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

Abstract

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 NN 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 via 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 vs. 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 (U_L(NRR)) in Mn/C₆₀ relative to the HER (U_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.