Soft chemical synthesis and the role of potassium pentahydrogen bis(phosphate) in a proton conducting composite electrolyte based on potassium dihydrogen phosphate

Proton conducting composites based on potassium dihydrogen phosphate (KH sub(2)PO sub(4)) have been successfully prepared and characterized as a potential electrolyte for intermediate temperature fuel cells. X-ray diffraction, thermal analysis, and conductivity measurements reveal that the molten potassium pentahydrogen bis(phosphate) (KH sub(5)(PO sub(4)) sub(2 )) phase enhances the proton conductivity of KH sub(2)PO sub(4)-KH sub(5)(PO sub(4)) sub(2) composites by more than four orders of magnitude. The addition of 10 wt.% SiO sub(2) is sufficient to alleviate the dehydration of KH sub(2)PO sub(4)-KH sub(5)(PO sub(4)) sub(2), and long-term stable conductivity is exhibited under a relatively low humidification level (pH sub(2)O = 0.03 atm).