Chemical stability in H₂S and creep characterization of the mixed protonic conductor Nd$_{5.5}$WO$_{11.25-δ}$

The integration of hydrogen permeable membranes in catalytic membrane reactors for thermodynamically limited reactions such as steam methane reforming can improve the per-pass yield and simultaneously produce a high-purity H2 stream. Mixed protonic-electronic materials based membranes are potential candidates for these applications due to their elevated temperature operation, good stability and potentially low cost. However, a specific mechanical behavior and stability under harsh atmospheres is needed to guarantee sufficient lifetime in real-world processes. This work presents the mechanical characterization and a study of the chemical stability under H2S containing atmospheres for the compound Nd5.5WO11.25-δ. Mechanical characterization was performed by micro-indentation and creep measurements in air. Chemical stability was evaluated by XRD and SEM and the effect of the H2S on the transport properties was evaluated by impedance spectroscopy. Under H2S atmospheres, the total conductivity increases at 600 °C and 700 °C. The conductivity increase is attributed to the incorporation of S2− ions in oxide-ion sublattice.