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

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.