Two-Dimensional CrCl₃-Layered Trihalide Nanoflake Sensor for the Detection of Humidity, NO₂, and H₂

This study demonstrates that few-layer two-dimensional (2D) CrCl 3 transition-metal trihalides (TMTHs; MX 3, where M = Ti, V, Cr, Mo, Fe, Ru, and X = Cl, Br, or I) exhibit promising capabilities as chemoresistive sensors for humidity and NO 2, H 2, and NH 3 gases, representing suitable 2D interfaces for gas-sensing applications. Liquid-phase-exfoliated 2D-CrCl 3 flakes spin-coated over interdigital substrates exhibit higher chemical stability than CrI 3 and VI 3 with an excellent reproducible and long-term stable electrical response at an operating temperature (OT) of 100 °C in dry/wet air environments. Results show that with an increase/decrease in resistance, 2D-CrCl 3 exhibits p -type responses to NO 2 (400 ppb to 1 ppm) and H 2 O (10–80% relative humidity (RH) at 25 °C), H 2 (10–250 ppm), and NH 3 (10–250 ppm) oxidizing/reducing gases, respectively. The humidity cross-response of 2D-CrCl 3 to NO 2 reveals that an environment with 40% RH improves the relative responses and limits of detection of exfoliated CrCl 3 . The humidity- and gas-sensing response mechanism of 2D-CrCl 3 sensor explains its reversal in resistance from an ionic (OT = 25 °C) to an electronic conduction regime (OT = 100 °C) under humid air conditions. These findings provide insights and possibilities for using 2D-CrCl 3 TMTHs as humidity- and gas-sensing interfaces.