Role of copper ion dissociation in DC conductivity studies of nanocomposite polymer electrolyte films

A solution cast method was used to prepare nanocomposite polymer electrolyte films of hydroxypropyl methylcellulose:polyvinyl alcohol (HPMC:PVA) blends complexed with copper oxide (CuO) nanoparticles. According to the XRD data, each sample’s percentage of crystallinity decreased as the concentration of CuO increased. The degree of percentage of crystallinity was found to be 31.59% for the highest conducting polymer electrolyte film, i.e. for HPMC:PVA mixture with 3 wt% nanoCuO. Scanning electron microscopy (SEM) showed different morphologies for all the samples. Differential scanning calorimetry (DSC) analysis revealed an increase in the glass transition temperature as well as in the melting temperature for all samples. This may be because the presence of CuO nanoparticles in the host polymer blend matrix increases their thermal stability. Compared with those of the HPMC:PVA blends, the tensile strength and modulus of the HPMC:PVA-CuO nanocomplexes improved. The electrical conductivity increased with increasing CuO dopant concentration and temperature. The activation energy values for all the samples reflect the predominance of ion-type charge transport. The HPMC:PVA mixture with 3 wt% CuO has the maximum ionic conductivity of 4.94 × \({10}^{-6}\) ${10}^{-6}$ at 313 K and 1.26 × \({10}^{-5}\) ${10}^{-5}$ at 393 K. Linear sweep voltammetry (LSV) analysis showed that the improved electrolyte electrochemical stability of the highest conducting electrolyte was 2.35 V. The transference numbers of ions \(\left({t}_{\text{ion}}\right)\) $\left(t_{\text{ion}}\right)$ and electrons ( \({t}_{\text{ele}}\) $t_{\text{ele}}$ ) measured for the HPMC:PVA with 3 wt% CuO electrolyte sample by Wagner’s DC polarization method were found to be 0.958 and 0.042, respectively. The results confirmed that \({\text{Cu}}^{+}\) ${\text{Cu}}^{+}$ ions were the dominant charge carriers in these electrolytes and are suitable for solid electrochemical cell device applications.