Research Journal of Recent Sciences _________________________________________________ ISSN 2277-2502 Vol. 3(6), 59-66, June (2014) Res.J.Recent Sci. International Science Congress Association 59 Conductivity study of Carboxyl methyl cellulose Solid biopolymer electrolytes (SBE) doped with Ammonium FluorideRamlli M.A.1 and Isa M.I.N.1,2 Advanced Materials Research Group, School of Fundamental Sciences, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, MALAYSIA Corporate Communication & Image Development Center, Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, MALAYSIA Available online at: www.isca.in , www.isca.me Received 14th April 2014, revised 22nd May 2014, accepted 28th May 2014Abstract Carboxyl methyl cellulose (CMC) doped with ammonium fluoride (NHF) solid biopolymer electrolyte (SBE) was prepared via solution cast technique. The ionic conductivity of CMC-NHF was measured using electrical impedance spectroscopy in temperature range from 303K to 333K. The highest conductivity observed is 2.6810-7 Scm-1 for sample containing 9 wt. % NHF at 303K. The ionic conductivity of the samples increases proportionally with temperature which implies that these samples obey Arrhenius behavior. Activation energy graph plotted shows highest conductive sample attain lowest activation energy value. The dielectric analysis of the CMC-CNF SBE as ascertained from electrical impedance spectroscopy reveals that the highest conductivity sample has the highest dielectric constant at ambient temperature. These samples appear to be ionic conductor of non-Debye type. Keywords: Solid biopolymer electrolyte, carboxyl methylcellulose, ammonium fluoride, ionic conductivity, dielectric analysis. Introduction In the past few decades, the study on developing solid biopolymer (SBE) electrolyte has caught the attention of many researchers1-7 due to the high potential of the solid biopolymer electrolytes to be used as an electrolyte in battery system. Since the environmental conditions at present is seriously polluted makes finding devices with green materials much more desired8, .Furthermore, with the electricity price is hiking up day by day makes low cost electrical devices more popular. SBEs have the advantages of good contact surface with the electrodes, low self-discharge in batteries and less problems in leakage or pressure distortion; furthermore it is easy to produce and very affordable-2,3,10. The bio-derived polymer such as Carboxyl methylcellulose1,2,5,6,11, methylcellulose3,12, cellulose acetetate13 and chitosan were made from natural materials and it is most abundant materials on earth respectively2,4. Carboxyl methylcellulose or CMC in short, is one of cellulose derivatives materials made from plants. In the other hand, CMC SBE thin films have good mechanical and electrical properties; furthermore it is non-toxic material, biodegradable and good film formability1,2,5,6,11,14. Generally, the ionic conductivity of CMC is not that impressive but it can be enhanced with the addition of proper dopant5,6,14. Hence in this work, ammonium fluoride was chosen to form CMC-NHF SBE system. Commercially, ammonium fluoride (NHF) is a white crystalline solid and it is highly soluble in water. The dielectric properties of the CMC-NHF SBEs films were analyzed via electrochemical impedance spectroscopy at ambient to elevated temperatures in this present work. Methodology Sample Preparation: All the CMC-NHF SBE films were prepared using solution cast technique at room temperature. CMC (Acros Organics Co, average molecular weight 90000, D.S. 0.7) was dissolved in distilled water. Then 3 wt. % of NHF (R&M Co) was added and was stirred continuously until homogenous solution was obtained. The obtained solution was cast into several petri dishes and dried at 50C for films to form. Similar method was used for different wt. % NHF (5-13 wt %). A sample of CMC without dopant was also prepared as control sample. Table-1 shows the composition of the CMC-NHF SBE. Table-1 Composition of electrolytes Sample CMC(g) NH 4 F (wt. %) CMC-0 2 0 CMC-3 2 3 CMC-5 2 5 CMC-7 2 7 CMC-9 2 9 CMC-11 2 11 CMC-13 2 13 Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(6), 59-66, June (2014) Res. J. Recent Sci. International Science Congress Association 60 Ionic Conductivity Analysis: The ionic conductivity of CMC-NHF SBE was determined by using HIOKI 3532-50 LCR Hi-Tester and calculated using equation-11-7.  (1) where is the thickness of the SBE thin film, is the bulk resistance of the sample and is the area of contact of the SBE with the electrodes. All samples were tested in the range from 303K to 333K and the temperature dependence graph was plotted to inspect the behavior of the samples with temperatures. The conductivity-temperature correlation of SBEs usually obeys Arrhenius behavior with the regression value is almost unity (R1). This can be determined by using equation-2.  \r  (2) Where is the pre-exponential factor, is the activation energy and k is Boltzmann constant. The relative permittivity of an ionic system is a dimensionless ratio of permittivity, to the permittivity of space,  and can be described as real and imaginary component in which has 90 out of phase between these two components10. These were represented in equation below.   ! #$  (3) Here is the dielectric constant, = 8.8541817 × 10-12 F m-1, is the dielectric loss and (#* respectively10.The dielectric constant and loss was calculated using equation-4 andequation-5. !-+1+ (4) !-1 + (5)Here = A/t ( is permittivity of free space), 5678 is frequency), is the imaginary part of the complex permittivity and is the real part of the complex permittivity11. The use of electric modulus analysis to study ionic transport dynamics is debatable since its inception in the 80’s. Never the less, function of electric modulus is generally successful at low frequencis10. The real part and imaginary part of electrical modulus were calculated using the equation-6 and equation-7. 1 (6) :1 (7) Here is the dielectric constant and is the dielectric loss. Results and Discussion Ionic Conductivity analysis: The ionic conductivity, of the CMC-NHF SBEs at room temperature is illustrated in figure-1. It can be observed from figure-1 that the ionic conductivity of the CMC-NHF SBE best explained into two regions. In region-1, the ionic conductivity increases with the increase in concentration of NHF. The highest ionic conductivity reached was 2.6810-7 Scm-1for sample containing 9 wt. % NHF. Figure-1 Ionic conductivity of CMC-NHF biopolymer electrolyte at 303K 0.0E+005.0E-081.0E-071.5E-072.0E-072.5E-073.0E-0702468101214S cm-1wt. %Region 2 Region 1 Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(6), 59-66, June (2014) Res. J. Recent Sci. International Science Congress Association 61 The increasing in ionic conductivity of the CMC-NHF SBE can be explained as the increasing in number of mobile charge carriers and also may due to the interactions between CMC and NHF brings to high dispersion of proton, H, thus enhance the ionic conductivity12. In region-2, the ionic conductivity was decreases to such a degree with the addition of NHF. It is believed that the ionic mobility decreases due to the overcrowded of the mobile ions from the ionic dopant as a result from too many ions disperse throughout the CMC-NHF system1, 14. The activation energy of CMC-NHF was determined using equation-2 and depicted in figure-2. Theoretically, activation energy, is the minimum energy required by an ion to escape from its bond by jumping to another region15,16. However, the ionic conductivity of sample CMC-3 and CMC-5 increases with increasing . The increased in ionic conductivity of the samples are believed to be influenced by the diffusion coefficient and mobility of mobile ions besides the number of mobile ions, despite having high activation energy. On the other hand, the value of a for other samples is inversely proportional to the ionic conductivity value. Figure-3 shows the temperature dependence plot for selected samples of CMC-NHF biopolymer electrolytes in the range from 303K to 333K. From the plot, it is observed that these samples are thermally activated where the conductivity increases with temperature. The increase in conductivity was due to the thermal expansion of the sample which creates more free volume for the charge carriers to move16. With increase in temperature, there are more free volume making the ions to move more freely thus increasing the ionic conductivity in return17. This suggests that the CMC-NHF system obeys Arrhenius behavior further confirming that these SBE are ionic conductor18. Figure-2 Activation energy of CMC-NHF biopolymer electrolytes Figure-3 Temperature dependence of selected samples 0.400.450.500.550.6002468101214Ea (eV)wt. % R² = 0.9358R² = 0.9039R² = 0.9014R² = 0.9848R² = 0.9357-7.1-7.0-6.9-6.8-6.7-6.6-6.5-6.4-6.32.953.053.153.253.35log 1000/T (K-1) 0wt% 3wt% 5wt% Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(6), 59-66, June (2014) Res. J. Recent Sci. International Science Congress Association 62 The analysis of dielectric for biopolymer electrolytes system is a reliable approach for obtaining information regarding the characteristics of the ionic and molecular interactions18. Figure-4 represents the frequency dependence of dielectric constant, with different composition of NHF with frequency. Meanwhile figure-5 and figure-6 represents the dielectric constant and loss for sample CMC-9 respectively. Figure-4 Dielectric constant for every sample with log frequency at 303K Figure-5 Dielectric constant for sample CMC-9 with log frequency  \n(Hz)   \n   10121401234567f (Hz) 303K 313K 323K 333K Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(6), 59-66, June (2014) Res. J. Recent Sci. International Science Congress Association 63 Figure-6 Dielectric loss for sample CMC-9 with log frequencyFrom figure-4, it is observed that with the addition of NHF the value of dielectric constant was increased. This trend clearly follows the conductivity analysis as described earlier with sample CMC-9 has the highest ionic conductivity and has the highest value of dielectric constant as well. The highest dielectric constant for the highest conductive sample was due to the increased number of charge carriers which resulted from the salt dissociation in the polymer matrix10. Figure-4 and figure-5 shows that the dielectric constant, raise sharply at low frequencies and gradually dropped at higher frequencies. The sharp rise at low frequency was probably acted by a number or more of different types of contribution polarization factors whether electronic, atomic, ionic, and interfacial but the dielectric constant at high frequency was depends on the ionic movement, ion-ion orientation, and space charge effects16, 20-22. The sharp rise at low frequencies signified that electrode polarization and space charge effects have occurred, confirming the non-Debye dependence for this samples13,20. Meanwhile, as the frequency increases, the decreases and this may be due to the electrical relaxation process which the ionic and orientation source of polarization start to decrease at higher frequency and finally disappears as a result from the inertia of mobile ions23. Dielectric loss is the direct measure of dissipated energy and generally contributes in the ionic transport and the polarization of the charge20. From figure-6, the shows the same pattern with (figure-5). The high value of at low frequency was observed and this event can be explained in which due to the enhancement in mobility of charge carrier and can be related to the free charge motion within the electrolytes. The value of decreases at higher frequencies may due to the lesser ions that can pile up at the interface which have faster rate in direction of the electric field change23. By using dielectric modulus, a successful analysis of dielectric behavior of CMC-NHF SBE was achieved which suppressed the effect of electrode polarization20. Figure-7 and Figure 8 shows the real, and imaginary, part of the modulus of sample CMC-9 respectively. Based on figure-7, the value of is low and approching zero at lower frequencies region. With frequency increases, the value of start to increase as well for all temperatures. From these observation, it may be related to a lack of restoring force leading the mobility of charge carriers under the action of an induced electric field. This behaviour supports the conduction occurrences because of the long-range of charge carriers. Both figures, the dispersion of real and imaginay part of the electrical modulus, shows sharp rise at higher frequencies20,24. From figure-8, it is observed that well defined peak are present and this demonstrates that this sample is an ionic conductor. This event has been reported in almost in every polymer electrolytes systems, the possible peak at higher frequencies represents that it is an ionic conductors20, 25. At lower frequencies, both and move towards zero implying that there is large association between the values of capacitance with the electrodes23. 1015202501234567f (Hz) 303K 313K 323K 333K Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(6), 59-66, June (2014) Res. J. Recent Sci. International Science Congress Association 64 Figure-7 Dispersion of real part of the electrical modulus for sample CMC- 9 with log frequency Figure-8 Dispersion of imaginary part of the electrical modulus for sample CMC- 9 with log frequency 101520251101001000100001000001000000Mrf (Hz) 303K 313K 323K 333K 10121101001000100001000001000000Mi (w)f (Hz) 303K 313K 323K 333K Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 3(6), 59-66, June (2014) Res. J. Recent Sci. International Science Congress Association 65 ConclusionSolid biopolymer electrolyte based on Carboxyl methyl cellulose (CMC) as host and doped with NHF ranged from 0 to 13 wt. % was successfully formed via solution cast technique. The highest ionic conductivity obtained is 2.6810-7 S cm-1 for sample containing 9 wt. % NHF at 303K. The value of activation energy of the highest conductive sample was found to be the lowest. The samples show Arrhenius behavior where the conductivity is thermally activated. The dielectric analysis shows that this sample follows the non-Debye dependence and the samples are ionic conductor since the ionic conductivity increases at higher temperature. Acknowledgements The authors would like to thank all of the members in Advanced Material Team, Ministry of Education Malaysia for the FRGS and ERGS grant. 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