# About the Relevance of Triboelectric Effects and Conductive Particles in Nanogenerators Based on Cellulose Materials and Their Composites

## TL;DR

This paper investigates how triboelectric effects and conductive particles influence voltage generation in cellulose-based nanogenerators, finding that triboelectric processes play a significant role.

## Contribution

The study reveals that triboelectric effects, not just piezoelectricity, significantly contribute to voltage output in modified cellulose nanogenerators.

## Key findings

- Modified cellulose films and aerogels showed voltage outputs between 2 and 10 V under mechanical stimulation.
- Ternary composites with conductive and piezoelectric ZnO particles generated up to 24 V.
- Voltage generation dropped to 0.2 V when NG configuration changed, indicating triboelectric effects are significant.

## Abstract

Cellulose is a well-known biopolymer with excellent properties for a broad range of applications, including piezoelectricity for the development of nanogenerators. However, similar to other piezoelectric materials, the voltage outputs currently reported from cellulose-based piezoelectric nanogenerators (PENGs) could be overestimated due to the appearance of triboelectric processes. To understand the appearance of both phenomena, cellulose films and aerogels that had undergone several modifications to improve their piezoelectric behavior (i.e., thermal treatment and presence of piezoelectric/conductive particles) were developed and characterized. Our results show that these modifications significantly changed the dielectric properties (ε) and the piezoelectric coefficients (d33), with increments as high as a factor of 4, although without a clear tendency regarding the sample characteristics. Under finger-tapping mechanical stimulation, nanogenerators (NGs) using pure cellulose films generated 6 V, whereas the modified cellulose films and aerogels either increased or decreased this value, with outputs between 2 and 10 V. Notably, ternary composites, having both conductive and piezoelectric ZnO particles, increased the generation up to 24 V. There was no correlation between the voltage generated and d33 or d33/ε values, although some relationship with ε was observed, meaning that a pure piezoelectric phenomenon was not observed. This lack of correlation and the drastic decrease in the voltage generated (around 0.2 V) after changing the NG configuration show that a triboelectric phenomenon from the multilayered structure significantly contributes to the voltage generation from cellulose samples.