Quasi-elastic neutron scattering reveals fast proton diffusion in ca-doped LaPO₄

We have investigated the diffusion dynamics of protons in hydrated 4.2% Ca-doped LaPO₄, a candidate electrolyte for proton-conducting intermediate temperature fuel cells. The macroscopic and microscopic dynamics have been studied using electrochemical impedance spectroscopy (EIS) and quasi-elastic neutron scattering (QENS), respectively. The conductivity of the bulk hydrated sample was determined in the temperature range of 500-850 °C by EIS and showed a clear signature of proton conductivity with an activation energy of about 1.0 eV. The QENS experiment revealed a fast dynamical process below 500 °C that was not observed by EIS. The activation energy of the fast proton diffusion is 0.09 eV in the temperature range from 150 °C to 500 °C.