From banana stem to conductive paper: A capacitive electrode and gas sensor

•The cellulose composite matrix is obtained from a renewable source that is considered as waste and is routinely discarded.•Production of functionalized nanomaterials, environmentally friendly.•Capacitive and sensor performance are shown in novel design 2D materials.•Flexible cellulose/carbon (from banana nanofiber a bio-based composite) can be considered alternative with significant interest in sensing principles and mechanisms.