Preparation Of Phosphorus Doped Urea Formaldehyde-based Carbons And Their Applications In Supercapacitors

With the rapid development of the economy and science and technology,people's requirement of energy is increasing,however,the shortage of the traditional oil energy and the environment problem by using of oil energy have threated to the survival and development of mankind.Thus,the exploitation and utilization of renewable energy is very emergency.As an advanced energy storage devices,supercapacitors have attracted a lot of attention from industries and academia,because of their excellent properties,such as high-power delivery capability and long-cycle life.The electrode materials is one of the most important factors of properties of supercapacitors.Carbon materials are the most common electrode materials of supercapacitors due to its good stability and high electrical conductivity.In the work,formaldehyde and urea were used to synthesize urea-formaldehyde resin microspheres.pH value and inorganic salt was added in the polymerization system of urea formaldehyde microspheres(UFMs)to control the size and morphology.Nitrogen/phosphorus co-doped carbon(NPCs)were prepared by these three kinds of urea-formaldehyde resin microspheres that is flower-like UFMs,submicro-size UFMs and micro-size UFMs.Then,the thermal degradation kinetics of phosphorus doped UFMs are studied by thermogravimetry analysis.The result shows that the weight loss of UFMs can be separated into three process.The removal of water molecular and other small monomers is the first process from 50 to 150?;The fast gravimetry part is the second process from 150 to 400?.And the low gravimetry process is the third process over 400?.Phosphorus doped micro-size UFMs was as a representative.FTIR test is used to study its chemical structure changes at the fast gravimetry process.And the thermal kinetics of thermal decomposition were studied by two kinds of modelless transformation methods.The result of the FTIR spectra and the thermal kinetics of thermal decomposition shows phosphoric acid will promote the ether bond hydrolysis,reduce the cross-linking density,and thus<0.3,the phosphorus-containing systems have lower activation energy.In addition,phosphoric acid at 270 ? is good for-NH-CH2-NH-to formlate and its thermal stability is good,so when>0.6,the activation energy of phosphorus-doped system can increase rapidly.Finally,SEM,XRD,XPS,nitrogen adsorption/desorption test are used to characterize the effert of H3PO4/UFMs weight ratio on the structure of porducts.CV test,galvanostatic charge/discharge test and EIS test are used to characterize the electrochemical properties of each products.All the tests show that by controlling the content of phosphorus acid in the precursor,the specific surface area,elemental composition and microstructure of the product can be tuned,along with tunable electrochemical properties.With increasing the H3P04/UFMs weight ratio,the specific surface area decline,which means the reduction of electric double layer capacitor.Oppositely,the surface phosphorus and nitrogen content increase with increasing the H3PO4 content,that can offer more pseudocapacitance.Electrochemical measurements shows that for all three UFMs precursors,N/P co-doped carbons prepared with 10%H3PO4/UFMS weight ratio possess the best electrochemical property.At 0.5A/g in 1M H2SO4,the specific capacitances of 15?m-NPCs-10%,F-NPCs-10%and 300nm-NPCs-10%are 245.2,201.2 and 211F/g respectively,all of them are higher than non-phosphorus doped urea formaldehyde-based carbons.