Potato starch (PS)-methyl cellulose (MC) blend solid biopolymer electrolytes infused with ammonium nitrate (NH4NO3) and glycerol as plasticizer are made via the solution cast technique. Fourier transform infrared (FTIR) spectroscopy indicates that NH4NO3 has interacted with the polymer blend host. The addition of 40 wt glycerol in the highest conducting plasticizer free electrolyte has improved the conductivity to the order of �10�3 S cm�1. The thermal stability of the electrolytes is identified by thermogravimetric analysis (TGA). Result from X-ray diffraction (XRD) analysis shows that the electrolyte with maximum conductivity value has the lowest degree of crystallinity. Differential scanning calorimetry (DSC) analysis reveals that the highest conducting plasticized electrolyte possesses the lowest glass transition temperature (Tg) of �27.5 °C. Conductivity trend is further verified by dielectric analysis. Transference numbers of ion (tion) and electron (te) for the highest conducting electrolyte are identified to be 0.98 and 0.02, respectively, confirming that ions are the dominant charge carriers. Linear sweep voltammetry (LSV) evaluates that the potential window for the electrolyte is 1.88 V. The internal resistance of the electrochemical double-layer capacitor (EDLC) is between 29 and 64 Ω. From the charged-discharged measurement, the value of Cs is 31 F g�1. The EDLC is stable over 1000 cycles. © 2017, Springer-Verlag Berlin Heidelberg.