Nanoionic proton conductivity enhancement in solid-state reactive sintered BariumCerium(0.7)Zirconium(0.1)Yttrium(0.1)Ytterbium(0.1)Oxygen(3-delta)

Abstract

The holy grail in the field of proton-conducting oxides is to decrease their minimum operating temperature so that they may be used in a wider variety of applications. In addition to this challenge, new synthesis techniques are needed so that these materials can be produced with greater ease and lower cost. The possibility of exploiting nano-scale interfacial phenomena in solid-state ionic materials has risen to prominence. However, this approach, dubbed "nanoionics" by the scientific community, has not been widely applied to proton conductors, with only a few studies showing modest improvements. In this study, a novel approach is taken to create nanoionic interfaces in a high-performing proton conductor, BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3-δ (BCZYYb). Thin nickel metal films are created at the grain boundaries of the BCZYYb bulk phase, creating space-charge layers at the interfaces. These nanoionic space-charge layers create a dramatic enhancement (up to 32X) in ionic conductivity. Using isotope and concentration cell experiments, which have never before been conducted on a proton conductor/metal nano-composite, it is shown that the enhancement is indeed protonic, suggesting space-charge layer enhancement. In addition to demonstrating a large nanoionic enhancement, the synthesis technique employed in this work used offers commercial viability. Using the recently discovered solid-state reactive sintering (SSRS) technique, these membranes are 1/10th the cost of normal polymeric/sol-gel synthesized materials, and in addition require less processing time due to the removal of the calcination step and the lower required sintering temperatures.