A parametric study of so-called "super growth" of single-walled carbon nanotubes (SWNTs) was done by using combinatorial libraries of iron/aluminum oxide catalysts.Millimeter-thick forests of nanotubes grew within 10 min, and those grown by using catalysts with a thin Fe layer (about 0.5 nm) were SWNTs. Although nanotube forests grew under a wide range of reaction conditions such as gas composition and temperature, the window for SWNT was narrow. Fe catalysts rapidly grew nanotubes only when supported on aluminum oxide. Aluminum oxide, which is a well-known catalyst in hydrocarbon reforming, plays an essential role in enhancing the nanotube growth rates.
A swift
potentiostatic anodization method for growing a 5–7
μm tall nanoneedle array of Cu(OH)2–CuO on
Cu foil within 100 s has been developed. This catalytic electrode
when screened for methanol oxidation electrocatalysis in 1 M KOH with
0.5 M methanol, delivered a current density as high as 70 ± 10
mA cm–2 at 0.65 V versus Hg/HgO which is superior
to the performance of many related catalysts reported earlier. The
observed activity enhancement is attributed to the formation of both
Cu(OH)2–CuO nanoneedle arrays of high active surface
area over the metallic Cu foil. In addition, the Cu(OH)2–CuO/Cu electrode had also exhibited excellent stability upon
prolonged potentiostatic electrocatalytic oxidation of methanol while
retaining the charge-transfer characteristics. Growth of such highly
ordered assembly of Cu(OH)2–CuO nanoneedles within
a minute has never been achieved before. When compared to its oxygen
evolution reaction activity, the addition of 0.5 M methanol has lowered
the overpotential at 10 mA cm–2 by 334 mV, which
is significant. This encourages the use of methanol as a sacrificial
anolyte for energy-saving production of H2 from water electrolysis.
We grow ultra-high mass density carbon nanotube forests at 450 °C on Ti-coated Cu supports using Co-Mo co-catalyst. X-ray photoelectron spectroscopy shows Mo strongly interacts with Ti and Co, suppressing both aggregation and lifting off of Co particles and, thus, promoting the root growth mechanism. The forests average a height of 0.38 μm and a mass density of 1.6 g cm−3. This mass density is the highest reported so far, even at higher temperatures or on insulators. The forests and Cu supports show ohmic conductivity (lowest resistance ∼22 kΩ), suggesting Co-Mo is useful for applications requiring forest growth on conductors.
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