Anomalous Electronic and Protonic Conductivity of 2D Titanium Oxide and Low‐Temperature Power Generation Using Its Protonic Conduction

Abstract In this study, a titanium‐oxide film is fabricated by stacking 2D nanosheets with a thickness of 1 nm layer‐by‐layer. The electrical properties of the titanium‐oxide film are investigated under various temperatures (25–300 °C) and a water vapor atmosphere. As a result, it is found that protonic conduction is dominant at low temperatures (<100 °C), while electronic conduction is highest at high temperatures (>200 °C). The electrical conductivity is about one billion times higher than that of conventional 3D titanium‐oxide. Protons, dominant charge carriers at low temperature, are transported along the pathway between layers of nanosheets. The protonic conductivity is as high as 10⁻⁴⁻⁵ S cm⁻¹ due to the increased interfacial density of the film. This anomalous electronic and protonic conduction is expected to be available in various applications. In this study, the developed 2D titanium‐oxide with high protonic conductivity is employed in the solid electrolyte of a solid oxide fuel cell using water as a fuel. A competitive power density of ≈0.22 mW cm⁻² is obtained at low temperature (75 °C) under a water concentration gradient.