Recent advances in cellulose-based piezoelectric and triboelectric nanogenerators for energy harvesting: a review

Cellulose is the most earth-abundant natural polymer resource, which with combined eco-friendly and extraordinary sustainable properties such as renewability, biodegradability, low cost and excellent biocompatibility has been widely used by humans for thousands of years. In the past few years, many novel cellulosic materials and their unique applications have been developed including the recent research focus on energy harvesting. The high crystallization and plentiful polar hydroxyl groups endow cellulose with a large number of dipoles and strong electron donating capacity, resulting in a promising potential of piezoelectric and triboelectric effects. However, there is no review about cellulose-based nanogenerators until now. In this paper, the most recent developments of designing, modification, processing and integration of cellulose-based piezoelectric nanogenerators (PENGs), triboelectric nanogenerators (TENGs) and hybrid piezo/triboelectric nanogenerators (PTENGs) for energy harvesting and other applications are reviewed in detail. For cellulose-based PENGs, representative basic piezoelectric cellulose and recent research on PENG devices are discussed. For cellulose-based TENGs, several effective strategies including rough modification of contact surface, addition of electronic functional fillers and chemical modification for improving the output performance are further summarized. Meanwhile, the latest cellulose-based hybrid PTENG is also introduced from the fundamental design to the investigations on enhanced strategies. The opportunities and challenges of these cellulose-based nanogenerator devices are put forward in the final part, which could enable this up-to-date and state-of-the-art review to be an effective guidance for the future research on cellulose-based nanogenerators in energy harvesting. Ingenious cellulose-based materials were applied in smart piezoelectric and triboelectric nanogenerators for highly efficient energy harvesting.