Metal- and Nitrogen-Codoped\nCarbon Nanotube Field\nEmitters for Low-Pressure Hydrogen Sensing

Metal-doped carbon nanotubes (CNTs) have great potential\nin hydrogen\ndetection because of their large specific surface areas, good catalytic\nactivity, and numerous defect states. However, CNT-based sensing materials\nhave the problem of insufficient hydrogen sensing responsiveness at\nlow pressure, and the effects of different types of catalytic metals\non low-pressure hydrogen sensing are still unknown. In this paper,\nlow-pressure hydrogen sensing properties were studied by construction\nof Fe/Co/Ni- and nitrogen-codoped CNT cathodes, and the pressure was\ndetected from 10<sup>–7</sup> to 10<sup>–4</sup> Pa.\nIn addition, the hydrogen sensing mechanism was studied using first-principles\nsimulations. The experimental results suggested that the Co–N-codoped\nCNT cathode exhibits the best hydrogen detection properties with a\nfield mission current increase of 224% in 5 min. Furthermore, the\nFE current could increase 145% in 1 min at a pressure of 4.28 ×\n10<sup>–4</sup> Pa, promising for quick detection. The simulation\nrevealed that the work functions of metal- and nitrogen-codoped CNTs\ndecreased rapidly with the increase of hydrogen atoms, leading to\nthe obvious improvement of hydrogen sensing properties. These conclusions\nnot only bring good insights into the hydrogen sensing enhancement\nmechanism for metal–nitrogen-codoped CNT cathodes but also\nprovide a promising way to develop practical cathodes for quick low-pressure\nhydrogen detections.