Sustainable high-energy supercapacitors via biomass-derived lignosulfonate-graphene hydrogel synergized with potassium ferrate.

The pursuit of carbon neutrality and the replacement of highly polluting energy sources drive the imperative need for a novel electrode material system. In this study, a ternary composite hydrogel (LPGH) with promising electrochemical properties was synthesized using a facile one-step hydrothermal method. This material features a graphene-based conductive scaffold, with lignosulfonate (LS) serving as a multifunctional dispersant and potassium ferrate (K2FeO4) incorporated as a multifunctional precursor. The LPGH electrode delivers a remarkable areal capacitance of 799 mF cm-2 at 1 mA cm-2, which is 2.1 times greater than that of the pure graphene hydrogel (377 mF cm-2). Furthermore, a symmetric supercapacitor fabricated with LPGH electrodes achieved an energy density of 41.1 μWh·cm-2 at a power density of 500 μW·cm-2. Moreover, the device exhibited excellent long-term stability, retaining 84.46% of its initial capacitance after 10,000 cycles. This work thus presents a sustainable strategy for designing high-performance, environmentally compatible energy storage materials from biomass resources.