Tailoring Alkaline Metals Ion-Doped La₂Ce₂O_7- Proton Conductor for Hydrogen Permeation Membranes

With the extensive use of hydrogen energy, hydrogen separation membranes with proton-electron mixed conductors have broad application prospects in hydrogen separation and purification. Herein, La1.85M0.15Ce2O7-delta (M = Li, Na, K, Rb, and Cs; LMC) proton conductors are prepared. The electron paramagnetic resonance, Raman, and X-ray photoelectron spectroscopy results indicate that the proposed method of replacing part of the La3+ in La2Ce2O7-delta with alkali metal ions produces more oxygen vacancies, which provides more possibilities for ion transport. Among them, La1.85Rb0.15Ce2O7-delta (LRC) exhibits the highest oxygen vacancy concentration. In addition, as the radius of the alkali metal doping ions increases, the corresponding LMC grains also increase. However, an excessively large ionic radius (Cs+) can hinder grain growth. LRC has the largest ionic radius, indicating that it has a smaller grain boundary resistance. This results in the maximum conductivity of the LRC (2.99 x 10(-2) S cm(-2)) in the atmosphere of wet 20% H-2 + 80% N-2 at 900 degrees C. Similarly, in the hydrogen permeability test, the LRC exhibits the highest hydrogen flux (2.74 x 10(-9) mol cm(-2) s(-1)) at 900 degrees C. Moreover, an increase in temperature and hydrogen partial pressure on the feed side can promote hydrogen permeability. Therefore, it is a potential material for ceramic hydrogen separation membranes.