Amorphous LaAlO₃-derived electrolyte: Harnessing structural disorder for high proton conductivity in LT-CFC electrolytes

The pursuit of advanced electrolyte materials for low-temperature ceramic fuel cells (LT-CFCs) has led to the investigation of amorphous oxides with tailored structural and ionic transport properties. This work reports the strategic incorporation of the rare earth element lanthanum into amorphous alumina oxide (LAO). We designed it purposely to enhance ionic transport by defect engineering and microstructural optimization. Through a systematic variation in lanthanum concentrations (10 %, 20 %, 30 % and 40 %) to incorporate into alumina oxide, where the 30 % La-Alumina (30-LAO) is an optimal composition acted as an electrolyte in a fuel cell that exhibits a remarkable ionic conductivity of 0.16 S cm⁻¹ and a peak power density (PPD) of 810 mW cm⁻² at 500 °C. It represents a substantial enhancement in ionic conductivity and PPD over pure alumina (ionic conductivity and PPD (0.077 S cm⁻¹ and 476 mW cm⁻², respectively)). Interestingly, the incorporation of 30 % La into Alumina has not affected its amorphous structure. Moreover, this significant performance stems from the inherent properties of the amorphous phase, where structural disorder reduces ion-migration energy barriers and enables isotropic ionic pathways. Nonetheless, lanthanum incorporation is pivotal for tailoring the local structure, introducing defect sites, and enhancing short-range ionic dynamics, thereby further facilitating proton transport. By influencing the coordination environment and defect chemistry, lanthanum helps optimize the ionic conduction network, amplifying the synergy between amorphousity and defect engineering. Hence, the tailored disorder and dynamic ionic pathways uniquely position 30-LAO as a robust and efficient electrolyte for next-generation LT-CFCs. This study highlights the dual impact of structural amorphousity and lanthanum modification in advancing amorphous oxide electrolytes for energy-efficient fuel cell technologies.