Preparation And Electrocatalytic Ammonia Synthesis Performance At Room Temperature Of ZIF-67-67 Derivatives/MoS₂ Composites

Ammonia（NH₃）,as an important chemical fertilizer raw material,is in large demand in agriculture and industry.The traditional industrial NH₃ production is still heavily dominant by Haber-Bosch process,which uses nitrogen in the air and hydrogen from any source to react to synthesize ammonia.On the one hand,hydrogen production methods such as early coal,coke to later natural gas,oil and even water electrolysis have serious defects of high energy consumption;On the other hand,the plant infrastructure of this method is complex and the carbon dioxide emission is serious.Among the many nitrogen fixation methods（biological strategies,photocatalytic and electrocatalytic）,electrochemical nitrogen reduction reaction（NRR）is the best route,because it can be driven by renewable energy to produce NH₃ from water.Due to the inherent activity of nitrogen and the competing hydrogen evolution reaction（HER）,the NRR has some problems such as low NH₃ yield,low faraday efficiency（FE）and poor selectivity.However,the bottleneck in NRR process is to construct a reasonable nitrogen reduction reaction system and search for a highly efficient catalyst.Recently,a nitrogen-doped carbon material（Co-NC）with metallic particles,derived from metal organic framework（ZIF-67）,which has good conductivity and good catalytic performance.However,it promotes the NRR reaction as well as the occurrence of HER competitive reaction.So,finding a way to weaken the HER competition reaction is an effective means to design NRR catalysts.Here,an effective strategy of adding HER attractant（MoS₂）is proposed to greatly boost the NRR activity and the Co-NC/MoS₂composite is prepared.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and other characterization methods are used to study the crystal structure and morphology.The NRR electrochemical tests indicate that the Co-NC/MoS₂-4 sample can obtain the highest NH₃ yield and FE are 54.66μg·h^-1·mg_cat^-1and 34.49%,respectively（0.1 M HCl）.The deep reason for the improvement of electrocatalytic performance was analyzed by poisoning test,electrochemically active surface area（ECSA）and density functional theory（DFT）calculation,and the important role of HER attractant（MoS₂）in NRR process was confirmed.At the same time,Co-NC/MoS₂-4 composite material was used as the N₂-cathode for Zn-N₂ battery.The preparation process of the electrode and the appropriate electrolyte composition of the battery were further determined,and the NH₃ production and discharge performance were tested.The NH₃ yield of the cell reached 40.23μg·h^-1·mg_cat^-1 in 0.1 M KOH electrolyte,which was better than the NH₃ production performance of Zn-N₂ batterys reported previously.In order to study the practical value of the battery,simulated seawater was prepared and used as electrolyte for discharge experiment.The battery can discharge stably at the discharge voltage of 1.2 V,which also provides the possibility for the further application of NRR catalyst in the field of energy conversion.