Built-in electric field in the Mn/C₆₀ heterojunction promotes electrocatalytic nitrogen reduction to ammonia

The electrochemical nitrogen reduction reaction (NRR) has been regarded as a green and promising alternative to the traditional Haber-Bosch process. However, the high bond energy (940.95 kJ mol^-1) of the NN triple bond hinders the adsorption and activation of N₂ molecules, which is a critical factor restricting the catalytic performance of catalysts and their large-scale applications. Herein, an Mn/C₆₀ heterostructure is constructed <i>via</i> a simple grinding and calcination process and achieves an extraordinary faradaic efficiency of 42.18% and an NH₃ yield rate of 14.52 μg h^-1 mg_cat^-1 at -0.4 V <i>vs.</i> RHE in 0.08 M Na₂HPO₄. Our experimental and theoretical results solidly confirm that the spontaneous charge transfer at the Mn/C₆₀ heterointerface promotes the formation of a built-in electric field, which facilitates the electron transfer from Mn towards C₆₀ and creates localized electrophilic and nucleophilic regions. The formation of the space-charge region effectively optimized the adsorption energy of the key intermediate *NH-*NH₂ and also reduced the free energy barrier for the hydrogenation step of *NH-*NH to *NH-*NH₂. Furthermore, the calculated lower limiting potential (<i>U</i>_L(NRR)) in Mn/C₆₀ relative to the HER (<i>U</i>_L(HER)) demonstrates its enhanced selectivity toward the NRR. This work provided new insights into enhancing the activity and performance of electrocatalysts for the NRR by constructing heterojunctions to improve nitrogen adsorption.