LAUSR

Abstract The switch-type humidity and water sensing composite material is fabricated by decorating carbonic pen ink on carbon fiber paper (CFP) substrate using a facile and efficient dip-coating method. The resultant pen ink/carbon fiber paper composites (PCFP) with varying ink loading have both flexible paper and electroconductive ink characteristics, which exhibit favorable mechanical strength as well as controllable surface resistivities (Rs). As a humidity sensor, flexible PCFP demonstrates ultrahigh humidity sensitivity, extraordinary hysteresis and an adjustable switch point. The relative electrical resistance change (Rrel) of PCFP remains almost constant at low RH and increases radically at humidity switch point, showing commendable humidity switch behavior. PCFP also displays such switch property when immersing in water and reliable repeatability render PCFP opportunity to be a liquid water molecule sensor. Therefore, the multifunctional PCFP with excellent sensitivity and prominent reproducibility can be used for humidity and water monitoring in wearable electronics and sensing applications.