The protons are the key players in ceramic proton conductors. But they are very elusive and had to detect. I will shows a suite of experiments, ex situ, in situ and operando, where the protons are shown as structural elements at low temperatures where they do not yet constitute charge carriers. They actually constitute OH groups in the crystal lattice. With increasing temperature, the protons participate with the lattice vibrations while and OH-bond breaking takes place at some transition temeprature where the protons become charge carriers. We have observed this on the Y-doped BaZrO3 and BaCeO3 model proton conductors with quasi elastic neutron scattering under ambient and under high temperature high pressure conditions. The phonon modes as determined from high presssure Raman spectroscopy propel the protons and cause a net protonic charge transfer via phonons. The changes in the chemical bond environment were observed with ambient pressre x-ray spectroscopy, particular changes in the oxygen core lecvel spectra and the Ce, Y and Zr resonant valence band spectra under humidified high temperature conditions. We are able to sketch the changes in bond breaking at exactly the temperature where the ptoton conductivty sets on.

[1] Q. Chen, F. El Gabaly, F. Aksoy Akgul, Z. Liu, B.S. Mun, S. Yamaguchi, A. Braun, Observation of 8.238 oxygen vacancy filling under water vapor in ceramic proton conductors in-situ with ambient pressure XPS; Chem. Mater., 2013, 25 (23), pp 4690–4696.

[2] Q. Chen, J. Banyte, X. Zhang, J. P. Embs, A. Braun; Proton Diffusivity in Spark Plasma Sintered BaCe0.8Y0.2O3-δ: in-situ combination of quasi-elastic neutron scattering and impedance spectroscopy; Solid State Ionics 252 (2013) 2–6.

[3] Q. Chen, T.-W. Huang, M. Baldini, A. Hushur, A. Pomjakushin, S. Clark, W. Mao, M. Manghnani, A. Braun, T. Graule, The Effect of Compressive Strain on the Raman Modes of the Dry and Hydrated BaCe0.8Y0.2O3 Proton Conductor, J. Phys. Chem. C, 2011, 115 (48), pp 24021–24027.