  Electrochemical capacitors with pure electric double layer capacitance are so
far largely been limited to carbon materials only. Conventional metal oxides
with Faradaic pseudocapacitance substantially suffer from material instability
at high temperatures and thus there is a demand for novel metal oxides
exhibiting thermally improved high electric double layer capacitance with
material stability. In this study, titanium sesquioxide, Ti$_2$O$_3$, a Mott
insulator in its metallic state at 300$^o$ C showed an anomalous increase of
$\approx$ 560% in the solid-state electrochemical capacitance as compared to
its pristine response at room temperature (RT). In aqueous electrolyte, the
maximum capacitance was obtained up to 1053 $\mu$F/cm$^2$, which is 307% higher
than with solid-state electrolyte. Moreover, the semiconducting state of
Ti$_2$O$_3$ demonstrated $\approx$ 3500% enhancement in its electrochemical
capacitance upon infrared illumination at RT. The observed electrochemical
responses in Ti$_2$O$_3$ are attributed to the transition of semiconducting to
the metallic state by redistribution of the localized electrons. Our
experimental results find a good agreement with the first-principles
density-functional theory calculations that revealed an increase in the charge
density with the rise in temperature, which is mainly attributed to the surface
Ti atoms. The study open has wide avenues to engineer the electrochemical
double layer capacitance of theory calculations that revealed an increase in
the charge density with the rise in temperature, which is mainly attributed to
the surface Ti atoms. The study opens wide avenues to engineer the
electrochemical double layer capacitance of Ti$_2$O$_3$ with high chemical
stability.
