Systematic tuning of deposition potential to enhance storage and electrochemical performance of binder-free bismuth oxide (β-Bi2O3) thin film electrodes for supercapacitors

Abstract

In this study, we systematically investigated the influence of deposition potential on the structural, morphological, optical, and electrochemical properties of binder-free tetragonal bismuth oxide (β-Bi₂O₃) thin films electrodeposited onto fluorine-doped tin oxide (FTO)-coated glass substrates. The three prepared films consistently exhibited the stable tetragonal bismuth oxide (β-Bi₂O₃) phase across all deposition potentials of -1.1 V, -1.2 V, and -1.3 V. However, variations in deposition potential had a pronounced effect on the films’ crystallinity, optical band gap, surface morphology, and supercapacitive behavior. Notably, films deposited at -1.1 V and -1.3 V exhibited higher crystallinity levels of 61 % and 56 %, respectively, compared to 51 % for the film prepared at -1.2 V. The morphology of the bismuth oxide (β-Bi₂O₃) nanostructures demonstrated a transition from quasi-spherical particles to cauliflower-like nanostructures with increasing potential, which was accompanied by a notable reduction in the optical band gap, decreasing from 2.5 eV at -1.2 V to 2.29 eV at the higher deposition potential of -1.3 V. Electrochemical measurements further emphasized the significant impact of deposition potential on the supercapacitive performance, with the bismuth oxide (β-Bi₂O₃) film deposited at -1.1 V delivering a superior areal capacitance of 138.5 mF cm^-2 (325.3 F g^-1). markedly outperforming films deposited at higher potentials. Moreover, charge storage analysis demonstrated a shift in the dominant charge storage mechanism, transitioning from diffusion-controlled behavior at lower potentials to a more pronounced capacitive contribution at higher potentials. Overall, these findings underscore the critical role of deposition potential in tailoring the properties of bismuth oxide (β-Bi₂O₃) thin films for enhanced supercapacitive performance.