A simple hydrothermal synthesis of an oxygen vacancy-rich MnMoO₄ rod-like material and its highly efficient electrocatalytic nitrogen reduction

Electrocatalytic nitrogen reduction (NRR) for artificial ammonia synthesis under ambient conditions is considered a promising alternative to the traditional Haber-Bosch process. However, it still faces multiple challenges such as the difficulty of N₂ adsorption and activation and limited Faraday efficiency. In this work, a bimetallic oxide MnMoO₄ was prepared by a hydrothermal method and low temperature calcination. The influence of the sintering temperature on the microstructure (crystallinity and oxygen vacancies) of the oxide and its NRR properties were systematically explored. The results showed that MnMoO₄ sintered at 500 °C had the highest concentration of OVs and showed excellent NRR performance, with the highest NH₃ yield (up to 12.28 μg h^-1 mg_cat^-1), high Faraday efficiency (23.04% at -0.30 V vs. RHE), and good stability at -0.40 V vs. RHE, and the catalytic performance was about two times higher than that of Mn₂O₃ and MoO₃. It is also superior to other bimetallic oxide NRR electrocatalysts reported in some cases. In addition, we also explored the ratio between Mn and Mo metals, and the catalytic effect was the best when Mn : Mo = 1 : 1. Due to the synergistic effect between Mn and Mo metals and the large number of OVs present internally, the catalytic activity for the NRR was largely improved. This study suggests that the bimetallic oxide MnMoO₄ may be a promising NRR electrocatalyst.