Giant Thermoelectric Performance of N‐Type Ionogels by Synergistic Dopings of Cations and Anions

• Published in: Advanced energy materials Vol. 13; no. 47
• Main Authors: Le, Qiujian, Chen, Zhijun, Cheng, Hanlin, Ouyang, Jianyong
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-12-2023
• Subjects: Anions; Cations; complexation; coulomb interaction; Doping; n‐type ionogels; Relative humidity; Seebeck effect; Silver; synergistic doping; Thermoelectric materials; thermopower; Vinylidene; Vinylidene fluoride
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.202302472

It is of great significance to develop high‐performance n‐type ionic thermoelectric materials. Herein, the turnover from p‐ to n‐type and great improvement in the n‐type ionic Seebeck coefficient of ionogels through synergistic dopings of cations and anions, is reported. Doping with silver trifluoromethanesulfonate (AgOTf) can turn the ionic Seebeck coefficient of the ionogels consisting of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) and 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIM:BF4) from 5.52 to −26.4 mV K−1 under a relative humidity (RH) of 75%. The TE performances can be further improved through the combination with the anti‐solvent method, and the ZTi value can be up to 1.7 under 91% RH, the highest for n‐type ionogels. Such p‐ to n‐type turnover and great improvement in the n‐type ionic Seebeck coefficient can be attributed to synergistic doping by Ag+ and OTf−. Ag+ can form a complex with BMIM+, and OTf− can have strong Coulomb interaction to BMIM+. Both can retard the migration of the BMIM+ cations and thus increase the difference in the mobilities of BMIM+ and BF4−. This is the first time that synergistic dopings by both cations and anions for ionic TE materials has been observed.
Doping with AgOTf can turn the ionic Seebeck coefficient of ionogels consisting of PVDF‐HFP and BMIM:BF4 from 5.52 to −26.4 mV K−1. This is attributed to both complex formation of Ag+ with BMIM+ and strong Coulomb interaction between OTf− and BMIM+. The ionogels can exhibit a ZTi of 1.7, which is the highest for n‐type ionogels.