Delignification Enhances Capacitance of Wood-Derived Electrodes

Thursday, 1 June 2017: 08:20
Churchill C1 (Hilton New Orleans Riverside)
Y. Zhao and M. F. Islam (Carnegie Mellon University)
In recent years, diverse types of biomass materials have been pyrolyzed and activated to generate carbon materials that are subsequently utilized as electrodes in electrochemical cells because they are inexpensive, abundant, and sustainable. The principal components of most biomasses are cellulose, hemicellulose and lignin. When pyrolyzed and activated, cellulose makes leading contribution to charge storage while hemicellulose and lignin add minor contributions, disproportionately increasing the mass and cost of electrochemical cells. Further, biomass-derived electrodes frequently only have shapes of extraordinarily thin supported films, which require multiple layers of electrodes to generate appreciable electrochemical performance, increasing cost and complexity of electrochemical cells. We have developed an acid-based strategy to delignify Balsa wood that removes hemicellulose and lignin while retaining cellulose, and then pyrolyzed and activated this wood to create freestanding thick (0.5 mm) electrodes that possess exceptional power and energy densities. The delignified wood derived electrodes exhibit a specific capacitance of 266 F/g (310 F/g) at 0.1 A/g, gradually decreasing to 170 (90) F/g at 20 A/g in aqueous electrolyte 1M Na2SO4 (room temperature ionic liquid, RTIL; 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), which are more than 50% greater than that of electrodes fabricated using non-delignified wood. Furthermore, the electrodes are highly durable, retaining 92% (82%) of capacitance after 10,000 charge-discharge cycles in aqueous (RTIL) electrolyte. The electrodes demonstrate a high energy density of 5 (73) Wh/kg and a corresponding power density of 4060 (16500) W/kg in aqueous (RTIL) electrolyte. Our work provides guidance on the use of delignification to enhance electrochemical performance of biomass-derived electrodes. This work has been partially supported by the NSF through Grant CMMI 1335417.