Side-Chain Engineered p or n-Type Nonaqueous Polymeric Ionic Gels for Sustainable Ionic Thermoelectrics

Although ionic hydrogels have been developed recently for innovative wearable electronics, they necessitate high humidity to diffuse ions in water and fast self-healing, which negatively impacts their performance and stability in ambient conditions (e.g., dry environments). In this study, a series of p- and n-type polymeric ionic gels (PIGs) with different ratios of ionic side chains are synthesized to allow only single-type ions to pass through them. The results demonstrate that our repeatedly stretchable PIGs are transparent, thermally robust up to 125 °C, and self-healing. Among the series of PIGs, p- and n-type PIGs with 75% ion moieties (P75 and N75) exhibit the optimum ionic conductivity (<i>σ_i</i>) (4.1×10^-4 and 2.7×10^-4 S cm^-1) and ionic Seebeck coefficients (<i>S_i</i>) (5.84, and -4.18 mV K^-1) under ambient conditions (25 °C and relative humidity (RH) of 30%), resulting in <i>ZT_i</i> values of 1.87×10^-3 and 1.18×10^-3. Moreover, the <i>σ_i</i> and <i>S_i</i> of PIGs were almost consistent under extremely low RH 10%. Accordingly, P(([EMIM⁺][SPA])_0.75-r-MA_0.25) (P75) and P(([APTA][TFSI^-])_0.75-r-MA_0.25) (N75) are used to achieve stretchable ionic thermoelectrics (iTEs) with stable operability under ambient conditions (RH of 30%), satisfying all of the requirements. The iTEs with five pairs of p/n couples exhibit a thermovoltage of up to ~0.8 V.