Intrinsically Freezing-Tolerant, Conductive, and Adhesive Proton Donor–Acceptor Hydrogel for Multifunctional Applications

Abstract

Hydrogels have unique liquid-like conductivity and solid-like mechanical properties and are promising materials for a wide range of applications, including tactile sensors and electrolytes for the energy storage device. However, combining suitable mechanical and functional properties in a single hydrogel system remains a central challenge from an application point of view. Besides, freezing of water at subzero temperature severely limits the functional potential of hydrogels. Herein, we have developed a soft yet tough proton donor−acceptor (PDA) hydrogel, combining intrinsic freezing tolerability, conductivity, and adhesiveness with ultrafast complete self-recovery (within 30 s). This unique combination of properties helps us prepare a highly durable tactile sensor (strain, pressure, and temperature) for human motion monitoring at ambient and subzero temperatures. The hydrogels were also used as a matrix to fabricate intrinsically compressible electrolytes for supercapacitor devices. The PDA-based supercapacitors show superior electrochemical performance at ambient temperature and substantially retain it at zero and subzero temperatures. This work also provides a detailed insight into the molecular interactions present in the system and correlates with the bulk mechanical and functional properties, which could guide the development of hydrogels.

Freeze–Thaw-Induced, Metal Ion Cross-Linked, Mechanically Robust, and Highly Stretchable Composite Poly(vinyl alcohol) Hydrogels for Flexible Electronic Applications

“…Compared to other hydrogel electrolyte-based supercapacitors operating at the same current density, this hydrogel showed higher values of specific capacitance. ,,− Coulombic efficiency was determined from the charge–discharge time and attained a high value (∼92%) at a current density of 2 A g –1 (Figure E). This hydrogel-based supercapacitor achieved a maximum power density up to 6 kW kg –1 and an energy density up to 5.5 Wh kg –1 (Figure F), which was comparatively higher than in other literature reports. ,,, To show the potential of our hydrogel materials, a comparison of electrochemical performances of various hydrogel-based supercapacitors with our current work is summarized in Table S5, Supporting Information. Due to the high compressive strength of the hydrogel, the capacitance behavior of the supercapacitor was explored further by performing the GCD under various loads (125, 250, 375, and 500 g cm –2 ) (Figure G).…”

“…However, with increasing frequency, both the storage and loss moduli increased due to faster bond dissociation and reassociation within the hydrogel network, but the G ′/ G ″ ratio gradually decreased. It may be due to the formation of a weak interaction in the hydrogel network, which lowers the elastic behavior in the high-frequency region. − …”

“…The GCD profiles demonstrated an isosceles triangle-like shape and exhibited a little IR drop at both low and high current densities, leading to nearly ideal capacitive behavior. 66 With increasing current density, the specific capacitance gradually decreased (Figure 9E). At a current density of 0.5 A g −1 , the highest specific capacitance of 111 F g −1 was achieved.…”

“…This hydrogelbased supercapacitor achieved a maximum power density up to 6 kW kg −1 and an energy density up to 5.5 Wh kg −1 (Figure 9F), which was comparatively higher than in other literature reports. 66,74,77,78 To show the potential of our hydrogel materials, a comparison of electrochemical performances of various hydrogel-based supercapacitors with our current work is summarized in Table S5, Supporting Information. Due to the high compressive strength of the hydrogel, the capacitance behavior of the supercapacitor was explored further by performing the GCD under various loads (125, 250, 375, and 500 g cm −2 ) (Figure 9G).…”

Thermoregulation of Hydrogel Spatiotemporal Mechanics by Exploiting the Folding–Unfolding Characteristics of Globular Proteins

“…Polymer hydrogels are three-dimensional cross-linked networks holding a significant amount of water and are regarded as the closest engineering material to mimic biological soft tissues. The biological resemblance makes polymer hydrogels attractive candidates for applications such as tissue engineering, , drug delivery, , wound healing, , sensors, , bioimplants, , etc. However, traditional synthetic polymer hydrogels are weak and brittle.…”