Proton-conducting I-Carrageenan-based biopolymer electrolyte for fuel cell application

The essential part of electrochemical devices, such as fuel cells and batteries, is the polymer electrolyte with good mechanical, thermal, and chemical stability. The search for a new proton-conducting membrane with easy processability, non-toxic, and low-cost has been growing rapidly. The bio-based polymer electrolytes are now receiving much attention due to the green environment. Among the commercially available biopolymers, iota-Carrageenan (I-Carrageenan) is one of the biopolymer with good film-forming nature and with good mechanical stability. I-Carrageenan-based biopolymer membranes doped with ammonium bromide (NH₄Br) have been prepared using solution-casting technique, and distilled water is used as a solvent. The prepared I-Carrageenan-based biopolymer membranes have been characterized using FTIR, XRD, and AC impedance techniques. The complexation between the polymer and salt has been revealed by FTIR. The increase in the amorphous nature of the film due to the addition of salt has been confirmed by XRD. From AC impedance technique, the conductivity of pure I-Carrageenan has been found to be 1.46 × 10⁻⁵ S/cm. The addition of different wt% of NH₄Br increases the conductivity and reaches the highest value of 1.08 × 10⁻³ S/cm for 20% NH₄Br, and the conductivity decreases on further addition of NH₄Br due to the formation of ion aggregates.

     

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.

     

Solid polymer electrolyte based on tragacanth gum-ammonium thiocyanate

Research towards solid polymer electrolytes based on biopolymers has grown extensively over the past years due to its abundance in nature, non-toxicity, low cost, and biodegradability. When compared to standard biopolymers, electrochemical study on natural gums is very limited. Therefore, in the present work, polymer electrolytes based on gum tragacanth have been prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS), thermogravimetry, and transference number studies. The polymer-salt complex formation is confirmed using FTIR studies while XRD spectra reveal the amorphous nature of the polymer membranes. The highest conductivity of 9.161?×?10^?3 S/cm was obtained for the film with 1 g of gum tragacanth and 0.5 g of ammonium thiocyanate. The Thermogravimetry study showed that the electrolyte is thermally stable. The transference number study confirmed that the main charge carriers are ions. The primary battery has been constructed using the prepared electrolyte, and the OCV was found to be 1.31 V.