First-Principles Calculations of Gas-Sensing Properties of Pd Clusters Decorated AlNNTs to Dissolved Gases in Transformer Oil

The potential decoration structures of Pd atom, Pd₂ cluster and Pd₃ cluster on the AlN nanotubes (AlNNTs) surface were initially studied. As the structure of Pd₂ decoration on AlNNTs is similar to that of two single Pd atom decoration, only Pd-AlNNTs and Pd₃-AlNNTs were further analyzed. It is found that Pd atom and Pd3 cluster preferred to adsorb on the surface surrounding N atom. Pd atom and Pd₃ cluster reduced the energy band gap, and increases the electrical conductivity of AlNNTs, especially Pd₃ decoration. The adsorption behavior, charge transfer, densities of states, projected densities of states, and molecular orbital analysis of AlNNTs towards four oil-dissolved gases, including H₂, CH₄, C₂H₂, and C₂H₄, were analyzed. These analyses indicated that Pd-AlNNTs and Pd₃-AlNNTs showed strong interaction to four gas molecules. Pd-AlNNTs and Pd₃-AlNNTs acted as the electron donators by transmitting electrons to the gas molecules during the interaction. According to the analysis of gas-sensing response, gas molecules adsorption on Pd-AlNNTs and Pd₃-AlNNTs decreases the conductivity of the whole adsorption system.