Highly conductive and tough double-network hydrogels for smart electronics

Abstract

Development and understanding of highly mechanically robust and electronically conducting hydrogels are extremely important for ever-increasing energy-based applications. Conventional mixing/blending of conductive additives with hydrophilic polymer network prevents both high mechanical strength and electronic conductivity to be presented in polymer hydrogels. Here, we proposed a double-network (DN) engineering strategy to fabricate PVA/PPy DN hydrogels, consisting of a conductive PPy-PA network via in-situ ultrafast gelation and a tough PVA network via a subsequent freezing/thawing process. The resultant PVA/PPy hydrogels exhibited superior mechanical and electrochemical properties, including electrical conductivity of ~6.8 S/m, mechanical strength of ~0.39 MPa, and elastic moduli of ~0.1 MPa. Upon further transformation of PVA/PPy hydrogels into supercapacitors, they demonstrated a high capacitance of ~280.7 F/g and a cycle life of 2000 galvanostatic charge/discharge cycles with over 94.3% capacity retention at the current density of 2 mA/cm2 and even subzero temperatures of −20 °C. Such enhanced mechanical performance and electronic conductivity of hydrogels are mainly stemmed from a synergistic combination of continuous electrically conductive PPy-PA network and the two interpenetrating DN structure. This in-situ gelation strategy is applicable to the integration of ionic-/electrical-conductive materials into DN hydrogels for smart-soft electronics, beyond the most commonly used PEDOT:PSS-based hydrogels.