Study On Electrocatalysis And Supercapacitor Properties Of {P₆Mo₁₈} Type Polyacid Bonded Polymer

Supercapacitor is a new type of green energy storage device,with long cycle life,fast energy transmission,high power density advantages,in many portable electronic products,hybrid electric vehicles,aerospace engineering and other fields have a wide range of applications.Electrode materials are the core components of supercapacitors.How to prepare high-performance electrode materials is a key scientific problem in the field of energy storage.As a unique class of non-classical POMs,the basket shaped{P₆Mo₁₈}is a mixed valence heteropolyl blue composed of Mo ^Vand Mo ^VI,showing good mixed valence electron delocalization.As mixed-valence heteropoly blue compounds,they not only have reversible multi-electron redox ability and overlapping peak potential,but also have stronger ion/electron transfer ability due to their unique cage structure,which makes them more ideal electrode materials and electrocatalysts for pseudocapacitors.From the idea of molecular design,the Poms-fund organic bond polymer was constructed by introducing metal/organic metal units into{P₆Mo₁₈}system by in-situ hydrothermal method,which can not only provide additional redox active center available,but also adjust and improve its specific surface area,electrical conductivity and solution stability.It is an effective strategy to synthesize Poms-based energy storage active materials.In this paper,six cases of phosphomolybdate compounds with novel basket structure were synthesized by hydrothermal method with appropriate organic ligands and transition metal cations at suitable p H.Elemental analysis,IR,TG,P-XRD and other characterization methods were used to determine the molecular formula of compounds 1-6 as follows:（H₂bpy）₅[{Co（H₂O）₂}{Co（H₂O）₃（bpy）}₂{Sr（?）P₆Mo₂^VMo ₁₆^VIO₇₃}₂]·8H₂O（1）（Hcz）₄[{Cu^Ⅰ（phen）}₂{Cu^Ⅱ（H₂O）（phen）}₂{Sr（?）P₆Mo₄^VMo₁₄^ⅥO₇₃}]·1.5H₂O（2）（H₂pz）（pz）_0.5{Cu ^I（bim）₂}[{Cu^Ⅱ（H₂O）_1.5（bim）}{Cu^Ⅱ（bim）₂}₂{Sr（?）P₆Mo₂^VMo ₁₆^VIO₇₃}]·6H₂O（3）（H₂bib）₃[{Co（H₂O）₂}{Sr（?）P₆Mo₂^ⅤMo₁₆^ⅥO₇₃}]·6H₂O（4）（H₂bpa）₄[{Cu_0.5^Ⅱ（H₂O）}₂{Cu^Ⅱ（H₂O）}₂{Sr（?）P₆Mo^VMo₁₇^ⅥO₇₃}₂]·10H₂O（5）（H₂imi）（H₂pz）（pz）₂[{Zn（H₂O）₂（pz）}{Zn（H₂O）₃（pz）}{Sr（?）P₆Mo₂^VMo₁₆^VIO₇₃}]·4H₂O（6）（bpy=4,4’-bipyridine,phen=1,10-Phenanthroline,cz=carbazole,pz=pyrazine,bim=2,2’-biimidazole,bib=1,4-Bis（imidazolyl）butane,bpa=Bis（4-pyridyl）amine,imi=imidazole）Structure analysis showed that compounds 1-3 were organic-inorganic hybrid supramolecular structures,and compound 1 was a single-arm basket dimer modified by{Co（H₂O）₃（bpy）}complex.Compound 2 is a 4-support structure modified by{Cu^Ⅱ（H₂O）（phen）}and{Cu^Ⅰ（phen）}complexes,and its abundantπ-πinteraction is characterized by spatial accumulation.Compound 3 is a phosphomolybdate with special pore structure formed by the asymmetric 3-support unit modified by{Cu^I/Cu^Ⅱ（bim）₂}and{Cu^Ⅱ（H₂O）_1.5（bim）}.Compounds 4 and 5 are three-dimensional supramolecular networks based on 1-D dimer chains with{Co（H₂O）₂}and{Cu^Ⅱ（H₂O）}as Bridges,respectively.The stacking pattern of ABAB results in their special interlayer structure.Compound 6 is composed of metallic organic chain{Zn（H₂O）₂（pz）}n embedded into a basket POM system.Glassy carbon electrode and carbon paper electrode were prepared with compounds 1-6 as active substances.The properties of six compounds were tested by CV,GCD,cyclic stability and EIS respectively.The results show that the charging and discharging processes of compounds 1-6 are electrochemical stored processes with diffusion control and pseudocapacitance control.The more stable structure and special interlayer structure of 1-D compounds result in their properties generally superior to those of 0-D compounds.The specific capacitance,conductivity and cyclic stability of0-D compound 3,1-D compound 6 are superior to other similar compounds.This is because the regular pore structure increases the specific surface area of the material,shorens the electron transfer channel,and effectively alleviates the volume change caused by charge and discharge.The best capacitive performance of compound 6 is due to the introduction of metal-organic chains which improve the conductivity and greatly enrich the redox center.Using 3 and 6 as negative terminals,the asymmetric supercapacitor devices exhibit high energy density,power density,capacitance retention and coulomb efficiency.The best performance of 6-CPE//AC is due to the fact that the introduction of metal-organic chains can greatly enrich the redox center of the active material while changing the conductivity.The catalytic oxidation of AA and reduction of H₂O₂ were tested with six glassy carbon electrodes.1-6-GCE showed good bifunctional catalytic activity.Comparing the catalytic effects and capacitances of the six compounds,the results are consistent,which further proves that the modification of metal-organic units,special interlayer structure and pore structure contribute to the improvement of electrochemical performance of the basket POM.This study not only investigated the redox capacity of{P₆Mo₁₈}type phosphomolybdate,but also laid a foundation for further functionalization of the basket compound to improve its electrochemical capacitance and catalytic performance.