Alkaline earth metal-doped La2Ce2O7 mixed-conductors: optimization of hydrogen permeation and environmental stability

Abstract

To enhance the conductivity of La₂Ce₂O₇ (LCO) for use as the proton-conducting phase in mixed-conducting membranes, alkaline earth metal ions (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) were substituted for 15 % of the La sites, forming La_1.85X_0.15Ce₂O_7-δ (LXCO, X = Mg, Ca, Sr, Ba) solid solutions. This doping strategy significantly increased oxygen vacancy concentration and improved conductivity, with La_1.85Mg_0.15Ce₂O_7-δ (LMCO) exhibiting the highest conductivity (0.028 S cm⁻¹ at 800 °C). A mixed-conducting membrane was fabricated using LXCO as the proton-conducting phase and Ni as the electronic-conducting phase. Optimizing the volume ratio of Ni to LMCO at 4:6 yielded a hydrogen permeation flux of 3.45 × 10⁻⁸ mol·cm⁻²·s⁻¹. The membrane demonstrated excellent stability during a 100-h exposure to impurity gases, with no significant degradation in phase structure or microstructure. These results highlight the potential of LMCO-based membranes for practical hydrogen separation applications.