Multifunctional polyaniline nanofiber conductive hydrogel for supercapacitors and flexible sensors

Abstract

A series of polyaniline (PANI) nanofibers were prepared as conductive fillers. A polyvinyl alcohol (PVA)/agarose (AG) double network hydrogel was used as a flexible substrate. A PANI/PVA/AG conductive hydrogel was prepared via in situ polymerization of polyaniline nanofibers in a PVA/AG double network hydrogel. The electrochemical performance of the PANI/PVA/AG hydrogel electrode material was linked to the fiber morphology of polyaniline. The doping of polyaniline with 0.020 mol L⁻¹ citric acid demonstrated superior fiber morphology compared to doping with other citric acid concentrations, achieving fiber ratios of 80%. The specific capacitance of the PANI/PVA/AG hydrogel electrode materials doped with 0.020 mol L⁻¹ citric acid was 285 mF cm⁻², while the conductivity was 7.1 S m⁻¹. The doping of polyaniline with 0.5 mol L⁻¹ hydrochloric acid demonstrated superior fiber morphology compared to doping with other hydrochloric acid concentrations, achieving fiber ratios of 65%. The specific capacitance of PANI/PVA/AG hydrogel electrode materials doped with 0.5 mol L⁻¹ hydrochloric acid was 249 mF cm⁻², while their conductivity was 7.6 S m⁻¹. After 500 cycles of charge–discharge, the specific capacitance retention of the material was 73%. Photosensitivity tests indicated that the hydrogel exhibited high sensitivity to shorter wavelengths of blue light (460 nm) and ultraviolet light (380 nm). The hydrogel sensor possessed high sensitivity to strain in the range of 0–120%. Gauge factors (GF) of the hydrogel strain sensor were 1.280, 2.141, 1.907, and 1.261 for strain ranges of 0–30%, 30–60%, 60–90%, and 90–120%, respectively. Cyclic strain tensile tests indicated that the relative resistance change rate (ΔR/R₀) of the hydrogel sensor demonstrated a certain degree of repeatability and stability within the range of 0–100%. Thus, the hydrogel sensor is reliable and stable in the signal transmission process of detecting human movements as a flexible strain sensor. These results suggest that the PANI/PVA/AG conductive hydrogel is a multifunctional composite with good electrochemical storage performance, photosensitivity, and strain sensitivity that can be used in applications such as supercapacitors, flexible sensors and electronic wearable devices.