In this work, a free standing and flexible solid polymer electrolyte (SPE) based on nonhazardous and environmental friendly material, carboxymethyl cellulose (CMC) was successfully produced in order to overcome environmental and pollution issues. The effect of doping ammonium thiocyanate (NH4SCN) into SPE based on carboxymethyl cellulose (CMC) on transport, thermal and electrochemical stability window properties have been investigated for potential application in electrochemical devices. CMC-NH4SCN SPE was prepared via solution casting technique. The properties of the prepared CMC-NH4SCN SPE were characterized via Fourier transform infrared spectroscopy (FTIR) deconvolution, transference number measurement (TNM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and linear sweep voltammetry (LSV) techniques. FTIR deconvolution was performed in order to investigate the dissociation of ions and transport properties of CMC-NH4SCN SPE system and it can be correlated with the ionic conductivity of CMC-NH4 SCN SPE system. The result of TNM was obtained via a DC polarization method where the ionic transference number for the highest conducting CMC-NH4SCN SPE was found to be 0.93. Thus, it can be suggested that the conducting species for the highest conducting CMC-NH4SCN SPE are mainly due to ions. TGA was performed to investigate the thermal stability of CMC-NH4SCN SPE. The value of glass transition temperature of CMC-NH4SCN SPE was obtained from DSC analysis. Electrochemical stability window of the highest conducting CMC-NH4SCN SPE obtained from LSV technique was up to 1.6 V. As a result, it can be inferred that the highest conducting CMC-NH4SCN SPE had shown a promising performance and has a great potential to be applied in electrochemical devices application such as proton batteries. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.