Spin Manipulation of Co sites in Co 9 S 8 /Nb 2 CT 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 (N 2 ) during the electrocatalytic nitrogen reduction reaction (eNRR). However, achieving this remains challenging. Herein, a novel 2D/2D Mott-Schottky heterojunction, Co 9 S 8 /Nb 2 CT x -P, is developed as an eNRR catalyst. This is achieved through the in situ growth of cobalt sulfide (Co 9 S 8 ) nanosheets over a Nb 2 CT x MXene using a solution plasma modification method. Transformation of the Co spin state from low (t 2g 6 e g 1 ) to high (t 2g 5 e g 2 ) is achieved by adjusting the interface electronic structure and sulfur vacancy of Co 9 S 8 /Nb 2 CT x -P. The adsorption ability of N 2 is optimized through high spin Co(II) with more unpaired electrons, significantly accelerating the *N 2 →*NNH kinetic process. The Co 9 S 8 /Nb 2 CT x -P exhibits a high NH 3 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 NH 3 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 Na 2 SO 4 . This work demonstrates a promising strategy for constructing heterojunction electrocatalysts for efficient eNRR.