Preparation And Electrocatalytic Performance Of Transition Metal Nanocomposites

At present,human society is facing serious fossil energy crisis and environmental pollution problems,these problems have greatly threatened the sustainable development of human society.A key factor in reducing society's dependence on traditional fossil fuels relies on the application of renewable energy conversion and storage devices.These equipment applications mainly include the following electrochemical processes:oxygen reduction reaction?ORR?,oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?.However,the sluggish kinetics of these electrochemical processes currently utilizes noble metal catalysts such as Pt,Ir and Ru to realize sufficient efficiency.Nonetheless,their scarcity and high price greatly inhibit their extensive commercial reach.Therefore,the design and synthesis of highly efficient non-precious metals electrocatalysts have received great attention.In this paper,we mainly designed and prepared a series of inexpensive metal-based electrocatalysts,and optimizes the activity of the materials in different types of electrocatalytic conversion reactions through reasonable design of structure.The main contents of this thesis are summarized as followed:?1?Porphyrin-based oxygen reduction catalyst:this work successfully demonstrated the iron porphyrins with different functional groups coated on carbon nanotubes?CNTs?were used as precursor,different structures and composition of Fe-N-C catalysts were formed after pyrolysis.Experiment data revealed that carbonyl groups in TPP-CHO could afford enough oxygen for the generation of Fe₃O₄,and the conversion from Fe element to Fe₃C crystalline structure is hampered.The Fe₃O₄@FeNC-700 displayed terrible ORR activity.Cyan groups on periphery in TPP-CN seem play positive role on synthesizing high activity site Fe-N_x,and Fe/Fe₃C@C nanopaticles and active sites Fe-N_x was evenly distributed on the CNTs surface after pyrolysis.The synergetic effect between Fe/Fe₃C nanoparticle and the Fe-N_x seem play essential role on achieving superior catalytic performance.Fe₃C@FeNC-700 catalyst exhibited the best ORR activity and also showed superior resistance to the methanol crossover effect and durability compared with commercial Pt/C catalyst.?2?Template-directed synthesis of Co₃O₄ catalysts:firstly,the morphological structure of Co-MOFs was regulated by template PVP and temperature.The prepared Co-MOFs was then calcined to obtain a series of Co₃O₄ nanocomposites with different morphologies.Among all the samples,Co₃O₄-85 hollow microflowers have the largest electrochemical surface area,good electrical conductivity and so on.Therefore,the Co₃O₄-85 hollow microflowers catalyst exhibited the best HER and OER performance in the alkaline electrolyte.When assembling a basic electrolyzer using Co₃O₄-85 hollow microflowers as cathode and anode,it demonstrated a excellent catalytic performance for overall water splitting to deliver 10 mA cm^-2 at a cell voltage of 1.67 V.The electrocatalytic performance of this catalyst was superior to many non-precious metal catalysts.These results make the catalysts promising in the water electrolysis applications.?3?A nanowire array of Cu₂O@CoV/CF heterostructure composites for water splitting:in this section,a bimetallic ion-doped hollow Cu₂O nanowire composite was prepared by a one-step hydrothermal method with Cu?OH?₂ nanowires and bimetallic salts.Electrochemical tests suggested that Cu₂O@CoV/CF exhibited high catalytic activity toward the water splitting with potential of only 1.55 V to achieve 10 mA cm^-2 in 1.0 m KOH.Notably,this catalyst not only exhibited high catalytic activity but also displayed high stability(the potential of Cu₂O@CoV/CF electrodes was almost stable for over 50 h continuous testing at a constant current of 20 mA cm^-2).Above all,our rational design of hollow nanoarchitectures presents a facile approach to fabricate advanced materials for water splitting.