Wearable Thermocells Based on Gel Electrolytes for the Utilization of Body Heat

Abstract

Converting body heat into electricity is a promising strategy for supplying power to wearable electronics. To avoid the limitations of traditional solid-state thermoelectric materials, such as frangibility and complex fabrication processes, we fabricated two types of thermogalvanic gel electrolytes with positive and negative thermo-electrochemical Seebeck coefficients, respectively, which correspond to the n-type and p-type elements of a conventional thermoelectric generator. Such gel electrolytes exhibit not only moderate thermoelectric performance but also good mechanical properties. Based on these electrolytes, a flexible and wearable thermocell was designed with an output voltage approaching 1 V by utilizing body heat. This work may offer a new train of thought for the development of self-powered wearable systems by harvesting lowgrade body heat.Given the recent developments in the area of wearable electronics and e-skins, [1][2][3][4][5][6] the emerging need for selfpowered energy supply has heightened the interest in energy harvesting from the environment or human beings. Among recognized energy-harvesting technologies, such as solar cells [7,8] and triboelectric and electret generators, [9,10] thermal energy is a potential power source that is widely available in the environment and in industrial processes. [11,12] However, human bodies are also a permanent heat source, with a surface temperature of about 32 8C and possibly tens of degrees temperature difference between the human body and its environment. [13,14] Hence, it is of practical meaning to convert body heat energy, a type of low-grade heat, into electricity for directly powering wearable electronics. [15][16][17] The most convenient strategy to utilize low-grade heat is thermal-electric conversion. Traditional thermoelectric generators utilizing the Seebeck effect are mainly based on solidstate semiconductors or conducting polymers, [18,19] with output voltages limited by the relatively low Seebeck coefficient (several hundreds mV K À1 ). Meanwhile, the frangibility and expensiveness of thermoelectric materials as well as their complicated fabrication processes are other obstacles restricting their application in wearable electronics. [20] Alternatively, a large thermovoltage can be derived from thermogalvanic effects, resulting from temperature-dependent entropy changes during electron transfer between redox couples and electrodes. [21][22][23][24] Previous reports mainly focused on the exploration of electrode materials, such as carbon nanotubes (CNTs) and graphene, [25][26][27][28] to achieve high thermal-electric conversion efficiencies. However, because of the aqueous electrolytes used in thermocells, large-scale integration and packaging of the units would be more difficult in applications, especially for wearable devices. [29] Inspired by the successful application of gel electrolytes in solid-state electrochemical energy storage systems and stretchable ionic conductors, [30][31][32][33] we surmised that solid-state or quasi-solidstate gel...

Self‐Powered Multimodal Temperature and Force Sensor Based‐On a Liquid Droplet

“…[1][2][3][4][5][6] Thed iversity of demand has inspired sensor devices based on many different mechanisms,i ncluding resistance sensors, [7][8][9] capacitive sensors, [10] piezoelectric sensors, [11][12][13] thermoelectric sensors, [14] and field-effect transistor (FET) devices. Owing to the reverse electrowetting phenomenon [21][22][23] of the droplet on the solid surface and the thermogalvanic effect [24][25][26] of the solution, the deformation of the droplet shape and the temperature difference across the droplet can induce an alternating pulse voltage and ad irect voltage,r espectively,w hich can be utilized to sense the external force and temperature.T he interference effect of temperature and force on the integrated voltage signal is also analyzed, so as to distinguish and derive the temperature and force stimuli separately.B ased on these properties,a n integrated sensing and lighting system is also demonstrated.These results may open an ew and cost-effective sensing approach for artificial intelligence systems. To realize the functionality,most of the designs integrate as eparate temperature and af orce senor by tiling or laminating,w hich in fact detect multiple stimuli by different sensors individually.…”

“…Owing to the reverse electrowetting phenomenon [21][22][23] of the droplet on the solid surface and the thermogalvanic effect [24][25][26] of the solution, the deformation of the droplet shape and the temperature difference across the droplet can induce an alternating pulse voltage and ad irect voltage,r espectively,w hich can be utilized to sense the external force and temperature.T he interference effect of temperature and force on the integrated voltage signal is also analyzed, so as to distinguish and derive the temperature and force stimuli separately.B ased on these properties,a n integrated sensing and lighting system is also demonstrated. Owing to the reverse electrowetting phenomenon [21][22][23] of the droplet on the solid surface and the thermogalvanic effect [24][25][26] of the solution, the deformation of the droplet shape and the temperature difference across the droplet can induce an alternating pulse voltage and ad irect voltage,r espectively,w hich can be utilized to sense the external force and temperature.T he interference effect of temperature and force on the integrated voltage signal is also analyzed, so as to distinguish and derive the temperature and force stimuli separately.B ased on these properties,a n integrated sensing and lighting system is also demonstrated.…”

Numerical modeling of the performance of thermoelectric module with polydimethylsiloxane encapsulation

“…1 As a promising approach, thermoelectric generators (TEGs) can directly harvest human body heat and convert it into electricity for the power supply of wearable electronics. 2,3 For wearable TEG, polydimethylsiloxane (PDMS), which features high flexibility and biocompatibility, has been Nomenclature: W leg , width of thermoelectric leg (mm); H leg , height of thermoelectric leg (mm); L 1 , width of PDMS between adjacent thermoelectric pairs (mm); L 2 , width of PDMS in the thermoelectric pair (mm); T, temperature (K); V, voltage (V); k, thermal conductivity (W m −1 K −1 ); j, current density (A m −2 ); h, convection coefficient (W m −2 K −1 ); C P , specific heat (J kg −1 K −1 ); T Ã P , temperature of the CV achieved in previous iteration step (K); V Ã P , voltage of the CV achieved in previous iteration step (V); T 0 P , initial temperature of the CV of the iteration (K); V 0 P , initial voltage of the CV of the iteration (V); P, output power (W); _ Q, heat flow at the hot side (W); q, heat flux at the hot side (W m −2 ); A, bottom surface area of TEM (m −2 ); R, external loading resistance (Ω)…”

Self‐Powered Multimodal Temperature and Force Sensor Based‐On a Liquid Droplet

“…[20] However,b oth the devices may face problems of sophistication in fabrication or post signal processing, since they involve nanoscale fabrication or micro current/ voltage signals.H ence an ew sensing approach with high accuracy and simple architecture is still highly desirable.Herein we report am ultimodal temperature and force sensor using only al iquid droplet of K 3 [Fe(CN) 6 ]/K 4 [Fe-(CN) 6 ]s olution. Owing to the reverse electrowetting phenomenon [21][22][23] of the droplet on the solid surface and the thermogalvanic effect [24][25][26] of the solution, the deformation of the droplet shape and the temperature difference across the droplet can induce an alternating pulse voltage and ad irect voltage,r espectively,w hich can be utilized to sense the external force and temperature.T he interference effect of temperature and force on the integrated voltage signal is also analyzed, so as to distinguish and derive the temperature and force stimuli separately.B ased on these properties,a n integrated sensing and lighting system is also demonstrated.These results may open an ew and cost-effective sensing approach for artificial intelligence systems. Figure 1a schematically illustrates the structure of the droplet sensor,w hich consists of al iquid droplet and two conducting plates,placed at the bottom and top of the droplet.…”

“…Herein we report am ultimodal temperature and force sensor using only al iquid droplet of K 3 [Fe(CN) 6 ]/K 4 [Fe-(CN) 6 ]s olution. Owing to the reverse electrowetting phenomenon [21][22][23] of the droplet on the solid surface and the thermogalvanic effect [24][25][26] of the solution, the deformation of the droplet shape and the temperature difference across the droplet can induce an alternating pulse voltage and ad irect voltage,r espectively,w hich can be utilized to sense the external force and temperature.T he interference effect of temperature and force on the integrated voltage signal is also analyzed, so as to distinguish and derive the temperature and force stimuli separately.B ased on these properties,a n integrated sensing and lighting system is also demonstrated.…”