G, L.S.Bhat, K.S.Mukesh, P.Hegde, A.P.Kumar, A.Brijesh, K.Nagaraja, H.S.2026-02-032025Ionics, 2025, 31, 5, pp. 4955-49699477047https://doi.org/10.1007/s11581-025-06217-0https://idr.nitk.ac.in/handle/123456789/20312Binary metal oxides have emerged as pSromising materials for advanced electrochemical energy storage systems due to their superior performance characteristics. In this study, we focus on bismuth oxide (Bi?O?), a material renowned for its high theoretical capacity, wide potential range, and exceptional power density, as a potential candidate for supercapacitors. Iron doping was employed as a strategy to enhance its electrochemical performance and modulate the band gap, thereby improving conductivity and charge storage efficiency. Fe-doped bismuth oxide (Fe-Bi?O?) was synthesized via a solvothermal method with varying iron concentrations (2%, 4%, and 6%), followed by annealing. The pure and iron-doped bismuth oxide samples revealed a combination of monoclinic and cubic phases and a prominent micro-sheet architecture. The introduction of iron doping led to a noticeable reduction in the band gap, highlighting its role in fine-tuning the electronic properties for enhanced energy storage capabilities. The electrochemical evaluation highlighted the 4% Fe-Bi?O? sample as the optimal composition, achieving a remarkable specific capacity of 904 F g?1, a substantial improvement over 101 F g?1 for pristine Bi?O?, at 1 A g?1 in a 2 M KOH electrolyte. Moreover, this sample exhibited outstanding cyclic stability, retaining 104 F g?1 after 2000 cycles at 10 A g?1. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.Bismuth compoundsCapacitor storageElectrolytesSemiconductor dopingSupercapacitorBinary metal oxidesBismuth iron oxideBismuth oxidesElectrochemical energy storageFe 3+Iron dopingMicrosheetPseudocapacitorsSolvothermal methodStorage systemsPotassium hydroxide