Outstanding Electrode-Dependent Seebeck Coefficients in Ionic Hydrogels for Thermally Chargeable Supercapacitor near Room Temperature

Abstract

Thermoelectric power generation from waste heat is an important component of future sustainable development. Ion-conducting materials are promising candidates because of their high Seebeck coefficients. This study demonstrates that ionic hydrogels based on imidazolium chloride salts exhibit outstanding Seebeck coefficients of up to 10 mV K −1 . Along with their relatively high ionic conductivities (1.6 mS cm −1 ) and extremely low thermal conductivities (∼0.2 W m −1 K −1 ), these hydrogels have good potential for use in heat recovery systems. The voltage behavior in response to temperature difference (stable or transient) differs significantly depending on the metal electrode material. We evaluated the electrode-dependent temperature sensitivity of the double layer capacitance of these hydrogels, which revealed that the thermally induced polarization of ions at the interface is one of the main contributors to the thermovoltage. Our results demonstrate the potential capability for ion and metal interactions to be used as an effective baseline for exploring ionic thermoelectric materials and devices. The developed thermoelectric supercapacitor exhibits reversible charging−discharging behavior under repeated disconnecting−connecting of an external load with a constant temperature difference, which offers a novel strategy for heat-to-electricity energy conversion from steady-temperature heat sources.

Hydrogels with Gigantic Thermopower for Low-grade Heat Harvesting

“…4e and Supplementary Video 1). This charging rate is faster than other reported ionic thermoelectric capacitors 22,27 . Our hydrogel can easily complete more than 100 charge/discharge cycles within ~ 600 s,…”

“…Furthermore, modi ed cellulose containing charged nanochannels generates a Seebeck coe cient of 24 mV K − 1 7 . Similar strategy has also been applied to quasi-solid ionic gels 26,27 . For example, through the dipole moment interaction between PVDF-HFP and an ionic liquid 1-ethyl-3-methylimidazolium dicyanamide (EMIM:DCA), the thermal voltage reaches 26.1 mV K − 1 8 .…”

Progress on the performances and applications of supercapacitors for thermoelectric conversion

“…mV 的电压，面积电容高达 1200 F/m 2 。这为小温差下热能利用提供了示例，开拓了热能收集的新领域。Horike 等 人 [29] 制备的咪唑氯盐的离子水凝胶具有优异的温度系数，可达 10 mV/K。离子水凝胶具有较高的离子导电性和极 低的热导电性，在热回收系统中具有良好的应用潜力。Zhao 等人 [30] 基于 Soret 效应，制备了一种由 NaOH 处理过 的聚氧化乙烯聚合物电解质结合负载有碳纳米管的金片电极的超级电容器，其具有优良的热电性能，温度系数高 达 11.1 mV/K，当温差达到 10 K 时，能量密度可达 9.4 Wh/kg。Kundu 和 Fisher [31] 采用廉价的碳布电极和铁/亚铁 氰化钾凝胶电解质制备一种全固态、质量小、灵活多变的柔性超级电容器，如图 3 所示，实验测得其温度系数为 1.21 mV/K，相比同种的液体电解质成本降低，应用领域极大拓宽。Kim 等人 [32] 采用一种简便的、可扩展的激光 辐照技术，将硫酸盐离子嵌入氧化石墨烯薄膜(graphene oxide films intercalated by sulfate ions, SGO)中来控制游离…”

The Interfacial Effect on the Open Circuit Voltage of Ionic Thermoelectric Devices with Conducting Polymer Electrodes

“…So far, most of the researches focus on developing the electrolytes to enhance the magnitude [10,11,15] and tuning the sign of the ionic Seebeck coefficient in devices using metal electrodes. [16,17] However, in order to enhance the energy stored in the ITESCs, electrodes with high capacitance are required.…”