Abstract
Solid acid electrolytes of cesium dihydrogen phosphate, CsH2PO4, have been used for fuel cell and electrolysis applications at high temperatures. This material exhibits very good proton conductivity and very high thermal stability, making it an ideal material for such fuel cells.
Synthesis and characterization of solid acid composites containing different weight ratios of CsH2PO4, NaH2PO4 and ZrO 2 were performed using the X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Thermogravimetric analysis and Differential Thermal Analysis techniques. Besides, the electrotransport and structural properties were characterized by impedance, IR spectroscopy and differential scanning calorimetry methods.
Room temperature XRD patterns of the solid solutions containing Ba and Rb were observed showing the monoclinic phase (spatial group P21/m). The diffraction peaks of the compounds containing Mo and W showed a shift to the left, indicating higher cell size.
In addition, a very significant increase in the conductivity of the polycrystalline compound was observed around 240 degC. This was attributed to the transition from the monoclinic to the cubic phase, which produced a dramatic improvement in the proton conductivity by several orders of magnitude.
Moreover, structural and dielectric studies revealed that the symmetry of the paraelectric state was not orthorhombic as previously assumed, but monoclinic with the spatial group of Cs. The conformation of hydrogen bond and the sequence of Cs and P differed substantially from those of KH2PO4, a kind of ferroelectrics with different atomic structure. These findings are a direct evidence that CsH2PO4 is a ferroelectric due to its atomistic structure differently from the one of KH2PO4.