MXene-Derived Nanocomposites as Earth-Abundant Efficient Electrocatalyst for Nitrogen Reduction Reaction under Ambient Conditions.

Abstract

NH3, as one of the most massively used chemical products in the world, not only serves as the main nitrogen source of chemical fertilizers but also is considered as a promising renewable energy source. Most ammonia in industry is produced by the Haber-Bosch process under extremely high temperature and pressure conditions, which is intensively energy consuming and environmentally unfriendly. Electrocatalytic nitrogen reduction reaction (NRR) has been regarded as a promising way to produce NH3 under ambient conditions in recent years, but the research for efficient earth-abundant electrocatalysts is still highly limited. In this work, different TiO2 phases (anatase and rutile)/carbon nanocomposites with a sandwich architecture are produced by annealing MXene at different temperatures, which shows excellent electrocatalytic NRR performance. In 0.1 M Na2SO4, anatase TiO2/C composites show better NRR performance than the rutile ones, which achieve a large NH3 yield of 14.0 μg h-1 cm-2, a high Faradaic efficiency of 13.3% at -0.2 V vs a reversible hydrogen electrode, and a high electrochemical stability. The sandwich architecture of anatase TiO2 nanoparticles well-dispersed on the surface of carbon layers could increase the conductivity of TiO2 and the exposure of active sites, which could explain the improved NRR activity of anatase TiO2/C composites compared with previous work. Density functional theory calculations suggest that the energy barrier of most steps for the surface of anatase TiO2 is relatively lower than that of rutile TiO2, which could explain the better electrocatalytic NRR performance for anatase TiO2/C composites compared with the rutile ones.