| Ammonia as an important hydrogen carrier,which energy density by volume is nearly double that of liquid hydrogen and conveniently storage and ship.So,ammonia is considered a green alternative fuel.Up to now,most of the world's ammonia is synthesized by using Haber-Bosch process,a century-old process that is triggered under rigorous thermochemical condition?high temperature and high pressure?,consuming a large amount of non-renewable energy corresponding to many serious environmental problems.In the field of clean energy technology,electrocatalysis nitrogen reduction reaction has attracted widely attention,which be powered from N2 and H2O by electricity from renewable energy sources such as solar and wind.Motivated by such facts,much effort was made to explore high-performance nitrogen reduction reaction?NRR?catalysts,including defect engineering catalysts.However,the synergetic mechanism between activity sites and defect or vacancy needed to be explained in detail.The findings obtained in this paper is to design Ru-based catalysts with defect or vacancy and recover the synergetic mechanism between activity sites and defect or vacancy,which have important guiding significance of designing and fabricating high performance electrocatalysts for NRR.The main research results are summarized as follows:1?Compounds of[Ru(C6H3O2N2)Cl4]and[Ru2O(C12H6O4N2)2Cl6]have been successfully synthesized using RuCl3 as a metal precursor to react with 3,5-pyridine dicarboxylic acid and 2,2'-bipyridine-4,4'-dicarboxylic acid,respectively.And their crystal structures were characterized,which shows Ru coordinated with two nitrogen of ligands in[Ru(C6H3O2N2)Cl4],and two Ru-nucleus combine with oxygen element to form Ru-O-Ru bond in[Ru2O(C12H6O4N2)2Cl6].Then,two well-dispersed Ru-NPs were loaded on porous carbon electrocatalysts obtained after pyrolysis using these two compounds to combine with ZIF-8,and using XRD?TEM technique to analyze its composition and morphology,then,taken to study the performance of NRR for the first time,the results shown that the ammonia yield rates of Ru/D-ZIF-PC and Ru2/D-ZIF-PC were 1.22?g·h-1·cm-2 and 0.98?g·h-1·cm-2,respectively,which shown Ru NPs played an importan role in the process of NRR.2?Supported catalysts,featuring unique properties derived from support and tiny noble-metal catalyst both geometrically and electronically,could achieve unexpected results for electrocatalysis.Ru/TiO2-Vo electrocatalyst was obtained by mechanically mixing Ru?acac?3 with TiO2-Vo in mortar after pyrolysis under high temperature.Significantly,the characterization results demonstrated that Ru NPs with an average size of 2.3 nm was uniformly supported on the TiO2-Vo,simultaneously,there were rich oxygen vacancies in the Ru/TiO2-Vo.XRD?TEM technique were used to analyze the composition and morphology of catalysts.As an electrocatalyst,the Ru/TiO2-Vo was confirmed to be electrochemically active for the NRR with a NH3 yield rate of 2.11?g·h-1·cm-2 and Faradaic efficiency of 0.72%at-0.15 V?vs.RHE?in 0.1 M KOH electrolyte under ambient conditions.The electronic structural analysis revealed that the existence of oxygen vacancy could strength the adsorption of N2 on Ru-NPs,which means oxygen vacancy plays an important role in regulating the charge between Ru-NPs and support,resulting in the improvement of NRR property.Meanwhile,the density functional theory?DFT?calculations demonstrated that the adsorption energy in TiO2-Vo is much higher than in TiO2,which suggested Ru on TiO2-Vo could more effectively activate than on TiO2 for nitrogen,thus demonstrated the Ru cluster and oxygen vacancy could have synergistic effect.In a word,this paper focused on studying the relationship between active sites,vacancies or defects and electrocatalytic nitrogen reduction reaction. |
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