A nitrogen-doped mesoporous carbon containing an embedded network of carbon nanotubes as a highly efficient catalyst for the oxygen reduction reaction.

A nitrogen-doped mesoporous carbon containing a network of carbon nanotubes (CNTs) was produced for use as a catalyst for the oxygen reduction reaction (ORR). SiO2 nanoparticles were decorated with clusters of Fe atoms to act as catalyst seeds for CNT growth, after which the material was impregnated with aniline. After polymerization of the aniline, the material was pyrolysed and the SiO2 was removed by acid treatment. The resulting carbon-based hybrid also contained some Fe from the CNT growth catalyst and was doped with N from the aniline. The Fe-N species act as active catalytic sites and the CNT network enables efficient electron transport in the material. Mesopores left by the removal of the SiO2 template provide short transport pathways and easy access to ions. As a result, the catalyst showed not only excellent ORR activity, with 59 mV more positive onset potential and 30 mV more positive half-wave potential than a Pt/C catalyst, but also much longer durability and stronger tolerance to methanol crossover than a Pt/C catalyst.

Lithiation of silicon nanoparticles confined in carbon nanotubes.

Silicon has the highest theoretical lithium storage capacity of all materials at 4200 mAh/g; therefore, it is considered to be a promising candidate as the anode of high-energy-density lithium-ion batteries (LIBs). However, serious volume changes caused by lithium insertion/deinsertion lead to a rapid decay of the performance of the Si anode. Here, a Si nanoparticle (NP)-filled carbon nanotube (CNT) material was prepared by chemical vapor deposition, and a nanobattery was constructed inside a transmission electron microscope (TEM) using the Si NP-filled CNT as working electrode to directly investigate the structural change of the Si NPs and the confinement effect of the CNT during the lithiation and delithiation processes. It is found that the volume expansion (∼180%) of the lithiated Si NPs is restricted by the wall of the CNTs and that the CNT can accommodate this volume expansion without breaking its tubular structure. The Si NP-filled CNTs showed a high reversible lithium storage capacity and desirable high rate capability, because the pulverization and exfoliation of the Si NPs confined in CNTs were efficiently prevented. Our results demonstrate that filling CNTs with high-capacity active materials is a feasible way to make high-performance LIB electrode materials, taking advantage of the unique confinement effect and good electrical conductivity of the CNTs.

A flexible sulfur-graphene-polypropylene separator integrated electrode for advanced Li-S batteries.

A flexible Li-S battery based on an integrated structure of sulfur and graphene on a separator is developed. The internal graphene current collector offers a continuous conductive pathway, a modified interface with sulfur, and a good barrier to and an effective reservoir for dissolved polysulfides, consequently improving the capacity and cyclic life of the Li-S battery.