Flexible Piezoelectric Nanogenerator Based on Cellulose Nanofibril/MXene Composite Aerogels for Low-Frequency Energy Harvesting

Cellulose is emerging as a green and sustainable material in piezoelectric nanogenerators (PENGs) for ambient energy harvesting, although its relatively low piezoelectric coefficient still remains a challenge, hindering the potential applications. In this report, a flexible PENG with considerable energy conversion capacity was fabricated by using a polydimethylsilane (PDMS)-encapsulated cellulose nanofibril (CNF)/Ti3C2Tx (MXene) composite aerogel film, which is capable of collecting low-frequency energy such as energy from human activities. The use of two-dimensional MXene nanosheets not only optimizes the structural regularity of the CNF network but also induces a local polarization locking to align cellulosic dipoles. This strategy essentially improved the piezoelectric property of cellulose, avoiding the conventional energy consuming method (i.e., electrical poling) to strengthen piezoelectricity. Moreover, the thin layer of PDMS endows the PENG with good mechanical stability and flexibility; meanwhile, it prevents MXene from oxidizing so as to maintain its activity. The optimized CNF/MXene-PENG containing 10 wt % MXene generates a dramatically improved voltage of 30.8 V and a current of 0.49 μA. This work provides an easy and effective pathway to access cellulosic materials with enhanced piezoelectricity, aiming to approach flexible, green, and low-cost PENGs for new-generation electronics.