Preparation and characterization of proton-conducting polymer electrolyte based on PVA, amino acid proline, and NH4Cl and its applications to electrochemical devices

Biodegradable solid polymer electrolytes based on PVA (polyvinyl alcohol) and amino acid (proline) with different molar mass percentages of ammonium chloride (NH4Cl) were prepared by solution-casting technique using distilled water as solvent. Their structural, thermal, vibrational, and electrical properties were studied. XRD analysis confirms the amorphous nature of the polymer electrolytes. DSC measurements show a decrease in Tg with increasing salt concentration. The FTIR analysis reveals the complex formation between the PVA, proline, and ammonium chloride. Transference numbers for the proton-conducting polymer electrolytes have been measured. The maximum ionic conductivity has been found to be 7.01 × 10−4 S/cm at ambient temperature for 75 Mwt% PVA;25 Mwt% proline:0.3 (m.m.%) of NH4Cl polymer electrolyte using AC impedance analyzer. The temperature-dependent conductivity of the polymer membranes obeys Arrhenius behavior. The highest ionic conductivity polymer electrolyte has low activation energy of 0.07 eV among the prepared polymer electrolytes. An electrochemical stability window of 3.10 V has been measured using linear sweep voltammetry for the highest ionic conducting membrane. The highest conductivity polymer electrolyte 75 Mwt% PVA:25 Mwt% proline:0.3 (m.m.%) NH4Cl has been used to construct a primary proton battery and fuel cell.