Surface Wetting Controlled by Coordination Regulation of the Cellulose Amorphous Region for Constructing High-Strength Triboelectric Materials

Abstract

Due to its remarkable advantages, such as unique multidimensional structure and excellent potential for adjustable surface chemical modification, cellulose has emerged as a highly promising triboelectric material. However, the surface of the cellulose nanofibers (CNF) is enriched with hydroxyl groups, rendering them highly hygroscopic. This property leads to a reduction in the charge density and mechanical properties of CNF materials, thus limiting their application as triboelectric materials in high-humidity environments. Therefore, in this study, an economical and straightforward ″minimally invasive intervention″ strategy was adopted. Metal ions M^x+ (such as Fe³⁺/Al³⁺) were coordinated with the hydroxyl groups in the amorphous region while causing minimal damage to the crystalline structure of cellulose as much as possible. Due to the formation of coordination bonds between the hydroxyl groups and the metal ions, the free rotation of the hydroxyl groups on the surface of cellulose was effectively restricted. Thus, it would retard the wetting rate of the cellulose surface and improve the mechanical properties and polarity of the cellulose. Compared with the pure CNF film, the mechanical properties of the M^x+-CNF films have been improved by 3.94-fold and 3.35-fold, respectively (from 32.41 to 128.81 and 108.89 MPa), and the open-circuit voltages have improved by 1.9-fold and 2.9-fold, respectively (from 15 to 23 and 36 V). Even at 90% RH, they continue to demonstrate good cyclic stability and reliability. This research provides an approach for cellulose to harvest energy in a high-humidity environment.