<p>Developing efficient and sustainable energy storage systems is critical to advancing modern technologies. Supercapacitors, offering high power density and long cycle life, are pivotal in this domain. This work investigates the potential of using Er-doped titania films as electrode materials for supercapacitors. The physical properties of an Er-doped titania film compared to those of an undoped titania film were investigated through detailed characterization. Electrochemical characterization revealed that Er-doped titania exhibits remarkably enhanced specific capacitance, rate capability, and energy density in both KOH and H₂SO₄ electrolytes, accompanied by improved cycling stability. More specifically, the specific capacitances of the undoped titania film are 133.7 and 94.9&#xa0;F∙g^‒1 at a scan rate of 50 mV∙s^‒1 in KOH and H₂SO₄ electrolytes, respectively. Introducing Er ions into titania films, increasing the specific capacitance to 171.5 and 104.0&#xa0;F∙g^‒1 in KOH and H₂SO₄ electrolytes, respectively. These findings offer crucial insights into how rare-earth doping can effectively tailor the properties of metal oxide films, thereby contributing to the design of next-generation energy storage devices.</p>