A pH‐Sensitive Stretchable Zwitterionic Hydrogel with Bipolar Thermoelectricity
Ling‐Chieh Lee, Kang‐Ting Huang, Yen‐Ting Lin, U‐Ser Jeng, Chia‐Hsin Wang, Shih‐Huang Tung, Chun‐Jen Huang, Cheng‐Liang Liu
Abstract
Abstract Amid growing interest in using body heat for electricity in wearables, creating stretchable devices poses a major challenge. Herein, a hydrogel composed of two core constituents, namely the negatively‐charged 2‐acrylamido‐2‐methylpropanesulfonic acid and the zwitterionic (ZI) sulfobetaine acrylamide, is engineered into a double‐network hydrogel. This results in a significant enhancement in mechanical properties, with tensile stress and strain of up to 470.3 kPa and 106.6%, respectively. Moreover, the ZI nature of the polymer enables the fabrication of a device with polar thermoelectric properties by modulating the pH. Thus, the ionic Seebeck coefficient ( S i ) of the ZI hydrogel ranges from −32.6 to 31.7 mV K −1 as the pH is varied from 1 to 14, giving substantial figure of merit ( ZT i ) values of 3.8 and 3.6, respectively. Moreover, a prototype stretchable ionic thermoelectric supercapacitor incorporating the ZI hydrogel exhibits notable power densities of 1.8 and 0.9 mW m −2 at pH 1 and 14, respectively. Thus, the present work paves the way for the utilization of pH‐sensitive, stretchable ZI hydrogels for thermoelectric applications, with a specific focus on harvesting low‐grade waste heat within the temperature range of 25–40 °C.