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. A capacitive, conductive and methanol sensor composite have been prepared by a simple process of acid hydrolysis, using potential cellulose source extracted from a residue of banana stem. The material was hydrolyzed with sulphuric acid in the presence of carboxylated multiwalled carbon nanotubes (MWCNTs) to promoted chemical interaction among cellulose and carbon surface. With these material was prepared a paper film used to design an electrode. The cellulose/MWCNT composite was investigated using x-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, transmission electron microscopy and size measurement. The electrical properties were evaluated by cyclic voltammetry, impedance spectroscopy, charge/discharge testing and simulation in an equivalent circuit. The gas sensor property was evaluated by an experimental apparatus, measuring the electric current front exposure the electrode to different concentrations of methanol in different temperatures. The cellulose/MWCNT electrode displays a strong dependence of a scan rate and potential range in capacitive properties. The chemical interaction archived between MWCNT and cellulose is relevant to develop a flexible cellulose composite, with specific capacitance of 3,08mF/cm2 as functional nanotube integration. The flexible electrode developed in this study would be the ideal matrix to anchorage sensitive molecules and particles on specific applications like biosensor or electronic device.