Synthesis And Properties Of Pt Single Atoms And Bimetal CuFe Electrocatalysts For Nitrogen Reduction Reaction

Ammonia?NH₃?is a main raw material for fertilizer for food supply and an ideal energy carrier and storage intermediate for renewable energy sources due to its easy transportation across the world.Compared with the energy-and capital-intensive Haber-Bosch process for NH₃ synthesis,ambient electrochemical nitrogen reduction reaction?NRR?is attracting more interest in achieving clean and sustainable NH₃production using renewable energy sources.However,design and development of efficient catalysts for NRR still remain a great challenge due to the high bond energy of N?N(940.95 k J mol^-1)and the competitive hydrogen evolution reaction?HER?.Therefore,this thesis focuses on the design and preparation of efficient NRR electrocatalysts via atomic structure modification and bimetallic synergistic effect.The Pt single atomic catalyst and CuFe bimetallic catalyst were prepared and their structural characterization was performed by all kind of modern measurements.The corresponding electrocatalytic performance of the prepared materials were tested,and the catalytic mechanism was discussed in detail.The results and conclusions are summarized as below:1.The preparation of isolated Pt sites for efficient electrocatalytic nitrogen reduction reaction.The Pt single atomic sites anchored onto WO₃ nanoplates?Pt SAs/WO₃?were prepared by in situ photo-deposition procedure.The obtained Pt SAs/WO₃ catalyst exhibited the distinguished electrochemical NRR performance with342.4?g h^-1 mg_Pt^-1 of NH₃ yield and 31.1%of Faradaic efficiency?FE?in 0.1 M K₂SO₄at-0.2 V vs.RHE.Our results reveal that the special electronic structure of isolated Pt sites decorated WO₃ nanoplates should have a good ability to chemisorb and activate the N₂,and meantime greatly depress the hydrogen evolution reaction,enhancing its FE for NRR.Based on the results of in situ FT-IR spectra and density function theory?DFT?calculation,it can be confirmed that positively charged isolated Pt sites with special Pt-3O structure can favorably chemisorb and activate the N₂ and the conversion of N₂ to NH₃ follows an alternating hydrogenation pathway.2.Bimetallic CuFe catalyst for ambient electrocatalytic nitrogen reduction.Highly dispersed CuFe bimetallic electrocatalysts were successfully achieved by calcination of CuFe O₂ precursor in H₂/Ar gases at different temperatures.The bimetallic catalyst was first reported to use in electrocatalytic NH₃ synthesis.According to the optimized parameters of calcination temperature via electrochemical testing,the as-prepared CuFe-450 catalyst exhibits a high FE of 8.3%and ammonia production rate of 3.5?g h^-1 mg^-1_cat in 0.1 M PBS?phosphate buffer saline?electrolyte at-0.3 V vs.RHE,which is obviously better than the single metal catalysts and the bimetallic catalyst prepared by co-precipitation process.This excellent performance is attributed to electronic synergistic interaction between two metallic components,high dispersion of metal nanoparticles,and good conductivity.The in situ FT-IR spectra further reveal electroreduction of N₂ to NH₃ via an associative pathway.This preparation method for bimetallic catalysts derived from binary metal oxide can keep the morphology of binary metal oxide intact and meantime avoid the aggregation of bimetallic nanoparticles themselves so as to make more active sites exposed.This work provides a new idea for preparation of bicomponent transition metal catalytic materials.