# Novel Highly Dispersed Additive for Proton-Conducting Composites
## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c} \hline
**Heating Temperature, \({}^{\circ}\)C** & **110** & **300** & **520** & **600** & **700** \\ \hline Phase composition & ZnSn(OH)\({}_{6}\) & amorphous & ZnSnO\({}_{3}\) & Zn\({}_{2}\)SnO\({}_{4}\)–SnO\({}_{2}\) \\ \hline Specific surface area, m\({}^{2}\cdot\)g\({}^{-1}\) & 18 & 80 & 85 & 36 & 15 \\ \hline Pore size, nm & \(\sim\)1 & 3 & 6 & 4 & 10 \\ \hline \end{tabular}
\end{table} 
Table 1: Results from the textural study of the initial ZnSn(OH)\({}_{6}\) and the products of its thermal decomposition obtained at different temperatures. Figure 6: (a) X-ray diffraction patterns of (1–\(x\))CsH\({}_{2}\)PO\({}_{4}\)–\(x\)ZnSnO\({}_{3}\) composites of various compositions in the comparison with the starting compounds: CsH\({}_{2}\)PO\({}_{4}\) (1); \(x\) = 0.2 (2); 0.4 (3); 0.8 (4); ZnSnO\({}_{3}\) (5). (b) Electrochemical impedance spectra for 0.8 CsH\({}_{2}\)PO\({}_{4}\)–0.2 ZnSnO\({}_{3}\) sample obtained at 230 \({}^{\circ}\)C (black symbols) and 190 \({}^{\circ}\)C (empty symbols). Points are experimental data; lines are theoretical curves obtained for the equivalent circuit, with the parameters listed in Table 2. The parameters of the equivalent scheme are described in detail the texts and Equations (5)–(7). As the molar percentage of ZnSnO\({}_{3}\) increased, an amorphous halo characteristic of zinc stannate appeared in the composite (such as at \(x\) = 0.8), and the salt was mostly in an amorphous state. Figure 6b shows the impedance plots of the composites at different temperatures. The impedance hodograph included an arc that represented the electrode processes in the lower frequency region, and a single semicircle that was due to the electrolyte transfer in the higher frequency region. The proton conductivity was calculated from the resistance values with the minimum capacitive component. As the temperature increased, the radius of the single semicircles significantly decreased, indicating greater proton conductivity due to an increase in the number and mobility of the current carriers. For interpretation of the experimental impedance data, the equivalent circuit presented in Figure 6b was used. The circuit includes three impedances, \(Z_{1}\), \(Z_{2}\), and \(Z_{3}\), connected in series. The first impedance includes the active resistance \(R_{1}\) connected in parallel to the constant phase element (CPE) \(Q_{1}\). The second and third impedances are related to the electrode: \(R_{2}\) and \(Q_{2}\) are charge transfer resistance and CPE taking into account the electrode polarization effects, respectively, and \(Q_{3}\) is the diffusion impedance contribution. As a result, the total impedance of the sample is equal to \(Z=Z_{1}+Z_{2}+Z_{3}\), where  
\[Z_{1}=\left[R_{1}^{-1}+Y_{1}(i\omega)^{n_{1}}\right]^{-1} \tag{5}\]  
\[Z_{2}=\left[R_{2}^{-1}+Y_{2}(i\omega)^{n_{2}}\right]^{-1} \tag{6}\]  
\[Z_{3}=Y_{3}^{-1}(i\omega)^{-n_{3}} \tag{7}\]  
As seen from Figure 6b, the theoretical curves obtained for this equivalent circuit fairly fit the experimental data. Results of the fitting are presented in Table 2.  
Figure 7 shows a comparison of the proton conductivity of the samples with the initial salts. The ZnSnO\({}_{3}\) matrix initially exhibited a low proton conductivity, not exceeding 2 \(\times\) 10\({}^{-8}\) S/cm in the temperature range below 250 \({}^{\circ}\)C. This conductivity was consistent with literature data [40; 41; 42]. The temperature dependence of the conductivity revealed two regions related to the superprotonic and low temperature phases of CsH\({}_{2}\)PO\({}_{4}\). The proton conductivity of the low temperature phase follows the Arrhenius law, with an activation energy of \(\sim\)0.9 eV, and does not exceed 3 \(\times\) 10\({}^{-7}\) S/cm at T \(<\) 200 \({}^{\circ}\)C due to the strong hydrogen bond network that impedes the proton transfer due to the high energy of defect formation. In the CsH\({}_{2}\)PO\({}_{4}\)-ZnSnO\({}_{3}\) composites, the conductivity can also be distinguished into two temperature ranges.