Controllable Synthesis Of Metal Organic Phosphate And Their Application In Supercapacitors

Metal-organic framework(MOFs)based on the coordination of metal ions with organic ligands has been widely studied because of their rich porous structure,ultra-high specific surface area and rich adjustable sites.The electrochemical properties of MOFs materials can be improved by adjusting the morphology,composition and size of the materials.In addition,the MOFs derivatives prepared with MOFs as precursor/sacrificial template can not only inherit the unique structural characteristics of MOFs precursor,but also have more abundant redox active centers,which is a potential excellent electrode material.In recent years,energy shortage and environmental pollution are the main challenges facing human beings.Researchers have studied a variety of renewable energy storage and conversion devices so far.Compared with batteries or other energy storage devices,supercapacitors(SCs)have high power density,good reversibility and long cycle life.In this paper,a series of metal-organic phosphonic acid materials were synthesized using phenyl phosphonic acid as ligands,and they were used as electrode materials for SCs,and their electrochemical properties were tested.1.Using cobalt acetylacetonate as metal source,phenylphosphonic acid as ligand,and changing the concentration of reactants,a series of three-dimensional(3D)organic cobalt phosphate nanostructures(COP)precursors with different thickness were obtained by stirring at room temperature.Using them as precursors,the derivatives preserving MOF skeleton were obtained by calcining at low temperature in air.At the same time,using the precursors and COP as the electrode materials of SCs,it was found that the electrochemical performance of M3 with the thinnest nano-sheet in the precursor was the best.The electro chemistry performance of M3-200 was the best when the calcination temperature was 200℃,and the specific capacitance reached 274.32 F g-1 in 3.0 M KOH at the current density of 0.5A g-1.This was due to the fact that after the crystal water in the sample was removed by calcination,there were small pores on the sample surface,which exposed more active sites in the electrochemical reaction process,thus improving the electrochemical performance of the sample.2.Because manganese-based MOFs have wider potential range and lower price,organic manganese phosphonate(Mn-MOP)was prepared by solvothermal method by changing the metal ion center from Co2+ to Mn2+.Different morphologies of Mn-MOP were obtained by changing the molar ratio of metal salts to ligands.With the change of molar ratio from 1:3,3:5 to 1:1,the morphology of Mn-MOP changed from palm leaves and nanoribbons to nanoflakes.The three different forms of Mn-MOP were applied to SCs electrode materials,and the electrochemical properties in alkaline electrolyte and neutral electrolyte were investigated.It was found that the electrode with a molar ratio of 3:5 had better electrochemical performance,and the specific capacitance can reach 158.3 F g-1 in 3.0 M KOH with a current density of 0.5 A g-1.This may be due to the fact that when the molar ratio of metal ions to ligands was 3:5,Mn-MOP was nanoribbon with thinner thickness,which was beneficial to ion embedding and ejection.3.Mn-DMF-0.05 was calcined as a precursor in air,and derivatives with different morphologies(Mn-0.05-x)were obtained by changing the calcination temperature.When the temperature was not higher than 350℃,Mn-0.05-x removed the crystal water and still maintained the MOF skeleton;when the temperature reached 550℃,the sample became Mn2P2O7,which retained the nano-ribbon morphology of the precursor,and the edge became more rounded.It was found that Mn-0.05-550 was a better electrode material for SCs.When the current density was 0.5A g-1 and the specific capacitance was 230.89 F g-1 in 3.0 M KOH,and it also showed good cycle stability.This was due to the appearance of small pores on the sample surface after calcination,which exposed more active sites.At the same time,manganese ion changed from bivalent to trivalent,which was more beneficial to the stability of material structure and electrochemical performance in electrochemical reaction.