Solvothermal Synthesis Of NiCoFe-MOF74 Series Materials With Microstructure Control And OER Catalytic Properties

In recent years,because hydrogen has the advantages of high combustion calorific value,abundant sources,convenient transportation and storage,and green and pollutionfree reaction products,hydrogen has been widely used as a clean energy source.In the process of preparing hydrogen by electrolyzing water,the anode half-reaction of oxygen evolution requires a high voltage and consumes a lot of energy.Therefore,in order to reduce the energy consumption in the process of electrolysis of water,it is very important to select a suitable oxygen evolution reaction catalyst.Metal-organic framework materials have become the most likely material to replace precious metal catalysts due to their high porosity and easy structure control.However,heat treatment is usually required to improve the conductivity of the metal organic framework material,and the process is complicated.In this paper,the catalytic performance of Ni Co Fe-MOF74 is improved by directly adding citric acid or Ti3C2 Tx during the synthesis of Ni Co Fe-MOF74.First,this article explored the influence of different reaction conditions on the synthesis of Ni Co Fe-MOF74.The Ni Co Fe-MOF74 synthesized at a reaction time of 24 h is uniform ellipsoidal particles with a size of about 1 μm × 0.6 μm(long axis × short axis);as the temperature increases,the size of the ellipsoid particles decreases,and the catalytic performance Improved.When the reaction temperature is 120 ℃,the overpotential required for the catalytic oxygen evolution reaction is 337 m V,and the Tafel slope is 76.91 m V/dec.When the reaction temperature is 180 ℃,the overpotential is 283 m V and the Tafel slope is 56.87 m V/dec.Secondly,heat treatment of Ni Co Fe-MOF74 in Ar and N2 atmospheres respectively.When the heat treatment temperature is 400 oC,the structure is destroyed,and the phase is a heterogeneous mixture of Ni Co Fe-MOF74 and Ni Co alloy.The catalytic performance is reduced,the overpotential is 362 m V and 342 m V,and the Tafel slope is 77.98 m V/dec and 142.81 m V/dec,respectively.The effect of the addition of layered Ti3C2 Tx on the catalytic performance of the material was explored.When the mass ratio of Ti3C2 Tx and Ni Co Fe-MOF74 synthetic raw materials is 15:1,because the obtained composite material has a lower content of Ni Co Fe-MOF74,the phase of Ni Co Fe-MOF74 is not observed,and the catalytic performance decreases;in When the mass ratio of synthetic raw materials is 3:1,it can be seen that Ni Co Fe-MOF74 phase exists,but due to too few active sites,the catalytic performance of the composite material is reduced compared with Ni Co Fe-MOF74 alone,the overpotential is 422 m V,and the Tafel slope is 91.07 m V/dec.Finally,adding citric acid to control the microscopic morphology and structure of Ni Co Fe-MOF74 during the reaction.The microstructure and catalytic performance of Ni Co Fe-MOF74 synthesized under different citric acid additions,different reaction temperatures and different solvent conditions were explored.The results show that at the same reaction temperature,increasing the amount of citric acid can refine the Ni Co FeMOF74 particles,adjust the ellipsoidal morphology to flower-like,and increase its specific surface area.However,when the citric acid addition ratio is greater than 3:10,the structure of Ni Co Fe-MOF74 will be destroyed;at the same citric acid addition ratio,increasing the reaction temperature can also refine the Ni Co Fe-MOF74 grains.When the reaction temperature is higher than 180 ℃,the structure damage.The study found that when the reaction temperature is 150 ℃ and the citric acid addition ratio is 1:10,the flower-like Ni Co Fe-MOF74 obtained has a uniform morphology,and the internal pores of the flower-like aggregate state are about 500 nm,which is beneficial to the transmission of oxygen and electrons.The overpotential of the Ni Co Fe-MOF74 catalyst for oxygen evolution reaction prepared under the optimal synthesis conditions is 249 m V,and the Tafel slope is 49.16 m V/dec.This paper also explored the influence of different solvents on the synthesis of Ni Co Fe-MOF74.The results show that Ni Co Fe-MOF74 synthesized in anhydrous solvent is amorphous spherical particles,and its catalytic performance is lower than that of crystalline Ni Co Fe-MOF74.