No abstract

In this work we demonstrate that biomass-derived proteins serve as an ideal precursor for synthesizing carbon materials for energy applications. The unique composition and structure of the carbons resulted in very promising electrochemical energy storage performance. We obtained a reversible lithium storage capacity of 1780 mA h g À1 , which is among the highest ever reported for any carbon-based electrode. Tested as a supercapacitor, the carbons exhibited a capacitance of 390 F g À1 , with an excellent cycle life (7% loss after 10 000 cycles). Such exquisite properties may be attributed to a unique combination of a high specific surface area, partial graphitization and very high bulk nitrogen content. It is a major challenge to derive carbons possessing all three attributes. By templating the structure of mesoporous cellular foam with egg white-derived proteins, we were able to obtain hierarchically mesoporous (pores centered at $4 nm and at 20-30 nm) partially graphitized carbons with a surface area of 805.7 m 2 g À1 and a bulk N-content of 10.1 wt%. When the best performing sample was heated in Ar to eliminate most of the nitrogen, the Li storage capacity and the specific capacitance dropped to 716 mA h g À1 and 80 F g À1 , respectively. Broader contextIt has been well-known that the residue nitrogen le in the activated carbons has a positive effect of on their electrochemical properties. However, this effect is limited by the relatively low content of nitrogen. Aer carefully tuning the preparation procedure to maximize the nitrogen functionalities in carbons, researchers recently found the N-rich carbons have much more potential than we achieved before for various energy applications, including supercapacitors, Li storage and ORR. The key is to make carbons with high surface area, right pore structure and high nitrogen content. In this work, by utilizing a very common Nrich renewable biomass-egg white and a well-known MCF template, we have obtained a mesoporous N-rich carbon with 10% N, bimodal mesopores and a specic surface area of 800 m 2 g À1 . The achieved carbon shows extremely promising properties for both Li storage (1780 mA h g À1 ) and supercapacitor (390 F g À1 ). Considering the large molecular weight of the proteins in egg white, the proteins from various biomass/biowaste may also be used as precursor. Beside the environmental benets and low cost, another signicant advantage of deriving carbons from biomass is the excellent cycle life since the functionalities are rmly incorporated in the backbone of carbons.

We created unique interconnected partially graphitic carbon nanosheets (10-30 nm in thickness) with high specific surface area (up to 2287 m(2) g(-1)), significant volume fraction of mesoporosity (up to 58%), and good electrical conductivity (211-226 S m(-1)) from hemp bast fiber. The nanosheets are ideally suited for low (down to 0 °C) through high (100 °C) temperature ionic-liquid-based supercapacitor applications: At 0 °C and a current density of 10 A g(-1), the electrode maintains a remarkable capacitance of 106 F g(-1). At 20, 60, and 100 °C and an extreme current density of 100 A g(-1), there is excellent capacitance retention (72-92%) with the specific capacitances being 113, 144, and 142 F g(-1), respectively. These characteristics favorably place the materials on a Ragone chart providing among the best power-energy characteristics (on an active mass normalized basis) ever reported for an electrochemical capacitor: At a very high power density of 20 kW kg(-1) and 20, 60, and 100 °C, the energy densities are 19, 34, and 40 Wh kg(-1), respectively. Moreover the assembled supercapacitor device yields a maximum energy density of 12 Wh kg(-1), which is higher than that of commercially available supercapacitors. By taking advantage of the complex multilayered structure of a hemp bast fiber precursor, such exquisite carbons were able to be achieved by simple hydrothermal carbonization combined with activation. This novel precursor-synthesis route presents a great potential for facile large-scale production of high-performance carbons for a variety of diverse applications including energy storage.