Synthesis Of NiCo-MOF-74 Based Electrocatalyst And Its Performance In Electrocatalytic Decomposition Of Water

Electrolytic water can produce hydrogen in a renewable way,which is another important way to solve the energy crisis after renewable energy such as wind energy or photovoltaic.In recent years,due to the highly ordered spatial arrangement of metal cations and specific chemical environment,metal organic frameworks（MOFs）have certain advantages in crystal structure,specific surface area and porosity,which has attracted extensive interest in the field of catalysis.Taking advantage of the unique structure and properties of MOFs,bimetallic oxides were designed based on MOF-74 precursors,and a series of electrocatalysts with excellent electrochemical properties were constructed withπ-conjugated molecules and MOF-74,which were used in the study of electrocatalytic water decomposition.The main research contents of this paper are as follows:1.Preparation of NiO/Co₃O₄ catalyst and its electrocatalytic hydrogen evolution（HER）performanceUsing nickel and cobalt as metal sources and 2,5-dihydroxyterephthalic acid as organic ligand,Ni_xCo_y-MOF-74 precursors with different molar ratios of metal ions were synthesized by low temperature solvothermal method.The porous NiO/Co₃O₄ catalysts were prepared by calcination at high temperature.It was found that compared with the Ni_xCo_y-MOF-74 precursor before calcination,the morphology of NiO/Co₃O₄ obtained after calcination was not changed significantly,and its specific surface area increased,which effectively improved its electrocatalytic performance.Among them,NiO/Co₃O₄ catalyst showed the best hydrogen evolution performance when the mass ratio of nickel ion to cobalt ion was 1:0.43.In 0.5 M H₂SO₄ electrolyte,when the current density is 10 m A/cm~2,the overpotential was 220 m V and the Tafel slope was 45.1 m V/dec.2.Preparation of NiCo-MOF-74/TCNQ catalyst and its electrocatalytic oxygen evolution reaction（OER）performanceNiCo-MOF-74/TCNQ composite catalyst was successfully synthesized by adding a certain mass ofπ-conjugated molecule 7,7,8,8-tetracyano-p-benzoquinone dimethane（TCNQ）in the preparation of NiCo-MOF-74 by simple solvothermal method.The results showed that TCNQ successfully entered the one-dimensional channel of NiCo-MOF-74 without changing its crystal structure.The above findings were proved by XRD,FT-IR and other analysis results.At the same time,due to the introduction of TCNQ,the conductivity of MOF-74 was improved and the electron transfer between TCNQ and MOF-74 was enhanced,which showed better electrocatalytic oxygen evolution performance.Among them,when the addition amount of TCNQ is 20 mg and the current density of NiCo-MOF-74/TCNQ in 1 M KOH solution is 10m A/cm~2,the overpotential was 330 m V.At the same time,it had the smallest Tafel slope,which proved that the catalyst had good electrocatalytic oxygen evolution performance.3.Preparation of HHTP@NiCo-MOF-74 catalyst and its electrocatalytic oxygen evolution reaction（OER）performanceA certain amount ofπ-conjugated molecule 2,3,6,7,10,11-hexahydroxytriphenyl（HHTP）was coated on NiCo-MOF-74 by two-step hydrothermal method（HHTP@NiCo-MOF-74）.It was found that the crystal structure of NiCo-MOF-74 had not been changed after the addition of HHTP.Compared with NiCo-MOF-74,its oxygen evolution（OER）activity has been significantly improved.This is mainly because HHTP can accelerate the electron transfer with NiCo-MOF-74 and produce abundant unsaturated active sites.When the addition amount of HHTP was 0.01 mmol,HHTP@NiCo-MOF-74 showd excellent electrocatalytic oxygen evolution（OER）performance.When the current density is 10 m A/cm~2,the overpotential was200 m V.