Metal- and Nitrogen-Codoped Carbon Nanotube Field Emitters for Low-Pressure Hydrogen Sensing

Metal-doped carbon nanotubes (CNTs) have great potential in hydrogen detection because of their large specific surface areas, good catalytic activity, and numerous defect states. However, CNT-based sensing materials have the problem of insufficient hydrogen sensing responsiveness at low pressure, and the effects of different types of catalytic metals on low-pressure hydrogen sensing are still unknown. In this paper, low-pressure hydrogen sensing properties were studied by construction of Fe/Co/Ni- and nitrogen-codoped CNT cathodes, and the pressure was detected from 10^–7 to 10^–4 Pa. In addition, the hydrogen sensing mechanism was studied using first-principles simulations. The experimental results suggested that the Co–N-codoped CNT cathode exhibits the best hydrogen detection properties with a field mission current increase of 224% in 5 min. Furthermore, the FE current could increase 145% in 1 min at a pressure of 4.28 × 10^–4 Pa, promising for quick detection. The simulation revealed that the work functions of metal- and nitrogen-codoped CNTs decreased rapidly with the increase of hydrogen atoms, leading to the obvious improvement of hydrogen sensing properties. These conclusions not only bring good insights into the hydrogen sensing enhancement mechanism for metal–nitrogen-codoped CNT cathodes but also provide a promising way to develop practical cathodes for quick low-pressure hydrogen detections.