Growth and Performance of High-Quality SWCNT Forests on Inconel Foils as Lithium-Ion Battery Anodes.

Large-scale production of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) on metal foils promises to enable technological advancements in many fields, from functional composites to energy storage to thermal interfaces. In this work, we demonstrate growth of high-quality (G/D > 6, average diameters ∼ 2-3 nm, densities > 1012 cm-2) VA-SWCNTs on Inconel metal for use as a lithium-ion battery (LIB) anode. Scale-up of SWCNT growth on Inconel 625 to 100 cm2 exhibits nearly invariant CNT structural properties, even when synthesis is performed near atmospheric pressure, and this robustness is attributed to a growth kinetic regime dominated by the carbon precursor diffusion in the bulk gas mixture. SWCNT forests produced on large-area metal substrates at close to atmospheric pressure possess a combination of structural features that are among the best demonstrated so far in the literature for growth on metal foils. Leveraging these achievements for energy applications, we demonstrate a VA-SWCNT LIB anode with capacity >1200 mAh/g at 1.0C and stable cycling beyond 300 cycles. This robust synthesis of high-quality VA-SWCNTs on metal foils presents a promising route toward mass production of high-performance CNT devices for a broad range of applications.

3D Printed Nickel-Molybdenum-Based Electrocatalysts for Hydrogen Evolution at Low Overpotentials in a Flow-Through Configuration.

Three-dimensional (3D) printed, hierarchically porous nickel molybdenum (NiMo) electrocatalysts were synthesized and evaluated in a flow-through configuration for the hydrogen evolution reaction (HER) in 1.0 M KOH(aq) in a simple electrochemical H-cell. 3D NiMo electrodes possess hierarchically porous structures because of the resol-based aerogel precursor, which generates superporous carbon aerogel as a catalyst support. Relative to a traditional planar electrode configuration, the flow-through configuration allowed efficient removal of the hydrogen bubbles from the catalyst surface, especially at high operating current densities, and significantly decreased the overpotentials required for HER. An analytical model that accounted for the electrokinetics of HER as well as the mass transport with or without the flow-through configuration was developed to quantitatively evaluate voltage losses associated with kinetic overpotentials and ohmic resistance due to bubble formation in the porous electrodes. The chemical composition, electrochemical surface area (ECSA), and roughness factor (RF) were also systematically studied to assess the electrocatalytic performance of the 3D printed, hierarchically porous NiMo electrodes. An ECSA of 25163 cm2 was obtained with the highly porous structures, and an average overpotential of 45 mV at 10 mA cm-2 was achieved over 24 h by using the flow-through configuration. The flow-through configuration evaluated in the simple H-cell achieved high electrochemical accessible surface areas for electrochemical reactions and provided useful information for adaption of the porous electrodes in flow cells.

Fast Permeation of Small Ions in Carbon Nanotubes.

Simulations and experiments have revealed enormous transport rates through carbon nanotube (CNT) channels when a pressure gradient drives fluid flow, but comparatively little attention has been given to concentration-driven transport despite its importance in many fields. Here, membranes are fabricated with a known number of single-walled CNTs as fluid transport pathways to precisely quantify the diffusive flow through CNTs. Contrary to early experimental studies that assumed bulk or hindered diffusion, measurements in this work indicate that the permeability of small ions through single-walled CNT channels is more than an order of magnitude higher than through the bulk. This flow enhancement scales with the ion free energy of transfer from bulk solutions to a nanoconfined, lower-dielectric environment. Reported results suggest that CNT membranes can unlock dialysis processes with unprecedented efficiency.

Bipolar electrochemical method for dynamic in situ control of single metal nanowire growth.

Fabrication plays a key role in determining the unique electrical, optical, and catalytic properties of metal nanowires. Here we present a bipolar electrochemical method for dynamically monitoring and controlling the rate of single metal nanowire growth in situ without a direct electrical connection. Solutions of a metal precursor and a reducing agent are placed on either side of a silica nanochannel, and a pair of electrodes is used to apply a tunable electric potential across the channel. Metal nanowire growth is initiated by chemical reduction when the two solutions meet and continues until the nanochannel is blocked by the formation of a short metal wire segment. Further growth is driven by a bipolar electrochemical mechanism which enables the reduction of metal precursor ions at one end of the nanowire and the oxidation of the reducing agent at the other. The growth rate is monitored in real time by simultaneously recording both the faradaic current and optical microscope video and can be adjusted accordingly by changing the applied electric potential. The resulting nanowire is solid, electrically insulated, and can be used as a bipolar nanoelectrode. This technique can be extended to other electrochemical systems, as well, and provides a confined reaction space for studying the dynamics of any process that can be optically or electrically monitored.

A silica nanochannel and its applications in sensing and molecular transport.

We present the preparation, characterization, and analytical application of silica nanochannels in the size range of 5-100 nm. These cylindrical-shaped nanochannels are prepared using a simple laser-assisted mechanical pulling process, followed by partial enclosure into a glass micropipet. The nanochannels are characterized using a combination of optical microscopy, scanning electron microscopy (SEM), and resistance measurements in an electrolyte solution. The SEM results show that the nanochannel has circular geometry at the orifice. Ohmic response has been obtained from current-voltage measurements in KCl solutions using a silica nanochannel as small as 9 nm in diameter. These nanochannels have been utilized to sense single 40 nm polystyrene nanoparticles. A linear response has been observed between the detection rate and the concentration of nanoparticles in the range of 0-25 nM. The silica nanochannels have also been applied to the study of molecular transport of double-stranded DNA. Electroosmosis-driven molecular translocation has been observed for genomic-length lambda-DNA through a 9 nm nanochannel in a 3 M KCl solution.