No abstract

We demonstrate that peat moss, a wild plant that covers 3% of the earth's surface, serves as an ideal precursor to create sodium ion battery (NIB) anodes with some of the most attractive electrochemical properties ever reported for carbonaceous materials. By inheriting the unique cellular structure of peat moss leaves, the resultant materials are composed of three-dimensional macroporous interconnected networks of carbon nanosheets (as thin as 60 nm). The peat moss tissue is highly cross-linked, being rich in lignin and hemicellulose, suppressing the nucleation of equilibrium graphite even at 1100 °C. Rather, the carbons form highly ordered pseudographitic arrays with substantially larger intergraphene spacing (0.388 nm) than graphite (c/2 = 0.3354 nm). XRD analysis demonstrates that this allows for significant Na intercalation to occur even below 0.2 V vs Na/Na(+). By also incorporating a mild (300 °C) air activation step, we introduce hierarchical micro- and mesoporosity that tremendously improves the high rate performance through facile electrolyte access and further reduced Na ion diffusion distances. The optimized structures (carbonization at 1100 °C + activation) result in a stable cycling capacity of 298 mAh g(-1) (after 10 cycles, 50 mA g(-1)), with ∼150 mAh g(-1) of charge accumulating between 0.1 and 0.001 V with negligible voltage hysteresis in that region, nearly 100% cycling Coulombic efficiency, and superb cycling retention and high rate capacity (255 mAh g(-1) at the 210th cycle, stable capacity of 203 mAh g(-1) at 500 mA g(-1)).

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.