Efficient electrocatalytic conversion of N2 to NH3 using oxygen-rich vacancy lithium niobate cubes

Abstract

Instead of the energy-intensive Haber-Bosch process, the researchers proposed a way to produce ammonia using water and nitrogen as feedstock, powered by electricity, without polluting the environment. Nevertheless, how to design efficient electrocatalyst for electrocatalytic nitrogen reduction reaction (NRR) is still urgent and challenging. Herein, a strategy is proposed to adjust the morphology and surface electronic structure of electrocatalyst by optimizing material synthesis method. LiNbO3 (lithium niobate, LN) cubes with oxygen-rich vacancy and regular morphology were synthesized by hydrothermal synthesis and followed molten salt calcination process, which were used for electrocatalytic NRR under mild conditions. Compared with LN nanoparticles synthesized by solid phase reaction, LN cubes exhibit better NRR performance, with the highest ammonia yield rate (13.74 μg·h−1·mg−1) at the best potential of −0.45 V (vs. reversible hydrogen electrode, RHE) and the best Faradaic efficiency (85.43%) at −0.4 V. Moreover, LN cubes electrocatalyst also demonstrates high stability in 7 cycles and 18 h current–time tests. Further investigation of the reaction mechanism confirmed that the structure of oxygen vacancy could adjust the electronic structure of the electrocatalyst, which was conducive to the adsorption and activation of N2 molecule and also increased the ECSA of electrocatalyst, thus providing more active sites for the NRR process.