Synthesis of multishelled SnOx/Co3O4 amorphous/crystalline heterophase with galvanic replacement reaction for superior HCHO sensing

Amorphous/crystalline heterophase composites possess expansive reaction interfaces and abundant oxygen vacancy defects, providing novel electron-hole transmittal mode and significantly facilitating the surface adsorptions and redox reactions . Herein, galvanic replacement reaction (GRR) was used to construct amorphous SnO x / crystalline Co 3 O 4 multishell heterostructures . Characterizations indicated the continuous transition from Co 3 O 4 to amorphous SnO x on each shell, generating abundant amorphous/crystalline interfaces. Moreover, the oxygen vacancy defects concentration also increased with the GRR proceeding. Benefitting from theses, the surface oxygen adsorption was facilitated due to more surface active sites and enhanced carrier densities. However, with further increasing the reaction time, decreased adsorbed oxygen concentrations were detected, owning to the unexpected high potential barriers induced by excessive heterojunctions . Gas sensing results showed that the sensors with 1 h GRR exhibited the best sensing performance with an exceptional response (1268) to 100 ppm formaldehyde gas and low detection limit (21 ppb) at low working temperatures (100 °C). The synergistic effects between oxygen vacancy defects and amorphous/crystalline heterophase interfaces on the superior gas sensing behaviors were also investigated. Most importantly, results presented will shed lights on the rational design of highly sensitive gas sensors through amorphous/crystalline interfaces constructions.