Effect of Graphene Oxide on the Properties of Its Composite with Polyaniline
Effect of Graphene Oxide on the Properties of Its Composite with Polyaniline
Hualan Wang,Qingli Hao,*Xujie Yang,Lude Lu,and Xin Wang*
Key Laboratory of Soft Chemistry and Functional Materials,Ministry of Education,Nanjing University of Science and Technology,Nanjing,P.R.China
ABSTRACT Graphene oxide,a single layer of graphite oxide(GO),has been used to prepare graphene oxide/polyaniline(PANI) composite with improved electrochemical performance as supercapacitor electrode by in situ polymerization using a mild oxidant.
The composites are synthesized under different mass ratios,using graphite as start material with two sizes:12500and500mesh.
The result shows that the morphology of the prepared composites is in?uenced dramatically by the different mass ratios.The composites are proposed to be combined through electrostatic interaction(doping process),hydrogen bonding,andπ-πstacking interaction.The highest initial speci?c capacitances of746F g-1(12500mesh)and627F g-1(500mesh)corresponding to the mass ratios1:200and1:50(graphene oxide/aniline)are obtained,compared to PANI of216F g-1at200mA g-1by charge-discharge analysis between0.0and0.4V.The improved capacitance retention of73%(12500mesh)and64%(500mesh)after500cycles is obtained for the mass ratios1:23and1:19compared to PANI of20%.The enhanced speci?c capacitance and cycling life implies a synergistic effect between two components.This study is of signi?cance for developing new doped PANI materials for supercapacitors.
KEYWORDS:graphene?graphene oxide?polyaniline?electrochemical properties?supercapacitor
INTRODUCTION
S upercapacitors are the promising power source and have attracted considerable attention in recent years
(1-3).The increasing pollution due to electrical ve-hicles and explosive growth of portable electronic devices has pushed the development of high-performance superca-pacitors as the urgent requirement.There are two main classes of electrochemical capacitors based upon charge-storage mechanism:(a)electrical double-layer capacitors (EDLCs)in which the capacitance arises from the charge separation at the electrode/electrolyte interface and(b)redox supercapacitors in which the pseudocapacitance arises from faradic reactions occurring at the electrode/electrolyte in-terface(4).High-surface carbons,noble metal oxides,and conducting polymers are the main families of electrode materials being studied for supercapacitor applications. Conductive polymers have been extensively studied in su-percapacitors.The main conductive polymer materials that have been investigated for the supercapacitor electrode are polyaniline(PANI)(5),polypyrrole(PPY)(6),polythiophene (PTH)and their derivatives(7),and so on.Among these polymers,PANI is considered the most promising material because of its high capacitive characteristics,low cost,and ease of synthesis(8,9).However,the relative poor cycling life restricts its practical applications.Recently,advancement of nanoscale binding technique provides an innovative route to prepare PANI-based composites with better performance as electrode material(10-12).It has been demonstrated that PANI composite with metal oxides exhibit improved super-capacitor performance(13).
Graphene is a two-dimensional form of graphite,the high surface area,excellent mechanical properties and conductiv-ity(14,15)of this new material have attracted great interests(16-22).Graphene oxide,bearing oxygen func-tional groups on their basal planes and edges,is a single sheet of graphite oxide and exhibits good performance.It can be obtained by exfoliation of graphite oxide(23).The tunable oxygenous functional groups of graphene oxide facilitate the modi?cation on the surface(24)and make it a promising material for composites with other materials. Recent reports on ultracapacitors based on graphene(14,25) have attracted great interest.Many graphene composites with conducting polymers have been developed(26,27). However,the effect of raw graphite material sizes and feeding ratios on the electrochemical properties of such composites have not been investigated intensively.
In our previous work(28),a simple in situ polymerization method was reported to synthesize the nanocomposites of graphene-oxide-doped PANI(GP)which were used as elec-trode materials.Herein,serious GP composites with different feeding ratios from raw graphite of two sizes have been prepared through in situ polymerization by using a mild oxidant.The introduction of less amount of graphene oxide into PANI is found to greatly enhance the electrochemical performance of PANI.The in?uence of raw material sizes and feeding ratios on the electrochemical capacitance and chemical structures of GP composites have been investigated systematically.
EXPERIMENTAL SECTION
Materials Synthesis.Graphite oxide was synthesized from powdered?ake graphite(12500,500mesh)by a modi?ed
*To whom correspondence should be addressed.Tel/Fax:+862584315054.
E-mail:haoqingli@https://www.wendangku.net/doc/3f1587009.html,(Q.H.);wangx@https://www.wendangku.net/doc/3f1587009.html,(X.W.).
Received for review November23,2009and accepted February22,2010
DOI:10.1021/am900815k
?2010American Chemical Society
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Hummers method (29).Nanocomposites with different mass ratios (from 1:370to 1:10)and raw material sizes were syn-thesized.The typical route,for example,when the mass ratio of graphite oxide/aniline is 1:50,is as follows.Before polymer-ization,aniline (3.7mL)was added into an aqueous solution of graphite oxide with a mass ratio of 1:50under ultrasonication (220V,250W);after being ultrasonicated for 1h,the graphite oxide was exfoliated to graphene oxide and a stable mixture of aniline/graphene oxide was obtained (28,30).The chemical polymerization was then performed by the slow addition of H 2O 2(4.1mL,30%),hydrochloric acid (3.3mL,37%),and 0.1mol L -1FeCl 3·6H 2O (0.8mL)under violent stirring to form a 200mL solution (31).The suspension was kept in an ice bath and stirred for 24h.The products were then ?ltered and washed with a large amount of 0.1mol L -1HCl and acetone and dried at 60°C for 24h under a vacuum.The nanocomposites synthesized from different graphite sizes and ratios are signed as S-GP ratio for 12500mesh graphite and B-GP ratio for 500mesh graphite,respectively,like S-GP 1:50,indicating that the mass ratio of graphene oxide (12500mesh)and aniline is 1:50.Herein,the pure PANI was synthesized chemically in the absence of graphite oxide via the similar procedure above.General Characterization.The chemical character and mor-phology of the samples were analyzed by X-ray photoelectron spectroscopy (XPS,Thermo ESCALAB 250),Raman (RENISHAW inVia Raman Microscope),scanning electron microscopy (SEM,JEOL JSM-6380LV),and transmission electron microscopy (JEM-2100),respectively.
Electrochemical Characterization.The test electrodes were prepared by mixing the sample,acetylene black,and polytet-ra?uoroethylene in the mass ratio 85:10:5,the mixture was dissolved in distilled water and grinded adequately to form a slurry.The slurry was coated onto a stainless steel,pressed at 10MPa,and dried under vacuum at 60°C for 24h.All electrochemical experiments were carried out in 1M H 2SO 4using a three-electrode system,in which platinum foils and saturated calomel electrode (SCE)were used as counter and reference electrodes.Cyclic voltammetry (CV)and electrochemi-cal impedance spectroscopy (EIS)measurements were per-formed with a CHI660B workstation.The scan rate of CV was in the range from 1mV s -1to 100mV s -1.EIS was recorded under the condition:AC voltage amplitude 5mV,frequency range 1×105to 1×10-3Hz at 0.5V.Galvanostatic charge -discharge testing was done from 0to 0.8V,using a Land Battery workstation at 22°C.
RESULTS AND DISCUSSION
Morphology Characterizations.The typical micro-structures of S-GPratio,PANI and graphene oxide synthe-sized from graphite with the size 12500mesh,are presented in Figure 1.The exfoliated layered structure for graphene oxide agglomerate (Figure 1a)can be observed,which is consistent with the report given by Dikin et al.(23).The pure PANI shows short ?brillar and granular agglomerate (Figure 1b).The composite morphology differs from individual components and changes with the increased feeding ratio of two raw materials.The composite S-GP 1:100show ?brillar morphology with dimensions of about 300nm in diameter and 2-3μm in length,and the large ?bers are in fact built from smaller nano?bers about 30nm in diameter and 100-150nm in length on the surface,and nanosheets in the backbone of the ?bers,as shown in Figure 1c,e.How-ever,with the increase in graphene oxide ratio,the com-posite S-GP 1:23exhibits mainly unregular morphology with multishapes including both ?brillar and agglomeration (Fig-ure 1d,f).The tremendous changes in morphology reveal that the introduction of graphene oxide and the feeding ratio play an important role in adjusting the surface shape in the synthesis process,which may affect the electrochemical performances greatly.
Chemical Analysis.Figure 2demonstrates the Raman spectra of graphite oxide,PANI and S-GP 1:23.The Raman spectrum of as-prepared graphite oxide displays two promi-nent peaks at 1350and 1598cm -1that correspond to the D and G modes,respectively (15,32).The G mode is related to the vibration of sp 2-hybridized carbon.The phonon mode at 1350cm -1,also known as the D mode,corresponds to the conversion of a sp 2-hybridized carbon to a sp 3-hybridized carbon (33).For pure PANI,out-of-plane C -H wag,out-of-plane C -N -C torsion,imine deformation,in-plane C -H bending,in-plane ring deformation,C -N ?+stretching,C d N stretching of quinoid,C -C stretching of benzoid situated
at
FIGURE 1.SEM images of (a)graphene oxide agglomerate par-ticles,(b)PANI,(c)S-GP 1:100,and (d)S-GP 1:23and TEM images of (e)S-GP 1:100and (f)S-GP 1:23
.
FIGURE 2.Raman spectra of S-GP ratio ,graphite oxide,and PANI (λ)514nm).
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416,517,780,1160,1217,1324,1491,and 1591cm -1were observed (34-36).The peaks at 1160,1324,and 1591cm -1indicate the doped PANI structure and shift to 1186,1349,and 1595cm -1when graphite oxide was introduced into the synthesis process of PANI in the form of graphene oxide.This is probably due to the doping of carboxyl acid of graphene oxide to PANI backbone and π-πstacking of PANI and graphene oxides sheets.The result reveals that PANI was also in a doped state in the composite,and this observation was also supported by the XPS analysis and UV -vis absorption spectra presented below.
The C 1s and O 1s core-level spectra of graphite oxide and that of S-GP 1:100are depicted in panels a and b in Figure 3,respectively.For graphite oxide,the XPS peaks of C 1s in Figure 3a are reasonably decomposed into four Gaussian peaks with binding energies of 288.0(C d O),286.7(C -O -C),285.7(C -OH),and 284.6eV (C -C/C-H)(37),respectively.When combined with PANI in GP 1:100,the peaks correspond-ing to C -O -C and C -OH of graphite oxide disappeared and formed a new peak situated at 287.2eV.This is probably due to the increased conjugation and the hydrogen bonds between the PANI backbone and graphene oxide sheets.These interactions lead to the shift in the C -O -C and C -OH binding energy and consequently the merging of the two peaks in the new broad peak in case of the low concentration of the graphene oxide in the composite.The increased conjugation comes from the doping of carboxyl acid of graphene oxide to PANI backbone and π-πstacking of PANI and graphene oxides sheets.The presence of the hydrogen
bonds is due to the oxygenous and nitrogenous functional groups in the composite.
The C 1s of C d O peak increased to 288.6eV,indicating that the COOH groups of graphene oxide were doped into PANI by electrostatic action.Besides,a new peak centered around 286.1eV attributed to C -N ?+/C d N ?+(C -N/C -N)was observed,corresponding to the structure of PANI (38).Remarkably,the πf π*shakeup satellite peak around 291.5eV,a characteristic of aromatic or conjugated systems,appeared after reaction,which means the increased conju-gation in the composites (39).The XPS peak of O 1s in Figure 3b of graphite oxide are composed of two Gaussian peaks with their binding energy of C -OH (C -O -C)at 533.1eV and C d O at 532.2eV,these peaks shift to 533.2and 531.4eV in S-GP 1:100,respectively.The downshift of C d O peak reveals the increased outer electron cloud density of oxygen atoms after doping.
Figure 4shows UV -vis spectra recorded in alcohol.An absorption peak was observd for graphene oxide at 235nm .The PANI sample has a sharp intense peak at 207nm,a weak peak at 253nm,and a broad peak at 419nm.The ?rst and second peaks are related to the molecule conjuga-tion.The third absorption peak originates in the charged cationic species,which are known as polarons (36,40).The last peak shifted to 415nm in B-GP 1:19,indicating that the PANI was also protonated in the synthesized composite.Moreover,the two peaks situated at 207and 274nm related to the molecule conjugation also can be observed,indicating the π-πinteraction between PANI and graphene oxide of the composite.Therefore,the UV -vis absorption results,together with the Raman spectra and XPS analysis,indicates that PANI chain in the composite is in the doped state.The possible combinding mode of graphene oxide/PANI com-posite is proposed including:(a)π-πstacking (b)electro-static interactions,and (c)hydrogen bonding,as presented in Scheme 1.
Electrochemical Properties.Figure 5shows repre-sentative CVs for S-GP ratio (Figure 5a)and B-GP ratio (Figure 5b)at a scan rate of 10mV s -1in 1M H 2SO 4recorded in the potential range of -0.2and 1V,and CVs for S-GP 1:23(Figure 5c)and B-GP 1:19(Figure 5d)at different scan rates.
Normally,as shown in Figure S2of the Supporting Information,pure PANI shows two couples of redox peaks.One is due to transition of polyaniline from the semicon-ducting-state (leucoemeraldine)to the conductive form (em-eraldine),the other is due to transition from emeraldine
to
FIGURE 3.XPS spectra in the (a)C 1s and (b)O 1s region of:top,graphite oxide;bottom,S-GP 1:100
.
FIGURE 4.UV -vis spectra of PANI,GO (500mesh),and B-GP 1:19in alcohol.
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the pernigraniline;the GO electrode also exhibits a pair of peaks that originated from the oxygenous groups on the surface.However,when graphene oxide and PANI are combined into GP ratio composites,their CV curves are dif-ferent from each component electrode and exhibit the characters of both double layered capacitance and pseudoca-pacitance (Figure 5a -d).More interestingly,the CV shapes of GP ratio (both S-GP ratio and B-GP ratio )change with different mass ratios.Because the binder (acetylene black and poly-tetra?uoroethylene)of each working electrode is inactive and occupies the same amount,the change in CV character is due to the nature of composite materials.The synergetic effect resulting from the interactions of PANI and graphene oxide may affect the shape and potential position of CV curves.
The existence of peak on each CV plot for the samples indicates the existence of the faradic processes.The charge storage in the faradic process is achieved by electron transfer that leads to chemical changes in the electroactive materials according to Faraday’s law related to the potential (41).The redox peaks can be ascribed to the changing in PANI
structures and the oxygenated groups attached to the surface of the graphene oxide nanostructures.Besides,the surface chemical functional groups signi?cantly in?uence the inter-facial capacitance by introducing pseudocapacitance as depicted in former reports (1,2,42-47).Thus,graphene oxide sheets with different amounts in the composites may play an important role in determining the CV shapes.
Compared with the CV of PANI electrode,the capacitance performances of GP ratio were enhanced to different degrees as the mass ratio changes for S-GP ratio samples with the ratio below 1:15and for all B-GP ratio prepared in our experiment.Therefore,the CV behavior actually exhibits the synergetic performance of the two components,PANI and graphene oxide,in the chemically combined composites.
It is notable that the synthesized materials also exhibited excellent electrochemical behavior in a wide range of scan rates (1-100mV s -1)in H 2SO 4electrolyte solution.For example,for S-GP 1:23and B-GP 1:19,the current density in A g -1of both samples increases with the scan rate and the curve shape is steady,indicating the good electrochemical stability of the electrode material.This is due to the introduc-Scheme 1.Proposed Possible Combinding Mode of Graphene Oxide/PANI
Composite
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tion of graphene oxide with high mechanical property (23)into the composites and the synergetic effect between the two components.The CVs shape of S-GP 1:23is a little differ-ent from B-GP 1:19,which is probably related to the different feeding ratios and different faradic charge-transfer reactions arising from the interaction and synergy between individual components.
An electrochemical impedance technique has also been employed in order to understand the difference in the electrochemical behavior between S-GP 1:23and B-GP 1:19compared with pure PANI with the mass of active material 16.1,16.5,and 3mg,respectively.Typical complex plane plots for these electrodes are presented in Figure 6,recorded under the condition:AC voltage amplitude 5mV,frequency range 1×105to 1×10-3Hz at 0.5V.At low frequency,the composite electrodes exhibit a more vertical line than pure PANI,showing a better capacitor behavior.At higher frequency,the impedance plot has a relatively small radius,which shows lower resistance.From the point intersecting with the real axis in the range of high frequency,the internal resistance (48)of S-GP 1:23and B-GP 1:19are much lower than that of PANI.The decreased internal resistance compared
with PANI electrode may be due to the doping process and π-πstacking (40)between graphene oxide and PANI.The galvanostatic charge -discharge method is a reliable way to characterize the electrochemical capacitance of materials under controlled current conditions (5,13).Figure 7represents the changes of initial speci?c capacitance (C 0)with the mass ratio measured at a constant current density of 200mA g -1in the potential range of 0.0-0.8V.The speci?c capacitance values (5)were calculated from the charging and discharging curves according to C )I /m (dv /dt ),where I is the constant discharge current,m is the mass of the active materials within the electrode,and dV /dt can be obtained from the slope of the discharge curve given by the instrument.In genaral,most composites with different ratios for both sizes of graphite exhibit the enhanced speci?c capacitances compared with pure PANI,indicating the synergistic effect of individual components.S-GP ratio shows the higher C 0in the lower mass ratio (graphene oxide/aniline)region and lower value in the higher mass ratio region than B-GP ratio as presented in Figure 7.Besides,for GP ratio with the same raw graphite size (both S-GP ratio and B-GP ratio ),the C 0goes up sharply to a maximum value and decreases slowly as the content of graphene oxide increases.The
maximum
FIGURE 5.CVs of (a)S-GP ratio and (b)B-GP ratio at 10mV s -1and (c)S-GP 1:23and (d)B-GP 1:19at different scan rates,in 1M H 2SO 4at room
temperature.
FIGURE https://www.wendangku.net/doc/3f1587009.html,plex plane plots for S-GP 1:23,B-GP 1:19,and
PANI.
FIGURE 7.Initial speci?c capacitance of the composites at different mass ratios (graphene oxide/aniline).
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C value for S-GP ratio and B-GP ratio are 746and 627F g -1,corresponding to mass ratios of 1:200and 1:50,respec-tively.These results are higher than the value obtained by the report (26)synthesized by a electrochemical method.The speci?c capacitance is higher for the lower mass ratio perhaps because of the lower material resistance.By in-creasing the mass ratio of graphite oxide as raw material,which in turn became graphene oxide as the experimental process went on,the increased resistance due to the poor conductivity of graphene oxide limits the double layer charging in the electrode depth;only the outer part of the electrode is active,leading to a capacitance loss (49,50).Figure 8shows the discharge curves of S-GP ratio (Figure 8a)and B-GP ratio (Figure 8b)in 1M H 2SO 4at a current density of 200mA g -1,these curves exhibit an evident pseudoca-pacitance performance as they deviate from perfect linear shape.Generally,the discharge time is enlarged for the majority of GP ratio samples after doping of graphene oxide compared with pure PANI.Moreover,the shape of discharge curves varies for different mass ratios,indicating the differ-ence of charge release process.These changes might be derived from different morphology for different ratios as shown in Figure 1.The mass of GP ratio adopted for charge -discharge measurements and the exact initial speci?c ca-pacitance in the potential range of 0.0-0.4V at a current density of 200mA g -1is presented in Table 1.In spite of the high ohmic drop in galvanostatic pro?les for some samples,the results demonstrate that the electrode main-tains its high capacitance value.For example,S-GP 1:370with a speci?c capacitance of 693F g -1is obtained.Moreover,we have examined the performance of samples for which the mass ratio exceeds 1:10for both S-GP ratio and B-GP ratio ;the capacitance decreases rapidly (not shown here),even below pure PANI.This is possibly due to the increased amount of graphite oxide with poor conductivity.This result
implies that the raw material size and the feeding ratio have a pronounced effect on the electrochemical capacitance behavior.
The cycling performance is also an important aspect to examine the character of electrode material.The cycling life test results (not shown here)indicate that both S-GP ratio and B-G Pratio exhibit better capacitance retention than pure PANI within the mass ratios conducted in our experiments,which is due to the introduction of graphene oxide with good properties (23).Furthermore,S-GP ratio shows better cycling performance than B-GP ratio for the same mass ratio.This is probably because the two components in the composites from smaller graphene oxide sheets can disperse more uniformly and combine more compactly with each other.This enhances the stability of the composites,leading to a better cycling life.Among these ratios,S-GP 1:23and B-GP 1:19show best cycling character with the capaci-tance retention of 73%and 64%compared to 20%of PANI after 500cycles,respectively,which is discussed in detail in the following experiments.
The electrochemical capacitance performances are fur-ther investigated for S-GP 1:23and B-GP 1:19in 1M H 2SO 4as shown in Figure 9.The performance between S-GP 1:23and B-GP 1:19are compared at 1-4cycles (Figure 9a)and 500-503cycles (Figure 9b)at a current density of 200mA g -1.The S-GP 1:23and B-GP 1:19electrode materials give an initial speci?c capacitance of 421and 456F g -1in the potential range from 0to 0.4V,respectively.After 500cycles,the speci?c capacitance maintains at 330and 293F g -1,which corresponds to 78and 64%of the initial capacitance,respectively.These values show a pronounced enhancement in capacitance and lifetime compared with pure PANI,the corresponding speci?c capacitance 216and 43F g -1with the capacitance retention 20%.Thus,it is further improved that the graphene-oxide-doped PANI shows a synergistic effect of the two components.The decrease in speci?c capacitance with cycling is in agreement with other studies on PANI-based redox supercapacitors (51,52).It is notable that the shape of the curve S-GP 1:23and B-GP 1:19at cycles 500-503is a little different than those of cycles 1-4,and the discharge time also decreases,which is probably due to the structure changing with the continuous cycling.
The charge -discharge plots of S-GP 1:23and B-GP 1:19at different current densities after 500cycles were given in panels c and d in Figure 9,respectively.At a current density of 400mA g -1,S-GP 1:23and B-GP 1:19give a speci?c capaci-tance of 305and 316F g -1with masses of 8.2and 13.2mg,respectively.These values are lower than the speci?c ca-pacitance obtained at 200mA g -1,so the speci?c capaci-tance strongly depends on current density;this result is consistent with another report (4).
The cycling performances of S-GP 1:23and B-GP 1:19at 1,100,200,300,400,and 500cycles are compared by charge -discharge curves in the voltage of 0.0-0.8V,as presented in panels e and f in Figure 9.There is no large IR drop even in the last cycle for both samples;as the cycles increased to cycle 500,the capacitance experiences
a
FIGURE 8.Discharge curves of (a)S-GP ratio and (b)B-GP ratio in 1M H 2SO 4at 200mA g -1.
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smooth fading and the shape of curves keeps a little differ-ence with the ?rst cycling and almost the same as cycle 100.Though the initial speci?c capacitance of S-GP 1:23is lower than that of B-GP 1:19,the cycling performance of S-GP 1:23,synthesized from smaller graphene oxide sheets,is better than that of B-GP 1:19.The charge -discharge characterization demonstrates that the graphene-oxide-doped PANI owns not only a high initial speci?c capacitance but also an enhanced cycling life when a proper feeding ratio is adopted.A recent report given by Wu et al.(53)revealed that the number of layers of graphene oxide obtained by heating was different for the two raw graphite sizes.However,according to the XRD analysis (shown in Figure S2in the Supporting Infor-mation)in our conditions,graphene oxide is mainly a single layer due to the missing re?ection peaks of S-and B-graphite oxide at ～10°in composites S-GP 1:23and B-GP 1:19.The highly dispersed graphene oxide sheets in the composite may play an important role in the improved cycling life.
CONCLUSIONS
This paper presents high performances of graphene-oxide-doped PANI nanocomposites synthesized by soft chemical method for supercapacitors.The nanocomposites exhibit excellent capacitance as high as 2times that with pure PANI below the mass ratio 1:50for S-GP and 1:15for B-GP.The retention on cycling can be enhanced greatly by adjusting the feeding ratio of materials.The raw material sizes and the ratio of graphene oxide have a pronounced effect on the electrochemical performance of the nanocom-posites.Such nanocomposites can be expected to show maximum capacitance and cycling life if further optimiza-tion of the experimental condition is done.The product shows good application potential in supercapacitors or other power source system.
Acknowledgment.This work was supported by Natural Science Foundation of China and China Academy of Engi-neering Physics (10776014),Science and Technology Sur-porting item of Jiangsu Province,China (BE2009159).SRF for ROCS,State Education Ministry and Ministry of Personnel of the PRC (2006),and Excellent Plan Foundation of NUST (2008).
Supporting Information Available:Experimental proce-dures and X-ray diffraction of graphite oxide and its com-posite (PDF).This material is available free of charge via the Internet at https://www.wendangku.net/doc/3f1587009.html,.
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Table 1.Weight and Initial Speci?c Capacitance (calculated in the potential range of 0-0.4V)of S-GP ratio and B-GP ratio Used for Charge-Discharge Measurements at 200mA g -1
GP ratio
GP 1:10GP 1:15GP 1:19GP 1:23GP 1:50GP 1:100GP 1:200GP 1:370PANI mass (mg)S-GP ratio 11.89.811.4188.214 5.352B-GP ratio 2.4 2.916.113.9 4.1 2.87.6 4.62C 0(F g -1)
S-GP ratio 74177332375411476746
693216B-GP ratio
348
429
456
479
627
530
520
435
216
FIGURE 9.Galvanostatic charge -discharge curves in 1M H 2SO 4between 0V and 0.8V.S-GP 1:23,B-GP 1:19(a)at initial 4cycles and (b)after 500cycles at a current density of 200mA g -1.(c)S-GP 1:23and (d)B-GP 1:19at different current densities of 200mA g -1and 400mA g -1,respectively.(e)S-GP 1:23and (f)B-GP 1:19at 1,100,200,300,400,500cycles at a current density of 200mA g -
1.
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