Atomic layer deposition of thin-film ceramic electrolytes for high-performance fuel cells

This feature article provides a progress review of atomic layer deposition (ALD) for fabrication of oxide-ion as well as proton conducting ceramic fuel cells. A comprehensive analysis of structural, chemical, surface kinetics, and electrochemical characterization results of ALD membranes is also presented. ALD is a surface reaction limited method of depositing conformal, high quality, pinhole-free, uniform thickness nanofilms onto planar or three-dimensional structures. Deposition by one atomic layer at a time also affords unprecedented opportunities to engineer surface termination, to form compositionally graded structures or graded doping, and to synthesize metastable phases that cannot be realized otherwise. Indeed, thin ceramic electrolyte membranes made by ALD exhibit enhanced surface exchange kinetics, reduced ohmic losses, and superior fuel cell performance as high as 1.34 W cm^-2 at 500 °C. More importantly, ALD offers the opportunity to design and engineer surface structures at the atomic scale targeting improved performance of not only ceramic fuel cells, but also electrochemical sensors, electrolysers and pumps.