Asymmetric capacitors using lignin-based hierarchical porous carbons

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 63 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. (C) 2016 Elsevier B.V. All rights reserved.