Joint Theoretical and Experimental Study on the La Doping Process in In2O3: Phase Transition and Electrocatalytic Activity

Joint Theoretical and Experimental Study on the La Doping Process in In₂O₃: Phase Transition and Electrocatalytic Activity

Abstract: In₂O₃ and La³⁺-doped In₂O₃ nanostructures were synthesized through a facile and fast chemical route based on the microwave-assisted hydrothermal method combined with rapid thermal treatment in a microwave oven. The presence of the La³⁺ doping process modifies the size and morphology of the In₂O₃ nanostructures and also stabilizes the rhombohedral (rh) In₂O₃ phase with respect to the most stable cubic (bcc) polymorph. X-ray diffraction (XRD) patterns and Rietveld refinements, Raman, UV–vis, and energy dispersive X-ray (EDX) spectroscopies, transmission electron (TEM) and field-emission scanning electron (FE-SEM) microscopies, as well as PL emissions have been performed. To complement and rationalize the experimental results, first-principle calculations, based on density functional theory, are carried out to obtain the formation energies of the In₂O₃ and bcc- and rh-In₂O₃-doped phases, their geometry and electronic properties. Theoretical results are able to explain the relative stabilization of the rh-phase with respect to the bcc-phase based on the analysis geometry changes and the electronic redistribution induced by the La³⁺ doping process. In addition, Wulff construction is employed to match the theoretical and experimental morphologies of the cubic phase. The synthesized samples were applied for the O₂ evolution reaction (OER). The La³⁺-doped In₂O₃ film presents superior electrocatalytic activity, with an onset potential lower than the undoped In₂O₃ film that can be associated with the increase in electron density caused by the La³⁺ doping process. This study provides a versatile strategy for obtaining In₂O₃ and La³⁺-doped In₂O₃ nanostructures for practical applications.