Phosphomolybdic Acid-Decorated Carbon Nanotubes for Low-Power Sensing of NH₃ and NO₂ at Room Temperature

Low-dimensional materials such as carbon nanotubes (CNTs) are promising candidates for gas sensing. Surface modification with specific molecules is considered an effective approach to enhance gas sensing. In this work, a kind of carbon hybrid is fabricated with phosphomolybdic acid (PMA) molecule-decorated single-walled CNTs (SWNTs) as a gas-sensing element and chemical vapor deposition-grown graphical graphene on prepatterned copper and nickel films as composite electrodes. According to the experimental results of NH3 and NO2 detection, the PMA-decorated carbon hybrids present much higher sensitivity, faster response, and lower power consumption than other previously reported oxide-modified CNT gas sensors. Responses of the DC resistance variation of approximately 23 or −21% to 5 ppm NH3 or NO2 are demonstrated at room temperature, with a power consumption of only hundreds of nanowatts (nWs). The enhanced gas sensitivity of the carbon hybrid is described by the first-principles calculation of the energy band and Schottky barrier in hybrid structures from the interface perspective. A significant change in Fermi level in SWNTs due to PMA decoration reduces the Schottky barrier at the SWNT/graphene interface and allows the hybrid to function at an appropriate status, which corresponds to a high response to the redox reaction between PMA and NO2 or NH3 molecules.