Based on the biopolymer Gellan gum with ammonium thiocyanate (NH₄SCN) salt, solid electrolyte has been prepared with distilled water as solvent, using solution casting technique. The prepared solid electrolytes are subjected to various characterization techniques such as XRD, FTIR, DSC, and Ac impedance technique. Amorphous/crystalline nature of biopolymer membrane is studied by XRD. The polymer–salt complex formation has been studied by FTIR technique. Biopolymer membrane of 1 g Gellan gum with 1.1 M wt% of NH₄SCN exhibits very high amorphous nature with a high proton conductivity of 1.41 × 10⁻² S/cm and a glass transition temperature (T_g) of 42.98 °C. Using the highest ionic conducting biopolymer electrolyte, proton battery and fuel cell have been fabricated and their performance is studied. Proton battery constructed shows the open circuit voltage of 1.62 V. A single fuel cell constructed using the highest conducting membrane gives the voltage of 580 mV.