This work presents the structural and electrochemical characterization of mixed conducting materials based on the system Nd5.5W1-xUxO11.25-delta where x = 0.1, 0.5 and 1. The evolution of the crystalline structure is studied as a function of the sintering temperature and the U content in the oxide lattice. The influence of hydration and pO(2) as well as the H/D isotopic effect are studied by DC-electrochemical measurements under reducing environments. Hydrogen permeation is carried out for Nd5.5WO11.25-delta and Nd5.5W0.9U0.O-1(11.25-delta) compounds in the range from 650 to 750 degrees C. Finally, stability of the developed materials at 800 degrees C is evaluated in contact with CO2-rich gas streams. This work completes previous reported studies On Ln(6-x)WO(12-y) based materials that show the possibility of engineering the conductivity properties of the Ln(6-x)WO(12-y) just by doping strategies. (C) 2015 Published by Elsevier B.V.