Asymmetric capacitors using lignin-based hierarchical porous carbons

Abstract

Hierarchical porous carbons (HPC) were fabricated from lignin by hard template method using Beta and Y zeolites as templates. Textural properties were dictated by the hard template, obtaining a bi-modal pore size distribution with similar micropore sizes but different mesopore sizes. These HPCs provide a well-connected and developed porosity that show capacitance values near to 140 F g−1 in 1 M H2SO4 at 1 A g−1 and a capacitance retention of ca. 50% and 40% when the specific current is increased from 1 to 64 A g−1 for the Y and the Beta-based carbons, respectively. A symmetric capacitor working at 1.2 V with energy densities of 4.2 Wh kg−1 at 1.3 kW kg−1 has been obtained using the Beta-based HPC. Asymmetric in mass design allowed to operate the capacitor safely at 1.4 V, yielding an energy density of 6.3 Wh kg−1 at 1.3 kW kg−1, an increase of 50% with respect to the symmetric configuration, while keeping a maximum power near to 50 kW kg−1. This capacitor has an energy density comparable to that of a symmetric supercapacitor built using a commercial activated carbon of much higher porosity development, outperforming it in terms of energy, coulombic efficiencies and maximum power.