Lignin reinforced conductive hydrogels with antibacterial properties for flexible supercapacitor applications

Lignin, a widely available yet underutilized natural polymer, has received significant interest for its environmentally friendly and sustainable benefits. Herein, a straightforward approach is presented to synthesize lignosulfonate sodium (LSS) ionic hydrogels through simple crosslinking with acrylamide (AAm) and aluminum chloride (AlCl₃), without using N, N'-methylenebisacrylamide (MBAA) and other external stimuli. The resulting LSS/PAAm/Al hydrogels are thoroughly analyzed using FTIR, XPS, mechanical testing, electrochemical workstation (ECW) and swelling/deswelling experiments. The abundant phenolic and sulfonic hydroxyl groups in the LSS-based hydrogels act a crucial role in providing multiple smart properties, including conductivity (as high as 5.79 S·m^-1), antibacterial activity and applications in supercapacitors. Robust hydrogen bonding and metal-coordination interactions among LSS, AAm and Al³⁺ imparted outstanding mechanical properties to the hydrogel. The hydrogel demonstrated a maximum tensile strength of approximately 321.4 kPa at an elongation of 175.6 % and a peak compressive strength of around 2.82 MPa with a maximum stretchability of 70 %. The hydrogel-based supercapacitor achieved a specific capacitance (C_s) of 467.7 F·g^-1, the highest energy density (E_d) of 64.96 Wh·kg^-1 and a power density (P_d) of 3.0 kW·kg^-1. This study provides a pathway for incorporating renewable and biodegradable materials into the next generation of sustainable, high-performance flexible electronic devices.