The development of the novel materials for the electrochemical power units i.e. low temperature fuel cells (FC) efficiently working up to 300 °C is a serious scientific problem related to hydrogen energy shift. Polyantimonic acid (PAA) is characterized by high conductivity and thermal stability can be regarded as a prospective proton conducting material. So the goal of the current work was the investigation of the structure, phase stability, and protonic conductivity of PAA based solid electrolytes.
PAA was synthesized using the controlled hydrolysis of SbCl5 in the tenfold excess of water. Then the precipitate was treated by 1N HCl and again washed with distilled water until the negative reaction to clorine ions. Then using 10 and 20 wt.% of fluoroplastic as a binder the cylindrical solid electrolytes (SE) of 30 mm in diameter and 5 mm in thickness were formed by cold uniaxial pressing. Structure of the formed membranes was investigated by thermo-XRD, SEM and EDX techniques, STA technique, and hydrostatic weighting. The conductivity of SE in the range 60-300 °C was investigated by electrochemical impedance study in the dry nitrogen, room air and presence of humidity. The transport properties of SE (diffusion, self-diffusion coefficient and proton transfer number) were measured using EMF technique.
Using STA and XRD it was shown that the structure of SE correspond to crystalline Sb2O5×3H2O. STA, Raman spectroscopy and thermo-XRD showed that the temperature increase results unit cell shrinkage and crystallinity decrease from ~91 to 75% because of step by step water removal. According hydrostatic weighting, SEM and EDX data, fully dense membranes were obtained, where a binder do not cover PAA grains enabling the ion transport though the grain bulk. The electrical behaviour was examined at ambient temperature by electrical impedance spectroscopy in the entire relative humidity (RH) interval (0–100%) and in the frequency range of 40 Hz up to 60 MHz. Electrical response of the materials correlated with the structural features of the membranes. Both 90PAA and 80PAA sensors showed total resistance 3 × 105 and 3.5 × 105Ω at 10% RH, respectively. A linear decrease of the resistance on RH was observed in the range 30–90% RH for both SE. The temperature dependence of conductivity of PAA is complex due to prolonged water losses and the increase of carrier charge mobility with temperature increase.
Acknowledgements. SEM and EDX data were obtained at the center for Nanoresearches, thermo-XRD data were performed at the Center for X-ray Diffraction Studies of SPBU Research park.