Study On The Relationships Between Composition,Structure And Properties Of Novel Transition Metals-Based Electrocatalysts

In the 21st century,electrochemical clean energy conversion and the production of sustainable chemicals are crucial in realizing a truly sustainable society.To move electrochemical storage and conversion devices toward commercialization,it is necessary to improve the performance of electrocatalysts and reduce costs.Among them,zinc-air batteries involve two basic electrochemical reactions,ORR and OER.High overpotentials lead to slow kinetic progress of these two reactions.Therefore,commercial ORR catalysts are still mainly made of noble metals such as platinum.However,precious Pt has disadvantages such as low reserves,high cost,and poor durability.Therefore,it is crucial to develop low-cost,high-performance electrocatalysts.Iron has an unfilled electron arrangement structure,which is conducive to the formation of adsorption bonds,and can coordinate with nitrogen-doped carbon materials to prepare electrocatalysts with good oxygen reduction performance.extensive attention.Based on the above advantages,three nitrogen-doped carbon materials supported by iron carbide nanoparticles were prepared in this paper.Scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and Raman spectroscopy（Raman）and other characterization methods to analyze the morphology and structure of the prepared materials,using cyclic voltammetry（CV）,linear sweep voltammetry（LSV）,rotating ring disk electrode（RRDE）,Chronoamperometry（it）and Accelerated Durability Test（ADT）and other test methods to study the electrocatalytic performance of the prepared catalysts,and the relationship between the composition and structure of the prepared electrocatalysts was obtained by analyzing the experimental results.It is summarized as follows:1.Polydopamine（PDA）microspheres with special morphology were prepared by adding two surfactants,P-123 and F-127,to alkaline dopamine solution.Then,using the PDA nanospheres adsorbing iron acetylacetonate and urea as precursors,nitrogen-doped carbon microspheres supported by iron carbide nanoparticles were prepared by high temperature calcination in an inert atmosphere,which were named Fe/N-CMSs-T（T represents the pyrolysis temperature）.After electrochemical tests,the prepared Fe/N-CMSs-900 catalyst exhibited the best electrocatalytic performance.The excellent oxygen reduction performance of Fe/N-CMSs-900 should be attributed to the large amount of active nitrogen functional groups,unique mesoporous structure and large electrochemical surface area of the catalyst.2.The polymer of tannic acid and melamine was prepared by a simple liquid phase method.Then,the iron-coordinated polymers were obtained by the strong coordination of iron ions with hydroxyl groups in tannic acid molecules in the polymers.The pyrolysis of iron-coordinated polymers resulted in a novel type of iron carbide nanoparticle-embedded nitrogen-doped carbon nanotubes with diameters of about 200–300 nm,named FeC-NCNTs-T（T stands for pyrolysis temperature）.Among them,the as-prepared FeC-NCNTs-800exhibited the best ORR performance in alkaline solution.The unique tubular structure,high graphitization degree,and small R_ct value of FeC-NCNTs-800 catalyst are responsible for its excellent performance.3.Using xanthine as substrate,melamine as nitrogen source,and ferric chloride as iron source,nitrogen-doped carbon nanotubes embedded with iron carbide nanoparticles were prepared by a combination of hydrothermal and pyrolysis methods.Has uniform length and diameter.After high temperature pyrolysis,the product still maintains the nanotube morphology and is named Fe-N@CNTs-T（T stands for pyrolysis temperature）.Among them,the Fe-N@CNTs-800 catalyst showed better ORR performance than the benchmark Pt/C.The assembled Zn-air battery exhibits an open circuit voltage as high as 1.504 V,a high power density of 106.14 mW cm^-2,and good rate capability.