{111} faceted Li4Ti5O12 octahedra as the reference electrode material in a nanostructured potentiometric CO2 sensor

Abstract

A viable methodology for the synthesis of lithium titanate (Li₄Ti₅O₁₂) octahedra via a one pot hydrothermal route in an aqueous medium using CTAB has been demonstrated. The synthesized Li₄Ti₅O₁₂ octahedral nanoparticles were observed to be highly crystalline with a side edge length ranging from 30 to 120 nm. A plausible formation mechanism is put forth based on the findings obtained from the physicochemical characteristics supported by electron micrographs as a result of varying key parameters such as CTAB concentration, hydrothermal reaction time, and temperature. Furthermore, a critical evaluation of a potentiometric CO₂ sensor with {111} faceted Li₄Ti₅O₁₂ octahedral phase employed as the reference electrode, along with other nanoarchitectures, namely, 2D Li₂CO₃ flakes, 1D BaCO₃ rods, and 3D TiO₂ spheres, showed agreeable ‘n’ (number of cell reaction electrons) and EMF (electromotive force) values. EMF was found to be linear with the logarithm of CO₂ partial pressure in the test range of 100–10 000 ppm. The sensor not only showed fair Nernstian behavior but was also found to be stable in both dry and humid environments at 500 °C. When compared to a potentiometric CO₂ sensor fabricated using commercially available powders, a marked improvement in the sensor response was shown by the nanostructured sensor with a nearly six and three-fold enhancement in response and recovery time, respectively. The improved performance of the nanostructured potentiometric CO₂ sensor was attributed to the high crystallinity and tailored morphologies of the nanomaterials employed as the sensing and reference electrodes.