The Electrochemical Properties Of Polyoxometalates And Graphene Composites

Polyoxometalates(abbreviated as POMs)is a kind of metal-oxides of V,Mo,and W eta.Due to the highest oxidation state of V,Mo,and W,they show richful oxidation-reduection capacility.They can accept as many as 32 electrons,which make them suitable candidates in electrochemistry.However,POMs are easy to leach,and they show poor electrical conductivity.As such,immobilization on certain conductive substrates is an efficient strategy to improve their immobilization and conductivity.In this paper,we develop the nanocomposites of POMs and graphene,and investigate their electrochemical perfoamance in supercapacitor and hydrogen evolution.1.Using the in-situ growth polyaniline array on the graphene oxide,we prepare GO-PANI arrays successfully.And then ion exchange of POMs with GO-PANM,results in the formation of the nanocomposites of GO-PANI-PMO12-xOx(x = 0,1,2,3).By adjusting POMs from PMo12to PMo9V3,a series of nanocomposites including GO-PAN-PMo12,GO-PANI-PMo11V,GO-PANI-PMo10V2,and GO-PANI-PMo9V3 have been obtained and fully characterized.Taking GO-PAN-PMo12 as an example,application it for supercapacitor,it shows the specific capacity of 1017 F g-1 at the current density of 1 A g-1.Furthermore,two electrode testing symmetry supercapacitor its energy density can reach 61.44 Wh kg-1,the specific capacity can remain 86%after 10,000 of circulation test.2.A facile one step mixture of P2Mo18 and three-dimensional nitrogen doped graphene leads to the formation the nanocomposite,futher calcination of the above nanocomposite at 500?,750?,900? results in the 3D-NRGO-MoOO2/MoO3,3D-NRGO-Mo2C,3D-NRGO-MoO2.Application of the resulting 3D-NRGO-MoO2/MoO3,3D-NRGO-Mo2C,3D-NRGO-MoO2 as hydrogen evolution clectrocatalyst indicates the overpotential are 363 mV,118 mV,281 mV r at the current density 10 mA cm-2 respectively.After 1000 circulation the LSV curve is almost coincide,indicating that 3D-NRGO-Mo2C has a high stability.After 10 hours testing,the current density is a little increase and then no longer reduced remain the same with the initial current density,indicating the 3 D-NRGO-Mo2C have high stability.POMs and 3D-NRGO recombination closely and this nanocomposite solve the disadvantages of POMs.The results show that 3D-NRGO-Mo2C has outstanding of hydrogen evolution performance,and reveals the excellent properties of POMs to prepare the nanocrystalline Mo2C nanocomposites synthesized by polyacid as molybdenum source.