Cobalt-doped praseodymium nickelate PrNi1-xCoxO3-delta (PNCx) and Y-doped ceria Ce0.9Y0.1O2-delta (YDC) oxides were synthesized via Pechini route. PNCx + YDC composites were prepared via ultrasonic dispersion of the mixture of perovskite and fluorite nanopowders in isopropanol with addition of polyvinyl butyral followed by drying, pressing and sintering at 1300 degrees C. The oxygen mobility and reactivity of powdered PNCx and composites obtained by crushing and milling of dense pellets were estimated by O-2-TPD and oxygen isotope exchange with O-18(2) and (CO2)-O-18 using both static and flow (SSITKA) reactors in isothermal and temperature-programmed (TPIE) modes. For PNCx samples sintered at 1300 degrees C comprised of (Ni,Co)O and Ruddlesden-Popper type phases (Pr2NiO4, Pr-4(Ni,Co)(3)O-10), the oxygen mobility and reactivity tend to decrease with Co content. For composites, the oxygen mobility is much higher due to Pr transfer into YDC thus disordering perovskite-like and fluorite-like phases. TPIE (CO2)-O-18 SSITKA experiments combined with SIMS analysis of the depth profiles of (PrO)-O-18 and (CeO)-O-18 suggest that fast oxygen diffusion in composites is provided by domains of disordered perovskite-like phases as well as Pr, Y-doped ceria. For best composites, the value of the oxygen chemical diffusion coefficient estimated by the weight relaxation technique exceeds that of well known LSFC-GDC composite. (C) 2014 Elsevier B.V. All rights reserved.