Research On The Performance Of Copper/carbon Based Supercapacitor Based On Thiourea Electrolyte Additive

At present,energy crisis and environmental problems have attracted the researchers'extensive attention.Researchers are striving to find clean,environmentally friendly and sustainable energy or production equipment,such as solar energy,geothermal energy and wind energy,etc.,but these energy sources are intermittent and extremely inconvenient in practical applications.Because of its high capacitance and power density,supercapacitor(SC)has become one of the hot spots for new energy storage devices.At present,the low energy density restricts the wide application of SC,and the main factors affecting the energy density of SC include electrode materials and electrolyte.Therefore,it is expected to solve the current problems by preparing excellent electrode materials and selecting suitable electrolytes.In this paper,firstly,the effect of thiourea(TU)electrolyte additives on the properties of activated carbon(AC)based SC was investigated.Then,the composite was prepared by loading copper chloride into the hydrogel containing nitrogen(N)and sulfur(S)three-dimensional network structure by impregnation method,which was calcined at high temperature to prepare Cu@N-C and Cu-Cu_xS@S-C complex.The structure and morphology of the prepared composites were characterized,and the capacitance properties of different composites in alkaline electrolyte containing TU additives were studied in detail.The details and results are as follows:(1)PVA-KOH-KCl and PVA-KOH-KCL-TU gel electrolytes were prepared.The electrochemical performance of the AC-based electrode SC in two different electrolytes was investigated.Compared with the PVA-KOH-KCl electrolyte,the voltage window and capacitance of SC in PVA-KOH-KCl-TU increased,indicating that the addition of TU contributed to the improvement of capacitance performance,which was mainly due to the redox reaction of TU.In addition,the effect of TU concentration on the performance of AC-based SCs was investigated,and the results showed that the capacitor performance was the best when the TU concentration was 0.2 M.For comparison,Cu Cl₂@AC electrodes were prepared and their electrochemical performance in alkaline electrolytes containing TU was investigated,and the results showed that the capacitive performance of Cu Cl₂@AC-based SCs in TU-containing gel electrolytes was better than that of AC-based SCs,indicating that copper has catalytic effect on TU.(2)The copper-based nitrogen-doped carbon(Cu@N-C)composite electrode was prepared by immersing polyaniline-polyvinyl alcohol hydrogel film(PPH)in copper chloride solution,freeze-drying,and calcining at high temperature.When the concentration of Cu Cl₂solution was 2 M and the calcination temperature was 600°C,the prepared Cu@N-C-600composite exhibited a wide voltage window(1.8 V)and extremely high capacitance in an electrolyte with TU(9571 mF cm^-2 at 5 m A cm^-2).For the symmetrical SC based on Cu@N-C composites in the alkaline gel electrolyte containing TU,whose capacitance was increased for5.9 folds:from 194 mF cm^-2(without TU)to 1154 mF cm^-2(with TU),the energy density(E)and power density(P)reach 314?Wh cm^-2 and 2798?W cm^-2,respectively,superior to most of inorganic materials-based SCs.This is mainly attributed to the pseudocapacitance generated by reversible redox reactions of TU and Cu compounds,and the porous nitrogen-doped carbon matrix can fix and protect the highly active copper nanocrystals,promoting the charge and mass transfer between electrode and electrolyte.(3)PPSH(poly-3,4 ethylenedioxythiophene-polyvinyl alcohol)was immersed in a Cu Cl₂solution for several hours,and then calcined at different temperatures to prepare a copper/nonstoichiometric copper sulfide based sulfur-doped carbon(Cu-Cu_xS@S-C)composite materials.The results show that the optimal Cu-Cu_xS@S-C-600 electrode has a capacitance of 9607 mF cm^-2 at a current density of 5 m A cm^-2 in alkaline electrolyte with TU.Meanwhile,the pseudocapacitance(960 mF cm^-2)of the symmetric SC based on the Cu-Cu_xS@SC-600 electrode in TU gel electrolyte was 4.6 times higher than that without TU(208 mF cm^-2),the E and P reach 261?Wh cm^-2 and 2800?W cm^-2,respectively.This is mainly attributed to the large lattice spacing of p-type Cu_xS conductors,which is favorable for the penetration of electrolyte ions,and the catalytic effect of Cu nanocrystals on the redox reaction of TU.