**Huixiang Wang 1, Subir Kumar Biswas 2, Sailing Zhu 1, Ya Lu 1, Yiying Yue 3, Jingquan Han 1,\*, Xinwu Xu 1,\*, Qinglin Wu <sup>4</sup> and Huining Xiao <sup>5</sup>**


Received: 8 December 2019; Accepted: 2 January 2020; Published: 6 January 2020

**Abstract:** Recently, with the development of personal wearable electronic devices, the demand for portable power is miniaturization and flexibility. Electro-conductive hydrogels (ECHs) are considered to have great application prospects in portable energy-storage devices. However, the synergistic properties of self-healability, viscoelasticity, and ideal electrochemistry are key problems. Herein, a novel ECH was synthesized by combining polyvinyl alcohol-borax (PVA) hydrogel matrix and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-cellulose nanofibers (TOCNFs), carbon nanotubes (CNTs), and polyaniline (PANI). Among them, CNTs provided excellent electrical conductivity; TOCNFs acted as a dispersant to help CNTs form a stable suspension; PANI enhanced electrochemical performance by forming a "core-shell" structural composite. The freeze-standing composite hydrogel with a hierarchical 3D-network structure possessed the compression stress (~152 kPa) and storage modulus (~18.2 kPa). The composite hydrogel also possessed low density (~1.2 g cm−3), high water-content (~95%), excellent flexibility, self-healing capability, electrical conductivity (15.3 S m<sup>−</sup>1), and specific capacitance of 226.8 F g−<sup>1</sup> at 0.4 A g<sup>−</sup>1. The fabricated solid-state all-in-one supercapacitor device remained capacitance retention (~90%) after 10 cutting/healing cycles and capacitance retention (~85%) after 1000 bending cycles. The novel ECH had potential applications in advanced personalized wearable electronic devices.

**Keywords:** cellulose nanofibers; carbon nanotube; polyaniline; hydrogels; supercapacitor
