Hygroscopic and moisture-stable cellulose nanofiber aerogel for effective and repeatable moisture-enabled electricity generation

Abstract

Cellulose nanofiber (CNF) aerogels with anisotropic porous channels have shown promise for various applications because of their ultralow density, efficient moisture transport, and sustainability. Moisture-enabled electricity generation (MEG) using CNF aerogels is of particular interest in the field of energy harvesting using sustainable materials. However, hydrophilic CNF aerogels collapse their porous channel structures under high-humidity conditions by disrupting the interfiber hydrogen bonds, thus hindering their repeated use in MEG. Although the hydrophobic treatment of CNF aerogels can improve their structural stability against moisture, this treatment hinders their moisture absorption and affects the MEG performance. Herein, we propose the loading of Al(III) into a CNF aerogel to enhance its moisture absorption and stability simultaneously. The introduction of deliquescent AlCl₃·6H₂O crystals and Al³⁺ crosslinking into the aerogel enhances its moisture absorption and stability, respectively. The enhanced moisture absorption significantly increased the MEG performance of the aerogel under high-humidity conditions. In addition, the improved moisture stability allows the repeated use of the aerogel, even after exposure to moist airflow and subsequent drying. The Al(III)-loaded CNF aerogel with an active electrode system exhibited enhanced and repeatable MEG performances under exposure to moist airflow with maximum open-circuit voltage, short-circuit current density, and power density of 950 mV, 112.9 μA cm⁻², and 106.1 μW cm⁻², respectively. This study provides a method for producing effective and repeatable MEG and boosts the stability of CNF aerogels for various applications.