Heterogeneous bilayer system of cellulose nanofibers for a moisture-enabled electric generator

This paper describes the fabrication of a bilayer system as a spontaneous power generator using an abundant natural bioresource known as cellulose nanofibers (CNFs). Although CNFs are naturally attracted to atmospheric moisture, surface functionalization is needed to generate sufficient electricity through dissociation and diffusion of oppositely charged ions. We used a heterogeneous bilayer film system based on CNFs that were chemically modified with carboxylate and quaternary ammonium functional groups to assemble a moisture-enabled electric generator (MEG) by inducing a heterogeneous distribution of mobile ions. The MEG bilayer consists of functionalized CNFs with optimum thickness and area, which enables ion dissociation and diffusion through a continuous ion-concentration gradient even at a high relative humidity (> 95%). The streaming potential and ion gradient acting on the bilayer enhance the output performance of the MEG. The thickness of the bilayer film, along with temporal variations, also influences device performance. A single unit can spontaneously produce approximately 0.7 V and 0.8 µA of output voltage and current, respectively, without the need for an external power source. When 20 MEG units are combined, they can produce up to 9.6 V of output voltage and can supply continuous energy for several hours at a power density of 7.4 µW/cm² by storing power in capacitors. This study provides a better understanding of high-performance cellulose-based MEGs for self-powered devices.