Study On ZIF-based Materials For Electrocatalytic Oxygen Evolution And Carbon Dioxide Reduction

Water-mediated electrochemical reduction of CO₂is a sustainable solution for CO₂recovery and fuel production.However,due to the slow CO₂reduction reaction rate in aqueous media,the excessive types of by-products,and the inevitable competition with hydrogen evolution reactions,this type of catalytic reaction is facing severe challenges.Therefore,high efficiency,high selectivity,and high stability must be developed Electrocatalyst.In addition,the entire CO₂electrolysis process is usually divided into two half-cell redox reactions:CO₂reduction reaction（CO₂RR）and oxygen evolution reaction（OER）.However,due to the complex multi-proton electron transfer process of the OER reaction,it suffers from the inherent hysteretic kinetics,which results in the reaction requiring a large overpotential.Therefore,the development of an efficient OER catalyst has an important impact on the entire CO2RR reaction.For carbon dioxide reduction reaction,excessive by-products and competition reaction of hydrogen evolution are also urgently needed to develop efficient and reasonable electrocatalyst.MOF has a diversified and designable frame/pore structure,high porosity,high surface area,and greater frame flexibility/dynamics,which has a good prospect in the field of electrocatalysis.However,MOFs are mostly poor electrical conductors,so they cannot be used directly as electrocatalysts.Therefore,MOF can circumvent the problem of low conductivity of MOF itself by acting as a precursor/template to accommodate other active units or generate MOF derivatives.According to reports,these derivatives show obvious advantages in electrocatalysis,such as oxygen reduction reaction（ORR）,nitrogen reduction reaction（NRR）,CO₂reduction reaction（CO₂RR）,hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）Wait.One of the most commonly used synthetic methods is high temperature treatment to prepare MOF-derived carbon-based materials.Therefore,based on the zeolite imidazole framework,this paper develops ZIF-67 and single atom Ni catalysts,which are applied to electrocatalytic oxygen precipitation and carbon dioxide reduction,respectively.（1）A simple,versatile and sustainable strategy was used to prepare a single-atom Ni catalyst loaded on a 3D ultra-thin carbon nanosheet network.In this strategy,the raw materials（zinc nitrate,ferric nitrate and 2-methylimidazole）are directly ground and mixed,and then a single atom Ni electrocatalyst is obtained by pyrolysis at high temperature.The obtained material is a 3D nano-network structure.It is confirmed by synchrotron radiation and spherical aberration transmission electron microscopy that the obtained material is a single atom structure and the coordination structure is Ni N₄.The temperature-programmed desorption proved that,compared with ZIF-8 as the precursor,the 3D monoatomic Ni catalyst obtained in this work fully exposed its active sites.The 3D monoatomic Ni catalyst exhibits excellent electrocatalytic reduction of CO₂.The Faraday efficiency is higher than 90%in the test voltage range,the TOF value is as high as 7025 h^-1,and it still maintains good stability after a long time electrolysis of 24 h.The enhanced CO₂RR performance is attributed to the effective doping of Ni single atoms,and the unique layered porous structure on the ultra-thin carbon layer increases the electrocatalytic activity and mass transfer rate.（2）A gentle and simple post-processing method was used to produce a multi-level ZIF-67 with a nanosheet structure on the surface.Through the surface treatment of weak acid buffer solution,a layered structure was created on the surface of ZIF-67 to expose more active sites.The multi-stage ZIF-67 greatly promotes the interface electron transfer of the electrocatalyst and enhances the mass transfer channel,showing excellent OER catalytic reaction activity and stability.The increase in catalytic activity can be attributed to the large specific surface area and high porosity of ZIF-67,the synergistic effect of the unique structure,and the exposure of more active sites.In addition,weak acid buffer solution etching is a gentle,simple and efficient strategy,which provides new ideas for the design of high-performance MOF catalysts in the future.