Ion-conducting, sub-100 nm-thick film of amorphous hafnium silicate

Ceramic electrolytes operating in the temperature range of 200 to 500 °C under dry atmosphere are a key material for the next-generation fuel cell and related applications. We discovered that nanometer-thick films of amorphous hafnium silicate (HfnSi1 − nOx) exhibited efficient ionic conduction at 100–400 °C in dry air. When the fraction of hafnium doping was around 0.1, the nanofilm showed a low area-specific-resistance (< 0.15 Ω cm2) at around 350 °C that was small enough for the practical fuel cell application. The sub-100 nm-thick membranes of Hf0.13Si0.87Ox, could be fabricated on porous Pt/alumina substrate to provide gas concentration cells. The electromotive force observed with H2 concentration cell indicated that the ceramic nanomembrane acted as predominant proton conductor without permeation of H2 gas. In addition, the Hf0.13Si0.87Ox and Zr0.11Si0.89Ox membranes responded to the change of O2 pressures in O2 concentration cells, while the Al0.16Si0.84Ox and Ce0.06Si0.94Ox membranes did not produce the electrical voltage by gradient of O2 pressure. We conclude that Hf0.13Si0.87Ox nanomembrane is promising as electrolyte material for fuel cells and related ionics devices.