Tailoring mixed ionic–electronic conduction in H2 permeable membranes based on the system Nd5.5W1−xMoxO11.25−δ

Abstract

Lanthanide tungstates (Ln₆WO₁₂) are promising candidates for the development of ceramic hydrogen transport membranes since they exhibit mixed ionic (proton and oxygen ion transport) and electronic conductivity and remarkable stability in a moist CO₂ environment at high temperatures. This work presents the structural and electrochemical characterization of mixed conducting materials for the specific system Nd_5.5W_1−xMo_xO_11.25−δ (x = 0, 0.1, 0.5 and 1). Evolution of the crystalline structure is studied as a function of the sintering temperature. Shrinkage behavior is analyzed for all compositions in the temperature range from 1000 °C to 1500 °C and these compounds show high sintering activity even at relatively low temperatures. The total conductivity in different environments is studied systematically for samples sintered at 1350 °C. The H/D isotopic effect is also studied by DC-electrochemical measurements. H₂ permeation is investigated for the selected compound Nd_5.5W_0.5Mo_0.5O_11.25−δ in the range of 700–1000 °C achieving values of 0.3 mL min⁻¹ cm⁻² for a 0.9 mm thick disc membrane. Finally, the stability of this material under different CO₂ and H₂S-rich atmospheres at high temperatures is proven.