Outstanding electrochemical performance of highly N- and O-doped carbons derived from pine tannin

Highly N- and O-doped carbons were prepared from pine tannins by hydrothermal carbonisation (HTC) and subsequently applied as materials for supercapacitor electrodes. Pine tannins were transformed into carbon materials by using environment-friendly solvents (water or ammonia) without applying any activation or functionalisation post-treatment. Depending on the solution used for extracting tannins and on the HTC method, carbons with different physicochemical and electrochemical properties were obtained. The material prepared from the water-extracted tannin and subjected to HTC in ammonia displayed a porous texture composed of: (a) low ultramicroporosity and well-developed mesoporosity; (b) a hydrophilic surface with a high density of surface functionalities; and (c) a high nanotextural order. These features accounted for the excellent electrochemical performance of the resultant carbon electrode in terms of high rate capability up to 1 V s(-1), high energy density up to similar to 1500 mA g(-1), low cell resistance and fast frequency response, making it a suitable material for practical supercapacitors.