Aligned cellulose nanofibril ionogels with continuous micro-nanochannels for ionic thermoelectrics and self-powered sensors

The growing demand for sustainable and distributed power sources, driven by advances in the Internet of Things and flexible wearable electronics, has intensified the focus on thermoelectric energy harvesting. Although inorganic thermoelectric materials (e.g., Bi 2 Te 3 ) exhibit high conversion efficiency, their rigidity, high cost, and dependence on scarce or toxic elements hinder their use in flexible applications. In contrast, ionic thermoelectric materials (i-TEs) show advantages, including high Seebeck coefficients, flexibility, and biocompatibility. However, conventional ionogels typically possess disordered polymer networks, which lead to low ionic conductivity and limited Seebeck coefficient enhancement. To address this challenge, we use cellulose nanofibrils (CNFs) to construct a well-aligned micro-nanochannel via directional freezing. This design offers continuous and low-resistance pathways, markedly facilitating ion transport. Meanwhile, nano-confinement effects enhance ion selectivity at low concentrations and promote asymmetric ion distribution, leading to a synergistic improvement of thermoelectric performance. The resulting ionic thermoelectric material achieves a Seebeck coefficient of 3.47 mV K −1 and an outstanding power output of 223.51 mW m −2  at ΔT∼20 °C, comparable or superior to many reported conventional i-TE systems. This work proposes a novel strategy for regulating ion migration pathways and provides a fundamental basis for developing high-performance flexible ion-thermoelectric devices and self-powered sensors.