The key pre-pyrolysis in lignin-based activated carbon preparation for high performance supercapacitors

Abstract

Lignin as second most abundant natural polymer after cellulose is the main by-product of conventional pulp and paper industry and mostly consumed as a low-grade fuel in industrial burner or boiler. It is necessary to explore the possibility for high value-added application of lignin. Lignin-based activated carbon (LAC) is prepared through a two-step pre-pyrolysis and activation or directly activation method for high-performance supercapacitors (SCs). This paper is devoted to examining the role of pre-pyrolysis treatment in the preparation of LAC. Pre-pyrolysis treatment is expected to alter the pore size distribution, maintain the morphology and improve the graphitization degree of lignin. Multiple characterization methods are used to measure the pore structure, morphology and graphitization degree of LAC. Consequently, LAC with pre-pyrolysis exhibits high Vmicro/Vtotal ratio, uniform morphology and relatively high graphitization degree in comparison with directly-activated LAC. In detail, The Vmicro/Vtotal ratio of LAC with pre-pyrolysis at 600 °C has increased from 22% to 66%. What’s more, the gravimetric capacitance reaches to as high as 312 F g−1 by improving 100 F g−1, the specific capacitance is 14.0 μF cm−2, and even after 10,000 cycles at 1 A g−1 a specific capacity of 261 F g−1 (about 95% retention ratio) remains while directly-activated LAC is only 218 F g−1. Hence, LAC with pre-pyrolysis is a promising material for high performance SCs.