Lignin as a green reductant and morphology directing agent in the fabrication of 3D graphene-based composites for high-performance supercapacitors

Reduced graphene oxide (RGO)-based materials have shown excellent performance as electrodes, but the green reduction and stabilization for RGO remains a great challenge. Here, lignin, the by-product of paper industry, was used as a green reductant for the synthesis of RGO and then acted as the morphology directing agent for the fabrication of 3D RGO-based composite. The effect of lignin on the reduction of GO was firstly illustrated. In comparison with those RGO solutions obtained by traditional reductants (ascorbic acid, sodium borohydride and hydrazine), the RGO solution obtained by lignin was the most stable, because lignin can prevent the aggregation of RGO sheets by π–π interaction. Moreover, lignin can modify the pore structure and give the 3D RGO-based composite with high specific surface area via hydrothermal carbonization. At last, the 3D lignin-RGO composite was employed as electrode and exhibited a good rate capability with high capacitance of 190 F g−1 at 0.5 A g−1 and 133.9 F g−1 at 10 A g−1, which is higher than those of biomass-based graphene materials and comparable to those of lignin-based carbon materials. Noteworthily, due to spatial structure modified by lignin, after 10,000 continuous cycles of galvanostatic charge/discharge, the 3D lignin-RGO electrode retained 86.5% of its specific capacitance.