Modification of Ce valence states by Sm/Sr co-doping of CeO2 nanoparticles for improved magneto-electrochemical properties

Abstract

Improved magnetic and electrochemical properties of CeO2 nanoparticles were obtained by co-doping with Sm3+ and Sr2+ to attain Ce4+/Ce3+ states with the associated generation of oxygen vacancies. Ce1‑x‑ySmxSryO2 (x=0, y=0 and y=0.05 for x=0.05, 0.1 and 0.15) nanoparticles were synthesized using the polymer pyrolysis method and calcined at 700°C for 3h in air. The structure, morphology, valence states and optical properties of the nanoparticles were characterized using X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–Visible spectroscopy (UV–Vis). The magnetic and charge-discharge properties of the nanoparticles were investigated using a vibrating sample magnetometer (VSM) and a potentiostat/galvanostat electrochemical cell system, respectively. All samples exhibited a face-centered cubic structure and the Ce3+ and associated oxygen vacancies were observed in all samples with low dopant levels. The resulting materials all exhibited ferromagnetic (FM) behavior at room temperature (RT) with the largest coercivity measured being 1400Oe. The origin of the ferromagnetism is explained in terms of an oxygen vacancy mediated F-center exchange (FCE) mechanism. The discharge capacity of electrodes made from Ce1-x-ySmxSryO2 nanoparticles increased strongly with increasing numbers of oxygen vacancies.