Hierarchical Bi2O3–CeO2 nanocomposites for multi-functional applications: Dielectric-Driven humidity sensing and electrochemical energy storage

Abstract

The bismuth–cerium bimetallic oxide (Bi₂O₃/CeO₂) nanocrystals were synthesized using a hydrothermal method and thoroughly analyzed for their dielectric, electrical, and electrochemical properties over a wide range of temperatures and frequencies. The nanocrystals exhibited significant dielectric relaxation and field-driven polarization characteristics, with the improved capacitive response at elevated temperatures being linked to thermally activated space-charge polarization within the Bi–O framework. A maximum dielectric constant (ε′) of 22.14 was recorded at 340 K, and the steady decline in dielectric loss with increasing temperature suggested enhanced dielectric stability and lower energy dissipation during thermal stress. The optimized Bi₂O₃/CeO₂ (1:1.25) composition demonstrated remarkable humidity sensitivity, low impedance, and excellent reversibility while exhibiting low hysteresis (∼ 1.2 % RH), affirming its multifunctional capabilities. The electrochemical analysis demonstrated a specific capacitance of 513 F/g at a scan rate of 5 mV/s (CV) and 410 F/g at a current density of 3 A/g (GCD), indicating exceptional charge storage capacity and stability under varying rates. The findings emphasize that the combined effect of Bi³⁺ and Ce⁴⁺ ions facilitates effective charge transfer, defect-mediated conduction, and consistent polarization dynamics. The Bi₂O₃/CeO₂ nanostructure presents itself as a compelling option for high-temperature dielectric applications, humidity sensors, and advanced electrochemical energy storage systems. Future exploration of flexible or integrated energy-sensor platforms may significantly enhance their technological applicability in multifunctional smart devices.