琼脂糖基离子热电凝胶材料的热电性能研究

  近年来，快速发展的物联网技术对传感器提出了自供能需求。基于塞贝克效应的热电器件可将环境或人体产生的低品位热能转换成为电能，实现传感器的自供能。然而以碲化铋为代表的商用热电器件输出电压较低，使其难以满足在小温差场景下的传感器自供能的电压需求。以离子作为能量载体的离子热电凝胶材料基器件，具有电势高和结构简单等特点，有望克服这一技术瓶颈。然而，目前离子凝胶材料刚处于起步阶段，离子热电凝胶材料的材料体较少。基于此，本文以开发出高热电势的新型离子热电材料为研究目标，并详细研究了琼脂糖基离子热电凝胶材料中尺寸非对称的阴阳离子与高热电势之间的关系。

  以琼脂糖(AG)为凝胶材料的基体，以十二烷基苯磺酸钠(SDBS)作为热电转换的能量载体，开发出一种P型的琼脂糖基离子热电凝胶材料(AG-SDBS)，热电势高达41.8 mV K^-1，较之前课题组所报道的明胶基离子热电材料Gelatin-KCl-FeCN^4-/3- 的热电势提高了145%。在热电性能方面有较大突破，本论文还系统研究了具有不同长度碳链的苯磺酸钠，盐浓度，水含量等参数对琼脂糖基离子热电凝胶材料热电性能的影响规律。

  基于琼脂基离子热电凝胶材料的热充电过程中动力学曲线和能谱分析元素分布等表征，发现该琼脂糖基离子热电材料AG-SDBS的巨热电势主要源于十二烷基苯磺酸钠中的阴阳离子非对称结构。阳离子亲水且尺寸较小，而阴离子疏水尺寸较大。琼脂糖基离子热电凝胶材料制备过程中，由于搅拌会产生大量气泡，十二烷基苯磺酸根离子（C₁₈H₂₉SO₃^-）会集聚在气泡周围而形成介稳态结构，在冷却成凝胶时琼脂糖凝胶层层之间形成微孔结构，该微孔结构为Na+提供快速扩散通道，而 C₁₈H₂₉SO₃^-的尺寸较大且拥有强疏水作用，扩散的阻力大，最终实现阴阳离子同向扩散的解耦，得到巨热电势。此外，基于上述机理，本文还选选用阳离子疏水基团的十二烷基三甲基溴化铵（DTAB），成功的制备出N型离子热电凝胶材料AG-DTAB。

In recent years，the new trend of Internet-of-things requires self-power supply technique for sensors. Thermoelectric devices which are based on Seebeck effect can transform the low-grade heat energy generated by the environment or human body into electrical energy to realize the self-energy supply of sensors. However, the output voltage of thermoelectric devices based on the bismuth telluride is low, which makes it difficult to use in sensors with small temperature differences. Ion thermoelectric gel material-based devices in which the ions are applied as energy carriers has the feature of high electrical potential and simple structure and are expected to overcome this technical bottleneck of low voltage. However, there are still few material systems for ion thermoelectric gel materials. In this work, a newly ionic thermoelectric material with high thermal potential was developed. The correlation between the size asymmetric anions and high thermal potential in agarose-based ionic thermoelectric gel materials is investigated in detail.

A P-type agarose-based ionic thermoelectric gel material (AG- SDBS) was prepared by using agarose (AG) as the matrix of the gel material and sodium dodecylbenzene sulfonate (SDBS) as the energy carrier for thermo-electric conversion. High thermoelectric potential with the value of 41.8 mV K^-1 was found in this material, which is 145% higher than the gelatin-based ionic thermoelectric gel material(Gelatin-KCl-FeCN^4-/3-) reported by our group. The effect of sodium benzene sulfonate with different lengths of carbon chains, salt concentration, and water content on the thermoelectric properties of agarose-based ionic thermoelectric gels was also investigated in detail.

The kinetic curves and energy spectrum analysis of the ionic thermoelectric gel material reveal that the giant thermal potential of this agarose-based ionic thermoelectric material (AG-SDBS) mainly originates from the asymmetric structure of anions and cations in sodium dodecylbenzene sulfonate. Because the cations are hydrophilic and smaller in size, while the anions are hydrophobic and larger in size. During the preparation of agarose-based ionic thermoelectric gel, a large number of bubbles are generated in the process of stirring. The dodecylbenzene sulfonate ions (C₁₈H₂₉SO₃^-) will cluster around the bubbles and form a metastable structure, which forms a microporous structure between the agarose gel layers during its cooling into a gel. This microporous structure provides a diffusion channel for Na⁺, while the large size of C₁₈H₂₉SO₃^- wiht strong hydrophobic effect proved a large diffusion resistance. Finally, a giant thermal potential was found by the decoupling of anion and cation isotropic diffusion. Based on the above mechanism, a cationic hydrophobic group named dodecyltrimethylammonium bromide (DTAB) was selected to prepare the N-type ionic thermoelectric gel material AG-DTAB.

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