Biopolymeric Ionotronics Based on Biodegradable Wool Keratin

Abstract The advent of ionotronics has revealed significant potential in flexible transistors, energy harvesting, and unconventional circuits. However, most ionotronic devices, often centered around synthetic polymers, involve complex grafting or synthesis that raise legitimate concerns about their environmental sustainability. Herein, a simple yet versatile approach for developing single‐composition ionotronic devices using wool keratin (WK), a biodegradable and pH‐responsive natural polymer is presented. By employing facile pH regulation processes, WK molecules with opposing polarities are successfully modified, which are combined to form an ionic heterojunction through entropically driven depletion. This ionic heterojunction functions as an ionic diode, enabling efficient rectification of alternating current signals (with a rectification ratio of up to 199). Furthermore, the application of this biopolymeric ionotronic device is extended to mechanical energy harvesting, self‐powered sensing, and ionic logic circuit. The biodegradability and renewability of WK offer a viable alternative to synthetic materials, highlighting its potential for sustainable applications.