Investigation Of Ruthenium-based Catalysts Preparation And The Performance Of Electrocatalytic Nitrogen Reduction

As one of the highest production of inorganic chemicals in the world,NH₃ is widely used in pharmaceutical,oil refining,synthetic fiber and other industrial fields.The traditional ammonia synthesis is carried out by the Haber-Bosch method,which is synthesized from hydrogen and nitrogen under the conditions of high temperature and pressure with the presence of catalysts.Most of the energy input of this process comes from fossil fuels,and the process emits a large amount of CO₂,which leads to a series of problems such as the consumption of non-renewable energy and the greenhouse effect.Therefore,electrochemical ammonia synthesis is studied as a potential alternative method.However,due to the high overpotential,low ammonia yield and selectivity,the application of electrochemical synthesis of ammonia is limited.The catalyst is the core component for the nitrogen reduction reaction（NRR）,and its performance affects the entire catalytic process.Therefore,the development of high-performance catalyst is very important for the development of NRR.Ru is an ideal catalyst material in the NRR process for its high NRR activity.In this study,Ru-based composite catalyst materials were prepared to further increase the utilization rate of precious metal Ru,in order to obtain NRR catalysts with high activity and high ammonia yield.The etched two-dimensional MXene（Ti₃C₂）is used as a carrier to synthesize Ru@MXene material loaded with Ru.The electrochemical test was carried out in a 0.1 M KOH solution saturated with N₂.At-0.4 V vs.RHE potential,the Ru@MXene catalyst achieved the maximum ammonia yield(39.10μg h^-1 cm^-2)and the maximum Faraday efficiency（FE:13.13%）.In the12-hours stability test,the current attenuation of the material is small and maintains good stability.Quantum chemical calculations show that among the five possible NRR reaction pathways,Ru@MXene catalyst has the best catalytic activity for the H₂NNH₂ dissociation pathway.Compared with MXene,the Ru@MXene catalyst can significantly reduce the reaction barrier in the NRR process and improve the overall catalytic efficiency.In order to further improve the NRR performance of Ru-based catalysts,transition metal Fe was introduced in the Ru@MXene catalyst,and Ru Fe@MXene materials of different proportions were prepared.It is expected that the synergy between Ru and Fe can be used to improve the catalytic performance.The experimental results showed that when the molar ratio of Ru:Fe is 3:7,Ru Fe@MXene has the best NRR catalytic activity.At potential of-0.4 V vs.RHE,the FE of the Ru Fe@MXene is 15.04%,and the ammonia yield is 40.23μg h^-1 cm^-2,compared with Ru@MXene under the same potential,the yields of FE and ammonia increased by 14.55%and 2.90%,respectively.Theoretical calculations show that the Ru Fe@MXene catalyst is most likely to undergo NRR process through the H₂NNH₂ dissociation pathway.The results of density of states reveals that Ru Fe@MXene has a large overlap area between the conduction band and the valence band,which is helpful for the electron transfer of the catalyst during the NRR.