Adjustable n-p-n gas sensor response of Fe3O4-HNTs doped Pd nanocomposites for hydrogen sensors

The Fe3O4-HNTs doped Pd nanocomposites were synthesized by the reduction-precipitation method. The surface modification by Pd is utilized to enhance the selectivity of the Fe3O4-HNTs doped Pd nanocomposites. The sensor shows the normal n-type response to other interfering gases; however, it shows a concentration-dependent n-p-n transition for its gas sensor response towards H-2. This unusual sensing characteristic can be described by the formation of n-Fe3O4-HNTs/p-Fe-O-Pd/n-Fe3O4 HNTs heterojunction structures. This type of gas sensors can be utilized in highly ultra-sensitive and selective H-2 sensing and this work also opens up a facile way for tailoring the selectivity of gas sensors by the surface modification.