Cellulose nanofibrils enhanced thermoelectric hydrogel with high negative Seebeck coefficient

•Cellulose nanofibril could simultaneously improve the thermal power and strength of ionic hydrogel.•The ionic thermoelectric (iTE) hydrogel possesses a high negative Seebeck coefficient of −20.1 mV·K−1.•Cellulose nanofibril was found to improve the tensile strength of the hydrogel to 260 kPa. Ionic hydrogels are emerging as promising candidates for ionic thermoelectric (iTE) due to their high thermopower and flexibility. In this work, we demonstrate that the ionic thermopower and strength of ionic poly(acrylamide) (PAM) hydrogel can be enhanced simultaneously by the introduction of cellulose nanofibrils (CNFs). The iTE hydrogel possesses a negative Seebeck coefficient of −20.1 mV·K−1 and a tensile strength of 260 kPa. Potential applications of the hydrogel are demonstrated for low-grade energy harvesting.