An all-lignin-based flexible supercapacitor based on a nitrogen-doped carbon dot functionalized graphene hydrogel

Designing flexible supercapacitors (FSCs) as energy storage devices for portable/wearable electronic products using the earth-abundant, renewable and environmentally friendly natural biomass has the prospect of building a green, sustainable society. Here, we report a new type of three-dimensional graphene hydrogel with lignin-based nitrogen-doped carbon dots as a decorative material. The nitrogen doped carbon dots are anchored in a graphene sheet through pi-pi bonds and electrostatic interactions, forming a stable three-dimensional network structure, which comprehensively improves the electrochemical performance of the electrode material. As an electrode, the specific capacitance reaches 387 F g(-1) at 1 A g(-1), and the rate performance reaches 75.7% when the current density increases to 7 A g(-1). In addition, an all-lignin-based supercapacitor assembled with a lignin hydrogel as the electrolyte has superior cycle stability (cycle life after 5000 cycles is 92.3%) and rate performance. When the power density is 243 W kg(-1), the energy density is 25.6 W h kg(-1); moreover, the FSC has excellent electrochemical stability even at different bending angles. This all-lignin-based FSC with excellent electrochemical performance and flexibility opens up a new path for the application of lignin in flexible energy storage devices.

Automated summary

Designing flexible supercapacitors using renewable natural biomass has the potential to build a green, sustainable society. A new type of three-dimensional graphene hydrogel with lignin-based nitrogen-doped carbon dots as a decorative material was reported here, showing excellent electrochemical performance.