Screen-printable water-based poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/ polypyrrole/ reduced graphene oxide ink for micro-supercapacitor and humidity sensor

The growing interest in multifunctional conductive ink formulations aligns with the growing demand for flexible devices such as energy storage systems and sensors. However, the integration of hydrophobic and hydrophilic materials in a water-based ink system remains challenging due to their inherent incompatibility in dispersion and interaction, which often results in phase separation. To address the phase separation issue, we employed a tailored binder system of hydroxyethyl cellulose (HEC), dipropylene glycol and water which enhances compatibility between hydrophobic polypyrrole, rGO and hydrophilic PEDOT:PSS through hydrogen bonding, electrostatic interactions. These conductive inks are printed on a polyethylene terephthalate (PET) substrate using a simple and efficient screen-printing technique. The optimized ink enables the fabrication of flexible micro-supercapacitors with areal capacitances of 193.16 mFcm⁻²for Polypyrrole-PEDOT:PSS (PP-5) and 219.7 mFcm⁻²for Polypyrrole-PEDOT:PSS-rGO (PPR) at 5 mVs⁻¹. The energy density reaches 8.45 μWhcm⁻², with a power density of 21.45 μWcm⁻². The same material seamlessly transitions into the fabrication of a high-performance humidity sensor. The single-printed PPR-2 sensor exhibited excellent humidity sensing performance across a wide relative humidity range 11–97 % RH with rapid response and recovery times of 47 s and 58 s.