Characterization of CH3SO3H-doped PMMA/PVP ...

Appl. Phys. A (2016)122:113 DOI 10.1007/s00339-016-9642-5

Characterization of CH3SO3H-doped PMMA/PVP blend-based proton-conducting polymer electrolytes and its application in primary battery C. Ambika1 • G. Hirankumar1

Received: 2 July 2015 / Accepted: 8 November 2015 Springer-Verlag Berlin Heidelberg 2016

Abstract Various compositions of solid blend polymer electrolytes based on poly(methyl methacrylate) (PMMA)/ poly(vinyl pyrrolidone) (PVP) complexed with methanesulfonic acid (MSA) as proton donor were prepared by solution casting technique. The complex nature of polymer blend with MSA was confirmed by Fourier transform infrared spectroscopy. Good thermal stability of PMMA/ PVP blend polymer electrolyte was identified by thermogravimetric analysis. The surface morphology of the prepared electrolytes was studied through optical microscopy. Ion transport number was determined in the range of 0.93–0.97 for proton-conducting blend polymer electrolytes. The maximum conductivity value was calculated as 2.51 9 10-5 S/cm at 303 K for 14.04 mol% MSAdoped polymer electrolytes. Dielectric studies were also carried out. The electrochemical stability window of blend polymer electrolyte was found to be 1.82 V. Primary proton battery was fabricated with Zn ? ZnSO47H2O/solid polymer electrolytes/MnO2. The discharge characteristics were studied at constant current drain of 5, 20 and 50 lA. The energy and power density were calculated as 0.27 W h kg-1 and 269.23 mW kg-1 for 20 lA of discharge, respectively.

& G. Hirankumar [email protected] 1

Centre for Scientific and Applied Research, PSN College of Engineering and Technology, Melathediyoor, Tamilnadu 627 152, India

1 Introduction Among the various types of polymer electrolyte systems, solid polymer electrolytes have been receiving great interest owing to their advantages such as high ionic conductivity, leak proof, solvent-free, ease of fabrication and less weight [1]. Solid polymer electrolytes having high ionic conductivity at ambient temperature are of special interest today. Many methods such as copolymerization [2], blending [3], plasticization [4] and addition of fillers [5] have been used to enhance the conductivity at room temperature. Among these techniques, blending is considered to be a viable approach. The mechanical stability of the blend polymer electrolyte can be increased by one polymer portraying itself as a mechanical stiffener and the other as a gelled matrix. In the present investigation, PMMA and PVP are taken as the mechanical stiffener and gelling agent, respectively, for the blend. Methanesulfonic acid is proton provider. PMMA has no harmful subunits and possesses good insulating properties and resistance to weathering corrosions. The presence of amorphous region and a polar functional group in its polymer chain contributes to a high affinity for ions which is credited as an added advantage [6]. PVP is a special conjugated polymer, and it deserves a special attention because of its high dielectric strength, higher ionic mobility, low scattering loss and good charge storage capacity. Rigid pyrrolidone group in PVP is a heart part to form complexes with iondonating salts or acids [7]. Methanesulfonic acid is a clear colorless strong organic acid but less corrosive and less toxic compared to inorganic acids. MSA is an ideal catalyst for esterification because of its good kinetic behavior, ease of handling and biodegradability. Methanesulfonic acid is usually described as a ‘‘Green acid’’ due to its environmental advantages [8, 9]. Reports with acid as proton donor

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in the study of proton conductivity variation on the addition of PMMA on liquid electrolytes containing trifluoromethanesulfonic acid (HCF3SO3) in propylene carbonate have been found [10]. Conductivity variation has been studied by varying the molecular weight of PMMA. The maximum conductivity is obtained for PMMA15000 in their polymer gel electrolytes complexed with NH4PF6 [11]. Hence, PMMA15000 is selected as one of the host polymer in the present work. Many investigations are present in the proton conduction on PVP-based solid polymer electrolytes doped with various ammonium salts [12, 13]. Random copolymers have been synthesized from PVP and PMMA. Lithium perchlorate has been doped into these copolymers, and their phase behavior and ionic conductivity studies have been carried out by Chiu et al. [14]. Literature survey indicates that limited number of works was carried out in the preparation of proton-conducting blend polymer electrolyte by taking PMMA and PVP. To the best of our knowledge, reports with MSA as a proton provider are very scarce. Hence, in this present work, PMMA/PVP-based solid blend polymer electrolytes have been prepared with MSA as proton donor and the conduction mechanism is analyzed by frequency-dependent conductivity as well as dielectric formalism. The prepared membranes were also characterized by Fourier transform infrared spectroscopy (FTIR), optical microscopy, thermal analysis such as differential scanning calorimetry and thermogravimetry (DSC and TG/ DTG) and ion transport number studies. Linear sweep voltammetric (LSV) technique is utilized to find the electrochemical stability, proton battery was also constructed with high conducting solid blend polymer electrolyte, and the discharge parameters are studied.

2 Experimental technique Polymethyl methacrylate (PMMA) of (Mw: 15,000) (HiMedia) and polyvinyl pyrrolidone (PVP) K30 (Mw: 40,000) (HiMedia), methanesulfonic acid (MSA) (Sd finechem.) and N,N-dimethyl formamide (DMF) (MERCK) were used as starting material. PMMA was preheated at 70 C for 1 h. PVP and MSA were used as received. The required amount of PVP was dissolved in DMF at 70 C, and the preheated PMMA was added to it and stirred for 12 h. Required amount of MSA was added and stirring continued for 36 h at the same temperature. This homogeneous solution was poured on polypropylene petri dishes. DMF was evaporated slowly at 70 C in an oven. After 12 h, films of uniform thickness were obtained and they were stored in a desiccator. The nomenclature of the samples is listed in Table 1.

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FTIR spectra were recorded with JASCO FT/IR—4100 FTIR spectrometer at room temperature in the wave number range of 550–4000 cm-1. DSC study was carried out by using TA-Q20 DSC, and differential scanning calorimeter is in the temperature range of 303–470 K. Tg values of the samples were determined from the thermal spectra. The thermogravimetric analysis (TG/DTG) was carried out using PerkinElmer STA 6000 system from room temperature to 700 C in air at a heating rate of 10 C per minute. The microstructure imaging of the prepared samples surface was recorded using OLYMPUS (model BX51 M) metallurgical optical microscope. Ion transport number was determined through Bio-Logic (model SP-300) electrochemical analyzer. For this measurement, a piece of polymer electrolyte was sandwiched between two stainless steel strips. The variation of current with respect to time at constant dc supply of 1 V was monitored. Conductivity measurements were taken by using two-probe method with the aid of two stainless steel blocking electrodes of area 1.4 cm2. Ionic conductivity of the samples was determined by IM6 Zahner elektrik workstation, in the frequency range of 100 mHz–1 MHz and in the temperature range of 303–373 K. Electrochemical stability window of the polymer electrolyte was determined by sandwiching the high conducting polymer electrolyte between two stainless steel blocking electrodes at a scan rate of 5 mV/s. The solid-state primary proton battery was constructed with maximum conducting film. Anode was comprised of zinc metal powder (50 wt%) (HiMedia), zinc sulfate (ZnSO47H2O) (40 wt%) (Sd finechem.) and activated carbon (AC) (10 wt%) (Fisher Scientific). The mixture was pressed gently to form a pellet using a pelletizer. The same procedure was adopted to obtain a cathode pellet which comprised of manganese dioxide (MnO2) (80 wt%) (HiMedia) and activated carbon (AC) (20 wt%). Discharge studies and LSV were carried out with computer-controlled Biologic electrochemical workstation (Biologic SP-300, France).

3 Results and discussion 3.1 FTIR spectral studies FTIR spectroscopy is used to deduce the possible interactions among atoms or ions in polymer complex systems. The complexation is evidenced through the change in intensity, shape and position of the peak. The FTIR spectra of the prepared electrolytes are shown in Fig. 1. The characteristic peaks of pure PMMA are observed at 826, 1013, 1189 and 1766 cm-1 that are assigned to CH2 bending, CH2 rocking, C–O stretching and C=O stretching,

Characterization of CH3SO3H-doped PMMA/PVP blend-based proton-conducting polymer…

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Table 1 Thermal parameters and conductivity values for polymer blend complexes Sample code

Compositions (mol%) PMMA:PVP:MSA

Conductivity (S/cm) at 303 K

Tg1 (K)

Tg2 (K)

BS0

50:50:0

1.13 9 10-11

–

–

BS1

47.975:47.975:4.05

7.17 9 10-9

356

–

BS2

44.96:44.96:10.08

6.04 9 10-6

347

399

BS3

42.98:42.98:14.04

2.51 9 10

-5

332

393

BS4

40.02:40.02:19.97

1.08 9 10-5

345

390

BS5

37.08:37.08:25.84

6.14 9 10-7

–

388

stretching in MSA gets shifted to 777 cm-1 and broadened in MSA-doped blend matrices. The disappearance of ms (O– H) peak in blend electrolytes indicates the complete dissociation of MSA. The peak position that corresponds to C–N and C=O vibrations of PVP gets shifted to lower and higher wave number in the blend electrolytes, respectively. There is no much perturbation observed in C=O group of pure PMMA upon addition of salt. This shows that MSA prefers to interact more with carbonyl group of PVP than PMMA. The appearance of broad peak around 3400 cm-1 in the blend electrolytes shows the hygroscopic nature of MSA. The observed changes in characteristic peaks of PMMA, PVP and MSA indicate the formation of complexes. 3.2 Thermal analysis Fig. 1 FTIR spectra of a pure PMMA, b pure PVP, c blend PMMA/ PVP (50:50), d pure MSA, e BS1, f BS2, g BS3, h BS4, i BS5

3.2.1 DSC analysis

respectively [15]. CH2 bending and CH2 rocking peaks in pure PMMA get shifted to higher and lower wave number regions, respectively, due to the blending with PVP. C–N pyridine ring and C=O stretching vibrations of pure PVP are observed at 1494 and 1644 cm-1, respectively. The peak at 1286 cm-1 corresponds to CH2 wagging and C–N stretching in backbone of PVP [16]. The peaks correspond to the carbonyl group of PMMA, and the carbonyl group of PVP is found broadened and shifted in blend electrolytes. The relative intensity of the peak at 1286 cm-1 gets reduced in the blend which may be due to the strong interaction between the backbone of PVP and PMMA. In the region of 2800–3000 cm-1, the peaks are attributed to symmetric and asymmetric stretching of CH2 in the side chain of both PMMA and PVP which get shifted to higher wave number region in the blend matrices. The observed changes in the peak position show the evidence for the blending formation between PMMA and PVP. Vibrational peaks of pure MSA are observed at 763, 888, 981, 1137 and 1330 cm-1 that are attributed to ms (C– S), ms (O–H), qs?as (CH3), ms (S=O)2 and mas (S=O)2, respectively [17]. The peak that corresponds to C–S

DSC thermograms obtained for blend complexes are shown in Fig. 2. The various compositions of blend polymer complexes and their DSC results are compiled in Table 1. Glass transition temperature (Tg) of the polymer concerns with the mobility of the polymer chain. Two glass transition regions are observed from Fig. 2a, within the temperature range studied, while single glass transition temperature has been observed for the random copolymer of PMMA/PVP [14]. Inflection observed in the region 345–356 K (Tg1) (shown in Fig. 2b) and 388–399 K (Tg2) corresponds to the glass transition temperature of PMMA and PVP, respectively [18, 19]. Tg1 and Tg2 values are listed in Table 1. Lower Tg1 value is observed for 14.04 mol% addition of MSA in blend matrices, while less Tg2 is noticed for higher salt concentration-doped blend electrolytes. Less Tg usually leads to enhanced segmental motions, resulting in higher conductivity. But, the Tg2 value gradually decreases with increase in the concentration of MSA. This decrease in Tg2 may be attributed to the more plasticizing effect of salt on PVP compared with PMMA. Since the scanning rate of DSC is too fast, Tg2 is not appeared as a step.

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Fig. 2 a DSC thermograms of BS1, BS2, BS3, BS4 and BS5 blend solid polymer electrolytes. b DSC thermograms of BS1, BS2, BS3 and BS4 blend solid polymer electrolytes of Tg1 region

3.2.2 TG/DTG analysis Thermogram of PMMA/PVP blend and 14.04 mol% of MSA-doped blend polymer electrolytes are depicted in Fig. 3. Relatively small weight loss of about 6 and 12 wt% is observed for undoped and MSA-doped polymer electrolytes in the temperature range of 303–393 K. This may be due to the removal of moisture from the sample [20], and the result is consistent with FTIR analysis. Incorporation of MSA results in increase in weight loss in 303–393 K temperature range which is due to the hygroscopic nature of MSA which is evident from the FTIR analysis also. For the undoped and 14.04 mol% of MSA-doped polymer electrolytes, the onset temperature of decomposition is found at 634 and 646 K, respectively. A sharp exothermic peak in DTG spectrum is observed at 667 K which corresponds to the decomposition temperature of PMMA (the decomposition temperature of pure PMMA is *673 K) [21], and small hump is appeared at 701 K which corresponds to the decomposition temperature of PVP (the decomposition temperature of pure PVP is *714 K) [22] for undoped blend electrolyte. For MSA-doped membrane, a small exothermic peak in DTG spectrum is observed around 612 K which may be due to the addition of MSA in blend matrices. A sharp exothermic peak and small hump at 698 and 723 K correspond to the decomposition temperature of PMMA and PVP, respectively. It is evident that the thermal stability is enhanced due to the doping of MSA.

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Fig. 3 TG/DTG curves for a blend PMMA/PVP b 14.04 mol% of MSA-doped blend polymer electrolytes

(50:50).


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Fig. 4 Optical microscopic image of the a pure PMMA/PVP blend, b BS1, c BS2, d BS3, e BS4, f BS5

3.3 Surface morphological characteristics Optical microscopic images of the prepared solid polymer electrolyte membranes are shown in Fig. 4. All the prepared membranes are observed to be homogeneous in appearance. For undoped blended polymer of PMMA and

PVP (a), crater surface is noticed which indicates the phase separation in the blend polymer electrolytes. Upon the addition of 4.05 mol% of MSA in PMMA/PVP (b), the image contained irregular tracks of MSA (black) distributed in the polymer matrices (white). Surface morphology consisted of slender worm-like pattern for

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C. Ambika, G. Hirankumar Fig. 6 a–f The experimental and fitted cole–cole plot for the undoped c and MSA-doped blend at various compositions. g Equivalent circuit for the impedance plot of BS0. h Equivalent circuit for the impedance plot of MSA-doped blend electrolytes

the range of 0.93–0.97 which proves that the charge transport is predominantly due to ions. 3.5 AC impedance analysis

Fig. 5 Polarization current as a function of time for BS2, BS3 and BS4 samples

10.08 mol% of MSA (c)-doped membrane. MSA track size increases with further increase in MSA content (d) and (e). There is a white dot in every track of BS5 electrolyte (e) which may be due to the adsorbed water molecules from the atmosphere on the surface. MSA is hygroscopic in nature that results in adsorbed water at high concentration of MSA-doped (BS5) electrolyte. 3.4 Transference number measurements The current is measured with respect to time by applying a dc voltage of 1 V to the cell. The value of tion and tele is calculated by using the formula, tion ¼

Ii If Ii

ð1Þ

tele ¼

If Ii

ð2Þ

where Ii and If are the initial and final residual current. The initial current decreases with time due to the depletion of the ions in the electrolyte and becomes constant in the fully depleted situation. The steady current is due to the migration of electrons across the electrolyte and interface. The transference number plot for BS2, BS3 and BS4 solid polymer electrolytes is shown in Fig. 5. The prepared polymer electrolytes have the ionic transference number in

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Figure 6a–f shows the experimental and fitted cole–cole plot for the samples at room temperature. Within the measured frequency window, the inclined straight line and depressed semicircular arc are observed. The impedance plot is fitted by using Z-View software. The equivalent circuit is shown in Fig. 6g, h. The semicircular arc is observed in Fig. 6a that corresponds to the blend electrolytes of PMMA and PVP which is due to the parallel combination of bulk resistance (R1) and constant phase element (CPE1). CPE is the constant phase element that it does not behave ideally as capacitor. Bulk resistance (R1) in equivalent circuit is due to the charge carrier transport within the polymer matrices, and the constant phase element (CPE1) is due to the polarization of polymer chains. The high-frequency semicircular arc followed by low-frequency inclined line is observed in Fig. 6b–f that shows the equivalent circuit of the parallel combination of R1 and CPE1 along with series connection of CPE2. CPE2 corresponds to the polarization of mobile ions at the electrode– electrolyte interface due to the applied electric field [23]. From the cole–cole plot, the bulk resistance R1 for each sample is found and the conductivity is calculated by using r = t/(R1A) where t and A are the thickness and area, respectively. The conductivity values for the prepared polymer electrolyte membranes are listed in Table 1. The conductivity increases with increase in MSA concentration. The highest conductivity at ambient temperature is found as 2.51 9 10-5 S/cm for the 14.04 mol% MSA-doped blend polymer electrolyte system. 3.6 Conductance spectra analysis Frequency-dependent conductivity spectra of PMMA/PVP blend polymer electrolytes complexed with various MSA concentration at 303 K are shown in Fig. 7. The low-frequency dispersion region arises due to the space charge polarization at the blocking electrodes. High-frequency dispersion region corresponds to bulk relaxation phenomena. The mid-frequency plateau region occurs due to the hopping of mobile ions. Extrapolating the plateau to the lower-frequency region makes an intercept on the Y-axis and gives the dc conductivity value. This conductivity values coincide with the conductivity values calculated


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Fig. 7 Frequency-dependent conductivity (inset figure concentrationdependent dc conductivity)

from cole–cole plot. The inset Fig. 6 represents the variation of ionic conductivity with different MSA concentration at room temperature. Conductivity increases with increasing MSA concentration up to 14.04 mol%. Increase in ionic conductivity with increase in MSA concentration is due to increase in number of mobile charge carriers and increase in amorphous nature of polymer electrolyte. Decrease in ionic conductivity is observed at 19.97 and 25.84 mol% of MSA. This may be due to the formation of ion pairs/ion aggregates. 3.7 Temperature-dependent conductivity Figure 8 shows the variation of logarithm of conductivity with inverse of temperature for 14.04 mol% of MSA-doped blend polymer electrolyte. Two linear regions (region I and region II) (shown in Fig. 8a) are observed within the temperature range studied. The appearance of two linear regions of Arrhenius plot is consistent with the result of DSC that confirms the existence of glass transition temperature (Tg1) in the temperature range studied. This suggests that the carrier transport is dependent on both inter-chain ion movements and polymer segmental motion [24]. Since blend polymer electrolytes have two glass transition temperatures (Tg1 and Tg2), Tg1 value alone is present within the analyzed region of the Arrhenius plots. The activation energy value for above and below the Tg1 calculated by using Eq. 3 is 0.21 and 0.25 eV, respectively. Arrhenius equation is given as Ea r ¼ ro exp ð3Þ kT where ro is the conductivity pre-exponential factor, Ea is the activation energy, and k is the Boltzmann constant. The

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Fig. 8 a Arrhenius plot of xm (calculated from Fig. 10) with conductivity for 14.04 mol% of MSA-doped blend polymer electrolyte. b VTF plot for 14.04 mol% of MSA-doped blend polymer electrolyte

polymer segmental motion is evidenced by Vogel–Tamman–Fulcher (VTF) plot. The nonlinear behavior of Arrhenius plot can be well explicated by the Vogel–Tamman–Fulcher (VTF) equation, B 12 r ¼ AT exp ð4Þ k ð T To Þ where A is a fitting constant proportional to the number of carriers, B is the pseudo-activation energy associated with the motion of the polymer segment, and To is taken as the equilibrium temperature of the system corresponding to zero configuration entropy. To is calculated by using the relation To = Tg - 50 K. The fitted VTF plot is shown in Fig. 8b. The linear behavior in VTF plot (regression value 0.989 within the experimental error) shows that the conduction is predominantly due to polymer segmental motion rather than hopping of ions.


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Fig. 10 Variation of dissipation factor with frequency for BS3 membrane

the field, so the dielectric constant approximately approaches zero. e0 increases with increase in isotherm which reveals that the charge careers are thermally activated. The peak in the lower-frequency side corresponds to the relaxation in dielectric loss spectra which is shown in Fig. 9b. This peak is shifted to higher frequency as the temperature increases (represented in inset Fig. 9b). Dielectric studies with the variation of frequency and temperature are based on Debye Kramers–Kronig and Maxwell–Wagner relationships. The dielectric features e00 show the logarithmic dependence on x, i.e., Log e00 ¼ Log Að1 nÞ Log x Fig. 9 Variation of dielectric constant (a) and dielectric loss (b) with frequency at different isotherms for BS3 sample

3.8 Dielectric spectra analysis The complex permittivity (e*) for the system is defined by the equation r 0 00 0 e ¼ e je ¼ e j ð5Þ xeo where e0 is real part of dielectric constant, e00 is imaginary part of dielectric constant, r is conductivity, x is angular frequency, and eo is the permittivity of free space. Figure 9a, b illustrates the variation of dielectric constant and dielectric loss with respect to the logarithm of angular frequency, respectively, for different isotherms of BS3 sample. The dielectric constant (Fig. 9a) rises sharply to the low-frequency region. At very low frequencies, dipoles follow the applied field and the value of the dielectric constant found to be very high due to electrode polarization effects [25]. As the frequency increases, dipoles lag behind

ð6Þ

where A is a constant and x is the angular frequency. Linear fall of dielectric loss is viewed in the higher frequency side which is due to the high periodic reversal of applied field. Slope of the linear line gives the -(1 - n) value, and it is found as -0.948 to -0.952 which prevails the dc conduction mechanism. By using this value, dielectric relaxation energy can be calculated by using the relation 6k 1n¼ T ð7Þ Ed where k is the Boltzmann constant and T is the temperature. n will take the value from 0 to 1. For low dielectric loss conduction, n value approaches unity and it drops to zero for high dielectric loss conduction [26]. The calculated values of dielectric relaxation energy for the sample BS3 are varied from 0.165 to 0.202 eV at different temperatures. 3.9 Power loss factor analysis Figure 10 represents the variation of dissipation factor (Tand) as a function of frequency at different temperature

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Fig. 11 Linear sweep voltammogram for BS2, BS3, BS4 and BS5

for high conducting sample. Tand increases with increasing frequency and reaches a maximum; then, it sinks down with further increase in frequency. The intensity of the Tand peak is found to increase with increase in temperature. This is due to the mobility of charge carriers which are enhanced with increasing temperature. The maximum frequency at which Tand attains maximum value is said to be a relaxation frequency (xm). The relaxation time (s) can be calculated from the relaxation frequency by using the formula xms = 1. Above 348 K, there is no peak appeared within the frequency range of measurement. Hence, in the Arrhenius graph, plot is shown up to 348 K. The relaxation mechanism of charge carriers follows the same mechanism as that of conduction within the glass transition temperature Tg1. Charge carriers follow different mechanism above Tg1 which is observed from Fig. 8. As the temperature increases, the charge carrier is thermally activated and the peak in tangent loss plot is shifted toward higher frequency. This shows that the relaxation time decreases with increase in temperature which results in an increase in conductivity. 3.10 Electrochemical stability The high conductivity along with the good electrochemical stability window of blend polymer electrolyte is essential for the electrochemical device applications. Consequently, the operating voltage range of electrolytes is an important parameter to evaluate the stability of polymer electrolyte. Figure 11 shows the linear sweep voltammogram for the blend polymer electrolytes. There is no obvious change in current until the potential reaches 1.8 V even with oxidation limit current of 0.25 lA for the area 1.4 cm2 for BS3 membrane (inset Fig. 11). This voltage is comparable with the potential breakdown voltage (1.8 V) obtained by Mohamad et al. [27] for their system of chitosan-based plasticized polymer electrolytes. Current increases

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Fig. 12 a Discharge profile at constant current drain of 5 and 20 lA. b Discharge profile at constant current drain of 50 lA

gradually, when the electrode potential is higher than 1.82 V for the high conducting sample. The electrochemical stability window for the 10.08 mol% MSA, 19.97 mol% MSA and 25.84 mol% MSA-doped protonconducting membranes is less than that of 1.8 V for limit current of 0.25 lA with the same area. Hence, the prepared blend polymer electrolyte is suitable for fabrication of proton battery. 3.11 Discharge characteristics of proton battery The open-circuit voltage of the constructed proton battery is monitored for 24 h and is found as in the range of 1.35–1.43 V. The discharge profile of the constructed proton battery is shown in Fig. 12a, b at the constant current drain of 5, 20 and 50 lA, respectively. The region in which the proton battery potential reaches a flat discharge rate is called plateau region. The load voltage of the proton battery drops

Characterization of CH3SO3H-doped PMMA/PVP blend-based proton-conducting polymer… Table 2 Electrochemical cell parameters for 5 and 20 lA current of discharge Battery parameters

For a current drain of 5 lA

For a current drain of 20 lA

Cell weight (g)

0.42

0.45

Effective area of the cell (cm2)

1.32

1.32

Mass of active material (mg) Time for plateau region (h)

104 9

104 1

Discharge capacity (lA h)

45

20

Power density (mW kg-1)

68.65

269.23

Current density (lA cm-2)

3.79

15.15

Energy density (W h kg-1)

0.614

0.27

to 1.25 from 1.37 V within 10 s for the battery which discharges 50 lA. The initial drop is attributed to the battery activation polarization which may be due to the rate of an electrochemical reaction at an electrode surface [28]. From the discharge profile, it is evident that this battery is suited for low current density applications. The important battery parameters are evaluated for 5 and 20 lA of current drain and are given in Table 2.

4 Conclusion Blend proton-conducting polymer electrolytes based on PMMA/PVP were prepared. The significant changes in the characteristic peaks of PMMA, PVP and MSA confirm the complexation of blend and MSA. Two glass transition temperatures were identified from DSC analysis. Enhanced thermal stability is observed due to the doping of MSA. Homogeneity of the prepared membranes was analyzed from the optical microscopic image. Transference number values were in the range of 0.93–0.97. Equivalent circuit was identified from the impedance plot by using Z-View software. The higher conductivity was found to be 2.51 9 10-5 S/cm at ambient temperature for 14.04 mol% of MSA-doped sample. Dielectric relaxation energy and the significance of n value were discussed using Debye Kramers–Kronig and Maxwell–Wagner relationships, and also the relaxation time was calculated for 14.04 mol% of MSA-doped membrane at various temperatures. Electrochemical stability of the MSA-doped sample was shown significant stability window of 1.8 V which is more suitable to construct a proton battery. The blend electrolyte was also tested for proton battery application, and it was analyzed with different constant current discharge. The

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calculated power density value for 5 and 20 lA of discharge is 68.65 and 269.23 mW kg-1, respectively.

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