| 1. |
- Gamage, Sampath, et al.
(författare)
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Reflective and transparent cellulose-based passive radiative coolers
- 2021
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Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 28, s. 9383-9393
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Tidskriftsartikel (refereegranskat)abstract
- Radiative cooling passively removes heat from objects via emission of thermal radiation to cold space. Suitable radiative cooling materials absorb infrared light while they avoid solar heating by either reflecting or transmitting solar radiation, depending on the application. Here, we demonstrate a reflective radiative cooler and a transparent radiative cooler solely based on cellulose derivatives manufactured via electrospinning and casting, respectively. By modifying the microstructure of cellulose materials, we control the solar light interaction from highly reflective (> 90%, porous structure) to highly transparent (approximate to 90%, homogenous structure). Both cellulose materials show high thermal emissivity and minimal solar absorption, making them suitable for daytime radiative cooling. Used as coatings on silicon samples exposed to sun light at daytime, the reflective and transparent cellulose coolers could passively reduce sample temperatures by up to 15 degrees C and 5 degrees C, respectively.
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| 2. |
- Gerasimov, Jennifer, et al.
(författare)
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A Biomimetic Evolvable Organic Electrochemical Transistor
- 2021
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X. ; 7:11
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Tidskriftsartikel (refereegranskat)abstract
- Biomimicry at the hardware level is expected to overcome at least some of the challenges, including high power consumption, large footprint, two-dimensionality, and limited functionality, which arise as the field of artificial intelligence matures. One of the main attributes that allow biological systems to thrive is the successful interpretation of and response to environmental signals. Taking inspiration from these systems, the first demonstration of using multiple environmental inputs to trigger the formation and control the growth of an evolvable synaptic transistor is reported here. The resulting transistor exhibits long-term changes in the channel conductance at a fixed gate voltage. Biomimetic logic circuits are investigated based on this evolvable transistor that implement temperature and pressure inputs to achieve higher order processes like self-regulation of synaptic strength and coincidence detection.
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| 3. |
- Sultana, Ayesha, et al.
(författare)
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An ionic thermoelectric ratchet effect in polymeric electrolytes
- 2022
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 10:37, s. 13922-13929
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Tidskriftsartikel (refereegranskat)abstract
- Ionic thermoelectric materials can generate extraordinarily high thermal voltage under small temperature differences due to their orders of magnitude larger Seebeck coefficient than that of electronic materials. Together with their low-cost, environmentally friendly compositions and solution processability, electrolytes have brought renewed prosperity in thermoelectric fields. Despite the rapid growing number of good-performance materials, yet to be implemented in devices, the main challenge is the understanding of the mechanism of the large Seebeck coefficient in practical electrolytes. Here, we show that the ion/polymer interaction in PEG based electrolytes does not only affect the mobility of the ions, but also has a great impact on the Seebeck coefficient. By delicately varying the types of solvent and the concentration of the solute, we could tune the molar conductivity of the electrolytes and correlate with the Seebeck coefficient. The linear relation between the Seebeck coefficient and the logarithm of the molar conductivity is in agreement with the recently reported thermoelectric ratchet effect in ions with hopping dynamics. This could lead to new design rules for ionic thermoelectrics.
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| 4. |
- Sultana, Ayesha, et al.
(författare)
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Enhanced ionic transport in ferroelectric polymer fiber mats
- 2021
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 9:39, s. 22418-22427
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Tidskriftsartikel (refereegranskat)abstract
- The limited ionic conductivity is the main issue for the application of solid-state ionic conductors. In this work, we have shown that increasing the ferroelectric phase content in a polymer matrix could enhance the molar ionic conductivity of the incorporated ionic liquid by two orders of magnitude compared to the original films with the same composition. The ferroelectric polymer fiber mats were prepared through electrospinning to induce the ferroelectric phase that ensure the polarization of the dipoles. After analyzing the ferroelectric phase content and polarization of the fiber mats and films containing different ion concentration with FTIR spectroscopy and piezoelectric characterization, a detailed mechanism explaining the improved conductivity in the ferroelectric fiber mats was proposed. Benefiting from the good flexibility, improved ionic conductivity and high temperature coefficient of the fiber mats, we fabricated an organic ionic thermistor. The temperature tracking and mapping function of the ionic thermistor was demonstrated by using two devices with 4 and 16 pixels.
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| 5. |
- Sultana, Ayesha, et al.
(författare)
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The enhanced ionic thermal potential by a polarized electrospun membrane
- 2024
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Ingår i: Chemical Communications. - : ROYAL SOC CHEMISTRY. - 1359-7345 .- 1364-548X.
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Tidskriftsartikel (refereegranskat)abstract
- Inspired by thermally sensitive ion channels in human skin, a polarized membrane composed of a ferroelectric polymer fiber matrix is used to double the heat-induced potential in ionic thermoelectric devices. The comparison of the thermal potentials between different directions of polarization and temperature gradient indicates the importance of cation-dipole interactions for the enhancement. Adding a polarized membrane to ionic thermoelectric devices induces dipole-ion interaction and enhances the thermal voltage by more than double.
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| 6. |
- Sultana, Ayesha, et al.
(författare)
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The Origin of Thermal Gradient-Induced Voltage in Polyelectrolytes
- 2023
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Ingår i: Small. - : WILEY-V C H VERLAG GMBH. - 1613-6810 .- 1613-6829.
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Tidskriftsartikel (refereegranskat)abstract
- Ionic thermoelectric materials can generate large thermal voltages under temperature gradients while also being low-cost and environmentally friendly. Many electrolytes with large Seebeck coefficients are reported in recent years, however, the mechanism of the thermal voltage is remained elusive. In this work, three types of polyelectrolytes are studied with different cations and identified a significant contribution to their thermal voltage originating from a concentration gradient. This conclusion is based on studies of the loss and gain of water upon temperature changes, variations in conductivity with water content and temperature, and the voltages induced by changes in water content. The results are analyzed by the "hopping mode" dynamics of charge transport in electrolytes. The hydration of different cations influences the water concentration gradient, which affects the barrier height and ion-induced potential in the electrodes. This work shows that the hydro-voltage in ionic thermoelectric devices can be one order of magnitude larger than the contribution from thermodiffusion-induced potentials, and becomes the main contributor to energy harvesting when implemented into ionic thermoelectric supercapacitors. Together with the rationalized theoretical discussion, this work clarifies the mechanism of thermal voltages in electrolytes and provides a new path for the development of ionic thermoelectric materials. The thermal voltage of polyelectrolyte films largely depends on the water concentration gradient under a temperature difference, which can be optimized to promote the generated total voltage up to over 30 mV K-1.image
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| 7. |
- Sultana, Ayesha, et al.
(författare)
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Toward High-Performance Green Piezoelectric Generators Based on Electrochemically Poled Nanocellulose
- 2023
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 35:4, s. 1568-1578
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Tidskriftsartikel (refereegranskat)abstract
- Internet-of-Everything (IoE) is defined as networked connections of things, people, data, and processes. IoE nodes, preferably shaped as printed flexible systems, serve as the frontier outpost of the Internet and comprise devices to record and regulate states and functions. To power distributed IoE nodes in an ecofriendly manner, a technology to scavenge energy from ambience and self-powered devices is developed. For this, piezoelectricity is regarded as a key property; however, the current technology typically based on polyvinylidene difluoride (PVDF) copolymers is expensive and produced via toxic protocols. We report piezoelectric characteristics of electrochemically poled cellulose nanofiber (CNF) thin films processed from water dispersions. Poling these films under humid conditions causes breaking and reorientation of CNF segments, which results in enhanced crystal alignment rendering the resulting material piezoelectric. Generators based on poled CNF show similar piezoelectric voltage and coefficient, here measured as d(33) = 46 pm V-1, to devices including PVDF copolymer layers of similar thickness. Our findings promise low-cost and printable ecofriendly piezoelectric-powered IoE nodes.
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| 8. |
- Zhao, Dan, et al.
(författare)
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The role of absorbed water in ionic liquid cellulosic electrolytes for ionic thermoelectrics
- 2022
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry. - 2050-7526 .- 2050-7534. ; 10:7, s. 2732-2741
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Tidskriftsartikel (refereegranskat)abstract
- The advantages of large output thermovoltage and sustainable constituent materials have generated a rapid growth in research about ionic thermoelectrics. Recently, giant values of ionic Seebeck coefficients up to 10-26 mV K-1 have been reported. However, the fundamental understanding of the ionic thermoelectric effect is still rudimentary and there is a lack of a well-established measurement standard. In this work, we systematically studied the ionic thermoelectric properties of gel electrolytes made of hydroxyethyl cellulose and an ionic liquid. We discovered that the absorbed water from the atmosphere into the cellulose/ionic liquid gel dramatically increases the apparent ionic Seebeck coefficient from 3 to 12.5 mV K-1. We identified the contribution of a hydrovoltaic voltage generated from water concentration difference as the main reason for the enhanced apparent ionic Seebeck coefficient, which depends on the kinetics of water absorption and desorption on the cold and hot side of the device. Finally, we demonstrated that it is possible to harvest electricity and charge a supercapacitor with intermittent temperature gradients by using this combination of ionic Seebeck voltage and hydrovoltaic voltage.
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