Vacancy engineering of oxidized Nb2CTx MXenes for a biased nitrogen fixation

The artificial nitrogen (N2) reduction reaction (NRR) via electrocatalysis is a newly developed methodology to produce ammonia (NH3) at ambient conditions, but faces the challenges in N2 activation and poor reaction selectivity. Herein, Nb-based MXenes are developed to remarkably enhance the NRR activity through the engineering of the stretched 3D structure and oxygen vacancies (VO). The theoretical studies indicate that N2 could be initially adsorbed on VO with an end-on configuration, and the potential determining step might be the first hydrogenation step. The catalysts achieve an NH3 production rate of 29.1 μg h−1 mgcat−1 and excellent Faradic efficiency of 11.5%, surpassing other Nb-based catalysts. The selectivity of NRR is assigned to the unique structure of the catalysts, including (1) the layered graphitic structure for fast electron transfer and active site distribution, (2) the reactive VO for N2 adsorption and activation, and (3) the expanded interlayer space for mass transfer.