Spin Manipulation of Co sites in Co₉S₈/Nb₂CT_x Mott–Schottky Heterojunction for Boosting the Electrocatalytic Nitrogen Reduction Reaction

Regulating the adsorption of an intermediate on an electrocatalyst by manipulating the electron spin state of the transition metal is of great significance for promoting the activation of inert nitrogen molecules (N₂) during the electrocatalytic nitrogen reduction reaction (eNRR). However, achieving this remains challenging. Herein, a novel 2D/2D Mott-Schottky heterojunction, Co₉S₈/Nb₂CT_x-P, is developed as an eNRR catalyst. This is achieved through the in situ growth of cobalt sulfide (Co₉S₈) nanosheets over a Nb₂CT_x MXene using a solution plasma modification method. Transformation of the Co spin state from low (t_2g ⁶e_g ¹) to high (t_2g ⁵e_g ²) is achieved by adjusting the interface electronic structure and sulfur vacancy of Co₉S₈/Nb₂CT_x-P. The adsorption ability of N₂ is optimized through high spin Co(II) with more unpaired electrons, significantly accelerating the *N₂→*NNH kinetic process. The Co₉S₈/Nb₂CT_x-P exhibits a high NH₃ yield of 62.62 µg h^-1 mg_cat. ^-1 and a Faradaic efficiency (FE) of 30.33% at -0.40 V versus the reversible hydrogen electrode (RHE) in 0.1 m HCl. Additionally, it achieves an NH₃ yield of 41.47 µg h^-1 mg_cat. ^-1 and FE of 23.19% at -0.60 V versus RHE in 0.1 m Na₂SO₄. This work demonstrates a promising strategy for constructing heterojunction electrocatalysts for efficient eNRR.