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, Pd
₂
cluster and Pd
₃
cluster on the AlN nanotubes (AlNNTs) surface were initially studied. As the structure of Pd
₂
decoration on AlNNTs is similar to that of two single Pd atom decoration, only Pd-AlNNTs and Pd
₃
-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 Pd
₃
cluster reduced the energy band gap, and increases the electrical conductivity of AlNNTs, especially Pd
₃
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 H
₂
, CH
₄
, C
₂
H
₂
, and C
₂
H
₄
, were analyzed. These analyses indicated that Pd-AlNNTs and Pd
₃
-AlNNTs showed strong interaction to four gas molecules. Pd-AlNNTs and Pd
₃
-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 Pd
₃
-AlNNTs decreases the conductivity of the whole adsorption system.