Energy Storage Capacity Studies of Frustrated Biphasic Carbon-Doped Zirconium Oxides

Pure zirconium oxides have a wide band gap energy with poor electronic conduction, leading to the limitations of potential applications in various fields. Attempts were made to synthesize biphasic zirconium oxides with three different levels of carbon doping to study and improve the electronic conductivity, tune the band gap, and investigating their energy storage capability. Carbon-doped zirconium oxides with a biphasic nature were prepared by the coprecipitation method using poly vinyl alcohol (PVA) as a carbon source mixed with a stoichiometry amount of the zirconium precursor, followed by annealing at three different temperatures, 100, 300, and 500 °C, resulting in three different samples, namely, C-ZO1, C-ZO2, and C-ZO3, respectively. The crystal structure, elemental, micro-structural, optical, room temperature dielectric, and electrochemical properties were studied and reported. Crystallographic information from X-ray diffraction and high resolution electron diffraction showed that all samples are biphasic (monoclinic and tetragonal) nanocrystalline materials, Raman and FT-IR studies also support the claim. The sample crystallinity improved with the increasing annealing temperatures, whereas X-ray photoelectron spectroscopy results exposed carbon content and oxygen compositions vary inversely with annealing temperatures. The optical band gap measurement results showed that all samples have an indirect band gap. Room-temperature dielectric studies showed a higher dielectric constant for C-ZO3 samples compared to the other two samples. The electrochemical studies confirmed that all materials showed Faradaic pseudocapacitive behavior and good stability up to 1000 cycles, having retention up to ∼85% and above. Power density is equal for all three samples, whereas higher energy density was obtained for C-ZO3 samples. This concluded that the biphasic zirconium oxide with composition Zr0.91C0.09O1.21 showed superior electrochemical and dielectric behavior, which will find potential application as energy storage devices.