Electrocatalysis has a wide range of applications in the field of clean energy and environmental protection,especially in the use of clean,efficient and sustainable energy and green organic synthesis,for example,the production of high-purity oxygen,hydrogen by electrolysis of water,methanol fuel cells,carbon hydrogen bond electrochemical oxidation,etc.,its core is developing high-efficiency electrocatalysts.However,the commercial catalysts is still metal-based catalysts such as Pt,Ir,Ru,Cr,etc.Because of the scarcity of precious metal resources,high cost,and toxicity of some catalysts,their application process is severely restricted.Therefore,the development of electrocatalysts with good stability,low cost and high activity is important significance to promote the development of the above-mentioned fields.MOFs have advantages in tailorability of its metal center and organic components,structural diversity,porosity,and high specific surface area,and it makes MOFs suitable to be electrocatalyst.In recent years,MOFs have been increasingly studied in the electrochemical field(including fuel cells,metal-air batteries,electrolyzed water,electrocatalytic methanol oxidation,lithium ion batteries and supercapacitors)due to their unique characteristics.In this paper,a series of new transition metal MOF materials have been synthesized based on the existing work of the research group and their properties of electrolytic water hydrogen evolution(HER)and electrocatalytic methanol oxidation(MOR)have been investigated.The first part of the introduction introduces MOFs materials and their preparation methods,as well as the recent research of MOFs in the electrolysis of water hydrogen evolution,oxygen evolution and methanol oxidation.The second part of this essay is mainly using the phthalic acid isomer H2Lx(x=1,2,3.H2L1=H2Cl4-pta,H2L2=H2Br4-pta,H2L3=H2F4-pta)and some nitrogen-containing ligands(bpy=4,4’-Dipyridyl,2,2’-bipy=2,2’-Dipyridyl,bpe=1,2-Di(4-pyridyl)ethylene,bpmp=1H-1,2,4-triazol-3-amine),reacted with transition metal ions(Co,Ni,Cu)through hydrothermal to construct 11 new MOFs.Then we analyzed their crystal structure and carried out basic physical and chemical characterization.The 11 examples of MOFs are crystalline material 1({[Co(Cl4-pta)(bpy)(H2O)2]}n),crystalline material 2({[Ni(Cl4-pta)(bpy)(H2O)2]}n),crystalline material 3({[Co(F4-pta)(bpy)(H2O)2]}n),crystalline material 4({[Ni(F4-pta)(bpy)(H2O)2]}n),crystalline material 5({[Co(Br4-pta)(bpy)(H2O)2]}n),crystalline material 6({[Ni(Br4-pta)(bpy)(H2O)2]}n),crystalline material 7({[Cu2(Br4-pta)2(2,2’-bipy)2]}n),crystalline material 8({[Ni(F4-pta)(bpe)](H2O)}n),crystalline material 9({[Cu(F4-pta)(bpe)]}n),crystalline material 10({[Co(F4-pta)(bpe)(H2O)2]}n)and crystalline material 11({[Ni(F4-pta)(bpmp)(H2O)2]}n).Most of the 11 crystalline materials have two-dimensional structures,two-dimensional materials theoretically have better electrocatalytic performance than three-dimensional materials because of their unique layered structure.We selected 3 Co-based crystalline materials 1,3,and 5 with isomorphic structure as electrocatalysts for the hydrogen evolution reaction(HER),and we investigated the influence of the use of different halogen-substituted ligand on HER performance of the materials.The study found that the crystalline material 1(Co-Cl4-pta)performance is better than the other two materials(Co-Br4-pta and Co-F4-pta),then we make the acetylene black(AB)and crystalline material 1 complex which improve the HER performance.When the mixing ratio is 3:4(AB:crystalline material 1),the HER performance is relatively best:the overpotential is 283 mv when the current density is 10m A·cm-2,and the Tafel slope is 86 m V·dec-1.It can be seen that introducing halogen elements into the MOF structure is an effective strategy to enhance the HER performance of crystalline materials.In addition,the MOR performance of 5 Ni-based crystalline materials 2,4,6,8,11was studied.We found that the MOR catalytic performance of crystalline material 11 was relatively best,mass activity and area activity are 129.375 m A/mg and 14.66 m A·cm-2.The third part of this essay used 9,10-Anthracendicarboxylic acid(adc),some nitrogen-containing ligands{dpp=Di(4-pyridyl)propane,dps=4,4’-Thiodipyridine}and transition metal ions(Co,Ni,Cu)to construct 7 new transition MOFs under hydrothermal/solvothermal condition.we resolved their crystal structure and characterized their basic physical and chemical properties.The 7 examples of crystalline materials are crystalline material 12({[Cu(adc)(dpp)]}n),crystalline material 13({[Co(adc)(dpp)(H2O)2]}n),crystalline material 14({[Ni(adc)(dpp)(H2O)]}n),crystalline material 15({[Cu(adc)(dps)(H2O)]}n),crystalline material 16({[Co(adc)(dps)(H2O)]}n),crystalline material 17({[Ni(adc)(dps)(H2O)]}n),crystalline material 18({[Ni(μ2-O)(adc)]}n).Among the 7 crystalline materials we constructed,crystalline material 13,14,15,16,17 are two-dimensional layered structure which formed by stacking due to weak intermolecular interactions(hydrogen bond,π-πStacking)and crystalline material 12 and 18 are three-dimensional structure.The central metal Co ion of the crystalline material 13 presents an octahedral configuration,which forms a two-dimensional structure by connecting with adc and dpp ligands,the smallest asymmetric unit of the crystalline material14 has two 6-connected Ni ions,adc and dpp ligands are connected to form a two-dimensional network.The crystalline material 15 is triclinic system with a space group of P-1,and its metal center Cu ion presents a twisted octahedral geometric configuration,which is connected to form a two-dimensional network through adc and dps.The crystalline materials 16 and 17 are isomorphic(Co/Ni)which are new structure not reported in the literature,and they are monoclinic system which the space group are P21/c.The metal center Co ion of crystalline material 16 presents an octahedral coordination configuration,which forms a two-dimensional network by connecting with adc and dps.Dps is a flexible ligand,the C-S-C bends at a certain angle,the C-S-C angles of crystalline materials 15,16,17 are 102.812°,101.977°and 101.820°,respectively.The crystalline materials 15,16,17 form a buckle shape and fits each other between the layer.The metal center Cu of the crystalline material 12 presents an octahedral configuration,unlike the aforementioned MOFs,the metal node Cu is directly interwoven with the dpp and adc to form a three-dimensional structure.The crystalline material 18 has a metal core chain structure,in which water molecules are deprotonated to form aμ2-O bridge,the metal nodes are connected through theμ2-O bridge to form a metal core chain.Finally these metal chain are connected with adc ligands to form a supramolecular three-dimensional network.In the experiment,the MOR performance of Ni-based crystalline materials 14,17,18 was mainly studied.Among them,the MOR performance of crystalline material 18 is better than crystalline materials 14 and 17,and the mass activity and area activity can reach 213.35 m A/mg and 24.164 m A·cm-2 respectively.This is related to the unique structure of 18,this unique core chain structure makes the material’s metal active sites dense,theoretically possessing good catalytic activity.The fourth part of this essay used 2,4,6-triste(4-pyridy)-1,3,5-triazine(tpt)and different carboxylic acid ligands(adc=9,10-Anthracendicarboxylic acid,etta=4,4’,4’’,4’’’-(ethene-1,1,2,2-tetrayl)tetrabenzoic acid,dtda=dithieno[3,2-b:2’,3’-d]thiophene-2,6-dicarboxylic acid)reacted with transition metal ions Co and Ni to construct 5 MOF materials under hydrothermal condition,and they are crystalline material 19({Co3(μ3-O)(tpt)(adc)3}n),crystalline material 20({Ni3(μ3-O)(tpt)(adc)3}n),crystalline material 21({Co(tpt)(tcpe)}n),crystalline material 22({{Ni(tpt)2(tcpe)(H2O)2}·4H2O}n)and crystalline material 23({Ni3(tpt)3(dtda)2(H2O)}n).The crystalline materials 19 and 20 are isostructural materials of Co and Ni.Taking the crystalline material 19 as an example,19 is theμ3O cluster[Co3(μ3-O)(COOH)3]as secondary structural unit interwoven with tpt and adc ligand,and a three-dimensional supramolecular network structure is formed,and the crystalline material 19 can be regarded as a simple three-party 6-connected acs network in topology.The central metal ion Co1 of the crystalline material 21presents an octahedral shape,and the metal nodes form a three-dimensional supramolecular structure through conecting with the tcpe and tpt.The metal center metal ion Ni1 of the crystalline material 22 presents an octahedral configuration,and the metal node Ni is connected by ligands to form a one-dimensional chain structure.The crystalline material 23 belongs to the orthorhombic crystal system,the space group is Cmce,in which the metal is connected byμ2O to form a tri-nuclear metal cluster,which is connected with the ligand to form a three-dimensional supramolecular structure,and there are obviousπ-πstacking and hydrogen bonding between the molecules.The MOR test for crystalline materials 20,22 and 23 shows that the performance of crystalline material 22 is relatively good,and its mass activity and area activity are 6.895 m A/mg and 0.7839 m A/cm-2,respectively.In addition,the i-t test chart shows that the stability of the three crystalline materials is good,and there is no obvious current decay after long-term cycling.In general,the lower MOR activity of crystalline materials 20,22,and23 may be related to the larger organic ligands,the longer distance between the metal clusters,and the weaker electron transport ability caused by the three-dimensional framework.The fifth part of this essay is the summary of this paper and prospective to the future.Focusing on the key scientific issues of the electrocatalytic process and combining the experimental data,we summarized and look forward to the future application of MOFs materials in the field of electrocatalysis. |