Evidence of proton transport in atomic layer deposited yttria-stabilized zirconia films

This study presents spectroscopic and electrochemical evidence that verifies proton transport in the temperature regime 300-450 °C in yttria-stabilized zirconia (YSZ) thin film membranes fabricated by atomic layer deposition (ALD). High-resolution X-ray photoelectron spectrometry (XPS) of O1s showed that the OH peak was significantly more pronounced in ALD samples than in single-crystal YSZ. Similarly, secondary ion mass spectrometry (SIMS) measurements, conducted for comparison on single-crystalline YSZ and atomic layer deposited YSZ, indicated that ALD YSZ contains 100 times higher deuterium concentration than single crystalline YSZ. SIMS depth profiles suggested diffusion of protons through protonic defects in YSZ. We have also fabricated fuel cells employing ALD YSZ with dense palladium layers to block oxygen but allow hydrogen transport. These performed as protonic fuel cells at intermediate temperatures achieving 10 mW/cm² at 450 °C. These results open the possibility to engineer ALD YSZ as electrolyte membranes for new protonic devices operating at relatively low temperature regimes.