Preparation And Electrochemical Properties Of Polyurethane-based Carbon Materials

The environmental and energy crisis is imminent,and the best solution is to use clean and renewable energy,such as solar energy and wind energy.However,these energy sources have the characteristics of large energy fluctuation and long collection time.Therefore,new energy storage devices are urgently needed to collect and store these renewable energy sources.Supercapacitor has attracted extensive attention because of high power density,fast charge and discharge rate and safety and durability.Porous carbon is the most commonly used electrode material for supercapacitors,which has the advantages of large specific surface area,simple manufacturing process and low price.Polyurethane is an excellent polymer precursor of porous carbon because of flexible molecular structure,controllable porosity and heteroatom doping ability.However,there is a lack of research on the application of polyurethane-based carbon-derived materials in supercapacitors.In this paper,the high-performance polyurethane-based carbon electrode materials are analyzed thoroughly and comprehensively for the first time.The main research contents and achievements are as follows:In this paper,a new method for recycling rigid polyurethane foam（RPUF）waste is proposed.Polyurethane porous carbons（PPCs）were synthesized by two steps:pre-carbonization and KOH activation.The effects of activation parameters such as pre-carbonization temperature,activation temperature and alkali-carbon ratio on the electrochemical properties of PPCs were systematically studied.Structural characterization shows that PPCs has a three-dimensional honeycomb pore structure,and the maximum specific surface area can reach 3,647 m² g^-1,and N and O heteroatoms are successfully co-doped into PPCs.These characteristics have a synergistic effect,which jointly enhances the electrolyte ion storage capacity and specific capacitance of PPCs.The experimental results show that the electrode material PPC-500-800-3 produces excellent specific capacitance in the three-electrode(487 F g^-1)and two-electrode(324 F g^-1)system under the current density of 1 A g^-1（in 1 M H₂SO₄ electrolyte）.After 10,000 cycles at a current density of 5 A g^-1,the initial specific capacitance can be maintained at 96.8%,which show high cycle stability for PPCs.In addition,in Li TFSI/H₂O/（ACN）_3.5 electrolyte,the maximum energy density of PPC-500-800-3 in the two-electrode system can reach 29.36 Wh kg^-1 at a power density of50 W kg^-1.RPUF with different densities were synthesized by using water as a foaming agent in a simple formulation,and porous carbon materials（PPC-X）with different densities were prepared under the optimal activation conditions of the previous step.Structural characterization showed that PPC-0.6 had excellent pore structure and abundant heteroatoms.Polyurethane porous carbon can get excellent electrochemical properties because of three-dimensional porous structure and abundant heteroatoms.The results show that in 1 M H₂SO₄electrolyte,the PPC-0.6 electrode has a maximum specific capacitance of 458.2 F g^-1 when the current density of the three-electrode system is 1 A g^-1.The two-electrode system assembled based on PPC-0.6 has a maximum energy density of 13.12 Wh kg^-1 at 50 W kg^-1power density.After 10,000 cycles at 5 A g^-1 current density,the initial specific capacitance can be maintained at 97.55%.This indicates that RPUF is an excellent polymer precursor for porous carbon.In addition,we systematically studied the relationship between the density of RPUF precursor and the density of activated carbon material and the electrochemical performance of supercapacitors composed of carbon materials.It was found that with the increase of water consumption,the density of RPUF gradually decreased,and the activation effect of KOH gradually increased.The density of carbon material is opposite to the total volume of pore.The volume specific capacitance of materials is determined by the mass specific capacitance and material density.The volume specific capacitance of PPC-0.8 with relatively low mass specific capacitance is the highest(242.8 F cm^-3).In addition,we prepared PPC-Zn Cl₂-X using Zn Cl₂ as the salt template,and found that the density of RPUF precursor has a significant effect on the density of carbon material and the electrochemical performance for different methods of preparing carbon materials.By adjusting the amount of catalyst,the shape of pore bubble was changed from round to oval.The results show that the electrochemical properties of the carbon materials remain largely unchanged.These studies can facilitate further research and understanding of the link between the structure of foamed polymer precursors and the electrochemical properties of their derived carbon materials.