Anomalous electrochemical capacitance in Mott insulator titanium sesquioxide

TL;DR

This study demonstrates that titanium sesquioxide (Ti₂O₃), a Mott insulator, exhibits an anomalously high increase in electrochemical capacitance at elevated temperatures and under infrared illumination, promising for stable high-capacity energy storage.

Contribution

The paper reports the discovery of anomalous electrochemical capacitance enhancement in Ti₂O₃, a thermally stable Mott insulator, supported by experimental and theoretical analysis.

Findings

560% increase in solid-state capacitance at high temperature

1053 μF/cm² maximum capacitance in aqueous electrolyte

3500% capacitance enhancement under infrared illumination

Abstract

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.