Transport properties and modification of potassium dihydrogen orthophosphate

Abstract

We have studied the thermal behavior, proton conductivity, and structural properties of composite proton electrolytes based on KH₂PO₄, the mixed salt K_0.97Cs_0.03(H₂PO₄)_0.97(HSO₄)_0.03, and silicon dioxide with a pore size of 70 Å in a wide composition range. The results demonstrate that the proton conductivity of the (1–x)KH₂PO_4–xSiO₂ (x = 0.1–0.5) composite systems increases by more than two orders of magnitude, reaching 3 × 10^–3 S/cm at a temperature of 225°C. The increase in conductivity is due to the formation of a disordered amorphous state of the salts as a result of partial KH₂PO₄ dehydration and the formation of K₄H₆(PO₄)₂P₂O₇ as an intermediate product. In the composites based on the highly conductive, disordered K_0.97Cs_0.03(H₂PO₄)_0.97(HSO₄)_0.03 mixed salt, close in composition to KH₂PO₄, heterogeneous doping causes no increase in conductivity, and the conductivity decreases with increasing doping level, which is caused by dispersion of the salt and the dehydration process, leading to the formation of K₄H₆(PO₄)₂P₂O₇ and KPO₃.