Synthesis and characterisation of novel solid state protonic electrolytes for use in electrochemical devices

Informations projet

N° de convention de subvention: INTAS-93-0913

Projet clôturé

Date de début 1 Juillet 1994

Date de fin 30 Juin 1995

Financé au titre de

• International Association for the promotion of cooperation with scientists from the independent states of the former Soviet Union (INTAS), 1993-

Coût total € 0,00

Contribution de l’UE € 50 000,00

Coordonné par

Centre National de la Recherche Scientifique
France

Résultats exploitables

Synthesis and characterization of novel solid state protonic electrolytes for use in electrochemical devices

The aims of this programme are the synthesis, spectroscopic, electrical and structural characterization of thermostable protonic conductors, which are potential solid electrolytes for various electrochemical devices operating at between 100 and 300°C New proton conducting compounds Cs5H3(SO4)4·xH2O, Cs5H3(SeO4)4·H2O and K9H6(SO4)8H·H2O have been grown and investigations including detailed X-ray diffraction analysis were carried out. Acid, but not water, protons are responsible for protonic conductivity in M5H3(AO4)4·xH2O and M9H6(SO4)8H·H2O crystals. Water molecules play a special role in the stabilization of highly-conducting (superprotonic) state: the loss of crystalline water leads to an increase of protonic conductivity at moderate temperatures by up to 5-6 orders of magnitude (to 10-4 S/cm-1). These compounds are promising proton electrolytes operating in dry atmospheres and under vacuum. The role of ammonium ions in order-disorder superprotonic and ferroelectric phase transitions in new mixed crystals ((NH4)1-xRb)3H(SO4)2 and their deuterated analogues has been studied and calorimetric, dielectric, conductivity measurements were carried out. The results show that the superprotonic ferroelastic phase transition is governed by ordering-disordering process of the acid H(D)-bond network itself, while the effect of weak ammonium H-bond is negligible. New families of protonic conducting oxides have been identified amongst crystals having the sheelite, apatite-like, palmierite and theolite structures e.g. lead tungstate germanates, lead phosphates. After annealing in wet nitrogen, Pb3(PO4)4 single crystals display an increase in conductivity by a factor 10-40 which reaches values 10-5 -10-4 S/cm at temperatures 400-600°C, close to those of the best high-temperature proton oxides such as yttrium-doped SrZrO3 and SrCeO3. A strong influence of water vapour on protonic conductivity was found also in Pb5GeO4(VO4)2 and Pb5SiO4(VO4)2 crystals with the apatite structure which, at T=700°C present a conductivity of 10-3 S/cm. These results provide guidelines for developing new commercial solid proton electrolytes with improved characteristics based on palmierate and apatite type oxides.