Water-dispersible, electrically recyclable cellulose paper for versatile surface applications

• Water-dispersible, recyclable cellulose paper enables green flexible electronics. • Conformal adhesion to curved surfaces via simple water-spray swelling process. • Hydrophobic encapsulation extends device function in humid/wet environments. • Foldable, bendable electrodes retain conductivity after repeated deformation. • Versatile sensors detect humidity, respiration, touch, and capacitive input. Green electronics are emerging as a prominent and environmentally responsible technology in response to the growing concern over electronic waste. This study introduces water dispersible and electrically recyclable functional paper for flexible electrodes and sensing materials, with the ability to conformally laminate onto dynamic surfaces. The conductive paper is formed by coating pulp fibers with conductive composites comprising sodium carboxymethyl cellulose and carbon black particles. Such functional paper enables conformal contact with curved and/or rough surfaces through a water spray application followed by a drying process, ensuring reliable performance across diverse surface geometries. When used in a parallel-plate capacitor, these electrodes enable keypad functionality on rough rock surfaces. The addition of hydrophobic encapsulation enhances the paper's usability in aqueous environments, allowing for a controllable operational period. Conversely, electrodes without hydrophobic encapsulation serve effectively as humidity sensors, demonstrating sensitivity to respiration and ambient humidity changes. This paper presents eco-friendly, water-dispersible, and electrically recyclable functional paper electrodes. Made by coating pulp fibers with a carbon black and cellulose-based composite, the paper can conform to curved or rough surfaces using water spray and drying. It enables keypad functionality even on uneven surfaces and, with hydrophobic encapsulation, operates in wet environments. Without encapsulation, it can function effectively as a humidity sensor responsive to breathing and ambient moisture.