A new perspective of lanthanide metal-organic frameworks: tailoring Dy-BTC nanospheres for rechargeable Li-O2 batteries.

Nanoscaled lanthanide metal-organic frameworks (NLn-MOFs) have emerged as attractive nanomaterials for photofunctional applications. To enhance the inherent properties and endow NLn-MOF materials with desired electrochemical performance for rechargeable Li-O2 batteries, rational design and synthesis of NLn-MOFs with tailored morphologies for high O2 accessibility and rich open metal sites to bind O2 molecules is highly desired and remains a grand challenge. Herein, we prepare Dy-BTC nanospheres, which are explored for the first time as an O2 cathode in Li-O2 batteries. Interestingly, the specific capacity and electrochemical stability of the Dy-BTC nanosphere-based electrode outperform significantly those of the bulk crystalline Dy-BTC. A full discharge capacity of 7618 mA h g-1 at 50 mA g-1 has been achieved by the Dy-BTC nanospheres. Furthermore, the Dy-BTC nanospheres stably deliver a discharge capacity of 1000 mA h g-1 at 200 mA g-1 for 76 cycles, which is remarkably longer than that of the bulk crystalline Dy-BTC with a cycling life of 26 cycles.

Interconnected Phosphorus and Nitrogen Codoped Porous Exfoliated Carbon Nanosheets for High-Rate Supercapacitors.

Carbon-based supercapacitors have high power density and long cycle life; however, they are known to suffer from problems related to low energy density and high inner resistance. Here, we report a novel hierarchically porous functional carbon that is made up of interconnected exfoliated carbon nanosheets with thickness of a few nanometers. Notably, these porous carbon nanosheets are doped with abundant nitrogen (N) dopants in the basal plane and phosphorus (P) functional groups at the edge of the graphene lattice. The specific surface chemistry and pore structure of the synthesized sample, combined with its large specific surface area, make it a high-performance active material for supercapacitor electrode. The obtained supercapacitor made with the optimized sample showed a high specific capacitance (265 F g-1 at 0.5 A g-1) as well as long-term stability (94% capacitance retention after 5000 cycles). Particularly, the enhanced electrochemical characteristics were maintained even at high electrode mass loading (time constant (τ0) is 1.10 s for an electrode mass loading of 12.38 mg cm-2 compared to 1.61 s for a mass loading of 4.17 mg cm-2 for commercial activated carbon), which is important for a high packing factor of the capacitor.

Fog-like fluffy structured N-doped carbon with a superior oxygen reduction reaction performance to a commercial Pt/C catalyst.

A high-performance N-doped carbon catalyst with a fog-like, fluffy structure was prepared through pyrolyzing a mixture of polyacrylonitrile, melamine and iron chloride. The catalyst exhibits an excellent oxygen reduction reaction (ORR) performance, with a half-wave potential 27 mV more positive than that of a commercial Pt/C catalyst (-0.120 vs. -0.147 V) and a higher diffusion-limiting current density than that of Pt/C (5.60 vs. 5.33 mA cm(-2)) in an alkaline medium. Moreover, it also shows outstanding methanol tolerance, remarkable stability and nearly 100% selectivity for the four-electron ORR process. To our knowledge, it is one of the most active doped carbon ORR catalysts in alkaline media to date. By comparing catalysts derived from precursors containing different amounts of melamine, we found that the added melamine not only gives the catalyst a fluffy structure but also modifies the N content and the distribution of N species in the catalyst, which we believe to be the origins for the catalyst's excellent ORR performance.