Preparation And Properties Study Of Electrocatalytic Materials Based On Metal-Organic Frameworks

With the continuous development of society,energy crises and environmental problems are increasingly serious.Carbon dioxide（CO₂）electrocatalysis,water splitting,and electrochemical sensing are significantly effective means to solve the energy crisis and environmental issues.However,there are still some challenges,such as the high activation energy barrier of CO₂ molecule;sluggish kinetics,and high overpotential caused by multi-electron transfer in the oxygen evolution reaction（OER）;high detection limit and narrow linear range of electrochemical sensors.In response to these challenges,four highly efficient electrocatalysts based on the metal-organic framework（MOFs）have been constructed in this paper.MOFs,with a large specific surface area and abundant pore structure,contribute to the adsorption and diffusion of reactants and have attracted extensive attention in the field of electrocatalysis.In addition,these materials can be modified by doping,pyrolysis,regulation,and compounding strategies,which provides new opportunities to deal with the challenges of electroreduction of CO₂,water splitting,and electrochemical sensing.The specific research contents of this paper are as follows:（1）The main difficulty of electroreduction of CO₂ lies in the activation of CO₂molecules.To solve this problem,we prepared Cu_x-ZIF-8（x=40%,50%,60%）by doping strategy.X-ray photoelectron spectroscopy（XPS）shows that the charge density around the Zn site of ZIF-8 increases with the doping of Cu²⁺,and active centers with rich electrons can facilitate the activation of CO₂ molecules.The experimental results show that Cu_50%-ZIF-8possesses the super electrocatalytic performance with an 80 m V decrease of initial potential and 1.4 times enhancement of Faraday efficiency（FE）compared to ZIF-8,which further indicates that the doping of Cu²⁺can promote the activation of CO₂ molecules on the catalyst.In addition,the doping of Cu²⁺improves the conductivity of the catalyst and further promotes the electrocatalytic reduction of CO₂.（2）Work（1）can just mitigate the problem of high activation energy barrier by preparing modified MOF catalyst,but it can not fundamentally reduce the inherent overpotential of CO₂ reduction.In order to essentially solve this problem,we have prepared core-shell catalyst ZIF-8@Co/C by partial pyrolysis strategy and developed a novel technology of cascading a photoactive process into electrocatalytic CO₂ reduction on this catalyst.This technology can change the original reaction path of electrocatalysis by cascading a photoactive process and reduce the activation energy barrier of CO₂ essentially,which leads to the enhancement of catalytic performance.Under the excitation of light,the opposite charges of the core and shell in ZIF-8@Co/C make photoelectrons transfer directionally from Co/C shell to ZIF-8 core and participate in the activation of CO₂.As a result,the initial potential and overpotential of CO₂ reduction decrease by 40 m V and 200m V respectively,and the yield of syngas increases by 5.2 times.More importantly,the energy conversion efficiency of solar-to-syngas（"Joule to Joule"）reaches up to 5.38%,which exceeds that of reported traditional photoelectrocatalysis.This work opens up a new way to reduce the overpotential of CO₂ electroreduction by introducing cheap sunlight.（3）The sluggish four-electron transfer process of OER is one of the major obstacles for water splitting applications.Based on this problem,we prepared a composite electrocatalyst[Mo₃S₁₃]^2-/Co-MOF-74 by a solvothermal method.The introduction of[Mo₃S₁₃]^2-can effectively modulate the morphology of Co-MOF-74 and improve the electron transfer ability of composite.In addition,[Mo₃S₁₃]^2-can induce Co-MOF-74 to produce more unsaturated metal sites,and the electron interaction between two components of the catalyst can increase the electron density of the Co sites,which facilitates the formation of the key intermediate in the process of OER,and thus accelerates the OER.Compared with Co-MOF-74 and[Mo₃S₁₃]^2-,the[Mo₃S₁₃]^2-/Co-MOF-74 composite reduces the overpotential and promotes the reaction kinetics of OER.This work provides a valuable reference for improving the OER catalytic performance of MOFs.（4）Electrochemical sensing plays a crucial role in the detection of drug and environmental pollutants,facing the major problems of low detection sensitivity and narrow linear range.Based on this problem,we have synthesized the composite catalyst MIL-101（Cr）/r GO by a one-step hydrothermal method for the detection of metronidazole and the simultaneous detection of Cd²⁺and Pb²⁺.The large specific surface area and rich pore structure of MIL-101（Cr）are beneficial to facilitate the diffusion and adsorption of metronidazole as well as heavy metal ions.At the same time,the introduction of r GO can improve the electron transport capacity of the catalyst and enhance the redox reactions of the tested species on the catalyst surface.As a result,the composite catalyst exhibits a higher detection sensitivity compared to the single component.Compared to the reported electrochemical sensors,the sensor based on MIL-101（Cr）/r GO delivers a wide linear range（0.5～900μM）and a low detection limit（0.24μM）for metronidazole detection.Moreover,trace simultaneous detection of Cd²⁺and Pb²⁺can be achieved with low detection limits of5.2 n M(Cd²⁺)and 3.0 n M(Pb²⁺)on this sensor,meeting WHO detection standards.This work provides a new idea for improving the detection performance of electrochemical sensors.