Two-Dimensional Molybdenum Carbide MXenes for Enhanced Selective Detection of Humidity in Air.

Two-dimensional transition metal carbides and nitrides (MXenes) open up novel opportunities in gas sensing with high sensitivity at room temperature. Herein, we have successfully synthesized 2D Mo2 CTx flakes with high aspect ratio. We study the chemiresistive effect in a sub-μm MXene multilayer for different organic vapors and humidity at 101 -104  ppm in dry air. Reasonably, the low-noise resistance signal allows the detection of H2 O down to 10 ppm. Moreover, humidity suppresses the response of Mo2 CTx to organic analytes due to the blocking of adsorption active sites. By measuring the impedance of MXene layers as a function of ac frequency in the 10-2 -106  Hz range, we show that operation principle of the sensor is dominated by resistance change rather than capacitance variations. The sensor transfer function allows us to conclude that the Mo2 CTx chemiresistance is mainly originating from electron transport through inter-flake potential barriers with heights up to 0.2 eV. DFT calculations, elucidating the Mo2 C surface interaction with organic analytes and H2 O, explain the experimental data as an energy shift of the density of states under the analyte's adsorption which induces increasing electrical resistance. This article is protected by copyright. All rights reserved.