Hollow Nanospheres of Red Phosphorus for Fireproof Flexible Sensors Fabricated via 3D Printing

High-power and high-temperature applications have brought increased demand for electrical sensing systems; however, conventional sensors have often been designed without consideration for stability in extreme environments (e.g., fire). Red phosphorus (RP) is a highly effective commercial flame retardant; however, its sensitive properties and large size predispose it to spontaneous combustion during shearing and make it difficult to combine with direct inkjet writing technology carrying micron-sized pinholes to fabricate sophisticated sensor devices. Here, bulk commercial red phosphorus (C-RP) is converted into red phosphorous hollow nanospheres (RPHNs). The ingeniously designed nanostructure effectively circumvents the flammability of C-RP extrusion processes and the risk of clogging the printing needle, and a fireproof pressure-sensitive sensor has been successfully fabricated. A load of RPHNs into a sensor matrix improves the moldability and fire safety properties. And with the assistance of the rapid charring mechanism, the peak of the heat release rate of the fireproof pressure-sensitive sensor is reduced by 58.9% compared to the pure matrix and withstands seven 2-s repetitive ignitions, thus allowing the sensor to respond continuously to flame stimulation. This work provides a broad perspective on the design of fireproof sensors and the application of red phosphorus hollow nanospheres.