Preparation Of Electrode Materials Based On Keggin-type Polyacid H₃PMo₁₂O₄₀in Supercapacitors

The development of various high-performance electrochemical energy storage devices is of great significance to solving the current energy shortage problem.As one of the new generation of energy storage devices,the research on electrode materials of supercapacitors has received more and more attention in recent years.In this paper,Keggin-type polyacid H₃PMo₁₂O₄₀ and several organic ligands are selected as precursors,and then pyrolysis is used to obtain new molybdenum-based compounds as electrode materials for super capacitors.Polyacid H₃PMo₁₂O₄₀ is a kind of inorganic metal oxygen cluster,its ligand structural unit,configuration and function difference and the diversity of coordination mode determine the diversification of the target product type and function of pyrolysis,and the pyrolysis product can be used to supercapacitors have become a research hotspot.The specific content of the paper includes the following:1.The polyacid H₃PMo₁₂O₄₀ and pyrrole were polymerized at the molar ratio of 1:1,1:5,1:10 and 1:15 respectively to form the PMo₁₂@PPy composite precursor,and then the precursor was pyrolyzed into free nanospheres at high temperature in N₂atmosphere.The precursor and Mo₂C@C were characterized by means of characterization,and their electrochemical tests were carried out.It was found that the capacitance of Mo₂C@C nanospheres prepared at the molar ratio of 1:5 reached the highest of 370.2 F g^-1 at 0.4 A g^-1and the retention rate reached 47.7%.In order to improve the cycle stability,different surfactants were added,and cetyltrimethylammonium bromide（CTAB）was added,the capacity was increased to 499.2 F g^-1,and the retention rate of 2000 cycles reached 63.2%.2.By hydrothermal method,the PMo₁₂@MIL-101（Fe）precursor was formed by the multi-acid H₃PMo₁₂O₄₀ composite Fe based organic framework,which was calcined at high temperature in N₂ atmosphere along a certain temperature gradient.The Mo O₂@FeMo O₄material was prepared and its electrochemical performance was tested in a three-electrode system.The results showed that the highest material capacity was obtained at 700℃,reaching346.8 F g^-1,and the retention rate was 56.7%after 2000 cycles.When the mass ratio of activated carbon to activated carbon was 1:2,the capacity reaches 544.2 F g^-1,and the specific capacitance retention rate was 63.4%of the initial specific capacitance.3.The precursors were prepared by one-pot hydrothermal method with polyacid H₃PMo₁₂O₄₀ as molybdenum source and glucose as carbon source.The hydrothermal temperature was 160℃,180℃,200℃,220℃,and the reaction time was 24 h.After a series of characterization and tests,it was found that the hydrothermal temperature has a great influence on the spherical Mo O₂@C prepared by the precursor thermal hydrolysis,and the capacity can reach 1217 F g^-1 at 180℃.Then,the influence of the hydrothermal time on the electrode material was investigated at 180℃,and the hydrothermal time was 12,24,36 and48 h,respectively.The results showed that the electrode material obtained at 24 h still had the best performance.