Hybrids of carbon nanotubes (CNTs) and poly(3,4-ethylenedioxythiophene) (PEDOT) treated by tetrakis(dimethylamino)ethylene (TDAE) have large n-type voltages in response to temperature differences. The reduced carrier concentration by TDAE reduction and partially percolated CNT networks embedded in the PEDOT matrix result in high thermopower and low thermal conductivity. The high electron mobility in the CNTs helps to minimally reduce the electrical conductivity of the hybrid, resulting in a large figure-of-merit.

In this work, the effect of pH on a nitrogen-doped ordered mesoporous carbon catalyst for the oxygen reduction reaction (ORR) is extensively investigated. Electrochemical methods, including cyclic voltammetry (CV), rotating ring-disk electrode (RRDE), and cathodic stripping voltammetry, are applied to investigate the electrochemical behavior in electrolyte solutions of different pHs (0–2, 7, 12–14). The CV result reveals that nitrogen-doped carbon has a variety of enriched reversible redox couples on the surface, and the pH has a significant effect. Whether these redox couples are electrochemically active or inactive to the ORR depends on the electrolyte used. In acid media, an oxygen molecule directly interacts with the redox couple, and its reduction proceeds by the surface-confined redox-mediation mechanism, yielding water as the product. Similarly, the first electron transfer in alkaline media is achieved by the surface-confined redox-mediation mechanism at the higher potentials. With decreasing potential, another parallel charge transfer process by the outer-sphere electron transfer mechanism gets pronounced, followed by parallel 2-e and 4-e reduction of oxygen. The proposed mechanisms are well supported by the following electrochemical results. At high potentials, the Tafel slope remains unchanged (60–70 mV dec–1) at all investigated pHs, and the reaction order of proton and hydroxyl ions is found to be 1 and −0.5, respectively, in acid and alkaline media. The electron transfer number is ∼4 at high potentials in both acid and alkaline media; however, at higher pHs, it shows a considerable decrease as the potential decreases, indicating the change in the reaction pathway. Finally, the nitrogen-doped carbon catalyst shows performance in alkaline media superior to that in acid media. Such a gap in performance is rationalized by considering the chemical change in the surface at different pH values.

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

High energy density and long-term stability of Li-S batteries are achieved by employing a 3D sponge-like carbon nanotube cathode and a liquid-type polysulfide catholyte. Carbon nanotubes not only provide excellent electron pathways and polysulfide reservoirs, but they can also be used as a standalone cathode without current collectors, which greatly alleviates problems arising from insulating sulfur and polysulfide shuttles as well as remarkably increasing the energy density.

Li-S batteries can potentially deliver high energy density and power, but polysulfide shuttle and lithium dendrite formations on Li metal anode have been the major hurdle. The polysulfide shuttle becomes severe particularly when the areal loading of the active material (sulfur) is increased to deliver the high energy density and the charge/discharge current density is raised to deliver high power. This study reports a novel mechanochemical method to create trenches on the surface of carbon nanotubes (CNTs) in free-standing 3D porous CNT sponges. Unique spiral trenches are created by pressures during the chemical treatment process, providing polysulfide-philic surfaces for cathode and lithiophilic surfaces for anode. The Li-S cells made from manufacturing-friendly sulfur-sandwiched cathodes and lithium-infused anodes using the mechanochemically treated electrodes exhibit a strikingly high areal capacity as high as 13.3 mAh cm −2 , which is only marginally reduced even with a tenfold increase in current density (16 mA cm −2 ), demonstrating both high "cell-level" energy density and power. The outstanding performance can be attributed to the significantly improved reaction kinetics and lowered overpotentials coming from the reduced interfacial resistance and charge transfer resistance at both cathodes and anodes. The trench-wall CNT sponge simultaneously tackles the most critical problems on both the cathodes and anodes of Li-S batteries, and this method can be utilized in designing new electrode materials for energy storage and beyond.to other batteries based on different chemistry due to the unsatisfactory energy density of Li-ion batteries particularly for large-scale applications like transportation and stationary energy storage. [1] On the cathode side, conversion chemistry has shown great promise for replacing the intercalation chemistry of Li-ion batteries. Conversion-type cathode materials like sulfur and oxygen can provide 2567 and 3505 Wh kg −1 , respectively, compared to 387 Wh kg −1 of the intercalation-type LiCoO 2 cathode. [2] In particular, Li-S batteries have attracted rapidly increasing attention and substantial progresses have recently been made to alleviate their inherent problems like lithium polysulfide dissolution and shuttle, insulating nature of the end products, and volume variations of sulfur cathode during cycling. [3] As a result, the specific capacity and cycling performance have been markedly improved when the areal loading of sulfur (active material) is low. The energy density based on the mass of sulfur only (not whole cathode or battery pack) has been good enough to beautify researchers' results, but the low sulfur loading has negated the high-energy-density merit of Li-S batteries, resulting in no improvement in the actual energy density of the "cell" or "battery pack" compared to the Li-ion batteries. To have a high "cell-level" energy density, the areal loading of sulfur needs to be increased to ≈10 mg cm −2 or higher, compared to typical literature values Lithium-Sulfur Batter...

Highly-porous, lightweight , and inexpensive three-dimensional (3D) sponges composed of interconnected carbon nanotubes (CNTs) without base materials synthesize with a facile and scalable one-step chemical vapor deposition process, and test as anode of microbial fuel cells (MFCs). The MFCs generates higher power densities of 2150 W m-3 (per anode volume) or 170 W m-3 (per anode chamber volume), comparable to those of commercial 3D carbon felt electrodes test under the same conditions. The high performances attribute to excellent charge transfer between CNTs and microbes owing to 13 times lower charge transfer resistance compared to that of carbon felt. The material cost of producing these CNT sponge estimates to be ~$0.1/g CNT , significantly lower than that of other methods. In addition, the high production rate of about 3.6 g h-1 compared to typical production rate of 0.02 g h-1 of other CNT-based materials makes this process economically viable. The one-step synthesis method allowing selfassembly of 3D CNT sponges as they grow is low cost and scalable, making this a promising method for manufacturing high-performance anodes of MFCs, with broad applicability to microbial electrochemical systems in general.

No abstract

No abstract