Three-dimensional N/Fe-containing carbon nanotube sponges showing striking improvements in catalytic activity and stability were grown using a facile/scalable synthesis method.

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In microbial fuel cells (MFCs), physical and electrochemical interactions between microbes and electrode surfaces are critical to performance. Nanomaterial-based electrodes have shown promising performances, however their unique characteristics have not been fully utilized. The developed electrodes here that consist of multi-wall carbon nanotubes (MWCNTs) directly grown in the radial direction from the wires of stainless steel (SS) meshes, providing extremely large three-dimensional surfaces while ensuring minimal ohmic loss between CNTs and SS meshes, fully utilizing the advantages of CNTs. Systematic studies on how different lengths, packing densities, and surface conditions of CNTs affect MFC power output revealed that long and loosely packed CNTs without any amorphous carbon show the highest power production performance. The power density of this anode electrode is 7.4-fold higher compared to bare carbon cloth, which is the highest reported improvement for MFCs with nanomaterial-decorated electrodes. The results of this study offer great potential for advancing the development of microbial electrochemical systems by providing a highly efficient nanomaterial-based electrode that delivers large surface area, high electrochemical activity, and minimum ohmic loss, as well as provide design principles for next-generation nanomaterial-based electrodes that can be broadly applicable for highly efficient microbial electrochemical cells.

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Lithium-oxygen (Li-O 2 ) batteries are considered to be the next generation energy storage technology due to their extremely high theoretical energy density and the simplicity of the battery cells. However, a large energy density can be obtained only with a slow discharge-charge rate, and quickly decreases upon cycling. These drawbacks can be attributed to the large overpotential and sluggish kinetics of the oxygen reduction and evolution reactions. To overcome the current problems, recent research has focused on developing catalysts made of inexpensive metal oxides and carbonaceous materials in addition to precious metals, but the role of non-precious metal catalysts in the battery performance is still largely unexplored. Here we present kinetic studies and comparative evaluation of enhanced oxygen reduction and evolution reactions with carbon nanotube (CNT) arrays containing in situ decorated a-Fe 2 O 3 nanoparticles as both a binder-free catalyst and a cathode for nonaqueous Li-O 2 batteries. Our Fe 2 O 3 -decorated CNTs greatly helped to form Li 2 O involving the four-electron reduction pathway in addition to Li 2 O 2 commonly formed via the one/two-electron reduction pathway, and thereby delivered a very large capacity of 26.5 A h g À1 at the 1 st discharge and a relatively long cycling performance (48 cycles with a capacity limit of 1.5 A h g À1 ). Unique and branch-like nanocrystalline Li 2 O and Li 2 O 2 after discharge would have lowered the overpotential for the oxygen evolution reaction. Our detailed compositional and morphological studies will be of great help to further improve the cycling performance as well as develop better non-precious metal catalysts and electrodes for Li-O 2 batteries.

The exceptional thermal conductivity of individual carbon nanotubes have rarely materialized in bulk materials mainly due to the large thermal contact resistance between carbon nanotubes (CNTs). This can be attributed to weak van der Waals bonding at the CNT junctions where the outstanding phonon transport along the strong covalent bonding on the graphitic layer is largely impeded. In bulk materials, however, it has been extremely difficult to achieve covalently bonded junctions between CNTs. Here we report polymer composites consisting of sponge-like CNT structures whose junctions between CNTs are covalently bonded, resulting in a high thermal conductivity and a low Young's modulus, which are hard to achieve at the same time. The low modulus allows thermal interface material (TIM) to easily deform to make the surfaces of heat sink/source fully in contact, which is essential for TIM. Our facile scalable preparation process also makes our composite very attractive as TIM as well as provides insight to better utilize high thermal conductivity of CNTs.