Facile fabrication of Ag-doped graphene fiber with improved strength and conductivity for wearable sensor via the ion diffusion during fiber coagulation

Graphene fibers with excellent mechanical and electrical properties are in great demand in the field of modern wearable microelectronics. However, presently the strength and electrical conductivity of graphene fibers are difficult to meet the requirements, limiting their application in wearable sensors. Herein, a facile approach is proposed for fabricating Ag-doped reduced graphene oxide fiber (Ag-rGOF) via introduction of Ag ion (Ag+) into fluid graphene oxide fiber (GOF) in the coagulation bath during wet-spinning followed by chemical reduction. The addition of Ag+ is beneficial to fiber coagulation and improves not only conductivity of the fiber, but also its mechanical properties. The tensile strength reaches up to 334 MPa and the conductivity to 1.14 ? 104 S/m, about 4 times as high as that of reduced graphene oxide fiber (rGOF). The fibrous strain sensor based on Ag-rGOF prepared with thermoplastic polyurethane as support shows high gauge factor of 177 at over 20% strain, rapid response time of 55 ms, and outstanding durability after 1000 stretch/release cycles. We also demonstrate that the fibrous sensors can be attached on skin to monitor sensitively facial expression and human motions.