Being stable to carbonization, praseodymium nickelates-cobaltites and their nanocomposites are promising materials for intermediate-temperature solid oxide fuel cells (IT SOFC) cathodes and oxygen separation membranes. This work aims to elucidate specificity of their structure and transport properties on the basis of synchrotron radiation studies. PrNi0.5Co0.5O3-δ (PNC), Ce0.9Y0.1O2-δ (YDC), Ce0.65Pr0.25Y0.1O2-δ (YPDC), CeO2 and PrO2-δ powders were synthesized with the Pechini technique. PNC - YDC nanocomposite was obtained via ultrasonic dispersion. The materials were characterized in in situ synchrotron XRD analyses with unit cell volume relaxation (CVR) and extended Xray absorption fine structure (EXAFS). Bulk and surface oxygen mobility and reactivity were studied with O2 temperature- programmed desorption and CVR methods. Strong cation redistribution between domains was revealed. Fast oxygen diffusion and exchange in the PNC - YDC nanocomposite were shown to be determined by developed interface and variation in the Pr3+/4+ cations' charge in the Y-Pr-Ce-O domains. Selected compositions were deposited as functional layers in asymmetric membranes for oxygen separation. According to the test results, the membranes demonstrated promising performance.