| With reversible redox properties,strong electron accepting and transferring ability and good stability,polymetallic oxides exhibit excellent electrochemical properties and are ideal candidates for supercapacitors and electrocatalysts.Among them,{PMo12}type and{P4Mo6}type polyacid derivatives are important constituent members of the phosphomolybdenum family.{PMo12}type polyacid derivatives are one of the classical structure types with high symmetry and fast electron transfer ability.The{P4Mo6}type polyacid derivatives are one of the representatives of non-classical structure types with unique spatial structures and abundant coordination oxygen atoms.Based on this,eight examples of polymetallic oxalate hybrid derivatives were synthesized by assembling different transition metals and organic nitrogen-containing ligands into the phosphomolybdate system using a hydrothermal synthesis method and selecting suitable reaction conditions.The compounds 1-8 were also subjected to elemental analysis,infrared absorption spectroscopy,thermal stability analysis and X-ray diffraction analysis to determine their structures and molecular formulae as follows:(（H2die）2（Hdie）[PMo12O40]·2H2O（1）（H2bpa）2（Hbpa）2[PMo12O40]2·9H2O（2）（H2dipy）1.5（dipy）0.5[PMo12O40]·3H2O（3）（Hpyra）（H2pyra）[(VVIO)2{PMo8V4VO40}]·6H2O（4）（dipy）（Hdipy）{FeⅢ（H2O）3}2{FeⅢMo12VO24（OH）6（HPO4）4（H2PO4）2（PO4）2}]·16H2O（5）（H2bimi）{Sr（H2O）3}4{MnMo12VO24（OH）6（HPO4）2（H2PO4）2（PO4）4}2}·8H2O（6）（ampy）2（Hampy）4{Mn（H2O）3}2{MnMo12VO24（OH）6（HPO4）4（H2PO4）2（PO4）2}2·15H2O(7（imi）（H2dipy）2{Cd（H2O）3}2{Cd（H2O）2}{Cd Mo12VO24（OH）6（HPO4）2（H2PO4）2（PO4）4}2]·4H2O（8）（die=1,2-di（1H-imidazol-l-yl）ethane,bpa=Bis（4-pyridyl）amine,dipy=4,4’-Dipyridyl,pyra=Pyrazine,bimi=2,2’-Biimidazol,ampy=2-Amino-4-methylpyridine,imi=Imidazole）The structural analysis showed that 1-4 are{PMo12}type supramolecular polyacid derivatives and 5-8 are{P4Mo6}type metal-bridged polyacid derivatives.Compounds1-3 are{PMo12}-type supramolecular hybrids formed by different organic ligands linked to polyacid anions through supramolecular forces;Compound 4 is a vanadium-substituted{PMo12}-type supramolecular hybrid modified by the rigid ligand pyra and vanadium cap;Compound 5 is a one-dimensional{P4Mo6}type polyacid derivative formed by metal Fe bridging;Compound 6 is a three-dimensional{P4Mo6}type polyacid derivative formed by bridging of metal Mnand Sr;Compound 7 is a two-dimensional{P4Mo6}type polyacid derivative formed by metal Mnbridging;Compound 8 is a one-dimensional{P4Mo6}type polyacid derivative with pore channels formed by metal Cd linked to a polyanion.Two types of working electrodes,glassy carbon and carbon paper,were made from the eight produced hybrids,and their supercapacitor performance was studied by an electrochemical workstation.The results showed that among the{PMo12}-type polyacid derivatives,compound 4 exhibited high specific capacitance(722.6 F·g-1 for Cs at3A·g-1),excellent multiplicative performance and capacitance retention（91.6%after5000 cycles）,which exceeded most of the pseudocapacitance materials reported so far.This is mainly attributed to the bonding of vanadium,which adds redox centers.Among the{P4Mo6}-type polyacid derivatives,compound 8 showed superior specific capacitance(682.5 F·g-1 for Cs at 3 A·g-1),excellent multiplicative performance and better capacitance retention（91.2%after 5000 cycles）than the other three compounds,showing excellent capacitive performance.This is mainly attributed to the introduction of metal Cd to increase the redox active sites and the rich pore structure to provide electron transfer channels and alleviate the volume expansion caused by ion embedding.The glassy carbon electrodes of eight compounds were tested for catalytic oxidation of AA and reduction of H2O2.1-8-GCE all exhibited good bifunctional catalytic activity.Consistent results were obtained comparing the catalytic effect and capacitive performance of the eight compounds,further demonstrating that the bonding of transition metals and the robust spatial structure contribute to the enhanced electrochemical performance of{PMo12}and{P4Mo6}.This study not only investigated the redox ability of two phosphomolybdates,but also laid the foundation for further functionalization of this class of compounds to improve their electrochemical capacitance and catalytic properties. |
PDF Full Text Request