Journal
ACS APPLIED ENERGY MATERIALS
Volume 2, Issue 4, Pages 2611-2619Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsaem.8b02222
Keywords
zirconates; defect engineering; proton conductivity; hydrogen fuel cells; acceptor doping
Funding
- National Science Foundation (NSF) Graduate Research Fellowship Program [1650114]
- Office of Science of the U.S. Department of Energy (DOE) [DE-FG02-07ER46434]
- Office of Science of the U.S. DOE [DE-AC02-05CH11231]
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Alkaline-earth zirconates (CaZrO3, SrZrO3, and BaZrO3) are under active investigation as solid-state electrolytes in hydrogen fuel cells. Their performance as proton conductors depends critically on the properties of acceptor dopants. Here, we use first-principles calculations to study the role of acceptors and point defects in incorporating protons through an oxygen-vacancy-mediated process. For CaZrO3, we find that Zr-ca antisites suppress formation of oxygen vacancies. Other intrinsic point defects are shown not to hinder performance. Common unintentional impurities, such as N and C, are not good acceptors but can incorporate in other configurations. Our results show that the effectiveness of common dopants such as Sc and Y is limited by self-compensation due to their incorporation on the wrong cation site, where they act as donors. We demonstrate that using alkali metal dopants overcomes this problem, as the formation energy of compensating donors is very high. Alkali metal dopants also have low binding energies for protons, reducing their tendency to act as traps and hence enhancing proton conductivity. Our guidelines for choosing acceptor dopants and optimizing synthesis conditions can greatly improve the efficacy of these proton-conducting oxides as solid-state electrolytes.
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