Sensing study of Fe- and Zn-doped MXene Nb2CO2 for the detection of dissolved gases H2, C2H4, and C2H2 in transformer oil: A DFT study.

Internal faults in oil-immersed transformers release characteristic dissolved gases(H2, C2H4 and C2H2), making high-performance gas-sensing materials essential for early diagnosis. Herein, using density functional theory (DFT) construct intrinsic and Fe-and Zn-doped MXene-based Nb2CO2 monolayer models and systematically investigate the adsorption thermodynamics, electronic-structure responses, and sensing kinetics of these three gases on the surfaces. Through multi-dimensional analyses of adsorption energy, charge transfer, density of states, frontier molecular orbitals, work function, desorption time, and sensitivity. The results show that intrinsic Nb2CO2 exhibits only weak physisorption toward all three gases, yielding no detectable electrical response. Fe and Zn doping markedly enhance the surface capture capability: Fe-Nb2CO2 forms chemisorption with C2H4 (-1.840 eV)and C2H2 (-1.556 eV), whereas Zn-Nb2CO2 displays weak chemisorption with C2H4(-1.306 eV) and C2H2(-1.110 eV). Both doped surfaces retain weak physisorption toward H2.Fe-Nb2CO2 achieves a favorable desorption time(∼13 s)and the highest sensitivity for C2H2 at 598 K, revealing outstanding C2H2 sensing potential. However, its excessively slow C2H4 desorption makes it more suitable as a C2H4 adsorbent. Zn-Nb2CO2 gives a C2H4 desorption time of 16.49 s at 498 K with moderate sensitivity, appropriate for resistive C2H4 sensing. This work provides a theoretical foundation for designing low-power, high-sensitivity MXene-based gas-sensing materials for dissolved gas analysis in transformer oil.