Molecular Engineering at Electrode Interface Enables Efficient Catalytic Nitrogen Reduction.

Molecular catalysts are promising for nitrogen (N2) 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 (PyMoBr3PNP) on graphdiyne (GDY) through π-π interactions. The resulting interface-assembled molecular electrode, PyMoBr3PNP/GDY/carbon paper (CP), catalyzed N2 conversion to ammonia (NH3) 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 N2 to NH3 turnover. Encouraged by the intrinsic N2 reduction activity, the PyMoBr3PNP/GDY/CP cathode was further coupled with a molecular hybrid photoanode (ZnTCPP/Al2O3/BiVO4) for photoelectrocatalytic N2 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 NH3 production, representing the highest performance reported to date for molecular-based electrochemical and photoelectrochemical N2 reduction. All of these results highlight the potential of molecular engineering platforms to enhance catalyst utilization, improve reaction efficiency, and lower energy consumption for N2 fixation.