting interface‐assembled molecular electrode, PyMoBr 3 PNP/GDY/carbon paper (CP), catalyzed N 2 conversion to ammonia (NH 3 ) using 2,4,6‐trimethylpyridinium triflate ([ColH][OTf]) as the proton source. Rigorous isotopic labeling and continuous time‐dependent controls confirmed the genuine nature of catalytic N 2 to NH 3 turnover. Encouraged by the intrinsic N 2 reduction activity, the PyMoBr 3 PNP/GDY/CP cathode was further coupled with a molecular hybrid photoanode (ZnTCPP/Al 2 O 3 /BiVO 4 ) for photoelectrocatalytic N 2 reduction. The integrated system decreased the applied bias, achieved a turnover frequency (TOF) of 47.52 h −1 and a turnover number (TON) of 157.54 over 4 h for NH 3 production, representing the highest performance reported to date for molecular‐based electrochemical and photoelectrochemical N 2 reduction. All of these results highlight the potential of molecular engineering platforms to enhance catalyst utilization, improve reaction efficiency, and lower energy consumption for N 2 fixation.