Synthesis And Properties Of Oxalic Acid MOF System And Its Derivatives

Energy is the cornerstone of economic development.Hydrogen（H₂）is one of the most important energy products in the world,which is widely used in industry,medicine,battery and other fields.It is of great practical significance to find a strategy for preparing hydrogen with low energy consumption and low pollution.Under this background,the preparation of hydrogen by electrolysis and oxygen reduction has attracted extensive attention.ORR is composed of oxygen evolution reaction（OER）and hydrogen evolution reaction（HER）.The higher the potential barrier of OER reaction,the lower the overall rate of OER reaction.Improving the activity and universality of OER catalyst is the biggest challenge in this field.At present,noble metal catalysts have reached the commercial level,but they are expensive and difficult to be applied on a large scale.Therefore,transition metal oxides,sulfides,phosphides,double-layer hydroxides（LDH）and metal organic frameworks（MOF）have become research hotspots because of their low cost.MOF material is a multifunctional oxide,which has the advantages of excellent chemical properties,rich sources and good catalytic activity for a variety of reactions.It is one of the most widely studied and applied catalyst materials.In this paper,oxalic acid MOF materials and their derivatives were studied,including:（1）(Ni_0.5Fe_0.5)C₂O₄ nanorods were synthesized by room temperature coprecipitation and adjusting the atomic ratio to realize the regulation of oxalic acid MOF nanostructures.The effects of different atomic ratios on OER catalytic activity were studied.It was found that when the atomic ratio of Fe:Ni was 1:1,the prepared samples had the minimum overpotential,that is,when the current density was 50 m A·cm^-2,the overpotential was 284 m V,which proved that(Ni_0.5Fe_0.5)C₂O₄ nanorods had good OER catalytic effect.XPS analysis of the phase changes of(Ni_0.5Fe_0.5)C₂O₄ nanorods before and after electrochemical test and the measurement of OER catalytic activity of the mixture of Fe C₂O₄ and Ni C₂O₄ nanorods after 1:1 grinding showed that the substance with OER catalytic activity was(Ni_0.5Fe_0.5)（OH）_x（C₂O₄）_1-x.In addition,a large-scale experiment was carried out to produce 40 g catalyst in 5 minutes.The morphology,composition and performance of the mass-produced catalyst were analyzed.It was found that the large-scale experiment would not change the performance and morphology of(Ni_0.5Fe_0.5)C₂O₄ nanorods.（2）The morphology and properties of Ce and Co doped(Ni_0.5Fe_0.5)C₂O₄ nanorods were studied by doping(Ni_0.5Fe_0.5)C₂O₄ nanorods with Ce and Co.The results show that the doping of Ce and Co alone cannot make(Ni_0.5Fe_0.5)C₂O₄ nanorods transform into nano blocks,showing an irregular rod shape.At the same time,the catalytic activity of OER is not increased,but decreased.However,when Ce and Co are doped at the same time,the morphology of(Ni_0.5Fe_0.5)C₂O₄ nanorods is transformed into nano blocks.When the doping amount of CE and CO is 5%,not only(Ni_0.5Fe_0.5)C₂O₄ nanorods are transformed into flower like nano blocks,but also the catalytic activity and stability of OER are significantly improved.From the linear sweep curve（LSV）,the overpotential is 270 m V when the current density is 50 m A·cm^-2.The relationship between current and time（i-t）shows that the stability of(Ni_0.5Fe_0.5)C₂O₄ nanorods is improved by 22%.（3）The OER catalytic activity of oxalic acid MOF material derivatives were investigated.The(Fe_0.66Co_0.33)C₂O₄ nanorods were synthesized by coprecipitation method.The derivative Fe Co alloy of(Fe_0.66Co_0.33)C₂O₄ nanorods was obtained by means of polyvinylpyrrolidone（PVP）adhesive and calcination.The results show that when the mass ratio of(Fe_0.66Co_0.33)C₂O₄nanorods to PVP is 1:2,the obtained Fe Co alloy is evenly embedded in the carbon layer,and the carbon connects the Fe Co alloy together to form a network structure and increase the electron transfer channel,so that the Fe Co alloy particles have good OER catalytic activity.When the current density is 10 m A·cm^-2,the overpotential is 314 m V,indicating that the oxalic acid MOF derivatives obtained by calcination also have OER catalytic ability,which increases the types of OER catalysts.In this paper,two kinds of oxalic acid MOF materials and a derivative of oxalic acid MOF materials were synthesized by coprecipitation method.Both of them have good catalytic activity,and the synthesis conditions are very easy to meet,which provides a feasible new angle for the large-scale promotion of MOF materials.