Proton-conducting biopolymer electrolytes based on pectin doped with NH4X (X=Cl,Br)

Research has been undertaken to develop polymer electrolytes based on biodegradable natural polymers such as cellulose acetate, starch, gelatin, and chitosan, which are being used as polymer hosts for obtaining new polymer electrolytes for their applications in various electrochemical devices such as batteries, sensors, and electrochromic windows. Pectin is a naturally available material which is extracted from the skin of citrus fruits. Pectins, also known as pectic polysaccharides, are rich in galacturonic acid. The present study focuses on the proton-conducting polymer electrolytes based on the biopolymer pectin doped with ammonium chloride (NH₄Cl) and ammonium bromide (NH₄Br) prepared by solution casting technique. The prepared membranes are characterized using XRD, FTIR, and AC impedance techniques to study their complexation behavior, amorphous nature, and electrical properties. The conductivity of pure pectin membrane has been found to be 9.41 × 10⁻⁷ S cm⁻¹. The polymer systems with 30 mol% NH₄Cl-doped pectin and 40 mol% NH₄Br-doped pectin have been found to have maximum ionic conductivity of 4.52 × 10⁻⁴ and 1.07 × 10⁻³ S cm⁻¹, respectively. The conductivity value has increased by three orders of magnitude compared to pure pectin membrane. The dielectric behavior of both the systems has been explained using dielectric permittivity and electric modulus spectra.

     

Synthesis and characterization of proton-conducting polymer electrolyte based on polyacrylonitrile (PAN)

Solid polymer electrolytes based on polyacrylonitrile (PAN) doped with ammonium iodide (NH₄I) have been prepared by solution casting method with different molar ratios of polymer and salt using DMF as solvent. The XRD pattern confirms the dissociation of salt. The FTIR analysis confirms the complex formation between the polymer and the salt. A shift in glass transition temperature (T _g ) of the PAN/NH₄I electrolytes has been observed from the DSC thermograms, which indicates the interaction between the polymer and the salt. The conductivity analysis shows that the polymer electrolyte with 20 mol% NH₄I has the highest conductivity equal to 1.106 × 10⁻³ S cm⁻¹ at room temperature. The activation energy (E _a ) has been found to be low for the highest conductivity sample. The dielectric permittivity (ε*) and modulus (M*) have been calculated from the alternating current (AC) impedance spectroscopy in the frequency range 42 Hz–1 MHz. The DC polarization measurement shows that the conductivity is mainly due to ions.

     

Development of proton conducting biopolymer membrane based on agar–agar for fuel cell

A proton-conducting polymer electrolyte based on agar and ammonium nitrate (NH₄NO₃) has been prepared through solution casting technique. The prepared polymer electrolytes were characterized by impedance spectroscopy, X-ray diffraction, and Fourier transform infra-red spectroscopy. Impedance analysis shows that sample with 60 wt.% NH₄NO₃ has the highest ionic conductivity of 6.57 × 10⁻⁴ S cm⁻¹ at room temperature. As a function of temperature, the ionic conductivity exhibits an Arrhenius behaviour increasing from 6.57 × 10⁻⁴ S cm⁻¹ at room temperature to 1.09 × 10⁻³ S cm⁻¹ at 70 °C. Transport parameters of the samples were calculated using Wagner’s polarization method and thus shows that the increase in conductivity is due to the increase in the number of mobile ions. Fuel cell has been constructed with the highest proton conductivity polymer 40agar/60NH₄NO₃ and the open circuit voltage is found to be 558 mV.

     

Effect of ethylene carbonate plasticizer on agar-agar: NH<Subscript>4</Subscript>Br-based solid polymer electrolytes

Proton-conducting polymer electrolytes based on biopolymer, agar-agar as the polymer host, ammonium bromide (NH₄Br) as the salt and ethylene carbonate (EC) as the plasticizer have been prepared by solution casting technique with dimethylformamide as solvent. Addition of NH₄Br and EC with the biopolymer resulted in an increase in the ionic conductivity of polymer electrolyte. EC was added to increase the degree of salt dissociation and also ionic mobility. The highest ionic conductivity achieved at room temperature was for 50 wt% agar/50 wt% NH₄Br/0.3% EC with the conductivity 3.73?×?10^?4 S cm^?1. The conductivity of the polymer electrolyte increases with the increase in amount of plasticizer. The frequency-dependent conductivity, dielectric permittivity (ε′) and modulus (M′) studies were carried out.     

Influences of LiCF3SO3 and TiO2 nanofiller on ionic conductivity and mechanical properties of PVA:PVdF blend polymer electrolyte

In recent years, solid polymer electrolytes have been extensively studied due to its flexibility, electrochemical stability, safety, and long life for its applications in various electrochemical devices. Interaction of LiCF₃SO₃ and TiO₂ nanofiller in the optimized composition of PVA:PVdF (80:20—system-A possessing σ ~ 2.8 × 10⁻⁷ Scm⁻¹ at 303 K) blend polymer electrolyte have been analyzed in the present study. LiCF₃SO₃ has been doped in system-A, and the optimized LiCF₃SO₃ doped sample (80:20:15-system-B possessing σ ~ 2.7 × 10⁻³ Scm⁻¹ at 303 K) has been identified. The effect of different concentration of TiO₂ in system-B has been analyzed and the optimized system is considered as system-C (σ ~ 3.7 × 10⁻³ Scm⁻¹ at 303 K). The cost effective, solution casting technique has been used for the preparation of the above polymer electrolytes. Vibrational, structural, mechanical, conductivity, thermal, and electrochemical properties have been studied using FTIR, XRD, stress-strain, AC impedance spectroscopic technique, DSC and TGA, LSV, and CV respectively to find out the optimized system. System-C possessing the highest ionic conductivity, higher tensile strength, low crystallinity, high thermal stability, and high electrochemical stability (greater than 5 V vs Li/Li⁺) is well suitable for lithium ion battery application.

     

Study of biopolymer I-carrageenan with magnesium perchlorate

The green revolution has led to the study of biopolymer for development of polymer electrolyte for electrochemical devices. Cellulose acetate, pectin, chitosan, and carrageenan are some of the biopolymers. Biopolymer-based membrane for proton conduction and lithium ion conduction have developed and characterized by different techniques. But the study of biopolymer based on Mg²⁺ ion is rare in literature. So, biopolymer based on I-carrageenan with magnesium has been studied. I-carrageenan biopolymer membrane with different concentration of magnesium perchlorate has been prepared by solution casting technique. Developed biopolymer membrane have been characterized by X-ray diffraction analysis (XRD), FTIR, differential scanning calorimetry (DSC), and AC impedance techniques. Pure I-carrageenan has shown a conductivity value of 5.90?×?10^?5 S/cm. I-carrageenan membrane with 0.6 wt% of magnesium perchlorate has shown a conductivity of 2.18?×?10^?3 S/cm. A primary Mg²⁺ ion battery has been constructed and its performance is studied. XRD has been undertaken to study the amorphous/crystalline nature of the sample. I-carrageenan with 0.6 wt% of magnesium membrane has shown highest amorphous nature. FTIR study confirms the complex formation between polymer and salt. AC impedance technique has been used to study the conductivity of the samples.     

Structural, vibrational and electrical characterization of PVA-NH4Br polymer electrolyte system

Polymer electrolyte based on PVA doped with different concentrations of NH₄Br has been prepared by solution casting technique. The complexation of the prepared polymer electrolytes has been studied using X-ray diffraction (XRD) and Fourier transform infra red (FTIR) spectroscopy. The maximum ionic conductivity (5.7×10⁻⁴ S cm⁻¹) has been obtained for 25 mol% NH₄Br-doped PVA polymer electrolyte. The temperature dependence of ionic conductivity of the prepared polymer electrolytes obeys Arrhenius law. The ionic transference number of mobile ions has been estimated by dc polarization method and the results reveal that the conducting species are predominantly ions. The dielectric behavior of the polymer electrolytes has been analyzed using dielectric permittivity and electric modulus spectra.     

Tamarind seed polysaccharide biopolymer membrane for lithium-ion conducting battery

Solid biopolymers have gained much attention in the development of polymer electrolytes due to its biocompatibility, film-forming nature, and non-toxicity. In the present work, biopolymer membrane has been prepared using tamarind seed polysaccharide (TSP) as host polymer and various concentrations of lithium chloride (LiCl) salt as dopant by solution casting technique. The prepared biopolymer electrolyte has been characterized by XRD, FTIR, differential scanning calorimetry (DSC) analysis, AC impedance spectroscopy analysis, and transference number measurement. XRD analysis has been done to investigate the amorphous/crystalline nature of the polymer membrane. The highest amorphous nature has been found for 1 g of TSP with 0.4 g LiCl. FTIR spectrum analysis confirms the complex formation between TSP biopolymer with LiCl. From AC impedance conductivity analysis, the maximum ionic conductivity is of the order of 6.7?×?10^?3 S cm^?1 at room temperature for 1 g TSP with 0.4 g LiCl, whereas for pure TSP biopolymer membrane, the ionic conductivity is of the order of 5.48?×?10^?7 S cm^?1. The glass transition temperature for the highest conducting biopolymer membrane for the composition of 1 g TSP: 0.4 g LiCl has been found to be 44.25 °C using the DSC technique. Employing the maximum conducting biopolymer membrane, a lithium-ion conducting battery has been fabricated and its discharge characteristics have been studied.     

Structural and ionic conductivity studies on proton conducting polymer electrolyte based on polyvinyl alcohol

An attempt has been made to prepare a new proton conducting polymer electrolyte based on polyvinyl alcohol (PVA) doped with NH₄NO₃ by solution casting technique. The complex formation between polymer and dissociated salt has been confirmed by X-ray diffraction analysis. The ionic conductivity of the prepared polymer electrolyte has been found by ac impedance spectroscopic analysis. The highest ionic conductivity has been found to be 7.5 × 10⁻³ Scm⁻¹ at ambient temperature for 20 mol% NH₄NO₃-doped PVA with low activation energy (~0.19 eV). The temperature-dependent conductivity of the polymer electrolyte follows an Arrhenius relationship, which shows hopping of ions in the polymer matrix.     

Electrical characterization of nano-composite polymer gel electrolytes containing NH4BF4 and SiO2: role of donor number of solvent and fumed silica

Nano-composite polymer gel electrolytes were synthesized by using polyethylene oxide (PEO), ammonium tetrafluoroborate (NH₄BF₄), fumed silica (SiO₂), dimethylacetamide (DMA), ethylene carbonate (EC), and propylene carbonate (PC) and characterized by conductivity studies. The effect of donor number of solvent on ionic conductivity of polymer gel electrolytes has been studied. The mechanical strength of the gel electrolytes has been increased with the addition of nano-sized fumed silica along with an enhancement in conductivity. Maximum room temperature ionic conductivity of 2.63 × 10⁻³ and 2.92 × 10⁻³ S/cm has been observed for nano-composite gel electrolytes containing 0.1 and 0.5 wt% SiO₂ in DMA+1 M NH₄BF₄+10 wt% PEO, respectively. Nano-composite polymer gel electrolytes having DMA have been found to be thermally and electrically stable over 0 to 90 °C temperature range. Also, the change in conductivity with the passage of time is very small, which may be desirable to make applicable for various smart devices.

     

Characterization of blend polymer PVA-PVP complexed with ammonium thiocyanate

Thin films of blend polymer electrolytes comprising poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) complexed with ammonium thiocyanate (NH₄SCN) salt in different compositions have been prepared by solution casting technique using distilled water as solvent. The prepared films have been investigated by different experimental techniques. The complexation of these films has been studied by FTIR spectroscopy. The increase in amorphousness of the films with increase in NH₄SCN content has been confirmed by XRD analysis. The addition of ammonium thiocyanate salt to PVA-PVP polymer blend shows a shift in T_g of the blend. The effect of salt concentration and temperature on the ionic conductivity of the polymer blend films has been analyzed using AC impedance spectroscopy. The maximum conductivity of 6.85 × 10^?4 S cm^?1 at room temperature has been observed for the blend with 50 mol% PVA-50 mol% PVP complexed with 40 mol% NH₄SCN. The activation energy has been found to be minimum (0.24 eV) for this sample. Wagner’s polarization technique shows that the charge transport in these blend films is predominantly due to ions. Using the highest conductivity blend polymer electrolyte, a proton battery has been fabricated and its discharge characteristics have been studied.     

Structural, vibrational, thermal, and conductivity studies on proton-conducting polymer electrolyte based on poly (N-vinylpyrrolidone)

The proton-conducting polymer electrolytes based on poly (N-vinylpyrrolidone) (PVP), doped with ammonium chloride (NH₄Cl) in different molar ratios, have been prepared by solution-casting technique using distilled water as solvent. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis confirms the complex formation of the polymer with the salt. A shift in glass transition temperature (T _g) of the PVP/NH₄Cl electrolytes has been observed from the DSC thermograms which indicates the interaction between the polymer and the salt. From the AC impedance spectroscopic analysis, the ionic conductivity of 15?mol% NH₄Cl-doped PVP polymer complex has been found to be maximum of the order of 2.51?×?10^?5?Scm^?1 at room temperature. The dependence of T _g and conductivity upon salt concentration has been discussed. The linear variation of the proton conductivity of the polymer electrolytes with increasing temperature suggests the Arrhenius type thermally activated process. The activation energy calculated from the Arrhenius plot for all compositions of PVP doped with NH₄Cl has been found to vary from 0.49 to 0.92?eV. The dielectric loss curves for the sample 85?mol% PVP:15?mol% NH₄Cl reveal the low-frequency ?? relaxation peak pronounced at high temperature, and it may be caused by side group dipoles. The relaxation parameters of the electrolytes have been obtained by the study of Tan?? as a function of frequency.     

Synthesis and characterization of dextrin-based polymer electrolytes for potential applications in energy storage devices

An attempt has been made to synthesise a new proton conducting polymer electrolyte using the biopolymer dextrin doped with ammonium thiocyanate salts using solution casting technique. The complexation has been studied using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The differential scanning calorimetry (DSC) thermograms of dextrin with NH₄SCN showed that T_g value increases with respect to the increase of NH₄SCN concentration. The electrical conductivity was measured using AC impedance analyser which showed that ionic conductivity increases with increase in salt concentration up to 40%. Transference number measurement was carried out to investigate the nature of the charge transport species in the polymer electrolyte. Surface morphology of the electrolytes was determined using scanning electron microscope (SEM) studies, and the chemical composition of the elements present was determined using EDAX. The proton battery was constructed with the highest conducting polymer electrolyte Dex-40%NH₄SCN and its open circuit voltage with load were carried out.     

AC impedance studies on proton-conducting PAN : NH4SCN polymer electrolytes

Solid polymer electrolytes based on polyacrylonitrile (PAN) doped with ammonium thiocyanate (NH₄SCN) in different molar ratios of polymer and salt have been prepared by solution-casting method using DMF as solvent. The increase in amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. A shift in glass transition temperature (T _g) of the PAN?:?NH₄SCN electrolytes has been observed from the DSC thermograms which indicates the interaction between the polymer and the salt. From the AC impedance spectroscopic analysis, the ionic conductivity has been found to increase with increasing salt concentration up to 30 mol% of NH₄SCN beyond which the conductivity decreases and the highest ambient temperature conductivity has been found to be 5.79?×?10^?3 S cm^?1. The temperature-dependent conductivity of the polymer electrolyte follows an Arrhenius relationship which shows hopping of ions in the polymer matrix. The dielectric loss curves for the sample 70 mol% PAN?:?30 mol% NH₄SCN reveal the low-frequency β-relaxation peak pronounced at high temperature, and it may be caused by side group dipoles. The ionic transference number of polymer electrolyte has been estimated by Wagner’s polarization method, and the results reveal that the conductivity species are predominantly ions.     

Acrylamide based proton conducting polymer gel electrolyte for electric double layer capacitors

A new class of polymer gel electrolyte (PGE) was synthesized using acrylamide as host polymer and LiClO₄ as dopant. The polymer gel was subjected to electrochemical AC impedance analysis and thermal analysis. The polymer has conductivity in the order of 10⁻³ S cm⁻¹ at ambient temperature. Thermogravimetric analysis (TGA) revealed the effect of dopant on host polymer matrix. A supercapacitor was fabricated using acrylamide based polymer gel electrolyte with activated carbon as electrode material and it was subjected to various electrochemical techniques like cyclic voltammetry, electrochemical AC impedance analysis and galvanostatic charge–discharge tests at various current densities. From cyclic voltammetry a specific capacitance of 28 F/g was obtained at a scan rate of 10 mV/s. The capacitor had good self-discharge behavior and good cycle life of more than 10,000 cycles. The coulombic efficiency was more than 95%. These results indicate that this acrylamide-based polymer gel electrolyte doped with LiClO₄ is a potential electrolyte for electric double-layer capacitors (EDLCs).     

Biopolymeric electrolyte based on glycerolized methyl cellulose with NH<Subscript>4</Subscript>Br as proton source and potential application in EDLC

In the present work, biopolymer electrolyte films based on MC doped with NH₄Br salt and plasticized with glycerol were prepared by solution casting method. Fourier transform infrared (FTIR) spectroscopy analysis confirms the interaction between MC, NH₄Br, and glycerol. X-ray diffraction (XRD) explains that the enhancement of conductivity is affected by the degree of crystallinity. This result is verified by field emission scanning electron microscopy (FESEM). For unplasticized system, sample containing 25 wt% of NH₄Br possesses the highest ionic conductivity of (1.89 ± 0.05) × 10^?4 S cm^?1. The addition of 30 wt% glycerol increases the conductivity value up to (1.67 ± 0.04) × 10^?3 S cm^?1. The conduction mechanism was best presented by the correlated barrier hopping (CBH) model. The linear sweep voltammetry (LSV) and cyclic voltammetry (CV) result confirms the suitability of the highest conducting electrolyte to be employed in the fabrication of electrochemical double layer capacitor (EDLC).     

Effect of hot pressing on the ionic conductivity of the PEO/LiCF3SO3 based electrolyte membranes

PEO/LiCF₃SO₃ (LiTFS) /Ethylene carbonate (EC) polymer electrolyte membranes were prepared with a solution casting method followed by a hot pressing process. The effect of the hot pressing process on the in-plane conductivity of the PEO electrolyte membranes was evaluated using a four-electrode AC impedance method. The composition, morphology, and microstructure of the composite polymer electrolyte were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The AC impedance measurement results indicate that the hot pressing process can increase the room temperature conductivity of the membranes 14 times to 1.7 × 10^− 3 S cm^− 1 depending upon the duration of the hot pressing process. The SEM, FTIR, XRD, and DSC results indicate that the hot pressing process could increase the amorphous part of the polymer electrolyte membrane or convert large spherulite crystals into nano-sized crystals.     

Effects of compositions on properties of PEO–KI–I2 salts polymer electrolytes for DSSC

The effects of compositions on properties of PEO/KI/I₂ salts polymer electrolytes were investigated to optimize the photovoltaic performance of solid state DSSCs. XRD pattern for the mole ratio 12:1 of [EO:KI] was showed the formation of complete amorphous complex. DSC results also confirmed the amorphous nature of the polymer electrolyte. The highest value of ionic conductivity is 8.36 × 10^− 5 S/cm at 303 K (ambient temperature) and 2.32 × 10^− 4 S/cm at 333 K (moderate temperature) for the mole ratio 12:1 of EO:KI complex. The effect of contribution of [I⁻] and [I₃⁻] concentration with conductivity were also evaluated. FTIR spectrum reveals that the alkali metal cations were co-ordinated to ether oxygen of PEO. The formation of polyiodide ions, such as symmetric I₃⁻ (114 cm^− 1) and I₅⁻ (145 cm^− 1) caused by the addition of iodine was confirmed by FT Raman spectroscopic measurements. The optimum composition of PEO–KI–I₂ polymer electrolyte system for higher conductivity at ambient and moderate temperatures was reported. A linear Arrhenius type behaviour was observed for all the PEO–KI polymer complexes. Transport number measurements were carried out for several polymer electrolyte compositions. Dye-sensitized solar cells were fabricated by using higher conductivity polymer electrolyte compositions and its photoelectrochemical performance was investigated. The fill factor, short-circuit current, photovoltage and energy conversion efficiency of the DSSC assembled with optimized electrolyte composition were calculated to be 0.563, 6.124 mA/cm², 593 mV and 2.044% respectively.     

Ionic transport properties of protonic conducting solid biopolymer electrolytes based on enhanced carboxymethyl cellulose - NH<Subscript>4</Subscript>Br with glycerol

The present work investigates the ionic conductivity as well as its transport properties of carboxymethyl cellulose–NH₄Br plasticized with various weight percentage of glycerol for solid biopolymer electrolytes (SBEs) prepared by solution-casting technique. It was shown from the FTIR analysis that the complexation transpires at C=O and C–O^? from COO^? of CMC upon the addition of glycerol into the SBEs system. The highest room temperature ionic conductivity of ~10^?3 S cm^?1 was achieved at 6 wt.% of glycerol owing to the broadening in the amorphous state as demonstrated in the XRD analysis. The conductivity-temperature plots were found to be in good agreement with the conventional Arrhenius relationship. It was further shown that the conducting element is mainly due to the protonation of H⁺ where ionic mobility and diffusion coefficient was found to contribute towards the enhancement in the ionic conductivity of SBEs system.     

NH4PO3/SiO2 composite as electrolyte for intermediate temperature fuel cells

NH₄PO₃/SiO₂ composite based electrolyte with SiO₂ as supporting matrix was prepared. A thermogravimetric analysis was performed. Its electrochemical properties were investigated by an impedance spectroscopy within the temperature range of 100–300 °C under dry and humid atmospheres. The maximum conductivity is 6 mS cm^− 1 at 300 °C under dry N₂ and 0.1 S cm^− 1 at 200 °C under humid N₂.