Electrocatalytic Nitrogen Reduction Performance Of Bimetallic Sulfide/PILs/PPy/GO Nanocomposites

As the main raw material for the synthesis of nitric acid,urea,melamine and other bulk chemicals,NH₃ plays an important role in agriculture,explosives,medicine and other fields.However,in industry,Haber-Bosch process is mainly used to synthesize ammonia,which brings huge energy consumption and high CO₂ emission.Ammonia synthesis with N₂ and H₂O as raw materials in ambient environment has been considered as one of the most promising alternative technologies,whose essential core is focused on exploring the NRR electrocatalysts with high efficiency,low cost and easy preparation.Transition metal sulfide is an ideal alternative for noble metal catalysts due to its abundant reserves,polytropic crystal structures and phase compositions,controllable morphology and adjustable defect engineering.Poly（ionic liquids）are excellent modifiers because they can effectively improve the surface morphology and electronic structure of the carrier by combining the advantages of ionic liquids and polymers.In this paper,poly（ionic liquid）was used as the linker to compound the bimetallic sulfide heterojunction with PPy/GO through interface engineering and defect engineering,and the NRR process and deactivation mechanism of the obtained electrocatalyst were systematically studied.The details are as follows:Firstly,we synthesized Mo S₂-Sn S₂/PVIPS/PPy/GO nanosheets by using poly（3-（1-vinylimidazolium-3-yl）propane-1-sulfonate）（PVIPS）as the inducers of Mo S₂ and Sn S₂ and the linkers between Mo S₂-Sn S₂ heterogeneous nanoplates and PPy/GO nanosheets.The semi-conducting Sn S₂ would limit the accessibility of surface electrons for suppressing HER process of 1T’-Mo S₂,and metallic might efficiently improve the NRR electroactivity of Sn S₂ by the creation of Mo–Sn–Sn catalytic sites.In addition,after NRR for 30 h,partial 1T’-Mo S₂ and Sn S₂ evolved into Mo₂N and Sn_xN_z due to the electrochemical reaction with N₂,meanwhile,partial Sn S₂ has been irreversibly evolved into Sn S due to the reduction of the power source in the electrochemical system.Secondly,we synthesized a series of electrocatalysts by loading Fe S₂-Sn S₂heterojunctions on PPy/GO surfaces induced by different poly（ionic liquids）under the same reaction conditions,among which Fe S₂-Sn S₂/PVEIB/PPy/GO,synthesized with poly（1-vinyl-3-ethylimidazole bromide）（PVEIB）as inducer,showed the best NRR activity.Due to the space-charge and stereo-hindrance effect of PVEIB,the stronger strain effect was induced by the mismatched lattice spacing,which may further result in the rich planar defects generating in Fe S₂-Sn S₂ heterogeneous nanoplates and improving the nitrogen activation capacity.However,the stability and durability of Fe S₂-Sn S₂/PVEIB/PPy/GO towards NRR were unsatisfactory.During the NRR process,Fe²⁺may catalyze Sn⁴⁺gradually converted to Sn~0 by electrochemical power source,which made partial hexagonal Sn S₂ irreversibly converted to tetragonal Sn blocks.Simultaneously,containing N intermediates generating during the NRR process may occupy the active sites of the exposed Fe²⁺and Sn~0,eventually resulting in the deactivation of Fe S₂-Sn S₂/PVEIB/PPy/GO towards NRR.