Multifunctional MXene-based smart thermal insulator for temperature sensing and ammonia leakage detection

• Ti 3 C 2 T X MXene is used to prepare MXene/melamine smart foam. • Smart foam integrates thermal insulation, temperature sensing, and ammonia detection. • Smart foam shows multifunctionality under liquid ammonia storage temperatures. • Smart foam is proposed as an advanced device for liquid ammonia storage systems. Demand for the safe storage of liquid ammonia is increasing from the interest in ammonia as zero-carbon fuel, hydrogen carriers. Although safety measures that serve individual tasks required for maintaining an optimal storage condition (thermal insulation, temperature detection, ammonia leakage detection) are available, multifunctionality is highly desired for reducing system complexity. In this work, Ti 3 C 2 T X MXene is used as a multifunctional material to function as both a temperature sensor and ammonia sensor. By using a highly porous melamine foam as the template, the MXene/melamine smart foam maintains 96.22 % of the temperature gradient at T sc =-50 °C after MXene coating. The Seebeck effect of Ti 3 C 2 T X MXene allows the detection of temperature from the change in a temperature gradient, which was demonstrated for both hot and cold temperatures. The MXene/melamine foam readily responds to the presence of ammonia gas due to the hydrophilic termination. A highly linear response of R 2 =0.9987 is observed over the concentration range of about 5-100 ppm. Moreover, a fast response, recovery time of 12.2 sec and 42.3 sec is achieved at 30 ppm NH 3 . Finally, the thermal insulation, temperature sensing, ammonia sensing performance of MXene/melamine smart foam is demonstrated under a simulated liquid ammonia storage condition of T sc =-40 °C.