High Power-Output and Highly Stretchable Protein-Based Triboelectric Nanogenerator

To meet the demand for wearable triboelectric nanogenerator (TENG) with high power output and a diverse application range, stretchable friction materials with high triboelectric charge densities are required. Soy protein (SP) is a prospective friction material; however, its application is limited by its brittle nature. Herein, we report the doping of an SP film with the hygroscopic CaCl 2 to afford a positive tribolayer with improved tribopositivity and stretchability. Ca 2+ disperses evenly in the SP film via electrostatic interactions. The water molecules adsorbed by CaCl 2 form hydrogen bonds with the SP chains, which improve the charge-donating ability. The optimal film, SP–CaCl 2 -0.30 (0.30 denotes the CaCl 2 -doping concentration in mmol), exhibits high resilience (elongation at break: 130%) compared with the pure SP film (elongation at break: 4%). The TENG composed of SP–CaCl 2 -0.30 as the positive tribolayer and Ecoflex as the counterpart yields an open circuit voltage (V OC ), a short circuit current (I SC ), and a short-circuit transferred charge quantity (Q SC ) of 130 V, 4.4 µA, and 44 nC, respectively. When the load resistance matches the device’s internal resistance, the peak transient power reaches 1125 mW/m 2 , which is up to 535.7 folds higher than those of reported protein-based TENGs. Moreover, the device output is maintained even after 5000 stretch and release cycles, and the amounts of harvested charge from the bending and release motions of a finger and an elbow reach 3.5 nC and 40 nC, respectively. This study demonstrates a practical approach for achieving protein-based TENGs with high stretchability and electrical output, which show significant potential for application in wearable electronics based on mechanical-energy harvesting.