Electrochemical Properties Of MnO₂/PPy Nanocomposites Prepared By Miniemulsion Polymerization

With the development of green energy,supercapacitors as a new type of practical and efficient green energy storage device have attracted more and more attention of researchers.Now,the preparation of electrode materials with high performances and low-cost for supercapacitors is the core content of research.Inorganic/organic composites combine the advantages of inorganic and organic,which can effectively improve the properties of composites via synergistic effects,and thus become the best choice for electrode materials.Among inorganic/organic composites,the low cost of MnO₂ and the excellent conductivity of conductive polymer PPy have attracted tremendous attention from scholars.There are many problems in the preparation methods of MnO₂/PPy composite materials,such as complicated procedures,preparation of precursors in advance,and uncontrollable particle size and morphology of composites,etc.In this paper,the MnO₂/PPy composite materials were prepared by miniemulsion polymerization method,which principle is the"droplet nucleation".Three kinds of emulsification devices were used to prepare the miniemulsion,then the MnO₂/PPy composite materials were synthesized by the prepared-welled miniemulsion.The physical and electrochemical properties of the prepared composites were preliminarily studied in order to obtain the MnO₂/PPy composite materials with smaller particle size and controllable shape and morphology.The main contents of this paper are summarized as follows:?1?The high speed disperser as an emulsification device applied to prepare miniemulsion,using Py as monomer,p-TSA as dopant,ultrapure water as aqueous phase,cyclohexane as oil phase,Span 80 as the oil surfactant,and KMnO₄ as the oxidant.The results show that the droplet size decreases first and then increases with the increase of rotor speed and dispersion time,while the stabilization time shows the opposite trend.The MnO₂/PPy nanocomposites were prepared by the prepared-welled miniemulsion under suitable operating conditions.The physical properties of the nanocomposites were analyzed.It was found that the MnO₂/PPy nanocomposites were successfully prepared by the miniemulsion method,the particle size of MnO₂/PPy nanocomposites was small and the morphology was spherical floral structure.The suitable operating conditions for the preparation of the miniemulsion by high speed disperser were the rotor speed of 4×2800 r min^-1 and the dispersion time of 4 min.The droplet size of the prepared miniemulsion was 65.8 nm and the stabilization time was 40 min under the suitable operating conditions.In addition,the suitable operating conditions for the preparation of MnO₂/PPy nanocomposites by high speed disperser were rotor speed of 4×2800 r min^-1,dispersion time of 4 min,p-TSA concentration of 0.84 mol L^-1,and KMnO₄ concentration of0.028 mol L^-1,reaction time of 2.5 h.The particle size of Mn O₂/PPy nanocomposites prepared under the condition was 86 nm,and the specific capacitance reached 216.9 F g^-1when the current density was 0.5 A g^-1.?2?The ultrasonic cell crusher was used as the emulsification device.The suitable operating conditions for the preparation of the miniemulsion were ultrasonic power of 380 W and sonication of 5 min.The droplet size of the miniemulsion was 54.6 nm and the stabilization time was 51 min under the suitable operating conditions.The physical properties of MnO₂/PPy nanocomposites were characterized by FTIR,XRD,HRTEM and BET.The results showed that the particle size of the prepared MnO₂/PPy nanocomposites was about58-88 nm,the specific surface area was 231.3 m² g^-1,the average pore size was 3 nm and belongs to the mesoporous material.The electrochemical properties of MnO₂/PPy composites were investigated by cyclic voltammogram,galvanostatic charge-discharge curves,AC impedance and cycle stability tests.The results show that the specific capacitance of MnO₂/PPy was 241.3 F g^-1 when the current density was 0.5 A g^-1.After 1000 cycles of charge and discharge,the specific capacity retention rate of the MnO₂/PPy nanocomposite electrode was 93.5%.?3?The impinging stream-rotating packed bed?IS-RPB?was used as the emulsification device,the droplet size of the prepared miniemulsion first decreases and then increases with the increase of a high gravity factor and the impact velocity,while the stabilization time show the opposite trend.The increase of the cycle number times is not conducive to the preparation of a stable miniemulsion.MnO₂ and MnO₂/PPy nanocomposites were prepared by miniemulsion method.By comparison,the average particle size of MnO₂/PPy nanocomposites was smaller than that of single component MnO₂;the specific surface area was larger than MnO₂;at the same current density,the specific capacitance of MnO₂/PPy is bigger than MnO₂,and the maximum specific capacitance of MnO₂/PPy was 231.9 F g^-1,which indicates that the synergistic effect of MnO₂ and PPy can effectively enhance the specific capacitance of the nanocomposite.?4?A comparative analysis of the properties of miniemulsion,which prepared by the three emulsification devices,experimental results indicate that all emulsification devices can prepare nanometer miniemulsion.The mechanism of prepare miniemulsion was different due to the structural differences of emulsification devices,and thus their application range is different.The operational power consumption of IS-RPB is equal to the ultrasonic cell crusher,what's more,the advantages of IS-RPB such as amplification effect is small,no heat is generated,and a high emulsification efficiency can be achieved instantaneously meet the requirements of industrialization preparation miniemulsion.The physical and electrochemical properties of MnO₂/PPy nanocomposites synthesized by different miniemulsions were compared and analyzed.It was concluded that the size of the droplets of miniemulsion have a great influence on the particle size of the nanocomposite material,and the droplet size was smaller,the smaller particle size of nanocomposites,the larger of specific surface area,which is beneficial to the improvement the capacitance performances of the nanocomposite materials.The storaged charge of MnO₂/PPy nanocomposites is achieved by both the surface adsorption and desorption theory and the redox reaction in the bulk phase.The contributions of the specific capacitance of the two mechanisms are related to the current density and the scan rate.These properties show that the miniemulsion polymerization method can be used as an effective method for preparing MnO₂/PPy nanocomposites,and IS-RPB can be used as an emulsification device for preparing a miniemulsion.Based on the principle of“droplet nucleation”,the dissertation prepared MnO₂/PPy composites with controllable particle size,and the agglomeration of nanoparticles was improved to a certain extent.Taking an example of MnO₂/PPy in this article,the miniemulsion polymerization method is not limited to prepare this composite material only,and can also be used for the preparation of other inorganic/organic composite materials.ased on industrial application considerations,it was demonstrated that IS-RPB can be used to continuously prepare miniemulsion and has a excellent industrial application potential.