Disordered Pr-alumina: Enabling fast proton dynamics across energy systems

This research unveils a groundbreaking class of amorphous semiconducting oxide electrolytes, spotlighted by Praseodymium-doped alumina (Pr_0.2Al_0.8O), which redefines ionic conduction principles with its exceptional proton conductivity and wide-ranging applications. Unlike conventional proton-conducting materials like barium zirconate (BZY) and Barium Cerate (BCY), which achieve 0.1 S/cm only at or above 800 °C, Pr-doped amorphous alumina demonstrates 0.165 S/cm at 550 °C, which is over an order of magnitude higher at much lower operating temperatures. Through the strategic doping of Pr, we successfully lower the band gap of undoped wide band gap alumina, bringing it into the semiconductor range with a band gap of 3.01 eV, benefiting semiconducting properties and disorder nature of material we achieved a power density of 971 mW/cm² and a stable operation with open circuit voltage (OCV) of 1.13 V. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) reveal exceptional weight loss and anomalous thermodynamic kinetics, which are not typically observed in crystalline proton conductors. This higher weight loss aids in the formation of oxygen vacancies, as confirmed by XPS and EPR analyses, which directly contribute to enhanced proton conductivity. Due to the high number of available configurational states and greater accessibility of hopping sites, Pr-doped amorphous alumina offers a lower electrochemical potential for protons. This is demonstrated by its reduced activation energy of 0.22 eV, significantly lower than the 0.52 eV observed for BZY, indicating that protons can move more easily through the material, enhancing its conductivity. This work highlights the advantages of amorphous oxide semiconductors, positioning Pr_0.2Al_0.8O as a promising candidate for future ion-conducting technologies. Our prepared amorphous semiconducting material opens a new path for researchers, offering innovative opportunities in the development of advanced ion-conducting applications.