【深圳大學(xué):增效型水凝膠電解質(zhì)，實(shí)現(xiàn)能量自主和可穿戴傳感】

傳統(tǒng)的熱電轉(zhuǎn)換技術(shù)以熱電發(fā)生器為特征，利用基于固態(tài)半導(dǎo)體的電子塞貝克效應(yīng)來實(shí)現(xiàn)熱流到電流的直接轉(zhuǎn)換。然而，這些熱電發(fā)生器通常具有剛性、毒性或熱功率低(約為 uV K-1)的缺點(diǎn)，這阻礙了它們?cè)诳纱┐麟娮釉O(shè)備中的進(jìn)一步發(fā)展。相比之下，熱電偶電池(TEC，又稱熱電化學(xué)電池或熱電偶電池)可在室溫下產(chǎn)生較大的熱功率，因此特別適用于收集人體和可穿戴電子設(shè)備的低品位廢熱。在溫度梯度下，一個(gè)電極發(fā)生氧化反應(yīng)，另一個(gè)電極發(fā)生還原反應(yīng)。這些連續(xù)的氧化還原反應(yīng)導(dǎo)致電子在外電路中不斷流動(dòng)，并在冷熱電極之間產(chǎn)生電位差，從而產(chǎn)生很大的熱電化學(xué)塞貝克系數(shù)(Se)，其數(shù)量級(jí)為mV K-1。

為了推動(dòng)柔性和可穿戴應(yīng)用的發(fā)展，近期有關(guān) TEC 的研究越來越多地將重點(diǎn)轉(zhuǎn)向水凝膠電解質(zhì)。對(duì)于柔性設(shè)備來說，水凝膠電解質(zhì)可以避免傳統(tǒng)液基 TEC 的電解質(zhì)泄漏和復(fù)雜封裝問題。然而，柔性和可穿戴 TEC 的開發(fā)面臨著一些挑戰(zhàn)，其中最主要的是如何提高其熱電化學(xué)性能。提高熱功率以實(shí)現(xiàn)高效率對(duì)于最大限度地利用低品位熱源進(jìn)行能量轉(zhuǎn)換至關(guān)重要。在提高熱功率的同時(shí)，還面臨著提高機(jī)械強(qiáng)度的挑戰(zhàn)，特別是對(duì)于基于水凝膠的 TEC 而言，因?yàn)樗鼈儽仨毦邆鋸?qiáng)大的機(jī)械性能，以承受撕裂、彎曲和扭曲。這一點(diǎn)在可穿戴應(yīng)用中尤為重要，因?yàn)樵谶@些應(yīng)用中，靈活性和耐用性是不可或缺的，而目前的研究卻在很大程度上忽視了這一點(diǎn)。除了熱功率低和機(jī)械強(qiáng)度不足外，目前的準(zhǔn)固態(tài) TEC 還缺乏在受到嚴(yán)重外部損壞后恢復(fù)的能力，這大大限制了它們?cè)谌嵝院涂纱?yīng)用中的實(shí)用性。

研究成果

柔性準(zhǔn)固態(tài)熱電偶(TEC)的快速發(fā)展為可穿戴電子設(shè)備提供了一條嶄新的發(fā)展道路。然而 機(jī)械強(qiáng)度和功率輸出的不足仍然阻礙著它們的進(jìn)一步應(yīng)用 。深圳大學(xué)陳光明教授團(tuán)隊(duì)研究展示了一種“一石二鳥”策略，可協(xié)同增強(qiáng)基于[Fe(CN)6]3-/4-的熱電偶的機(jī)械和熱電化學(xué)特性。通過甜菜堿齊聚物引入多種非共價(jià)相互作用，傳統(tǒng)脆性明膠水凝膠電解質(zhì)的機(jī)械強(qiáng)度從50 kPa 大幅提高到440 kPa，伸展性接近 250%。同時(shí)，甜菜堿齊聚物強(qiáng)烈影響了[Fe(CN)6]3-的溶解結(jié)構(gòu)從而擴(kuò)大了熵差，并將熱電化學(xué)塞貝克系數(shù)從1.47 mVK-1提高到2.2 mV K-1。由此產(chǎn)生的準(zhǔn)固態(tài) TEC 顯示出0.48 mW m-2 K-2的超高歸一化輸出功率密度，與未進(jìn)行齊聚離子調(diào)節(jié)的同類產(chǎn)品相比，整體性能有了顯著提高。此外，固有的熱可逆特性使TEC能夠通過溶膠轉(zhuǎn)化反復(fù)進(jìn)行自我恢復(fù)，從而確?？煽康哪芰枯敵觯踔猎诎l(fā)生極端機(jī)械損壞的情況下也能對(duì) TEC 進(jìn)行回收利用。作者還進(jìn)一步設(shè)計(jì)了一種由18個(gè)獨(dú)立TEC組成的能量自主智能手套，它可以同時(shí)監(jiān)測任何被觸摸物體不同位置的溫度，在可穿戴應(yīng)用中展現(xiàn)出巨大的潛力。

圖文導(dǎo)讀

Figure 1. (a) An illustration of the forming process of the GB-HCF hydrogel. (b) An SEM image of the GB-HCF and the corresponding elemental mapping images. (c) FTIR spectra of various samples. (d) Raman spectra of various samples. (e) XPS full spectra of various samples. (f) XPS C1s spectra of various samples. (g) XPS Fe2p spectrum of the GB-HCF.

Figure 2. (a) Stress-strain curves of various samples. (b) The corresponding tensile strength and elongation at break of various samples obtained from (a). (c) Demonstration of the GB[1]HCF hydrogel lifting a weight of 2.5 kg. The schematic diagram highlights the role of betaine in the hydrogel network, where the betaine molecules can bind the gelatin chains tightly through multiple non-covalent interactions including hydrogen bonds and electrostatic interactions. (d) Compression curves of various samples. (e) The corresponding compressive strength of various samples obtained from (d). (f) Stress-strain curves of cyclic compression of the GB-HCF. (g) Demonstration of the tailorable GB-HCF hydrogels and their healing capability. (h) Stress[1]strain curves of the GB-HCF before and after healing. (i) Stress-strain curves of the GB-HCF subjected to five recovery cycles. Insets show its self-recovery process based on the sol-gel transformation.

Figure 3. (a) UV-vis spectra of the [Fe(CN)6]4? and [Fe(CN)6]4? + betaine sample. (b) UV-vis spectra of the [Fe(CN)6]3? and [Fe(CN)6]3? + betaine sample. (c) XPS N 1s spectra of various samples. (d) The calculated binding energies for [Fe(CN)6]4-betaine and [Fe(CN)6]3?-betaine. Insets show the optimized binding structures. (e) The radial density profiles between [Fe(CN)6]3?/[Fe(CN)6]4? and water/betaine molecules. (f) The illustration of the solvation structures of [Fe(CN)6]3? and [Fe(CN)6]4? with the presence of betaine.

Figure 4. (a) The effect of betaine concentration on the Se. (b) The effect of betaine concentration on the ionic conductivity. (c) The Se change during the rest in air for 7 days. (d)The fitted plots of voltage-temperature difference for different recovery cycles. (e) The measured Se values after different recovery cycles. Insets show the recovery cycle. (f) Current density-voltage plots under different ?Ts. (g) Power density-voltage plots under different ?Ts. (h) The calculated maximum specific output power density. (i) Comprehensive comparisons between the GB-HCF based TECs and conventional gelatin-based TECs in terms of Pmax/?T2, Se, σ, tensile strength, and stretchability.

Figure 5. (a) An optical image of the smart glove consisting of 18 TEC blocks. (b) Schematic of the configuration of a single TEC block. (c) Photos showing a TEC block powering a light[1]emitting diode bulb by utilizing the body heat with the assistance of a voltage amplifier. (d) Corresponding infrared thermal images. (e) A schematic of the hand-shaped smart glove. (f)Demonstration of wearing the smart glove device to hold different objects. The schematics in the lower part show the voltage responses in different zones of the hand. (g) The variation of ?U/U0 values with the variation of the target temperature. (h) The relationship between the ?U/U0 values and the target temperature. (i-l) The voltage responses of the device when the hand was touching a pentagram toy, a duck toy, a cylinder, and a cold/hot water cup. Insets are the photos showing how the hand was holding the objects.

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