Realization of Oriented and Nanoporous Bismuth Chalcogenide Layers via Topochemical Heteroepitaxy for Flexible Gas Sensors

Most van der Waals two-dimensional (2D) materials without surface dangling bonds show limited surface activities except for their edge sites. Ultrathin Bi 2 Se 3 , a topological insulator that behaves metal-like under ambient conditions, has been overlooked on its surface activities. Herein, through a topochemical conversion process, ultrathin nanoporous Bi 2 Se 3 layers were epitaxially deposited on BiOCl nanosheets with strong electronic coupling, leading to hybrid electronic states with further bandgap narrowing. Such oriented nanoporous Bi 2 Se 3 layers possessed largely exposed active edge sites, along with improved surface roughness and film forming ability even on inkjet-printed flexible electrodes. Superior room-temperature NO 2 sensing performance was achieved compared to other 2D materials under bent conditions. Our work demonstrates that creating nanoscale features in 2D materials through topochemical heteroepitaxy is promising to achieve both favorable electronic properties and surface activity toward practical applications.