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

Abstract

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 *NH₂NH₂ desorption losses, while the distal pathway requires prohibitive activation energy for N₂ 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 Mo₂TiC₂T_x/MoO₂ by upshifting the d-/p-band center toward the Fermi level, unveiling the dominant a hybrid “distal-alternating” pathway that favors the *NNHH → *NHNH₂ 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 MoO₂ to the B@Mo₂TiC₂T_x surface further ensures a sufficient electron supply for N₂ activation and stepwise hydrogenation. As a result, B@Mo₂TiC₂T_x/MoO₂ 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.