Unveiling the dominant distal-alternating hybrid mechanism in B-modulated Mo2TiC2Tx/MoO2 MXene for highly selective ambient NRR

Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions offers a sustainable alternative to the energy-intensive Haber-Bosch process. However, the two canonical catalytic pathways face intrinsic limitations: the alternating mechanism suffers from high *NH 2 NH 2 desorption losses, while the distal pathway requires prohibitive activation energy for N 2 protonation. The simultaneous realization of high activity and selectivity thus remains a critical challenge. Here, we demonstrate that boron doping modulates the electronic structure of Mo 2 TiC 2 T x /MoO 2 by upshifting the d -/ p -band center toward the Fermi level, unveiling the dominant a hybrid “distal-alternating” pathway that favors the *NNHH → *NHNH 2 transition rather than the *NNHH → *N cleavage. In addition, the electron-deficient B sites weaken the binding affinity toward Lewis-acidic protons under acidic conditions, thereby effectively suppressing the competing hydrogen evolution reaction. Significant interfacial charge transfer from MoO 2 to the B@Mo 2 TiC 2 T x surface further ensures a sufficient electron supply for N 2 activation and stepwise hydrogenation. As a result, B@Mo 2 TiC 2 T x /MoO 2 delivers an impressive ammonia yield of 121.18 μg h −1 mg cat. −1 with a Faradaic efficiency of 75.94% at a mild potential of –0.2 V vs . RHE. This work unveils the mechanistic feasibility of a non-classical hybrid NRR pathway and establishes a rational strategy for designing next-generation high-efficiency nitrogen reduction electrocatalysts.