Ni2+-Rich Collagen/Lignin Composite Hydrogel: Transforming Industrial Waste Materials into Flexible Electronics

Polymer-based conducting hydrogels have drawn significant interest for supercapacitors because of their fascinating features, including excellent conductivity, tunable mechanical properties, porous structure, outstanding flexibility, scalable processability, environmental friendliness, and low production cost. Herein, a dynamic redox process was designed utilizing collagen (CG), poly(acrylic acid) (PAA), lignosulfonate (LS), and Ni²⁺ to synthesize CG/PAA/LS/Ni hydrogel. The hydrogel’s unique features, including high ionic conductivity (IC) (4.89 S/m), outstanding flexibility, and stretchability, were assigned to the effective complex formation of Ni²⁺ with the numerous functional groups of CG, LS, and PAA. With a maximum tensile strength of approximately 0.61 MPa at an elongation of 1595% and a maximum compressive strength of ∼208 kPa with the highest stretchability of 65%, the CG/PAA/LS/Ni hydrogel demonstrated exceptional mechanical properties. The prepared hydrogel can also monitor human motion with high sensitivity. The supercapacitor, assembled from the CG/PAA/LS/Ni hydrogel, manifested specific capacitance (C_s), highest energy density (E_d), and power density (P_d) of 245.6 F/g, 27.63 Wh/kg, and 2.7 kW/kg, respectively. Even after 5000 consecutive cycles of charging and discharging, the supercapacitor can retain its capacitance of 95.4%. This study opens up possibilities for the effective use of industrial waste in flexible electronics.