Preparation And Application Of Ferro-based Electrocatalysts Derived From Metal-organic Framework

The energy crisis and environmental pollution are two pressing global issues currently faced.According to statistics,global energy consumption is increasing at a rate of 2.3%per year,and the reserves of traditional fossil fuels will face great pressure in the coming decades.At the same time,the combustion of traditional fossil fuels also emits large amounts of greenhouse gases such as carbon dioxide,exacerbating global climate change and posing a serious threat to human beings and the Earth’s ecosystem.Currently,governments,enterprises,and individuals worldwide are actively taking measures to address energy crisis and environmental pollution,with the development of renewable energy,improving energy efficiency,promoting clean production,and promoting circular economy measures becoming the main direction.The development of new energy systems based on electrochemical technology,such as fuel cells and water electrolysis devices,is crucial for promoting the development of renewable energy industries.Among them,the design and synthesis of high-activity,low-cost new electrocatalysts are one of the keys to achieving efficient conversion in new energy systems.MOF materials(Metal-Organic Framework materials)are composed of metal ions or metal clusters and organic ligands.Their highly tunable electrochemical properties,unique pore structures,and good biocompatibility make them potential materials for catalysts,sensors,electrochemical energy storage devices,biosensors,and medical diagnostics.In particular,MOF materials can effectively catalyze a variety of electrochemical reactions,such as oxygen reduction reaction,water splitting reaction,and carbon dioxide reduction reaction,achieving high selectivity and efficiency of catalytic reactions.The oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)play a crucial role in electrochemical energy storage technology,especially in secondary metal-air batteries,where ORR and OER are needed for reversible discharge and charge.In this thesis,a series of electrocatalysts were prepared using MOF materials as sacrificial templates through solid-liquid reactions and annealing strategies,targeting these two reactions.By adjusting the local electronic structure and regulating the active sites,the electrocatalytic efficiency was significantly improved,the cycling stability was enhanced,and good selectivity was achieved in competitive reactions.This thesis provides a reference for further addressing issues such as slow reaction kinetics,high cost,and poor stability of electrocatalysts.The main contents of this thesis are as follows:1.Preparation and Electrocatalytic Oxygen Evolution Performance Study of Prussian blue analogue(PBA)selenide nanosheetsAn efficient oxygen evolution reaction(OER)catalyst is an important component of industrial water alkaline electrolysis cells.In this study,a carbon-nitrogen-based iron-nickel-doped selenide OER catalyst was successfully prepared using a Prussian blue analog(PBA)as a template through a two-step annealing method.The experimental results showed that the cyanide radicals from the decomposition of PBA would be encapsulated in the outer layer of the metal in the form of carbon and nitrogen,thereby limiting the metal particle size to the nanoscale,increasing the sample surface area,and enhancing the number of active OER sites.The selenide coating on the material surface improved the material’s conductivity and provided a fast charge transfer pathway while also protecting the metal from oxidation and corrosion,thus increasing the material’s stability.Importantly,this carefully designed OER catalyst had an overpotential of only 220 mV at a high current density of 100 mA cm-2,which was superior to commercial IrO2,indicating the potential of our catalyst as a substitute for precious metal catalysts and providing more choices and possibilities for water electrolysis reactions.Therefore,the results of this study provide new ideas and methods for developing efficient and low-cost water splitting catalysts.2.Preparation of Transition Metal Particle Catalysts Based on zeolitic imidazolate framework(ZIF-8)Precursors and Their Electrocatalytic Oxygen Reduction ApplicationsThe oxygen reduction reaction(ORR)is an important half-reaction that occurs during the operation of fuel cells and metal-air batteries.This study reports on the preparation process of a catalyst using ZIF-8 as a template and the structure,active sites,and electronic structure of its derived carbon-nitrogen-based catalysts.A series of transition metal-doped ZIF-8 was synthesized through a dual-solvent ion exchange method,and a range of Fe-Co NP/NC catalysts(Fe-Co NP/NC-1000,Fe-Co NP/NC-900,Fe-Co NP/NC-1100,Fe NP/NC,and Co NP/NC)were subsequently produced using this as a precursor.This method avoids the use of expensive and scarce noble metals,significantly reducing the cost of synthesis while retaining the high activity required for electrocatalytic ORR reactions.This series of catalysts inherits the advantages of the porous framework structure of the metal-organic framework ZIF-8,which prevents the excessive aggregation of metals.The optimal ratio of doping metals was discussed using the modifiable components.The effects of different heating rates and annealing temperature points on the obtained nanoparticle morphology and its composition were compared.The Fe-Co bimetallic doping catalyst developed has significantly improved activity compared to single-metal doping catalysts,with a half-wave potential(E1/2)of 0.915 V.The electronic local structure of the metal in the catalyst and the valence state changes were discussed using X-ray photoelectron spectroscopy(XPS)and X-ray absorption spectroscopy(XAFS)techniques.The optimized catalyst improved the oxygen intermediate adsorption and desorption properties of the active center,accelerated the reaction kinetics,and annealing caused graphitization,which is beneficial for electron transfer,making it a highly promising non-noble metal ORR catalyst.