Conducting polymer hydrogels (CPHs) have emerged as a fascinating class of smart soft matters important for various advanced applications. However, achieving the synergistic characteristics of conductivity, self-healing ability, biocompatibility, viscoelasticity, and high mechanical performance still remains a critical challenge. Here, we develop for the first time a type of multifunctional hybrid CPHs based on a viscoelastic polyvinyl alcohol (PVA)-borax (PB) gel matrix and nanostructured CNFs-PPy (cellulose nanofibers-polypyrrole) complexes that synergizes the biotemplate role of CNFs and the conductive nature of PPy. The CNF-PPy complexes are synthesized through in situ oxidative polymerization of pyrrole on the surface of CNF templates, which are further well-dispersed into the PB matrix to synthesize homogeneous CNF-PPy/PB hybrid hydrogels. The CNF-PPy complexes not only tangle with PVA chains though hydrogen bonds, but also form reversibly cross-linked complexes with borate ions. The multi-complexation between each component leads to the formation of a hierarchical three-dimensional network. The CNF-PPy/PB-3 hydrogel prepared by 2.0 wt % of PVA, 0.4 wt % of borax, and CNF-PPy complexes with a mass ratio of 3.75/1 exhibits the highest viscoelasticity and mechanical strength. Because of a combined reinforcing and conductive network inside the hydrogel, its maximum storage modulus (∼0.1 MPa) and nominal compression stress (∼22 MPa) are 60 and 2240 times higher than those of pure CNF/PB hydrogel, respectively. The CNF-PPy/PB-3 electrode with a conductivity of 3.65 ± 0.08 S m has a maximum specific capacitance of 236.9 F g, and its specific capacitance degradation is less than 14% after 1500 cycles. The CNF-PPy/PB hybrid hydrogels also demonstrate attractive characteristics, including high water content (∼94%), low density (∼1.2 g cm), excellent biocompatibility, plasticity, pH sensitivity, and rapid self-healing ability without additional external stimuli. Taken together, the combination of such unique properties endows the newly developed CPHs with potential applications in flexible bioelectronics and provides a practical platform to design multifunctional smart soft materials.

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A high-performance flexible supercapacitor electrode with a core–shell structure is successfully developed from cellulose nanocrystal (CNC)-stabilized carbon nanotubes (CNTs). By incorporating poly­(vinyl alcohol) (PVA) and poly­(acrylic acid) (PAA), a cross-linked nanofibrous membrane (CNT–CNC/PVA–PAA) is prepared as the core material via directional electrospinning, followed by a thermal treatment. The flexible supercapacitor electrodes are eventually fabricated via the in situ polymerization of polyaniline (PANI), which was used as the coating shell material, on the aligned electrospun nanofibers. By taking advantage of the thermally induced esterification cross-linking that occurs among PVA, PAA, and the CNT–CNC nanohybrids, the membranes present with enhanced water resistance, mechanical strength, and thermal stability. After the surface coating of the PANI shell, the optimized PANI@CNT–CNC/PVA–PAA nanofibrous membranes exhibit a large porosity, an enhanced specific surface area, a superior tensile strength of ∼54.8 MPa, and a favorable electroconductivity of ∼0.44 S m–1. As expected, the nanofibrous electrodes with a specific capacitance of 164.6 F g–1 can maintain 91% of the original capacitance after 2000 cycles. The symmetrical solid-state supercapacitor assembled by the nanofibrous electrodes shows an excellent capacitance of 155.5 F g–1 and a remarkable capacitance retention of 92, 90, and 89% after 2000 cycles under flat, bending, and twisting deformations, respectively.

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