Effect of valence state on electrochemical nitrate reduction to ammonia in molybdenum catalysts

Intended to investigate the alternative to the traditional Haber−Bosch process for generating ammonia, electrocatalytic nitrate reduction reaction (NRA) ensures a lower energy path and decentralized manner. Inspired by the nitrate reductase, we propose two Mo-based electrocatalysts with different Mo valences: MoO2-C nanoball-flower (MoO2-C NBF) with Mo (IV) sites and MoO3-C nanoball-flower (MoO3-C NBF) with Mo (Ⅵ) sites. The theoretical prediction reveals that the Mo (IV) sites have an enhanced catalytic activity and selectivity to ammonia rather the Mo (Ⅵ) sites. Similarly, the experimental results show that the MoO2-C NBF exhibits a superior NH3 yield (109.28 µmol h−1 cm−2) and Faraday Efficiency (99.05 %). This work sheds light on the structure–activity relationship between valence state with NRA activity and paves the way for design and mechanism study of the Mo-based NRA electrocatalyst for the further development of sustainable NH3 synthesis.