The main theme of this presentation is to cross-link several techniques including DFT calculations and neutron techniques to discuss the medium-low temperature (150℃ to 450℃) protonic conduction in barium-based perovskite system.

Protonic conducting fuel cells (PCFC), compared with conventional oxide-ion conductors, generally possess the advantage of lower operating temperatures, due to the smaller activation energy required for the protonic hopping.

BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ (BZCYYb), reported by Yang et al. [1] was regarded as the promising PCFC due to its high ionic (mixed protonic and oxide-ion) conductivity (10² Scm^-1 at 600 ℃) under humid condition. However, this measured conductivity was not solely the protonic part, and other components such as electronic conduction (from the change of oxidation state in cerium) also contribute. Moreover, there are few studies focusing on the medium-low-temperature (<500℃) protonic conduction, at which the PCFC should possess more advantages.

In order to evaluate the medium-low temperature protonic conduction of BZCYYb, four topics are included in this presentation: The effect of hydrogen incorporation (via hydration annealing) on the crystal structure by X-ray Diffraction (XRD) and Neutron Diffraction (ND); The localised proton motion probed by Density Functional Theory (DFT) calculation and Quasi-Elastic Neutron Scattering (QENS) techniques [2]; The long-range protonic diffusion measured by EIS and Isotopic-exchange Secondary-Ion Mass Spectrometry (SIMS) methods; The proton/hydration incorporation amounts measured by Thermogravimetric Analysis (TGA) and Neutron Prompt-gamma ray Activation Analysis [3] (PGAA) techniques.

As suggested in the Grotthuss mechanism[4], proton incorporation is accompanied with the hydrated condition. In first section (hydration incorporation effect), the change of crystal structure after hydration annealing will be discussed. Though many existing literature discovered the phase transition of BZCYYb with increasing temperature[5], the effect of hydration is not available. The high-temperature XRD complemented with ND technique are applied to study the relationship between hydration and phase transition.

BZCYYb achieves higher conductivity than its undoped primitive BaCeO3 with small percent of b-site doping, but the localised effect brought by this small degree of doping is not well discussed. With better understanding of the structure change with humid annealing, in second section (localised proton motion), the localised hopping information such as hopping distance, preferred route and activation energy will be suggested by complementing the QENS data with ab-initio molecular dynamics (AIMD) and Nudged Elastic Band (NEB) calculation.

Generally, the protonic conductivity will be measured by EIS under dry and humid condition, but the obtained conductivity can be affected by other terms such as electronic and oxide-ion conduction. In third section (long-range protonic diffusion), by applying the Nernst Einstein equation [6] the tracer coefficient of proton isotope measured by SIMS could suggest its corresponding protonic conductivity .

To connect the diffusion coefficient with conductivity by Nernst Einstein equation, the concentration of incorporated protons is needed, but the exact number of protons in BZCYYb system is missing. Though normally proton/hydration incorporation is measured by TGA in an indirect way [5], the measured mass change can be affected by other factors such as change in oxygen stoichiometry. In fourth part (amount of incorporated protons), the PGAA neutron technique is applied to measure the proton amount directly, hence to obtain the amount of hydrogen under different annealing conditions.

In summary, the unique points of this research is applying "proton-sensitive" techniques (which could locate directly the proton dynamics and incorporation amount) and cross-linking them to evaluate the medium-low temperature protonic conductivity of BZCYYb system.