NbO 2 Electrocatalyst Toward 32% Faradaic Efficiency for N 2 Fixation

The electrocatalytic N 2 reduction reaction (NRR) to produce ammonia is an attractive but highly challenging approach, due to the extreme inertness of N 2 molecules and significantly lower N 2 concentration compared to the surrounding water molecules. Herein, NbO 2 nanoparticles are demonstrated as an efficient NRR electrocatalyst with significantly improved electrochemical performances. Compared to Nb 2 O 5 with a similar crystal structure unit but different linkage, the Nb 4+ cation not only provides empty d‐orbitals for strong N 2 adsorption, but also a single d‐electron to further enable back donation to activate the NN triple bond. As a result, the NbO 2 nanoparticles present an outstanding ammonia production rate of 11.6 µg h −1 mg cat. −1 at −0.65 V versus reversible hydrogen electrode (RHE) and an excellent electrochemical stability, significantly higher than those of the Nb 2 O 5 nanorods under similar conditions. More importantly, a peak faradaic efficiency of ammonia production of 32% is obtained for NbO 2 at −0.60 V versus RHE, which is one of the highest reported NRR faradaic efficiencies to date.